IT201800004117A1 - METHOD AND APPARATUS FOR THE CONTINUOUS CHARACTERIZATION OF FORMATION FLUIDS DURING DRILLING - Google Patents

Description

The present application relates to an apparatus and a method for use at the bottom of an oil or gas well, and in particular an apparatus and a method for analyzing the content of drilling muds and / or other fluids of the bottom of the hole. while drilling or other downhole operations are being carried out.

STATE OF THE INVENTION TECHNIQUE

In oil wells, drilling muds are used for various applications including lubrication and cooling of the bit, stability of the well and its cleaning through the transport of rock fragments (cutting) on the surface. In a well, mud moves through a mud loop.

When drilling into a porous rock containing forming fluids such as water, oil and / or gas, the forming fluid contained in the rock is released into the mud. By analyzing the formation fluids contained in the sludge at a given time, it is possible to obtain useful information on the fluid content of the perforated formation.

Hydrogen sulphide and carbon dioxide can pose a significant risk to the safety of workers and also to the damage they cause to downhole equipment. Currently, acid gases are generally neutralized by adding scavengers (for hydrogen sulphide), soda or other alkalis (for carbon dioxide), removing the gases from the mud. For this reason, the detection of acid gases during drilling is not possible. Electrochemical sensors are frequently used to detect the presence of hydrogen sulphide on the surface. However, detection can only take place in extreme cases, when the hydrogen sulphide has already passed the barrier and has been released to the surface. At this point, it is too late to intervene.

Currently, the detection of hydrocarbons is performed only on the surface (so-called Gas While Drilling / GWD analysis), in which the results of the analysis are related to the relevant depth in the well. The detection and analysis of the hydrocarbon content present

necessarily a delay dependent on depth, volume and / or flow; this delay can be several hours and must therefore be corrected (lag time). A known method of detecting hydrocarbons involves sampling the fluid using probes, which however require interruption of the drilling while the probes are in place.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a downhole detection apparatus for use in an oil or gas well is described, the apparatus comprising a conduit adapted for the passage of fluid therethrough, the apparatus further comprising a inner surface forming the hole, and an outer surface and at least two sensors;

in which the first sensor is positioned above or inside the apparatus in such a way that it is in fluid communication with the fluid in the hole, and is adapted to analyze said fluid; and in which the second sensor is positioned above or inside the apparatus in such a way that it is in fluid communication with the fluid outside the apparatus, and is adapted to analyze said fluid.

Generally, the apparatus comprises a housing and the housing preferably comprises said internal surface and preferably the external surface. Typically, the first sensor is positioned on or in the internal surface of the housing. Generally, the second sensor is positioned on or in the external surface of the housing.

Optionally, the downhole detection apparatus is a recording tool during drilling. Generally, the positioning of the apparatus at the bottom of the hole inside the well creates an annulus between the surface of the internal wall of the well and the external surface of the apparatus. Preferably, the second sensor is in fluid communication with the fluid in the annulus.

Optionally the apparatus is placed in the mud circuit. Optionally, the device is incorporated into a bottom battery.

Optionally, the apparatus includes at least a first module, optionally comprising the first and second sensors. Optionally the first module is adapted to analyze the fluid part of the drilling mud. Optionally, the fluid in the hole is pumped from the surface. Optionally, the fluid in the annulus is brought back to the surface. Optionally the first module is adapted to continuously sample, analyze and expel the fluid. Optionally, the sensors, and therefore the first module, analyze the sludge or fluid as such, optionally thus providing a continuous flow of data relating to the composition of the sludge or fluid in the sampling position.

Optionally, the data from the first sensor is compared with the data from the second sensor and the sensors are optionally calibrated to isolate the difference in the data corresponding to the analytes transported within the drilling fluid or mud from the point of drilling. . This result can optionally be obtained by subtracting the data detected by the first sensor (relating to the less contaminated sludge injected into the well) from the data detected by the second sensor, which includes anything that can be reconnected to the formation fluid (for example heavy or light hydrocarbons , CO2, H2S or water).

Optionally, the first and / or second sensor are molecularly imprinted polymers (MIPs). MIP sensors are cross-linked engineered polymers, which can show high affinity and selectivity towards a particular analyte of interest, for example a single compound, or a "class selectivity" for a family of related compounds, with the sensor acting as a natural chemical receptor for the analyte. The MIP sensor is capable of binding to analytes even when the analytes are present in complex matrices.

MIP sensors offer the advantage of being able to accurately analyze specific components of a complex fluid, such as a drilling mud, as they have low detection limits and high selectivity. Therefore, different MIP sensors can be placed in the first and second sensors, intended for a multitude of different analytes, for example in the form of a heterogeneous set of several sensors. Furthermore, the analysis

of the fluid by a MIP sensor is not affected by the presence of solid elements such as debris or cutting.

MIP sensors can be used to bind, for example, carbon dioxide or hydrogen sulfide. The analyte binds to the sensor and forms bonds with the surface of the polymer, which is positioned on a conductive substrate. The change in the chemical-physical properties of the sensor is measured and refers to the amount of the related analyte that is captured by the sensor. The early detection of these substances allows interventions aimed at mitigating the damage or the release of dangerous components in the drilling mud.

Optionally, the first and / or second sensors are attenuated total reflectance (ATR) sensors. Optionally the ATR sensors can be used in addition to the MIP sensors and positioned similarly to the latter, with one ATR sensor placed in the inner surface of the housing of the first module, facing the hole, and the other ATR sensor placed in the surface outer housing of the first module, facing the annulus. The ATR sensor has less selectivity than the MIP sensor and provides a more general indication of the families of chemical compounds present in the sludge.

Inside an ATR sensor, a germanium, silicon or zinc selenide-based crystal is placed to form a layer along the base of the sensor. The sample to be analyzed, as it flows through the sensor, forms a layer on top of the crystal. An infrared ray is directed through the crystal and is reflected by a virtual boundary layer inside the sample, which has a lower optical density than the crystal. The wave must be reflected at least once outside this virtual interface, thus forming an evanescent wave that partially extends inside the sample. The analytes present within the sample absorb light at characteristic wavelengths and the absorbance is related to the concentration of analyte present within the sample. The sensor data produce absorbance peaks that can be represented graphically and provide an indication of the chemicals present within the drilling mud.

Optionally, the first and second sensors can be 2D sensors of the family that includes carbon nanotubes, graphene and molybdenum sulfide. Optionally, the sensors can be or include chemical or electronic languages, or any other suitable sensor that can be adapted to detect the analytes of interest, while being resistant to the extreme conditions present in the environment of the bottom of the hole.

The sensors should allow an accurate and continuous analysis of the constituents of the mud or drilling fluid, preferably even at very low concentrations in which the chemicals have been strongly diluted within the mud or fluid.

Optionally, the first sensor is placed inside a cavity or recess formed inside the housing of the first module, into which a part of the mud / fluid flowing inside the hole of the apparatus is diverted. Optionally, the second sensor is placed inside a cavity or recess formed inside the housing of the first module, in which a part of the mud / fluid flowing inside the annulus is diverted between the external surface of the housing of the apparatus and the internal surface of the well. Optionally each cavity or recess is covered with a filter, for example a mesh or grid, optionally a metal grid, which allows the passage of fluid into the cavity / recess, but which at the same time prevents the entry into the cavity / recess of debris or particles that may be present within the fluid. For example, inside the annulus, the filter prevents the drilling cuttings from entering the cavity or recess containing the second sensor, but allows the entry of fluid, for example the fluid part of the drilling mud.

