RU2165016C1 - Process testing tightness of operational string in injection well - Google Patents

Abstract

FIELD: oil production industry. SUBSTANCE: operational mode of well is changed by closing partly gate valve across well-head: flow rate of fluid decreases by 30-50% of initial value. Pressure change ΔP is recorded in time interval Δt from moment of change of operational mode of well in process of which maximum rate of pressure drop is observed till it stabilizes. Coefficient of pressure drop K₁ is determined as ΔP/Δt. Coefficient K₂ of pressure drop curve is found in same manner at least once a year. K₁ and K₂ are compared. If K₂ ≤ K₁, then operational string is tight. If K₂ > K₁ and no work to raise penetrability of pool in this well was conducted then operational string is not tight. In the last case well is examined additionally with use of geophysical instruments to define more exactly character and point of loss of tightness of operational string. EFFECT: simplified approach to testing and reduced time for realization of process. 1 cl, 1 dwg

Description

 The invention relates to the oil industry, and in particular to methods for monitoring the technical condition of the production casing of injection wells in order to determine its tightness.

 Known methods for monitoring the technical condition of the production casing of injection wells, namely for tightness, using flow measurement, thermometry [1 and 2] and crimping.

 Their implementation is associated with the involvement of research crews and requires a lot of time to prepare access roads and wellheads. At the same time, the necessity of killing a well requires the call of a team of overhaul of wells and tripping operations, which leads to a rise in the cost of research. Due to the high cost of research work, this kind of work is often carried out in insufficient volume, which is fraught with negative consequences, namely salinization of the upper drinking water due to the untimely detection of leakage in the production string.

 There is also a known method for testing the casing string for leaks [3], which includes injecting a working agent, crimping the string with internal pressure, and after changing the pressure, the casing is additionally filled with a working agent until the initial pressure is restored and the tightness is judged by the amount of injected agent.

 The disadvantage of this method is the complexity of the work associated with prolonged shutdown of the well.

 There is also a method of determining damage to the production casing in the well [4], which includes injecting into the space between the casing and working casing a liquid not miscible with water with a specific gravity of less than one, forcing it through the air to the depth of the casing lowering, then bleeding the air and removing the liquid to the surface, and damage to the columns is judged by the decrease in fluid volume.

 Its disadvantage is the danger of explosive situations due to the formation of an explosive mixture of atmospheric oxygen and gas.

There is also a method for determining the location of damage to technological columns of wells [5], which includes injecting liquid into the annulus that is insoluble in water and having a density less than the density of water, followed by measuring the established overpressure at the wellhead in the pipe and annulus, and the depth of the damage site determined on the basis of the following ratio:
H = 10 (P ₁ -P ₂ ) / (γ ₁ -γ ₂ ).
In this case, in the case of reducing the overpressure to zero, measure the static fluid levels in the pipe and annular spaces of the well, and the depth of the damage site is determined based on the following ratio:
H = (H ₁ γ ₁ -H ₂ γ ₂ ) / (γ ₁ -γ ₂ ),
where H ₁ - the depth of the static water level in the pipe space, m;
H ₂ - the depth of the static level of the fluid pumped into the annulus, m;
P ₁ - steady-state pressure at the mouth, in the annulus, kg / m ² ;
P ₂ - steady-state pressure at the mouth, in the pipe space, kg / m ² ;
γ ₁ - the density of water in the pipe space, kg / m ³ ;
γ ₂ - the density of the fluid pumped into the annulus, kg / m ³ ;
H is the depth of the violation of the column, m

 The disadvantages of the method are the high cost of time associated with stopping the operation of the well, the preparation of the working fluid, as well as the complexity of determining the leakage of the process column, the borrowing technique.

 As a prototype, a method for monitoring the tightness of the production casing of the injection well [6], which includes changing the mode of operation of the well and fixing the change in pressure at the wellhead, is adopted. The leakage of the column is judged by a sharp change in the steady-state value of pressure (discharge) compared with previous measurements.

 The disadvantage of this method is that it is applicable only in conditions when the reservoir pressure is lower than hydrostatic.

 The technical result of the present invention is to provide a method, as far as possible devoid of the above disadvantages.

 The technical result is solved by the described method for monitoring the tightness of the production casing of the injection well, including changing the operating mode of the well and fixing the change in pressure at the wellhead.

