GB2396011A

GB2396011A - Analysing noise generated by fluid flow inside production tubing of a well

Info

Publication number: GB2396011A
Application number: GB0228120A
Authority: GB
Inventors: Klas Goran Eriksson
Original assignee: ABB Offshore Systems Ltd
Current assignee: Baker Hughes International Treasury Services Ltd
Priority date: 2002-12-02
Filing date: 2002-12-02
Publication date: 2004-06-09
Also published as: GB0228120D0

Abstract

Acoustic sensors 1 are located between the production tubing and the well casing of a well. The acoustic sensors may be those already installed in the well for providing information about seismic and microseismic events (eg geophones, accelerometers). The output from the sensors 1 is amplified 7 and filtered 8 to isolate the noise generated by the fluid flowing in the tubing. The fluid flow sound data may be obtained by windowing 9 the sensor output either side of the transient sound data, or by subtracting 10 transient sound data from the sensor output. Once processed, the fluid noise is analysed to derive one or more characteristics of the flow (eg velocity, flow rate, composition).

Description

239601 1

FLOW NOISE DIAGNOSIS

The present invention relates to a method of and installation for analysing fluid flow inside the production tubing of a well.

s A hydrocarbon well-bore generally consists of two approximately concentric tubes, an inner tube, known as the production tubing, acting as a conduit through which fluid can be extracted or injected, and an outer tube, known as the well casing, providing mechanical support for the surrounding rock. One possibility for monitoring fluid flow inside the 10 production tubing of a hydrocarbon well involves the use of in- line flow meters or the like positioned inside the production tubing. However, such devices are intrusive and generally have problems with coping with the variety of contaminants in the extracted fluid which typically in the case of oil extraction include gas, water and sand.

15 According to one aspect of the present invention, a method of analysing fluid flow inside the production tubing of a well comprising production tubing and a well casing is provided, said method comprising: a) providing an acoustic sensor between the production tubing and well casing of said 20 well so as to pick up an adequate level of fluid flow sound for analysis; b) processing the output of said sensor in order to obtain fluid flow sound data substantially fi ee of seismic, microseismic and other unrelated transient sound data; and c) analysing said fluid flow sound data so as to derive one or more characteristics of 25 the fluid flow therefrom.

According to another aspect of the present invention, an installation for analysing fluid flow inside a production tubing of a well is provided, said installation comprising: 30 a) an acoustic sensor positioned between the production tubing and a well casing of said well so as to pick up an adequate level of fluid flow sound for analysis; and

b) data processing means for processing the output of said sensor in order to obtain fluid flow sound data substantially flee of seismic, microseismic and other unrelated transient sound data and analysing said fluid flow sound data so as to derive one or more characteristics of the fluid flow therefrom.

Thus the present invention is based on the concept of recording the noise generated by the fluid flow with at least one suitably positioned acoustic sensor, processing the recorded noise to remove any components attributable to sources of sound other than the fluid flow itself, and then using the flow generated noise as a source of data to allow diagnosis of the 10 flow characteristics in the production tubing.

It is possible to determine characteristics of the fluid flow from the noise produced thereby because typically the flow of oil, gas, water and sand each produces different acoustic flow noises, and by processing the complex signal produced by the flow generated noise, for 15 example using frequency content and/or polarisation, it is possible to derive information on the components of flow. This allows the well operator to have information regarding, for example, how much different zones of the well are producing, unsteady flow conditions and the break through of water and/or gas. This information can, in turn, be used to justify and adjust the well productivity index and applied, using a suitable model, to management 20 of the well flow.

Processing ofthe or each sensor's outputs in order to separate ofthe sound data attributable to fluid flow from that generated by transient events, such as microseismic events, seismic events and surface operations, may be effected either by windowing data recorded by the 25 sensor either side ofthe transient sound data (i.e. separating out and ignoring all sound data recorded at the same time as the transient sound) and/or by subtracting the transient sound data from the recorded data, such that the remaining sound data is attributable, at least for the most part, solely to acoustic flow noise.