Optionally, the first module includes a protective collar (for example including a reinforced blade) aimed at protecting the second sensor from damage when the apparatus is lowered into the well, while allowing the entry of fluid. Optionally, the protective collar surrounds at least a portion of the external surface of the apparatus, optionally the housing. Optionally, a recess is obtained or formed within a portion of the protective collar. Optionally, the recess allows fluid communication between the second sensor and the annulus.

Optionally, the recess includes a communication path for the fluid between the second sensor and the annulus, optionally in the form of a fluid conduit, which optionally extends between the cavity in which the second sensor is located and the outer surface of the 'housing. Optionally, the communication path for the fluid extends between the cavity in which the second sensor is located and the recess. Optionally, the fluid communication path allows fluid to enter the cavity where the second sensor is located. Optionally, a filter is placed above the entry point of the fluid communication path, optionally on the opening of the duct on the external surface of the housing. Optionally, the fluid communication path allows the circulation of fluid between the cavity in which the second sensor is located and the annulus, providing a continuous supply of drilling mud for analysis by the second sensor. Unlike the discontinuous sampling of the mud, a circulation or a flow of mud that comes into contact with the second sensor provides a real-time representation of the contents of the drilling mud at the depth of the apparatus, while the mud returns to the surface.

Preferably there are no mechanical or moving components installed as part of the first and / or second sensor, which reduces the probability of failure of such sensors. For example, it is not necessary to install a pump to circulate the fluid around these sensors, since the surface mud pumps ensure a continuous flow of mud inside the drill string. Given the absence of mechanical components, the aforementioned sensors have better resistance to high temperatures and shocks.

The data emitted by the first sensor and / or the second sensor can be communicated on the surface by any suitable means such as impulses of mud, electromagnetic systems, wired telemetry inside the drill string and any other communication system.

Furthermore, according to the first aspect of the invention, a method is described for analyzing the chemical profile of the fluid in an oil or gas well, the method comprising the following steps: -

the positioning of a downhole detection apparatus comprising a first and a second sensor in the oil or gas well, the downhole detection apparatus includes a hole defined by an internal surface of the device;

the analysis of the fluid in the hole with the first sensor, e

the analysis of the fluid outside the apparatus using the second sensor.

Optionally, the method includes the analysis phases of the fluid inside the hole and then the determination of a first chemical profile of said fluid; the analysis of the fluid outside the apparatus and then the determination of a second chemical profile of said fluid; and the comparison of these chemical profiles in order to identify the differences between the first and the second chemical profile.

Optionally, the apparatus is a part of the bottom battery. Optionally the method includes pumping the drilling mud from the surface along the hole and returning the drilling mud to the surface through an annulus formed between the inner surface of the well and the outer surface of the apparatus, optionally an outer surface of a housing which it is part of the apparatus. Optionally, the method includes the analysis of the least contaminated drilling mud injected into the hole to determine a basic chemical profile. Optionally, the method includes the comparison of the chemical profile of the fluid inside the annulus with the chemical profile of the fluid inside the hole to identify the chemicals present in the formation that is being perforated.

Optionally, the chemicals present in the formation are identified by comparing the chemical profile of the drilling mud inside the bore of the apparatus, before the drilling mud comes into contact with the formation; and the chemical profile of the drilling mud outside the apparatus, after the drilling mud has come into contact with the formation.

More advantageously, drilling can continue while the fluid analysis is being performed, unlike what happens with current systems, for example with formation testing.

On the basis of a second aspect of the present invention, a downhole detection apparatus is described for use in an oil or gas well, the apparatus includes at least one sampling unit and at least one sensor;

in which at least one sampling group is arranged above or inside the apparatus and is adapted to sample fluid from at least one sampling position at the bottom of the well;

wherein at least one sampling assembly comprises a chamber with at least one valve, wherein at least one valve is adapted to be open in order to allow fluid flow between the sampling position and the chamber, and closed to prevent further flow of the fluid between the sampling location and the chamber;

in which the chamber is capable of decompressing the sampled fluid contained therein, thus creating a gaseous portion and a liquid portion; And

in which at least one sensor is adapted to analyze at least a part of the gaseous portion.

Optionally, the apparatus includes at least a second module, in which the second module includes at least one expansion cylinder, optionally within the sampling group. Optionally, the expansion cylinder is connected to at least one analysis cylinder within the analysis group. Optionally, at least one analysis cylinder comprises at least one sensor. Usually the expansion cylinder and the analysis cylinder (s) are adjacent to each other. Optionally the cylinders are embedded in the walls of an instrument and arranged around the circumference. Optionally, cylinders are embedded in the walls of a drill collar.

Optionally, the downhole detection apparatus is a recording tool during drilling. Optionally, the fluid being sampled is a drilling mud. Optionally, the drilling mud is pumped from the surface, optionally through a hole in the apparatus. Optionally, the internal surface of the apparatus defines the hole.

Generally, the positioning of the apparatus, for example inside the drill collar, at the bottom of the well creates an annulus inside the well between the wall of the internal surface of the well and the external surface of the apparatus.

The expansion cylinder comprises at least one piston. Optionally, the piston can comprise a linear actuator system. Optionally, the apparatus can also comprise one or more gear systems, a motor, a magnetic coupling between the gear system and the motor, an energy source and an electronic module, possibly adapted to recognize the signals sent by the surface control, for example, the taking and analysis of a new sample. Optionally, the linear actuator system guides the movement of at least one piston inside the expansion cylinder.

Optionally, the chamber includes a fluid communication path with the annulus. Optionally, the sampling position is a position on the external surface of the second module of the apparatus. Optionally, the fluid communication path includes a duct that extends between the external surface, with an opening towards the annulus, and the chamber. Optionally, the opening towards the annulus is at least partially covered by a filter, for example a metal grid, to limit the entry of particulate material into the chamber. Optionally, the at least one valve is located within the fluid communication path. Optionally at least one valve is controllable, optionally in response to signals (e.g. mud pulses) sent from the surface.

Alternatively, the sampling assembly may have a fluid communication path between the chamber and the bore. Optionally the drilling mud that has been pumped from the surface can be sampled by the sampling group.

Optionally, there can be more than one sampling group within the second module. Optionally, the second module includes a first sampling group configured to sample from the hole of the second module, and optionally a second sampling complex configured to sample the fluid from the annulus of the well. Optionally each sampling group

comprises at least one chamber and at least one valve. Optionally, the sampling group, or each sampling group, can include a sensor. Optionally, the data collected by the analysis group, or by each analysis group, relating to the drilling mud in the hole, can be compared with the data collected by the drilling mud that returns to the surface in the annulus. Optionally, the samples taken from the hole are analyzed by a first analysis group, and the samples taken from the annulus are analyzed by a second analysis group, thus facilitating the identification of the location from which the samples were taken and simplifying the comparison of the data. Optionally, the comparison can provide information regarding any additional chemical substances that may be present in the mud inside the annulus, ie fluids and / or gases collected from the drilling mud when it comes into contact with the formation.

