RU2099510C1 - Method for killing development well - Google Patents

Abstract

FIELD: oil-producing industry, in particular, killing the development wells in performance of repair jobs. SUBSTANCE: injected into annular space with tubing open at the wellhead is viscoelastic compound in volume equalling the volume of annular space and tubing, then it is closed at the wellhead, and injected through annular space is viscoelastic compound in volume of well below the tubing. Then injected through annular space is killing fluid with density determined by mathematical expression. If pressure at wellhead does not rise above the casing tests pressure, the killing fluid is injected in volume equals to that of annular space with tubing closed at wellhead. The tubing is opened and killing fluid is injected in the volume equals to volume of tubing. Tubing is closed at wellhead and excessive pressure is built up at wellhead. Then well is shutoff for process holding. If wellhead pressure rises above the casing test pressure, killing fluid is injected through annular space with tubing open at the wellhead. Tubing is closed. Excessive pressure is built up at the wellhead, well is shutoff and left for process holding. EFFECT: higher efficiency. 5 cl

Description

 The invention relates to the oil industry, in particular to a method for killing production wells with underground pumping equipment.

A known method of killing production wells by injection through the annular space of a well of viscoelastic composition and killing fluid [1]
The disadvantage of this method is that under conditions of abnormal reservoir pressure, high gas factors, it is impossible to remove all reservoir fluid from the wellbore and thereby balance the reservoir pressure with a hydrostatic column of kill fluid.

Closest to the proposed invention by technical essence is a method of killing production wells, when a viscoelastic composition is pumped into tubing, and then into the annulus and after technological soaking, killing fluid (for example, saline) is pumped through the annulus of the well in the well’s volume - prototype [2]
The disadvantage of this method is the impossibility of its use in wells equipped with sucker-rod and electric spring pumps, since their layouts have a check valve that does not allow the injection of a viscoelastic composition through tubing from the wellhead.

 The aim of the invention is to increase the efficiency of killing wells equipped with deep pumps, while reducing water cut and cleaning the bottom of the formation from muds.

 This is achieved by the fact that in the method of killing production wells, which includes injecting a viscoelastic composition into the annular space of the well when the tubing is closed at the mouth, pumping the killing fluid through the annular space in the volume of the annular space and tubing and technological exposure, before injecting the viscoelastic of the composition into the annular space when the tubing is closed at the mouth, the well fluid is displaced at the wellhead by injection of a viscoelastic fluid tava into the annular space when the tubing is open at the mouth, followed by the injection of a viscoelastic composition through the annular space when the tubing is closed in the volume of the well below the tubing, then the kill fluid is injected and the well is closed with overpressure at the wellhead excerpt.

 If during injection of the killing fluid through the annular space when the tubing is closed at the wellhead, the pressure at the wellhead does not rise above the pressure of the well test, then the killing fluid is pumped into the annular space in the volume of the annular space with subsequent injection of the killing fluid when the pump is open at the wellhead -compressor pipes in the volume of tubing.

 If during injection of killing fluid through the annular space when the tubing is closed at the wellhead, the pressure at the wellhead rises above the pressure of the well test, the killing fluid is pumped into the annular space when the tubing is open at the mouth in the volume of the tubing and annular space.

где ρ плотность жидкости глушения, кг/м³;
Р_пл пластовое давление, кг/м²;
h_нкт глубина спуска насосно-компрессорных труб, м;
Н глубина залегания кровли продуктивного пласта, м;
g плотность вязкоупругого состава, кг/м³;
t_o предельное напряжение сдвига вязкоупругого состава, кг/м²;
d внутренний диаметр обсадных труб скважины, м.Before leaving the well for technological exposure, create excess pressure at the wellhead from the condition:
P _od ≥P _y ≥ (0.05 0.15) P _pl ,
where P is _the overpressure at the wellhead, kg / m ² ;
P _ODA pressure test wells, kg / m ²
R _pl reservoir pressure, kg / m ²
The density of the kill fluid is determined from the expression:

where ρ is the density of the kill fluid, kg / m ³ ;
R _pl reservoir pressure, kg / m ² ;
h _tubing depth of descent of tubing, m;
N the depth of the roof of the reservoir, m;
g density of viscoelastic composition, kg / m ³ ;
t _o ultimate shear stress of viscoelastic composition, kg / m ² ;
d inner diameter of the well casing, m

