RU2567581C1 - Method for determination of formation intervals with viscous or highly viscous oil - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention is referred to oil industry and may be used to determine intervals in the well log with viscous or highly viscous oil. The method for determination of formation intervals with viscous or highly viscous oil includes geophysical survey in the well and analysis of obtained data. The survey is performed at the stage of hole director drilling, propagation distance is assessed preliminary for all logging instruments and the instrument with the least propagation distance is selected; the borehole is drilled with drill bit having diameter that allows surveying by the instrument with the least propagation distance, the borehole is worked out with the drill bit and contractions in the borehole are eliminated, the borehole is filled in with clay drilling mud, at geophysical surveying in the well compensatory dual neutron logging plus gamma-ray logging and carbon/oxygen logging are performed, logging is doubled in the assumed interval of formation with viscous or highly viscous oil, the instruments are removed from the well, the borehole is drilled out with the drill bit as per hole director diameter, and at analysis of the obtained data intervals with high porosity and increased carbon/oxygen ratio and symmetric reduced calcium/silicon ratio are selected.

EFFECT: invention allows determining formations with viscous or highly viscous oil in the well log.

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Description

The invention relates to the oil industry and may find application in determining formations in the context of a well with viscous or highly viscous oil.

A known method for determining oil-saturated formations, according to which a core is taken and examined in the well, determine the oil saturation coefficient for the core, conduct complex logging, determine the oil saturation coefficient for the log, determine the relative coefficient as the ratio of the oil saturation coefficient for the core to the oil saturation coefficient for the log, analyze the well logs in the terrigenous section of the productive horizon, reservoirs with apparent resistivities are identified for induction logging of less than 3 Ohm · m, among the identified formations, select formations, in the mineral composition of which, by core and sludge, the presence of minerals that reduce resistivity is noted, and according to the logging data, an increased content of conductive elements is noted, for the revealed formations, the true value of the oil saturation coefficient is specified by multiplication the oil saturation coefficient for the log by a relative coefficient, the obtained value is compared with the values of the oil saturation coefficient for weak oil whelping and oil-saturated reservoirs and accordingly include the oil-saturated reservoir to the weak or oil saturated (RF patent №2517730, publish. 05/27/2014).

Closest to the proposed invention in technical essence is a method for determining oil-saturated formations, according to which core is selected and investigated and induction logging and neutron gamma-ray logging or neutron-neutron logging are carried out and the logging curves in the roofing part of the productive layer are analyzed. In this case, formations with apparent resistivities of induction logging of not more than 6-8 Ohm · m and indications on the neutron gamma-ray or neutron-neutron logging curves, representing 85% or less of the values of the lower layers, are identified. Among the identified formations, formations are chosen without clay bridges with formations of carbonated oil-saturated rocks and with apparent resistivity values of at least 15 Ohm · m. Then, the lithological composition of the identified strata is clarified and, if there is oil-saturated sandstone in their composition, a conclusion is made about the terrigenous origin of these strata. Next, they specify the values of the coefficients of porosity, permeability and oil saturation, when exceeding the lower boundaries of which for this region the identified formations are classified as productive (RF Patent No. 2487239, published. 07/10/2013 - prototype).

A common disadvantage of the known methods is the impossibility of determining formations with viscous or super-viscous oil within the horizons with fresh or weakly mineralized waters.

The proposed invention solves the problem of determining in a section of a well formation with viscous or super-viscous oil.

The problem is solved in that in the method for determining the intervals of occurrence of formations with viscous or highly viscous oil, including conducting geophysical surveys in the well and analyzing the results obtained, according to the invention, the studies are carried out at the stage of drilling the conductor of the well, the depth of investigation of all logging tools is preliminarily evaluated and the device is identified with the smallest depth of research, the wellbore is drilled with a bit with a diameter that allows you to perform research with the device with the smallest depth studies, work out the borehole with a chisel and eliminate the narrowing of the borehole, fill the borehole with clay mud, when conducting geophysical studies in the well, conduct two-probe neutron compensation plus gamma and carbon / oxygen logs, duplicate the logging in the estimated interval of occurrence of the stratified formations or high-viscosity oil, lift the instruments from the well, drill the wellbore with a bit with a diameter in accordance with the diameter of the conductor, and when analyzing the floor obtained results was isolated intervals of high porosity and simultaneously with increased oxygen to carbon ratio and symmetrical reduced calcium to silicon ratio.