Optionally, the second module comprises at least one sampling group and one chamber. Optionally, the chamber includes at least two fluid communication paths, where optionally a fluid communication path extends between the chamber and the hole and optionally another fluid communication path extends between the chamber and the annulus of the well. Optionally, each fluid communication path comprises at least one controllable valve. Optionally the valves are configured to open and close fluid communication paths as required, optionally in response to signals from an operator. Optionally the valves can be operated independently.

Optionally, the apparatus is lowered into the well, optionally on a drill string, with the expansion piston fully inserted and optionally with the valve closed. When the piston is fully inserted, there is no free volume available inside the chamber to accommodate any fluid. Optionally, the valve is opened, allowing the fluid to enter the chamber of the sensor unit until an optionally predetermined volume of fluid is accumulated inside the chamber. Optionally, the valve is closed after the volume of fluid inside the chamber has been accumulated. Optionally the piston extracted in whole or in part.

Optionally, the further stroke of the piston determines the increase in the volume inside the chamber and therefore correspondingly the decrease in the pressure of the fluid. Optionally, the pressure is initially reduced to a value at which the fluid sample boils, taking into account the parameters of the downhole environment: for example, temperature and pressure.

Optionally when the fluid sample boils, the vaporization of at least a portion of the fluid sample occurs, optionally of at least some constituent parts of the fluid sample, and the fluid sample is then, at least partially, degassed when the vaporized part undergoes its phase change in its gaseous phase. Optionally, after the pressure has been reduced sufficiently, the chamber (and the fluid sample) is then held at a constant value and temperature to facilitate degassing. Optionally, the sampling assembly comprises at least one heating device adapted to heat the chamber, and optionally the sample of fluid and / or gas contained therein. Optionally the heater can be used to maintain a constant temperature profile or optionally to adjust the temperature profile during the degassing process.

Optionally, the chamber or each chamber contains a sensor, possibly adapted to detect the temperature and / or pressure inside the chamber or each chamber, optionally positioned above the level of the fluid sample inside the chamber. Optionally, the sensor analyzes at least a part of the gas or gaseous portion that is released from the fluid, for example the sensor can measure the temperature and / or pressure inside the chamber in order to determine the characteristics of the gas or the gaseous portion that is released from the liquid.

Optionally, the sampling assembly includes a duct for the fluid, optionally configured to allow the transfer of the gas extracted from the fluid sample between the chamber and the analysis assembly or each of them. Optionally, the analysis assembly, or each of them, comprises a chamber, in which the chamber comprises detection equipment for analyzing the components of the gas.

Optionally at least one sensor within the analysis group is a gas chromatograph (GC), optionally a micro gas chromatograph (μGC). The sensor is optionally a MEMS-based micro gas chromatograph (μGC), for example in the form of a “lab-on-a-chip” device. Gas chromatography based sensors are advantageous in that they are highly selective and can detect several linear hydrocarbons and differentiate them from each other. At least part of the vaporized sample is injected into a carrier gas flow, such as nitrogen, argon or helium, inside at least one analysis chamber, which moves through a column (forming the "mobile phase"). The sample is separated into its components. The gas phase analysis by the sensor is a discontinuous analysis that provides point-like analysis of the composition of the formation fluids (for example light hydrocarbons) contained in the drilling mud at a given time. In addition, the sensors are robust and capable of operating in the extreme conditions found at the downhole. MEMS-based μGC sensors perform fast and sensitive analysis of a sample with low carrier gas consumption.

Optionally further sensors, for example optical sensors or the like, can be added to the analysis group to detect other gases, such as carbon dioxide, or to act as alternative sensors for the gas phase extracted from the fluid sample. The addition of additional sensors increases the accuracy of the data provided.

Furthermore, according to the second aspect of the invention, a method of sampling and analyzing the fluid flowing inside an oil or gas well is described, including sampling the fluid using a sampling assembly arranged inside a downhole detection apparatus, said sampling assembly comprises at least one chamber and at least one valve; and the analysis of the chemical profile of the sampled fluid using a sensor placed inside said downhole detection apparatus; the method includes the following steps: - sampling a portion of the fluid by opening the valve, thus allowing communication of the fluid between the sampling position and the chamber;

closing the valve to prevent further communication of the fluid between the sampling position and the chamber;

the degassing of said portion of the sampled fluid inside the chamber, thus creating a gas phase and a liquid phase; And

the analysis of at least part of the gas phase.

Optionally, the apparatus includes an internal surface that defines a hole adapted for the passage of fluid through it and an external surface. Generally, the apparatus comprises a housing having an internal surface that defines a hole adapted for the passage of fluid through it and an external surface. Optionally, the apparatus is incorporated within the walls of an instrument, for example a drilling collar, and optionally the instrument defines the internal and external surfaces of the apparatus.

Optionally, the method includes the sampling of a fluid such as the mud coming from the annulus of the well, degassing and analysis of the gaseous part of the sample. Optionally the method includes the communication of the analysis data to the surface.

Optionally the method includes sampling a fluid from a sampling location located on the inner surface of the apparatus housing, and sampling a fluid from a sampling location located on the outer surface of the apparatus housing, and comparing of the chemical profiles obtained by analyzing the respective samples. The comparison of the fluid samples provides an indication of any difference present in the chemical constituents of the two samples. For example, when the drilling mud is pumped down the well through the hole and brought back to the surface through the annulus, any recycled analyte can be identified by comparing the profile of the mud samples.

Optionally, the apparatus includes several tubular portions that can be connected to each other that can form modules of the apparatus. Optionally, the first (first and second sensors arranged on the internal and external surfaces of the housing of the first module) and the second (detection system comprising a chamber, a valve and at least one

sensor) aspect of the invention, as described above, can be arranged in a first and a second module that can be mounted on a bottom battery and work together. Optionally the modules can be used separately. Optionally, the first aspect of the invention can be used independently of the second aspect of the invention. The modular arrangement of the first and second aspects of the invention allows better accessibility for maintenance or for the replacement of the components of the apparatus by an operator.

The various aspects of the present invention may be employed alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more optional features of the other aspects of the invention. Furthermore, the optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any object covered in this specification can be combined with any other object in the specification to form a new combination.

Various aspects of the invention will now be described in detail with reference to the attached figures. Further aspects, features and advantages of the present invention are easily evident from the entire description contained therein, including the figures, which illustrate various aspects and exemplary implementations. The invention can also be implemented according to other and different examples and aspects, and its numerous details can be modified in various aspects, all without departing from the scope of the present invention. Consequently, each example herein should be understood as capable of broad application, and having the purpose of illustrating a possible embodiment of the invention, without wishing to indicate that the scope of this description, including the claims, is limited to that example. Furthermore, the terminology and phrases used in this document are used exclusively for descriptive purposes and should not be construed as limiting in relation to the scope of the present invention. Terms such as "including", "comprising", "having", "containing" or "involving" and their variants, are to be understood in a broad sense and include the object listed below, the equivalents and the additional object not described , and they do not intend to exclude others

additives, components, whole numbers or steps. Likewise, the term “comprising” is considered to be synonymous with the terms “including” or “containing” for the relevant legal purposes. Therefore, in the specifications and claims, unless the context requires otherwise, the word "comprise" or variants thereof such as "comprise" or "comprising" will be understood as implying the inclusion of an integer or group of integers declared but not the exclusion of any other integer or group of integers.