30 Preferably, the present invention makes use of at least one seismic sensor, which may in some cases already be installed in side the well for the purpose of providing information

on seismic and/or microseismic events, such sensor then having the dual purpose of seismic signal detection and flow noise recordal.

It is known to fit seismic sensors, such as geophones, hydrophores or accelerometers, 5 inside fluid extraction or injection wells in order to detect the seismic or microseismic signals produced by controlled seismic sources during an active survey, such as Vertical Seismic Profiling (VSP), or by seismic and microseismic events occurring naturally, or as the consequence of fluid extraction or injection, in the strata surrounding the bore hole.

The seismic sensors are normally attached to the casing of the well to provide the best 10 possible acoustic coupling to the strata, as for example illustrated in UK Patent Application No. 0122929.3, and fitted as strings of sensors down the bore so as to provide sufficient spatial sampling of seismic signals, and also in some cases to facilitate steering of the detection sensitivity in different directions.

15 Typically each seismic sensor consists of an arrangement of 3 or 4 individual sensors, as illustrated in GB-A- 2 275 337, the output fiom the strings of sensors being processed in order to determine details of the strata which can be of use in improving the fluid extraction process efficiency. However the sounds picked up by the seismic sensors are not purely those from seismic events but also comprise background noise generated by the

20 flow of fluid through the production tubing, and also surface operations noise (such as pump noise) transmitted down the well.

In order to minimise the amount background noise reaching such a sensor, great effort has

in the past been made to acoustically insulate the geophones from the noise from flow in 25 the production tubing and the surface operations. In order further reduce the effect of background noise of the sensors, considerable signal processing has also been employed

to minimise the contamination of the required seismic sound data, as well as the derivation of the further data therefiom, see for example GB-A- 2 372 568. However, once the necessary data regarding the seismic event has been isolated, the remainder of the data, 30 including the data regarding the acoustic noise from the flow in the production tubing, has in the past been discarded.

Where seismic sensors are to be used for seismic signal detection and flow noise recordal, standard seismic processing algorithms can be used to detect and separate seismic, microseismic and other transient sounds *om fluid flow noise on the basis of known 5 trigger signals fiom controlled sources, or using triggering algorithms based on the expected characteristics of the seismic signals (for example amplitude, frequency, phase content or polarisation) at a single geophone or variations across an array of geophones (for example phase delay), the latter being particularly useful for identifying and separating out transient sounds that are generated from surface operations and are transmitted down 10 through the well. Thus where suitably positioned seismic sensors are used, it is possible to separate out two data signals from the sensors' outputs, the first attributable, at least for the most part, to fluid flow noise inside the well, and the second attributable, at least for the most part, to the sound generated by seismic events.

15 An embodiment of the invention will now be described, by way of example, with reference to the following drawings, in which: Fig. I is a graph illustrating the relationship between the flow rate inside the production tubing of a well and the acoustic noise produced thereby; Fig. 2 shows, in simplified form, an installation for monitoring fluid flow and at the same time detecting microseismic events; and Fig. 3 shows, in simplified form, a possible configuration for processing the sensor outputs.

Fig. I shows an example of acoustic noise (RMS noise) dependency on flow rate for a variety of seismic sensors (geophones and accelerometers) attached to different points on the inside of casing and outside of production tubing. The data illustrates the strong dependency of acoustic noise on the flow rate and the potential for using flow induced 30 acoustic noise to characterise flow (e.g. velocity, flow r ate, composition).

