RU2246613C1 - Method for controlling pressurization of force well - Google Patents

Abstract

FIELD: oil and gas extractive industry.

SUBSTANCE: during recording of pressure change pressure is measured at mouth at tubing column entrance and in inter-tubular space. Recording of pressure change is performed on basis of pressures comparison before and after stopping of well on basis of speed of pressure fall at mouth and in inter-tubular space after stopping of operation well and on basis of pressures comparison before and after well launch for forcing on basis of speed of pressure increase at mouth and in inter-tubular space after well launch. As criterion of pressurization estimation a calculated value of liquid flow, which enters and exits inter-tubular well space is taken.

EFFECT: higher trustworthiness.

1 ex

Description

The invention relates to the oil and gas industry and may find application in the control of tightness of cased injection wells equipped with a tubing string and a packer.

There is a method of monitoring the tightness of the production casing of an injection well, which involves changing the mode of operation of the well by covering the valve at the wellhead with subsequent recording of the change in pressure. At the same time, the flow rate of the injected fluid is reduced to 30-80% of the initial one, and the pressure change is fixed in the time interval from the moment the well operating mode changes, during which the maximum rate of pressure drop is observed until it stabilizes. In this case, the coefficients of the pressure drop curve K ₁ and K _{2 are} determined by calculation. The production string is not tight if K ₂ > K ₁ , provided that after determining K ₁ no work has been done in this well to increase the permeability of the formation (RF Patent No. 2214508, class E 21 V 47/00, E 21 V 17 / 00, publ. 2003.10.20).

The known method allows you to quickly monitor the tightness of the production casing of the injection well. The disadvantage of this method is the presence of a large number of errors in determining the tightness due to the changing rate of pressure drop, a large period of time required for the measurement and the influence of reservoir pressure on the pressure gauge.

Closest to the invention, the technical essence is a method for testing the tightness of the production casing of an injection well, including lowering the packer into the well, closing the borehole with the packer, creating pressure above the packer by injecting fluid into the well, and recording pressure changes with the wellhead pressure gauge, which is used to judge production leaks the columns. The change in pressure is recorded simultaneously under the packer using a similar pressure gauge as on the mouth, which is lowered together with the packer through the tubing space of the tubing, while judging by changes in the indicators of both manometers, the tightness of the packer is judged, and if the pressure gauge changes the mouth with a constant pressure gauge reading under the packer concludes that the production string is leaking (Application No. 2002111062, class E 21 B 47/00, publ. 2003.11.10 - prototype).

The disadvantage of this method is the risk of places of leakage of the production string when creating excessive pressure in the annulus. In addition, due to the communication between the under-packer space and the formation, the formation pressure influences the measurement readings, which reduces the accuracy of the studies.

The invention solves the problem of increasing the reliability of determining the tightness of an injection well.

The problem is solved in that in a method for monitoring the tightness of an injection well, including stopping the well, recording a change in pressure in the annular space blocked by the packer and in the well space and determining the tightness of the annular space, according to the invention, when measuring pressure changes in the well space, the pressure at the wellhead is measured at the entrance to the string of tubing, the registration of pressure changes is carried out by comparing the pressures before and after stopping the well at the pressure drop growth at the wellhead and in the annulus after stopping a working well and comparing the pressures before and after starting the injection well according to the rate of increase in pressure at the wellhead and in the annulus after starting the well for injection, while determining the tightness of the annulus for the evaluation criterion the tightness of the annulus take the calculated value of the flow rate of the fluid entering or leaving the annulus of the well.

The features of the invention are:

1. well shutdown;

2. registration of changes in pressure in the annular space blocked by the packer;

3. registration of changes in pressure in the borehole space;

4. determination of the tightness of the annulus by the ratio of the measured pressures;

5. when registering changes in pressure in the borehole space, measuring pressure at the mouth at the inlet to the tubing string;

6. registration of changes in pressure compared to pressures before and after well shutdown by the rate of pressure drop at the wellhead and in the annulus after shutting down a working well;

7. registration of changes in pressure compared to pressures before and after starting the well for injection at the rate of increase in pressure at the wellhead and in the annulus after starting the well for injection;

8. the choice as a criterion for assessing the tightness of the annulus is the calculated value of the flow rate of the fluid entering or leaving the annulus.

Signs 1-4 are common with the prototype, signs 5-8 are the essential distinguishing features of the invention.