SUMMARY OF THE INVENTION

Recently, stocks of high-quality oils have been depleted at an accelerated pace and their prices are rapidly growing. In this regard, increasing attention is being paid to heavy oils and natural bitumen as alternative sources of fuel and energy raw materials. So, the reserves and prospective resources of high-viscosity and ultra-high-viscosity oils (UHV) located in the Upper Permian deposits in the Volga-Ural oil and gas province are estimated by scientists in the range from 2.5 to 4.0 billion tons. Thus, exploration and additional exploration of known hydrocarbon deposits (HC) in Permian deposits is an urgent task for deep drilling. Traditional methods of well geophysical research (GIS) successfully solve the problem of determining oil-bearing strata in horizons where high salinity of formation water is noted. So, in the strata of the terrigenous Devonian at the Romashkinskoye field, the salinity of the formation water is about 270 g / l, and in the layers of the lower Carboniferous about 240 g / l. In the Upper Permian sediments, produced water is fresh or slightly mineralized with a total salinity of 0.5 to 3 g / l. Due to this, freshwater and oil-bearing strata do not differ in electrical resistivity (from 10 or more ohm). In this case, only C / O logging can solve the problem of assessing the nature of reservoir saturation. But this method has limitations, namely: a small depth of study equal to 20 cm. In view of this study, this method is not carried out in an open hole due to the penetration of the mud filtrate into the reservoir at a distance exceeding the depth of the study. In addition, for drilling under a conductor string, a bit with a diameter of 293 mm is used.

The problem of determining formations with viscous and highly viscous oil is solved as follows:

- viscous and highly viscous oils are practically not displaced by the mud filtrate;

- the interval of the conductor is drilled with a bit with a diameter that allows you to conduct research with the device with the smallest depth of study, which after geophysical studies is expanded with a bit to the diameter necessary for lowering the conductor.

Practical example

Determine the intervals of occurrence of formations with viscous or highly viscous oil in well No. 1 of the Novo-Elkhovsky field. To a depth of 184 m, the well was drilled with a bit with a diameter of 150 mm, i.e. a bit with a diameter that allows you to perform research with the device with the smallest depth of study. In the interval 140-184 m, drilling was performed with coring. According to the core description, the interval 152-156 m is represented by intensely bituminous sandstones. In the range of 156-164 m of clay, in the range of 164-172 m of water-bearing sandstones, lower to a depth of 184 m of clay. Work out the wellbore with this bit and eliminate the narrowing of the wellbore. Fill the wellbore with clay mud. Investigations are carried out at the stage of drilling the conductor of the well. Assess the depth of research of all logging tools and identify the tool with the smallest depth of research. Such a device is a C / O logging tool with a research depth of about 200 mm. The C / O logging was performed by the MARKA-INGS instrument, in which the diameter of the downhole tool is ⌀89 mm, the detector is a BGO crystal, and the crystal size is ⌀50 × 120 mm. For reliable coverage of the rocks discovered by the well, the following condition must be met:

(Dskv-dkr) / 2 <L,

where Dskv - well diameter,

dcr is the diameter of the detector (crystal) of the device,

L is the depth of the study of the GIS method.

Hence: Dskv <2L + dkr.

So for the C / O logging tool (MARKA-INS), the diameter of the well should be less: 2L + dcr = 2 × 200 mm + 50 mm = 450 mm.

During geophysical surveys in the well, two-probe neutron compensation plus gamma and carbon / oxygen logs are performed. Duplicate logging in the estimated interval of occurrence of formations with viscous or highly viscous oil. They lift the instruments from the well, drill the wellbore with a bit with a diameter in accordance with the diameter of the conductor.

In the well, C / O logging, compensation neutron logging (KNK) with gamma-ray logging (GK) were performed, see FIG. 1. The interval 152-156 m, represented by core of bitumen-rich sandstones, according to C / O logging, has increased carbon to oxygen ratios (C / O) and reduced calcium to silicon ratios (Ca / Si); aquifers in the range 164-172 m have lower readings of carbon to oxygen (C / O) and calcium to silicon (Ca / Si) ratios.

Using compensatory neutron logging (KNK) with gamma ray logging (GK), the coefficients of porosity (Kp) and clayiness (Kgl) were determined: in the reservoir 152-156 m Kp - 24%, Kgl - 2-4%; in the reservoir 164-172 m Cp - 27%, Cgl - 0.5%.

Thus, in the interval 152-156 m, a bituminous layer has been identified, in the interval 164-172 m there is an aquifer.

Application of the proposed method will allow to solve the problem of determining, in a section of a well, formations with viscous or super-viscous oil.

Claims (1)

A method for determining the intervals of occurrence of formations with viscous or highly viscous oil, including conducting geophysical surveys in the well and analyzing the results obtained according to the invention, the studies are carried out at the stage of drilling the conductor of the well, preliminary assess the depth of the study of all logging tools and identify the device with the smallest depth of study, the wellbore drill a bit with a diameter that allows you to perform research with the device with the smallest depth of study, working out open the borehole with a chisel and eliminate the narrowing of the borehole, fill the borehole with clay mud, during geophysical studies in the well, conduct two-probe neutron compensation plus gamma-ray and carbon / oxygen logs, duplicate logging in the estimated interval of occurrence of viscous or highly viscous oil , lift the instruments from the well, drill the wellbore with a bit with a diameter in accordance with the diameter of the conductor, and when analyzing the results obtained, t intervals of high porosity and simultaneously with increased oxygen to carbon ratio and symmetrical reduced calcium to silicon ratio.

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