Any discussion of documents, records, materials, devices, articles and the like is included in the specifications for the sole purpose of providing context for the present invention. It is not suggested or stated that some or all of these objects formed part of the basis of the prior art or that they were qualifiable as common general knowledge in the field relating to the present invention.

In this description, whenever a composition, element or group of elements is preceded by the term "comprising", the same composition, element or group of elements with phrases such as "essentially consisting of", "consisting of "," Selected from the group of "," composed of "," included ", or" is "preceding the description of the composition, element or group of elements and vice versa. In this description, the words "typically" or "optionally" must be understood as indicative of optional or non-essential features of the invention which are present in some examples but which can be omitted in other examples without departing from the scope of the invention.

All numerical values in this description are intended as modified by the term "about". All singular forms of elements, or any other component described here, include the inclusion of plural forms and vice versa. References to directional and positional descriptions such as "upper" and "lower" and directions for example "up", "down", etc., should be interpreted by an expert in the context of the examples described to refer to the orientation of the characteristics shown in the drawings and should not be interpreted as limiting the invention to the literal interpretation of the term, but should instead be interpreted in the sense attributed to them by an expert. In particular, the positional references relating to the well such as "su" and similar terms

will be interpreted to refer to a direction towards the well's entry point into the ground or seabed, and "down" and similar terms will be interpreted to refer to a direction away from the entry point, if the well being referred to is a conventional vertical well or a diverted well.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached drawings:

Figure 1a shows a perspective view of an example of the first module, in accordance with the first aspect of the present invention, located inside an exemplary drill string;

Figure 1b shows a close-up view of a recess and a fluid entry point of a first module as shown in Figure 1a;

Figure 1c shows a close-up view of the recess in Figure 1b, with a filter placed over the opening of the recess;

Figure 1d shows a partial sectional view of the first module of Figure 1a with the recess of Figure 1b, in which the illustrated sensor is located;

figure 2a shows a cross-sectional view of the first module of figure 1a showing the recess in which the first sensor is located;

figure 2b shows a plan view of the first module of figure 1a showing the recess in which the first sensor is located;

figure 3a shows a cross-sectional view of the first module of figure 1a showing the second sensor;

figure 3b shows a plan view of the first module of figure 1a showing the second sensor;

Figure 4a shows a perspective view of an example of the second module based on the first aspect of the present invention, located inside an exemplary drill string;

Figure 4b shows an exploded view of the component parts of the second module of Figure 4a, which consists of an expansion cylinder and two analysis cylinders;

figure 5 shows a cross section of the expansion cylinder of the second module of figure 4a;

figure 6 shows a simplified schematic view of the expansion cylinder of the second module of figure 4a;

Figures 7a-7l show cross-sectional views of the expansion cylinder of the second module of Figure 4a, and the steps of opening the valve in the fluid path to the annulus, sampling the sludge, closing the valve and degassing of the mud sample;

Figure 8a shows the initial composition of the sludge sample when it is compressed by the expansion piston, prior to degassing;

Figure 8b shows the subsequent composition of the sludge sample when the expansion piston is retracted;

Figure 9a shows a close-up view of the gas conduit in a closed configuration; Figure 9b shows a close-up view of the gas duct in an open configuration; Figure 10 shows the gas transfer path from the expansion cylinder to the analysis cylinder;

Figure 11 shows a side view of a section of the second module, in particular the components of the analysis cylinder;

Figures 12a-c show the initialization of the analysis system during the entry phase; figure 13 shows a schematic view of the analysis system, indicating in particular the path that the gas takes during the inlet phase;

figures 14 a-c show the analysis system during the compression phase;

figure 15 shows a schematic view of the analysis system, indicating in particular the initial portion of the gas path during the compression phase;

Figure 16 shows a further schematic view of the path traveled by the gas during the compression phase;

Figures 17a-d show schematic views of the sequence of the micro gas chromatograph that fills with the gas to be analyzed and the injection of the carrier gas for analysis;

Figure 18 shows an example of a bottom battery comprising both the first module of Figure 1a and the second module of Figure 4a based on the first and second aspects of the present invention;

Figure 19a shows the tool with a cut in cross section indicated towards the upper end of the second module;

Figure 19b shows a cross section of the second module, illustrating the positioning of the analysis cylinders and the expansion cylinder around the instrument; and Figure 20 shows a cross section of an analysis cylinder of the second module of Figure 4a;

DETAILED DESCRIPTION OF THE EXAMPLES OF THE INVENTION

Referring to FIGS. 1a-3b, an example of a downhole logging while drilling (LWD) tool 2 is shown for use in an oil or gas well in accordance with a first aspect of this letter. invention as included in a bottom battery 200 which further comprises a stabilizer 5, in this example spiral blade stabilizers; a drilling collar 4; and a first module 1. The instrument 2 has a central hole 22 (better visible in Figures 2a-3b) adapted for the passage of fluid through it. In particular, the hole 22 is suitable for the passage of the drilling mud pumped from the surface to the tip of the bit (which is located at the lower end or at the front end of the drill string) and then towards the annulus 6 of the well. , where annulus 6 is the space between the internal surface of the well and the external surface of the drill string. The first module 1 comprises a housing 28 having an inner surface 29 which defines the hole 22, and an outer surface 11 which defines the inner diameter of the annulus 6 in the well. The first module 1 comprises at least two sensors 15, 20, a first sensor 20 positioned inside a cavity 25 formed in the internal surface 29 of the housing 28, and a second sensor 15 positioned inside a cavity 12 formed in the surface 11 of the housing 28 as shown in Figure 3b.

The first and second sensors 20, 15 are in fluid communication with the drilling mud as it is pumped to and from the surface, respectively. A part of the drilling mud that flows through the hole 22 or the annulus 6 is diverted into the respective cavities 25, 12 for analysis by the respective sensors 20, 15.

In order to protect the second external sensor 15 from damage, for example during the use of the instrument, or due to impacts between the instrument and the hole, the sensor 15 and the

cavities 12 are protected by a protective collar 8 which surrounds at least a portion of the outer surface 11 of the housing 28. To maintain the fluid communication path to the sensor 15, the protective collar 8 has a recess 10 machined into it in order to allow fluid to enter the sensor 15 through the fluid communication path 14. The fluid communication path 14 may optionally consist of a fluid conduit 14 extending between the cavity 12 and the annulus 6 and / or the recess 10, and allows fluid to enter the cavity 12. Optionally, the fluid conduit 14 allows fluid circulation between the cavity 12 and the recess 10 so that there is a continuous supply of drilling mud. for analysis by the sensor 15, providing a more accurate real-time analysis of the drilling mud content as it returns to the surface.