 When operating oil and gas wells, casing strings and underground equipment lose their functions over time, for example, due to corrosion, the integrity of casing strings, tubing, insulation of the power supply cable is damaged, parts of deep pumps wear out, etc. As a result, in some cases, the productivity of the wells sharply decreases, in others the flow of formation fluid to the surface is stopped, in the third an emergency situation arises, leading to gryphon formation and, as a result, explosions and fires.

 Therefore, in production wells, underground and capital repairs are periodically carried out. To carry out these works, it is first required to “plug” the well, that is, to create safe conditions under which the well ceases to manifest with gas, oil or water.

 The only way to stop the formation fluid from entering the wellbore is to create a hydrostatic column of fluid that balances the formation pressure.

 For this purpose, various combinations of injection of viscoelastic composition and saline solution of various densities are used.

 The greatest difficulties in plugging production wells arise with abnormal reservoir pressures and high gas factors, as well as with violations of the tightness of casing strings and tubing.

 In the prototype method, the viscoelastic composition is first pumped into the tubing. This is done in order to separate the space of the tubing from the annular space, and then, closing the tubing at the wellhead, pump the viscoelastic composition along the annular space. In this case, the well fluid is displaced into the formation. Then a significant part of the well fluid is mixed with a viscoelastic composition. This is especially true for gas. Therefore, after filling the well with a viscoelastic composition, technological exposure is necessary so that the free gas dissolves in the viscoelastic composition, and as a result a homogeneous system forms in the well. After that, the carbonated viscoelastic composition is replaced with a kill fluid of the required density. The described method can be applied only in fountain and gas lift wells. In wells with sucker rod pumps, this method cannot be used due to the presence of a check valve in underground equipment. In wells with electrically loaded pumps, the prototype method has limited application. It is applicable when a “knockout valve” is installed in the arrangement of underground equipment, and it can be knocked down. Usually, it is rare to open the knockout valve opening.

 According to the invention, a combined method is used to remove the wellbore fluid. First, the borehole fluid is displaced to the surface by a viscoelastic composition from the annular space and tubing by pumping it through the annular space with the tubing open, and then the borehole fluid remaining in the borehole below the tubing is displaced into the formation. Then, the viscoelastic composition in the annular space and tubing is replaced with a kill fluid with a density determined by the formula above. If there is no necessary density at the disposal of the kill fluid (saline), then a viscoelastic composition with other structural and mechanical properties should be used.

 In addition, in cases where it is possible to pump a viscoelastic composition into the formation (annular volume), then, simultaneously with the well killing, the effect of isolating aquiferous layers is achieved and the bottom-hole zone of the formation is cleaned of various muds. When, however, it is not possible to crush the viscoelastic composition into the formation after technological exposure, before lowering the new underground equipment, tubing with a funnel should be lowered to a depth of 100 m below the estimated depth of installation of the deep pump and the well should be flushed with a solution of the required density.

In all cases, before stopping the well for technological exposure in the well, it is necessary to create excess pressure from the condition:
P _od ≥P _y ≥ (0.05 0.15) P _pl
The technological exposure time is determined depending on the component composition of the viscoelastic composition and the final pressure at the wellhead during the injection of the viscoelastic composition into the formation.

Example 1. The well has a production string with a diameter of 168.3 mm, lowered to a depth of 1923 m with wall thicknesses in the range 0-1723 m ≈ 7.32 mm and 1723 1923 mm ≈ 8.94 mm; oppressed at 209 kg / cm ² ; underground equipment: ЭЦН-5-125 on tubing with a diameter of 73 mm in the range of 0-195 m and 60 mm in the range of 195-1440 m; perforation interval: 1778.8-1781.8 m, 1808.5-1811.0 m (formation A _2-3 ); reservoir pressure of 204 kg / cm ² (according to the isobar map), the actual reservoir pressure determined in a direct way to 235 kg / cm ² ; injectivity of the well 500 m ³ / day at an overpressure of 70 kg / cm ² ; repeated killing with salt solutions of various densities of 1.11-1.18 g / cm ² did not give a positive result.