SUMMARY OF THE INVENTION

Leakage in the annulus of the injection well, i.e. the space bounded by the production string, tubing string and packer installed in the lower part of the well leads to undesirable fluid flows in the annulus (behind the production string), fluid passages by the packer or leaks of injected fluid through the discontinuities of the tubing string into the annulus space. Such overflows and leaks contribute to the removal of anticorrosive fluid from the annulus, increased corrosion of the production string and its premature failure. Existing methods for assessing leaks determine leaks or only production casing without determining leaks of other equipment in the well, such as a packer, tubing string, or determine leaks with any one type of change in well condition, i.e. only when it is stopped without leakage analysis when starting a well for injection. All this introduces errors in the determination of leaks and reduces the accuracy of the definitions. The proposed method solves the problem of increasing the accuracy of determining the leakage of the annular space of the well. The problem is solved as follows.

In the injection well, equipped with a production string, tubing string and a packer overlapping the annulus slightly above the interval of the reservoir, tightness of the annulus is monitored. For this, pressure changes are recorded at the wellhead in the annulus and at the inlet to the tubing string. The registration of pressure changes is carried out by comparing the pressures before and after stopping the well by the rate of pressure drop at the wellhead and in the annulus after shutting down a working well and by comparing the pressures before and after starting the well for injection by the rate of pressure increase at the wellhead and in the annulus after starting the well for download. This approach to recording pressure changes is caused by the fact that the intensity of fluid flows with increasing and decreasing pressure in the well may be different and not coincide in absolute value. So, for example, a packer can pass fluid in one direction and not pass in the other, overflows in the annulus can occur and occur not instantly, but with a time delay, etc. The detection of pressure changes only when the well is suspended or only when the well is started for injection even if they do not coincide already indicates a leakage in the annulus.

The slower the pressure changes in the annulus compared to the pressure in the tubing string, the more tight the annulus. Simultaneously with the measurement of pressure changes, you can measure the change in liquid level in the annulus, for example, using an echo sounder. If the liquid level in the annulus decreases after the well stops or a very low constant level, it can be assumed that the annulus is not tight. If the well is not under injection, then to determine the leak, the well is temporarily launched for injection. The registration of pressure changes is carried out by comparing the pressures before and after stopping the well by the rate of pressure drop at the wellhead and in the annulus after shutting down a working well and by comparing the pressures before and after starting the well for injection by the rate of pressure increase at the wellhead and in the annulus after starting the well for download.

In the proposed method, the change in the volume dV of the droplet fluid in the annulus when the pressure in the annulus is changed by dP is determined by the equation:

dV = -β V ₀ dP,

where dV is the magnitude of the volume change with a pressure drop of dP within the volume changes from 0 to 0.15 m ³ ;

V ₀ - the initial volume of fluid in the annulus, m ³ , within the range of 6 to 26 m ³ in the presence of a string of tubing;

V ₀ = S ₀ L,

where S ₀ is the area of the annulus, m ² , in the range of changes from 0.005099 m ² to 0.015763 m ² ;

L is the length of the production string to the packer, m, within the range from 900 to 1900 m;

D _int - inner diameter of the production casing, m, within the range of changes from 0.102 to 0.168 m;

d _nar - the outer diameter of the tubing string, m, within the range of changes from 0.0603 to 0.102 m;

β is the average coefficient of volumetric compression in the pressure range P ₁ -P ₂ = dP;

The coefficient β depends on the type of liquid, its temperature and pressure.

Limits of change β = (4-7) · 10 ^-10 Pa ^-1 (for oil without gas)

For most reservoir oils, β = (7-30) · 10 ^-10 Pa ^-1 .

Limits of change β = 4.5-5.29 · 10 ^-4 Pa ^-1 (for fresh water)

Limits of change β = 3.7 · 10 ^-10 -5.0 Pa ^-1 (for produced water)

dP = (P _mezhtr1- P _mezhtr2 ) - change in pressure in the annulus during the measurement, MPa;

dP can vary from 0.1 to 15 MPa (10 ⁵ Pa to 15 · 10 ⁶ Pa) depending on the pressure of the pumped liquid and the tightness of the annulus.

P _mezhtr1 - the first measurement of pressure in the annulus with a working well;

P _mezhtr2 - the last measurement of pressure in the annulus when the well is stopped;

Q is the leakage rate of the system within the range from 0 to 3.5 m ³ / h (from 0 to 3500 l / h);

where T is the time during which the pressure drop is determined. The measurement time depends on the pressure drop and can range from 5 minutes to 1 hour or more.

To determine the degree of tightness of the system: production casing - tubing string - packer, this method also uses the system leakage coefficient K _n = dP _shutter / dP _mouth . This coefficient shows the relationship between the rate of change of pressure in the annulus of the well and the rate of change of pressure at the wellhead over the same period of time.

When K = 1, (dP _shutter = dP _mouth ) the system is leaking.

At K = 0, (dP _shut = 0) the system is tight.