As shown in Figure 1c, a filter 18 can be placed over the opening at the recess 10. Alternatively, and depending on the configuration of the first module 1, the filter can be positioned directly over the opening of the fluid conduit 14. The filter 18 can consist, for example, of a metal grid. The filter 18 acts to prevent debris from entering the cavity 12 and potentially damaging the sensor 15. The first module 1 can analyze the fluid portion of the drilling mud and detect, for example, carbon dioxide or hydrogen sulphide dissolved in the mud.

By virtue of the positioning of the first sensor 20 and the second sensor 15, the data from the first sensor 20 can be compared with the data from the second sensor 15 and used to calibrate the second sensor 15. The first sensor 20 samples and analyzes the sludge as it is being pumped from the surface, before it comes into contact with the formation. This provides a baseline against which the data produced by the second sensor 15 can be compared. The second sensor 15 samples and analyzes the sludge after it has come into contact with the formation, and therefore the sludge sampled by the second sensor 15 can contain analytes of interest to operators. The basic measurement of "clean" sludge made by the first sensor 20 (containing, for example, recycled hydrocarbons, carbon dioxide) can be removed from the data set produced by the second sensor 15, leaving only the analytes collected from the sludge by the formation (for example e.g. hydrocarbons, carbon dioxide, hydrogen sulphide, water).

The first module is adapted to sample, analyze and continuously expel the fluid from the cavities 12, 25. Optionally the sensors 15, 20, and therefore the first module 1, analyze the sludge as it is and provide a continuous flow of data relating to the composition of the mud present at the depth where the instrument is located.

The first sensor 20 and the second sensor 15 may be molecularly imprinted polymer (MIP) sensors. MIP sensors are engineered crosslinked polymers that can show high affinity and selectivity towards a particular analyte of interest, for example a single compound, or a “class selectivity” for a family of related compounds. The sensor acts as a natural chemical receptor for the analyte. The MIP sensor is able to bind analytes even when the analytes are present in complex matrices. MIP sensors offer the advantage of being able to accurately analyze specific components of a complex fluid, such as drilling muds, as they have low detection limits and high selectivity. Therefore, several MIP sensors, intended for a multitude of different analytes, can be placed in the first and second sensors, for example in the form of a heterogeneous array of sensors. Furthermore, the analysis of the fluid by a MIP sensor is not affected by the presence of solid elements such as debris or fragments.

MIP sensors can be used to attach themselves to, for example, carbon dioxide or hydrogen sulphide. The analyte binds to the sensor and forms cross-links with the polymer model, which is located on a conductive substrate. The change in the chemical-physical properties of the sensor is measured and refers to the quantity of the connected analyte that is captured by the sensor. The early detection of these substances is of particular importance as it allows interventions aimed at mitigating the damage or the release of dangerous components in the drilling mud.

Alternatively, the first sensor 20 and the second sensor 15 can be attenuated total reflectance (ATR) sensors. The ATR sensors can also be used in addition to the MIP sensors and similarly positioned, with one ATR sensor placed in the inner surface 29 of the housing 28 of the first module 1, facing the hole 22, and the other ATR sensor placed in the external surface 11

of housing 28, facing the annulus 6. The ATR sensor has a lower selectivity than the MIP sensor and provides a more general indication of the families of chemical compounds present in the mud.

Inside an ATR sensor, a germanium, silicon or zinc selenide-based crystal is placed to form a layer along the base of the sensor. The sample to be analyzed, in this case the drilling mud as it flows along the sensor, forms a layer over the crystal. An infrared ray is directed through the crystal and is reflected by a virtual boundary layer inside the sample, which has a lower optical density than the crystal. The wave must be reflected at least once outside this virtual interface, thus forming an evanescent wave that partially extends inside the sample. The analytes in the sample absorb light at characteristic wavelengths and the absorbance is related to the concentration of the analyte present within the sample. The sensor data produce absorbance peaks that can be represented graphically and provide an indication of the chemicals present in the drilling mud. ATR sensors can be sensitive to the presence of particles, and it is therefore particularly useful to cover cavity 12 (and optionally also cavity 25) when ATR sensors are used.

Optionally, the first sensor 20 and the second sensor 25 can be 2D sensors of the family that includes carbon nanotubes, graphene and molybdenum sulphide. Optionally, the sensors 15, 20, can be or include chemical or electronic languages, or any other suitable sensor that can be adapted to detect the analytes of interest, while being resistant to the extreme conditions present in the downhole environment. The sensors 15, 20, should allow an accurate and continuous analysis of the constituents of the drilling mud, preferably even at very low concentrations in which the chemicals have been strongly diluted within the mud.

Preferably there are no mechanical or moving components installed as part of the first module 1 and / or the sensors 15, 20, which reduces the likelihood of failure of the sensors 15, 20. For example, it is not necessary to install a pump to circulate the fluid around said sensors, since the surface mud pumps guarantee a continuous flow of

mud within the mud circuit through and around the drill string. Given the absence of mechanical components, the 15.20 sensors have better resistance to high temperatures and shocks.

The data emitted by the sensors is transmitted to the surface to provide the operators present there with training information. Data can be transmitted using known telemetry methods, such as wirelessly.

Referring now to Figures 4a-6, there is shown an example of an instrument for recording during drilling 2 (LWD) for use in an oil or gas well according to a second aspect of the present invention, comprising a second module 100. The second module 100 comprises an expansion cylinder 110, a first analysis cylinder 120 and a second analysis cylinder 130. The cylinders 110, 120, 130 are arranged inside the wall of the instrument 2 in a ring arrangement around the hole 122 of the tool 2, as can be better seen in Figure 19b. Optionally, the cylinders 110, 120, 130 are incorporated, by way of example, into the walls of a drilling collar.

The sampling chamber 141 includes a fluid communication path 148 between the annulus 106 and chamber 141. The fluid communication path 148 includes a conduit 148 extending between the outermost surface of the module 100, with an opening towards annulus 106, and conduit 148 has at least one controllable valve 142 which is adapted to be opened and closed in order to allow and prevent the flow of fluid into or from chamber 141 as required. A filter can also be placed above the inlet of duct 148 or close to it, to limit the entry of debris into chamber 141.

The conduit 148 can alternatively be positioned to sample fluid from port 122. Also, alternatively, an additional conduit (not shown) with a separate valve (not shown) can be provided to draw fluid from port 122, in addition to conduit 148. Optionally, more than one group of sensors can be present inside the second module 100, and a first group of sensors can be configured to sample from hole 122 while a second group of sensors

sensors can be configured to sample from annulus 106. Similarly to the first module 1, this arrangement can provide a means to calibrate the second group of sensors by comparing the basic measurements of the first group of sensors with the data produced by the second group of sensors. sensors and thus isolating the analytes taken from the mud from the formation.

In use, and referring to the schematic example of figure 6, the second module 100 is used on a bottom battery 200 included in a drill string, with the piston 143 completely approached so that there is no free volume available. for fluid inside chamber 141, and valve 142 closed to prevent fluid from entering. When sampling and analysis must begin, valve 142 is opened and piston 143 is partially extracted. This creates a volume inside the chamber 141 into which the fluid can enter from the annulus 106. The piston 143 can be extracted to create a predetermined volume to be filled with the drilling mud. Once the desired volume of drilling mud 144 has entered the chamber 141, the valve 142 is closed.