New is that the change in the mode of operation of the well is carried out by covering the valve at the wellhead with a decrease in the flow rate of the working fluid by 30 - 50% of the original, and the change in pressure is recorded in the period from the moment of changing the mode of operation of the well, during which the maximum rate is observed pressure drop, until it stabilizes, after which the coefficient of pressure drop is determined from the ratio
K ₁ = ΔP ₁ / Δt ₁ ,
where ΔP ₁ is the change in pressure in the time interval from the beginning of the maximum rate of decline to its stabilization, MPa;
Δt ₁ is the time during which a change in pressure was recorded, min,
and similarly determine the coefficient K _{2 of} the pressure drop curve with a frequency of at least once a year, while if K ₂ ≤ K ₁ , the production casing is tight and not tight if K ₂ > K ₁ , provided that after the determination of K ₁ in this well, no work was carried out to increase the permeability of the formation.

In the event that K ₂ > K ₁ , the well is additionally examined using geophysical instruments to clarify the nature and location of the leakage of the production string.

 The drawing shows the pressure drop curves obtained at different times.

 The method is carried out in the following sequence.

 At the well under injection, wellhead instruments measure the flow rate of the pumped working fluid and the current wellhead pressure. Then, by covering the gate valve at the wellhead, the well operating mode is changed, while the flow rate of the working fluid is reduced by 30-50% of the initial one, which is controlled by the wellhead flowmeter. In the time interval from the moment the operating mode of this well changes, during which the maximum rate of pressure drop is observed until it stabilizes, the pressure change in time is recorded, i.e. at every specified time intervals, the pressure is recorded using a technical or electronic pressure gauge. As practical research in the fields shows, the maximum rate of pressure drop before it stabilizes is usually about 1.5 hours.

Further, according to the data obtained, which for clarity of comparison can be listed in the table, a pressure drop rate curve is constructed (curve 1). The coefficient K _{1 of} the pressure drop curve is determined by the formula
K ₁ = ΔP ₁ / Δt ₁ ,
where ΔP ₁ is the change in pressure in the time interval from the beginning of the maximum rate of decline to its stabilization, MPa;
Δt ₁ - time during which a change in pressure was recorded, min.

Similarly, with a frequency of at least once a year, determine the coefficient K _{2 of} the pressure drop curve with a frequency of at least once a year (curves 2 and 3).

 Compare the obtained pressure drop coefficients with each other.

If K ₂ ≤ K ₁ (curves 1 and 2), then make a conclusion about the tightness of the production string.

If K ₂ > K ₁ (curves 1 and 3) and after determining K _i in this well, no work was done to increase the permeability of the formation, then the production string is not tight.

 In this case, the well is additionally examined using geophysical instruments to clarify the nature and location of the leakage of the production string. To clarify the place and nature of leakages in the production casing, a major overhaul team and a geophysical lot are involved, and the violations are eliminated using existing isolation work technologies.

 The use of the invention allows you to quickly monitor the condition of the production casing in injection wells with minimal time, without involving (for monitoring) the workover team, which makes it possible for these teams to purposefully stand on the wells with identified violations and timely repair work to eliminate the leakage of the casing instead of wasting working time searching for leaking wells, which ultimately leads to the preservation and improvement of environmental environmental conditions in the area of water injection to maintain reservoir pressure, where depressurization of the production string occurred.

Sources of information
1. V.M. Dobrynin "Interpretation of the results of geophysical research", M., Nedra, 1988

 2. The book "Sputnik oilfield geologist", M., Nedra, 1989, p. 246.

 3. A.S. USSR N 829867, E 21 B 43/00, B.I. N 18, 1981

 4. A.S. USSR N 1218080, E 21 V 43/00, B.I. N 10, 1986

 5. Patent R.F. N 2094608, E 21 B 47/00, B.I. N 30, 1997

 6. A.S. USSR N 1810516, E 21 В 47/00, B.I. N 15, 1993

Claims (2)

1. The method of monitoring the tightness of the production casing of the injection well, including changing the operating mode of the well and fixing the change in pressure at the wellhead, characterized in that the changing of the operating mode of the well is carried out by covering the valve at the wellhead with a decrease in the flow rate of the working fluid by 30-50% of initial, and the pressure change is fixed in the period of time from the moment of changing the well operating mode, during which the maximum rate of pressure drop is observed, until it stabilizes tion, after which the pressure drop coefficient of correlation

where ΔP ₁ is the change in pressure in the time interval from the beginning of the maximum rate of decline to its stabilization, MPa;
Δt ₁ is the time during which a change in pressure was recorded, min,
and similarly determine the coefficient K _{2 of} the pressure drop curve with a frequency of at least once a year, while if K ₂ ≤ K ₁ , then the production casing is tight, and it is not tight if K ₂ > K ₁ , provided that after determination of K ₁ in this well, no work was conducted to increase the permeability of the formation. 2. The method according to claim 1, characterized in that in the case of K ₂ > K _{1, the} well is additionally investigated using geophysical instruments to clarify the nature and location of the leakage of the production string.