The annular tightness criteria are as follows: Q less than 5 l / h (5 · 10 ^-3 m ³ / h) - the system is considered airtight; Q more than 5 l / h - the system is considered leaky.

The tightness value at a flow rate of Q up to 5 l / h (5 · 10 ^-3 m ³ / h) was determined by comparative tests by measuring the pressure change, calculating the fluid flow rate using the formula and by bleeding pressure from the annulus and determining the presence of circulation from the annulus during field tests.

With a flow rate of Q up to 5 l / h, flows into and out of the annulus are negligible, while the losses of anticorrosive fluid and the effect of injection pressure on the production string are small.

Concrete example

The tightness of the injection well equipped with a production casing, a tubing string and a packer covering the annular space 1690 m above the interval of the reservoir is performed. Water is injected through the injection well with a pressure at the mouth of 10 MPa and a flow rate of 289 m ³ / day. (12 m ³ / hour). Pressure is measured at the mouth at the inlet to the tubing string and in the annulus with a MP4-UU2 pressure gauge. The measurement data is as follows: the pressure at the mouth at the inlet to the tubing string is 10 MPa, in the annulus - 6 MPa. Stop the well. The pressure change is recorded 1 hour after the well stops at the wellhead at the inlet to the tubing string and in the annulus. The measurement data is as follows: the pressure at the mouth at the inlet to the tubing string is 7 MPa, in the annulus - 4.45 MPa. They let a well under water injection. The pressure change is recorded 13 minutes after the well is launched at the wellhead, at the inlet to the tubing string and in the annulus. The measurement data is as follows: the pressure at the mouth at the inlet to the tubing string is 9.3 MPa, in the annulus - 4.9 MPa.

Determine the leakage rate of the annulus of the injection well when the well is stopped for 1 hour.

Q = β V _{0 Difficult} dP / T = -7 · 10 ^-10 · 3 · 16.8585 · 10 ^6/1 = 0.01828 m ³ / H.

V ₀ - the initial volume of fluid in the annulus of 16.8585 m ³ ,

V ₀ = S ₀ · L,

where S ₀ - the area of the annular space of 0.00997 m ² ;

L is the length of the production string to the packer, 1690 m;

D _int - inner diameter of the production casing 0.152 m;

d _nar - the outer diameter of the tubing string 0.102 m;

dP _shut = 155 * 10 ⁴ Pa.

T = 1 hour. Β = 7 · 10 ^-10 Pa ^-1 ;

We determine the leakage rate of the annulus of the injection well 13 minutes after the start of the well.

Q = -β V ₀ dP _shut · 60 / T = -7 · 10 ^-10 · 16.8585 · 45 · 10 ⁴ · 60/13 = 0.0245 m ³ / hour.

dP _shutter = 45 · 10 ⁴ Pa.

T = 13 min, β = 7 · 10 ^-10 Pa ^-1 ; (oil-based anticorrosive fluid is pumped into the annulus)

The tightness of the annulus is judged by the rate of pressure drop at the wellhead and in the annulus after shutting down a working well and by comparing the pressures before and after starting the well for injection, by the rate of increase in pressure at the wellhead and in the annulus after starting the well for injection. When determining the tightness of the annular space for the criterion for assessing the tightness of the annular space take the estimated value of the flow rate of fluid entering or leaving the annular space of the well, which in this case is equal to 0.0245 m ³ / hour and 0.01828 m ³ / hour (more than 5 l / hour) Conclusion: the annulus is leaking.

The system leakage coefficients in this case are equal

For the period of well shutdown K = dP _shut / dP _mouth = 1.55 / 3 = 0.516;

The system is 50% leaky.

For the start-up period of the well, K = dR _shutter / dR _mouth = 0.45 / 2.3 = 0.196.

The system is leaky by 19.6%.

This is due to the fact that when starting a well, the pressure at the wellhead increases faster than when shutting down, and the packer’s efficiency is different.

Application of the proposed method will improve the reliability of determining the tightness of the production casing of an injection well.

Claims (1)

A method for monitoring the tightness of an injection well, including stopping the well, recording a change in pressure in the annulus blocked by the packer and in the borehole, and determining the tightness of the annulus, characterized in that when registering a change in pressure in the borehole, pressure is measured at the mouth at the entrance to the column tubing, registration of changes in pressure is carried out by comparing the pressures before and after stopping the well at the rate of pressure drop at well and in the annulus after shutting down a working well and comparing the pressures before and after starting the injection well according to the rate of increase in pressure at the wellhead and in the annulus after starting the injection well, while determining the tightness of the annular space, the criterion for assessing the tightness of the annular space is taken the estimated amount of fluid flow entering or leaving the annulus of the well.