The piston 143 is then further extracted, optionally it is completely extracted. The movement of the piston 143 increases the free volume inside the chamber 141, and since the valve 142 is closed, correspondingly decreasing the pressure of the fluid. Optionally, the fluid pressure is initially reduced to a value at which the fluid sample 144 boils, taking into account the temperature and pressure parameters present within the downhole environment.

After the pressure has been reduced sufficiently, the chamber (and the fluid sample) is then maintained at a constant pressure and temperature to facilitate degassing. When the fluid sample 144 boils, vaporization of at least some constituent parts of the fluid sample 144 occurs and the fluid sample 144 is then at least partially degassed as the evaporated constituent parts undergo a change of state in their gas phase. Optionally, the expansion cylinder 110 includes at least one heating device 147 adapted to heat the chamber 141, and optionally the fluid sample 144 and / or the gas 146 contained therein. The device of

heating 147 can be used to maintain a constant temperature profile or optionally to adjust the temperature profile during the degassing process.

The expansion process is particularly advantageous as, during drilling, a minimum concentration (from tens to thousands of ppm) of the formation fluids could be released into the mud. The real-time characterization of the formation fluids present in the sludge at the bottom battery level is problematic, however, by expansion (preferably isothermal expansion) of the sludge samples, the analytes of interest are effectively separated from the sludge and characterized more easily.

The chamber 141 can be connected to a gas conduit 150 which is arranged to transfer the gas sample 146 to at least one analysis cylinder. The analysis cylinders may each comprise a detection apparatus adapted to analyze the components of the gas sample 146, optionally different detection equipment in each analysis cylinder to measure different substances, or optionally the same detection apparatus in each analysis cylinder. to allow comparison of gas sample measurements.

Optionally one or more of the sensors is a gas chromatograph (GC), optionally a micro gas chromatograph (μGC). Optionally, at least one sensor inside the second module 100 is a MEMS-based micro gas chromatograph (μGC), for example in the form of a "lab-on-a-chip" device. Gas chromatography based sensors are advantageous in that they are highly selective and can detect several linear hydrocarbons and differentiate them from each other. At least part of the vaporized sample 146 is injected into a carrier gas stream, such as nitrogen, argon or helium, inside at least one of the analysis cylinders 120, 130 which moves through a column (forming the "mobile phase" ). The column also contains a stationary phase in the form of a liquid or solid layer, in which the compound and / or liquid that forms the layer can be selected based on the analyte to be detected. Sample 146 is separated into its components. The analysis of the gas phase by the sensor is a discontinuous and point-like analysis, which provides snapshots of the composition of the formation fluids (for example light hydrocarbons) contained in the drilling mud at a given time. In addition, the sensors are robust and able to function

in the extreme conditions present at the bottom of the well. MEMS-based μGC sensors perform fast and sensitive analysis of a sample with low carrier gas consumption.

Optionally further sensors, for example optical sensors or the like, can be positioned within one or more parts of the sensor group to detect other gases, such as carbon dioxide, or to act as alternative sensors for the extracted gas sample 146 from the 144 fluid. The addition of additional sensors improves the accuracy of the data provided.

The expansion cylinder 110 further includes a cylinder system 152 through which the piston body 143 moves as it is inserted or withdrawn.

In a more detailed example as shown in Figures 7a-7l, the expansion cylinder 110 comprises a sampling chamber 141. The sampling chamber 141 comprises a mud valve 142a, controlled by a piston system which includes a first piston 149a and a second piston 149b. The second piston 149b comprises a central hole, into which the first piston 149a retracts when the first piston 149a is withdrawn. The first piston 149a and the second piston 149b are moved towards a closed configuration of the mud valve 142a by two elastic devices, in this example the internal and external springs 140a, 140b. The outer spring 140a is positioned around the outer circumference of the second piston 149b and the inner spring 140b is positioned within the inner circumference defining the central hole of the second piston 149b. The outer spring 140a acts on the second piston 149b and the inner spring 140b acts on the first piston 149a.

The sampling chamber 141 further comprises a gas valve 142b which is controlled by the interaction of the first piston 149a with an expansion piston 143. The first piston 149a comprises, at its end opposite the sludge valve 142a, an adapted projection to seal inside a hole 150 of the expansion piston 143. The stroke of the first piston 149a in the hole 150 of the expansion piston 143 is limited by a circular projection 149as on the first piston 149a. When the first piston 149a and the expansion piston 143 seal, no gas can enter the bore 150. When the

first piston 149a and the expansion piston 143 separate, the gas can enter the hole 150, which then acts as the gas conduit 150.

The mud valve 142a consists of a tapered end of the second piston 149b which forms a tight seal with a correspondingly tapered opening within the sampling chamber 141. The mud flows from the annulus through the fluid path 148 into the chamber sampling valve 141 when the sludge valve 142a is opened.

The movement of the expansion piston 143 is driven by a linear actuation system 143 (figure 5), in which the actuation system is driven by a coupled gearbox 154 and by an electric motor 153. Optionally there is a magnetic coupling 155 between the gearbox 154 and electric motor 153.

The expansion cylinder 110 further comprises an electronic module 156, a battery module 157 and an accumulator 151 (better visible in Figure 5) which act jointly to power and control the movement of the expansion piston 143. For example, the electronic module 156 can be programmed in advance to detect the signals sent from the surface and respond to them, controlling the second module 100 in order to take a new sample of mud from the annulus 106, on which the electronic module 156 operates the expansion piston 143 to open the valve of mud 142a. The accumulator 151 is at a pressure equal to the downhole pressure, which keeps the body of the expansion piston 143 in a state of tension, reducing the probability of damage to the piston 143 during insertion (ejection / compression phase ).

Figure 7a shows the first step in the sampling procedure. The pressure inside the sampling chamber 141 is relatively low, equal to about 3-4 bar (300-400 kPa), usually about 3.7 bar (370 kPa), and this pressure depends on the ambient temperature of the bottom of the hole; for example, if the sampled sludge containing the analytes of interest is at a temperature of 60-70 ° C, the final pressure will be approximately 0.2-0.3 bar (20-30 kPa). In this example, optionally, the temperature of the

sampling chamber 141 is assumed to be constant at 140 ° C, although the temperature is adjustable according to the conditions present at the bottom of the well. The mud valve 142a is in a closed configuration, while the gas valve 142b is in an open configuration, and the gas conduit 150 is also open and fully aligned. The first piston 149a and the second piston 149b are not moving. The expansion piston 143 begins to be inserted into the sampling chamber 141.

In figure 7b, the expansion piston 143 is displaced and fits into the end of the first piston 149a. The gas valve 142b is therefore in a closed configuration and the gas conduit 150 is interrupted. Furthermore, the movement of the expansion piston 143 has moved the gas duct 150 out of alignment, as shown in the right part of figure 7b. The mud valve 142a remains closed and the internal pressure of the sampling chamber 141 remains, for example, at about 3.7 bar (370 kPa) at a downhole temperature of about 140 ° C.