Fig. 2 shows an installation comprising a plurality of geophones 1 fitted as strings (only one string of five geophones shown) located against well casing 2 of a production well comprising the well casing 2 and production tubing 3. Despite the mechanical isolation of the geophones 1 fiom the production tubing 3, the sensitivity of the geophones 1, 5 distance between the geophones 1 and production tubing 3 and well bore environment are such that an adequate level of flow noise is still detected by the geophones. The geophone 1 outputs are fed, via electrical connections 4, to a processing unit 5, that is also located against the well casing 2 within the borehole (though it could equally be located top-side).

Once processed, the sound data is then transmitted to the well head by cables 6, which may 10 be electrical or optical.

Fig. 3 illustrates a possible form of signal processing that can be carried out on a geophone 1 output in order to separate the data into fluid flow noise and seismic / microseismic signals. The output of the geophone is first amplified by an amplifier 7 and then passed 15 through an adaptive filters 8, these elements being the same elements that are employed in the standard use of the geophones for seismic detection, in order to isolate any seismic signals present in the data which can then be analysed for the purpose of deducing the characteristics of the seismic event. At the same time, a copy of the geophone output which has been amplified but not filtered is processed in one of two ways in order to 20 isolate a fluid flow noise signal. The first option is to pass a copy of the geophone output through a windowing element 9 which carries out a windowing operation wherein all acoustic data detected at the same time as a seismic signal is simply excised such that the data r emaining represents, at least for the most part, only fluid flow noise. The second option is to pass the copy of the geophone output through a subtraction element 10 which 25 cancels the seismic signal fiom the copy of the geophone output, such that the data remaining represents, at least for the most part, only fluid flow noise.

Claims

CLAIMS:

1. A method of analysing fluid flow inside the production tubing of a well comprising production tubing and a well casing, said method comprising: s a) providing an acoustic sensor between the production tubing and well casing of said well so as to pick up an adequate level of fluid flow sound for analysis; b) processing the output of said sensor in order to obtain fluid flow sound data 10 substantially free of seismic, rnicroseismic and other unrelated transient sound data; and c) analysing said fluid flow sound data so as to derive one or more characteristics of the fluid flow therefi om.

15

2. A method according to claim 1, wherein said fluid flow sound data is obtained by windowing the sensor output either side of said transient sound data.

3. A method according to claim 1, wherein said fluid flow sound data is obtained by subtracting said transient sound data fi om the sensor output.

4. A method according to any preceding claim, wherein said sensor is a seismic sensor positioned so as to pick up seismic and/or microseismic sounds, the output of said sensor being processed to obtain seismic and/or microseismic sound data substantially fi ee of unrelated transient sound data and fluid flow sound data.

5. A method according to any preceding claim, wherein the or each characteristic of the fluid flow is used for management of the well.

6. An installation for analysing fluid flow inside a production tubing of a well, said 30 installation comprising:

a) an acoustic sensor positioned between the production tubing and a well casing of said well so as to pick up an adequate level of fluid flow sound for analysis; and b) data processing means for processing the output of said sensor in order to 5 obtain fluid flow sound data substantially free of seismic, rncroseismic and other unrelated transient sound data and analysing said fluid flow sound data so as to derive one or more characteristics of the fluid flow therefrom.

7. An installation according to claim 6, wherein the data processing means obtains 10 said fluid flow sound data by windowing the sensor output either side of said transient sound data.

8. An installation according to claim 6 or 7, wherein the data processing means obtains said fluid flow sound data by subtracting said transient sound data fi om the 15 sensor output.

9. An installation according to any one of claims 6 to 8, wherein said sensor is a seismic sensor positioned so as to pick up seismic and/or microseismic sounds and the data processing means is adapted to process the output of said sensor in order 20 to obtain a seismic and/or microseismic sound data substantially free of unrelated transient sound data and fluid flow sound data.

10. An installation according to any one of claims 5 to 9, wherein the data processing means comprise one or more data processors located within the well and/or topside.

1 1. A method substantially as hereinbefore described with reference to Figures 1, 2 and 3. 12. An installation substantially as hereinbefore described with reference to Figures 1, 30 2 and 3.