The expansion piston 143 continues its travel through the sampling chamber 141 to the sludge valve 142a (FIG. 7c). While the expansion piston 143 continues to be inserted, and while sealing with the first piston 149a, it in turn acts against the spring 149b which moves the first piston 149a towards the sampling chamber 141. The expansion piston 143 includes a gasket circular 143r having a larger diameter than the rest of the expansion piston 143, which is sealed against the inside diameter of the sampling chamber 141. As the expansion piston 143 moves towards the mud valve 142a, the mud valve 142a remains closed , at least initially, and therefore the volume of the sampling chamber 141 is reduced. The pressure inside the sampling chamber 141 begins to increase.

Figure 7d shows the head 149as of the first piston 149a which fits into the tapered portion of the second piston 149b. The expansion piston 143 continues to move and pushes the first piston 149a against the thrust force of the spring 140b, and at this point, the expansion piston 143 also begins to act against the thrust force of the outer spring 140a. Figure 7e shows the mud valve 142a which begins to open, thus allowing the expulsion of the fluid contained within the chamber

sampling 141. In this phase, the gasket 143r of the expansion cylinder 143 approaches the opening of the mud valve 142a and the volume of the sampling chamber 141 is now significantly reduced. The pressure inside the portion of the sampling chamber between the rib 143r and the mud valve 142a is now approximately equal to the external pressure in the annulus of the well; in an extreme example, the pressure inside the sampling chamber 141 can increase up to 700 bar (70 MPa).

Figure 7f shows the mud valve 142a fully open. The sludge that was previously present within the sampling chamber 141 is expelled, and fresh sludge flows from the well annulus through the fluid path 148, which includes an opening to the annulus leading to the valve. of mud 142a. After opening the mud valve 142a, the expansion piston 143 begins to flow, capturing a sample of mud within the restricted volume of the sampling chamber 141, while the mud valve 142a closes with the movement of the second piston 149b by effect of the thrust force of the outer spring 140a. This arrangement, in which the mud valve 142a is at least partially open and the expansion piston 143 is slightly spaced from the mud valve 142a, can be maintained for a period of time to allow renewal of the mud within the resulting space in the sampling chamber 141. The internal pressure of the sample in the sampling chamber 141 is again equal to the external pressure present in the annulus at this point.

In order to extract a gas sample for analysis, the expansion piston 143 is withdrawn and the first piston 149a is moved (inserted) together with the expansion piston 143 due to the thrust force of the internal spring 140b, maintaining a seal welds between the pistons 143, 149a, and thus keeping the gas valve 142b closed. As the expansion piston 143 is extracted, the pressure inside the sampling chamber 141 decreases until it reaches about 3-4 bar (300-400 kPa), preferably about 3.7 bar (370 kPa) (figures 7g -7k), when the temperature at the bottom of the well is about 140 ° C. The mud sample inside the sampling chamber 141 will now contain a mixture of liquid and about 10% of water vapor by volume.

The reduction of the fluid pressure inside the sampling chamber 141 determines the partial vaporization and degassing of the sludge sample. A heating element can be included as part of the sampling chamber 141, for example by surrounding the sampling chamber 141, in order to improve the degassing of the sludge sample by creating an isothermal environment inside the sampling chamber 141. Figure 7l shows the expansion piston 143 extracted and separated from the first piston 149a to open the gas valve 142b. A closer view of the closed and open configuration of the gas valve 142b is shown in Figures 9a and 9b. The gaseous portions of the mud sample can now be extracted through the gas conduit 150 to carry out the analysis.

Figures 8a and 8b show a schematic illustration of the change in sample composition as the expansion piston 143 goes from full sample compression at approximately 700 bar (70 MPa) to fully expand into a volume of, for example, 100cm < 3> with a pressure of about 3.7 bar (370 kPa). Initially, the sample consists of a supercritical mixture of mud, water and forming fluids. After expansion, at least part of the formation fluids is vaporized with about 10% of water vapor by volume. Expansion of the sample to a gas-to-liquid ratio of 10% by volume of total sample vaporization improves the detectability of the analytes by the sensors in the analysis cylinders 120, 130, as less water vapor is mixed with the fluids / training analytes. Inside chamber 141 a liquid mixture of mud and water remains. The remaining liquid portion of the sample left after degassing, which consists mainly of water, creates a very thin film along the inner surface of chamber 141. This film can also form in very deviated wells.

Figure 10 shows the path that the gas travels from the sampling chamber 141 into the first analysis cylinder 120. The gas enters the gas conduit through the open gas valve 142b and flows into the conduit 150 (which is contained in the external walls of the instrument 2). The gas initially enters a solenoid valve 160 contained inside

of the analysis cylinder 120 which therefore allows the movement of the gas towards the micro gas chromatograph (μGC).

Figure 11 shows a further view of the first analysis cylinder 120 with the gas conduit 150 aligned between the first analysis cylinder 120 and the expansion cylinder 110. The analysis cylinder 120 further comprises a pressure compensator 164, a tank of helium 165 and a gas treatment piston 162 which includes three control valves 163a-c.

In order to initialize the gas analysis system, the gas treatment piston 160 is repeatedly inserted and withdrawn to alternate the phases of aspiration and compression of the gas. Figure 12a-c shows the gas suction phase when the piston 160 is ejected. Figure 13 shows the path of the gas during aspiration. The gas first flows through the gas duct 150 into the solenoid valve 160, and then into a pre-chamber, or inlet chamber 161i of the micro gas chromatograph 161. The inlet chamber 161i thus begins to accumulate the gas just sampled with "new" analytes . Any old gas remaining in the inlet chamber 161i will be expelled along the path 167a to the gas handling piston 162. At the same time that the "fresh" gas is entering the inlet chamber 161i, the gas from the previous analysis, kept in the measurement of the micro gas chromatograph μGC or in the outlet chamber 161o, it is expelled from the micro gas chromatograph μGC 161 into the pressure compensator 164. A small portion of the old gas will also be forced by the pressure compensator 164 and along the gas path 167b towards the piston The check valves 163b and 163c are both open and the gas that is expelled from the inlet chamber 161i into the pressure compensator 164 passes through the check valves 163b, 163c and into the gas treatment piston 162.

The gas treatment piston 162 is then subjected to a compression step as shown in FIG. 14, in which the check valves 163b and 163c close and the valve 163a opens and the piston 162 is inserted. The gas inside the gas treatment piston 162 is expelled and passes through an exhaust port 167c (figure 15), which leads to an exhaust gas tank 168 as shown in figure 16. The use of a gas tank 168 allows the expulsion of the gas measured in the analysis

immediately preceding the gas analysis system before proceeding with any new measurements. This reduces the contamination of the current analysis by "old" analytes.

Figures 17a-17d show the gas accumulation process in the inlet chamber 161i. In Figure 17a the inlet chamber 161i is empty and gas is introduced into the system through the solenoid valve 160. The suction and compression cycle of the gas handling piston 162 begins and the gas moves along the gas path 167a when the inlet chamber 161i fills up. In Figure 17b, chamber 161i is now filled with new gas containing the analytes and the analysis process can begin. In Figure 17c, valve 171 of the carrier gas supply system, helium in this example, is closed and helium cannot move out of the helium reservoir 165. In Figure 17d, valve 171 is opened and helium flows. from tank 165 through path 166 to inlet chamber 161i. This creates a helium circulation which produces a flow of gas between the inlet chamber 161i and the outlet chamber 161o through the flow path 161p between the chambers 161i, 161o.

The new gas from the expansion cylinder 110 is thus forced to enter and fill the inlet chamber 161i of the micro gas chromatograph μGC 161 before being transported by the carrier gas, in this example consisting of helium, from the inlet chamber 161i into the column of the μGC micro gas chromatograph inside the 161o outlet chamber for analysis. The data collected by the sensor (s) of the μGC micro gas chromatograph can then be communicated at the surface, for example by means of mud pulses, electromagnetic systems, wired telemetry for boreholes or any other suitable means of communication.

As shown in Figure 20, the analysis cylinder 120 can further comprise an electronic unit of the sensor 175 adapted to record and transmit the data received from the sensors of the micro gas chromatograph 161; a general electronic assembly 173 which can react to signals from the surface, control the components of the test cylinder 120 and / or transmit data to the surface; optionally a linear actuator 172 connected to the gas treatment piston 162, and optionally a motor and gearbox assembly 174, in which the

motor and gearbox unit 174 is optionally adapted to operate the linear actuator 172, and optionally the movement of the gas treatment piston 162.

Optionally, the LWD instrument 2 comprises several connectable tubular portions which can form modules of the instrument 2, for example the stabilizers 5, the drilling collar 4, the first module 1, the second module 100, as illustrated in the figures. As shown in Figure 18, the first (first and second sensors 20, 15 arranged on the inner and outer surfaces 29, 11 of the instrument housing 28) and the second (sensor assembly comprising at least one expansion cylinder 110 and the analysis cylinders 120, 130) aspect of the invention as described above can be arranged in a first module 1 and a second module 100 which can be mounted on a bottom battery 200 and work together. Optionally, modules 1, 100 can be used separately. Optionally, the first aspect of the invention, relating to the first module 1, can be used independently of the second aspect of the invention, relating to the second module 100.

Changes and improvements can be made to the embodiments described here without departing from the scope of the invention.

Claims (25)

CLAIMS 1. A downhole sensing apparatus for use in an oil or gas well, the apparatus comprising a conduit adapted for passage of fluid therethrough, the apparatus further comprising an inner surface forming the hole, an outer surface and at least two sensors; in which the first sensor is positioned above or inside the apparatus in such a way that it is in fluid communication with the fluid in the hole, and is adapted to analyze said fluid; And in which the second sensor is positioned above or inside the apparatus in such a way that it is in fluid communication with the fluid outside the apparatus, and is adapted to analyze said fluid. 2. A downhole detection apparatus according to claim 1, in which the apparatus is incorporated within a bottom battery. 3. A downhole detection apparatus according to claim 1 or 2, in which the apparatus is a recording instrument during drilling. A downhole detection apparatus according to claims 1-3, wherein the downhole detection apparatus is positioned inside the well in such a way as to create an annulus between the wall of the internal surface of the well and the external surface of the apparatus; and in which the second sensor is in fluid communication with the fluid present in the annulus. 5. A downhole detection apparatus according to claims 1-4, in which the apparatus comprises at least a first module, in which said module comprises the first and the second sensor; and in which the first module is adapted to sample, analyze and continuously expel the fluid flowing through at least one of the holes and / or the outside of the apparatus. A downhole detection apparatus according to claims 1-5, wherein the data from the first sensor is compared with the data from the second sensor and the sensors are optionally calibrated to isolate any differences in the data. A downhole detection apparatus according to claims 1-6, wherein the first and / or second sensor comprise polymer molecular imprint (MIP) sensors. A downhole detection apparatus according to claims 1-7, wherein the first and / or second sensor comprise several MIP sensors, wherein at least one of the MIP sensors is configured to detect a different analyte from another of the sensors MIP. A downhole detection apparatus according to claims 1-6, wherein the first and / or second sensor comprise attenuated total reflectance (ATR) sensors. 10. A downhole detection apparatus according to claims 1-9, in which the first sensor is located inside a cavity formed inside the apparatus, and in which a part of the fluid flowing inside the hole of the apparatus is diverted into said cavity. A downhole detection apparatus according to claims 1-10, wherein the second sensor is located inside a cavity formed inside the apparatus, and in which a part of the fluid flowing outside the The apparatus is diverted into said cavity. 12. A downhole detection apparatus according to claims 10 or 11, in which at least one cavity is covered with a filter configured so as to limit the entry of particulate material into the cavity. 13. A downhole detection apparatus according to claims 1-12, in which the apparatus comprises a protective collar that surrounds at least a portion of the external surface of the apparatus. 14. A downhole detection apparatus according to claim 13, in which the protective collar comprises a recess, in which the recess is configured to allow fluid communication between the second sensor and the outside of the apparatus. 15. A downhole detection apparatus according to claim 14, in which the recess comprises a fluid communication path between the second sensor and the outside of the apparatus. 16. A downhole detection apparatus according to claim 15, in which the fluid communication path comprises a filter configured so as to limit the entry of particulate material while allowing, at the same time, the passage of the fluid. 17. A downhole detection apparatus according to claims 14-16, in which the fluid communication path allows the circulation of the fluid between the cavity in which the second sensor is positioned and the outside of the apparatus. 18. A downhole detection apparatus according to claims 1-17, in which the apparatus comprises a housing, said housing comprising the internal surface and the external surface. 19. A downhole detection apparatus according to claim 18, in which the first sensor is positioned on the internal surface of the housing or in the same. 20. A downhole detection apparatus according to claim 18 or 19, in which the second sensor is positioned on the external surface of the housing or in the same. 21. A downhole detection apparatus according to claims 5-20, wherein the apparatus also comprises at least a second module, said second module comprising at least one sensor group; in which at least one group of the sensor is arranged above or inside the apparatus and is adapted to sample fluid from at least one sampling position of the bottom of the hole; wherein at least one sensor assembly comprises a chamber with at least one sensor and at least one valve, wherein at least one valve is adapted to be open in order to allow fluid flow between the sampling position and the chamber, and closed to prevent further fluid flow between the sampling location and the chamber; in which the chamber is capable of degassing the sampled fluid contained therein, thus creating a gaseous portion and a liquid portion; And in which the sensor is adapted so as to analyze at least a part of the gaseous portion. 22. A method for analyzing the chemical profile of the fluid in an oil or gas well, the method comprising the following steps: - the placement of a downhole detection apparatus comprising a first and a second sensor in the oil well or gas, the downhole detection apparatus comprising a hole; the analysis of the fluid in the hole with the first sensor, e the analysis of the fluid outside the apparatus using the second sensor. 23. A method according to claim 22, comprising the steps of analyzing the fluid inside the hole and then determining a first chemical profile of said fluid; the analysis of the fluid outside the apparatus and then the determination of a second chemical profile of said fluid; and the comparison of these chemical profiles in order to identify the differences between the first and the second chemical profile. 24. A method according to claim 22 or 23, comprising positioning the apparatus on a bottom battery. 25. A method according to claim 24, in which the fluid to be analyzed is a drilling mud, and in which the chemicals present in the formation are identified by comparison of the chemical profile of the drilling mud inside the bore of the apparatus, before the drilling mud comes into contact with the formation; and the chemical profile of the drilling mud outside the apparatus, after the drilling mud has come into contact with the formation.