 We started killing the well by the proposed method.

33 m ^{3 of} viscoelastic composition (total well volume) was prepared and 26 m ^{3 of} viscoelastic composition (total volume of annular space and tubing) was pumped through the annular space with open tubing, while the formation fluid was removed from the annular space and pump compressor pipes. The pump and compressor pipes were closed and another 7 m ^{3 of} viscoelastic composition was pumped through the annular space (the well volume is lower than the pump and compressor pipes).

где Р_пл 235•10³ кг/м², h_нкт 1440 м, Н 1779 м, γ = 900 кг/м³, d 0,153 м, τ_o= 39 кг/м², ρ = 1,180 кг/м³.Then we started the injection of saline, the density of which was determined from the expression:

where R _pl 235 • 10 ³ kg / m ² , h _tubing 1440 m, N 1779 m, γ = 900 kg / m ³ , d 0.153 m, τ _o = 39 kg / m ² , ρ = 1,180 kg / m ³ .

Thus, we choose the density of the saline solution equal to 1.18 g / cm ³ .

When the tubing was closed at the wellhead, 23 m ^{3 of} brine was pumped with a density of 1.18 g / cm ³ (ring volume), the tubing was opened and another 3.0 m ^{3 of} brine of the same density was pumped, having washed this is a viscoelastic composition of tubing. Then the tubing was closed and another 1.0 m ^{3 of} saline was pumped. The pressure at the wellhead was 90 kg / cm ² , which is greater than the pressure 235 • 0.15 35 kg / cm ² .

They closed the annulus and left the well under overpressure at the wellhead of 90 kg / cm ² for technological shutter speed (in this case, 48 hours).

After technological exposure, the pressure on the mouth was vented, which after 48 hours was 75 kg / cm ² .

The well does not show. We started repair work. After repair work after 1 day, the well returned to normal operation, with Q _w 160 m ³ / day with a water cut of 60% Q _mn 51.0 t / day.

Prior to the cessation of well operation in 1993, the mode of operation of the well was as follows: Q _w 150 m ³ / day, water cut 65% to Q _n 42 t / day.

 Thus, the well was not only put into operation after more than three years of downtime, but also increased productivity while reducing water cut.

Example 2. The well has: production casing with a diameter of 168.3 mm, lowered to a depth of 2300 m with a wall thickness of 9 mm; tested at 150 kg / cm ² ; underground equipment: tubing with a diameter of 73 mm in the interval 0-270 m and 60 mm 270-1550 m and ETSN-80; perforation interval: 2252-2277 m (reservoir B ¹⁰ ); reservoir pressure 232 kg / cm ² (06.12.94); injectivity of the well 80 m ³ / day at an overpressure of 120 kg / cm ² .

The well shows a dispersion of P _kp 70 kg / cm ² .

где Р_пл 232000 кг/м², h_нкт 1550 м, Н 2252 м, γ = 600 кг/м³, τ_o= 16 кг/м², d 0,15 м, ρ = 1140 кг/м³.We started killing the well by the proposed method. Prepared 40 m ³ viscoelastic composition and through the annular space with open tubing pumped 27.6 m ³ (the volume of the annular space and tubing) viscoelastic composition, while the injection pressure did not exceed 50 kg / cm ² . The tubing was closed at the wellhead and pumped into the annular space of 12.0 m ³ (well volume below the tubing) of a viscoelastic composition, while the pressure at the wellhead rose to 160 kg / cm ² . Opened at the wellhead pumping pipes and injected saline in a volume of 28 m ³ (the volume of the annular space and tubing) with a density determined from the expression:

where R _pl 232000 kg / m ² , h _tubing 1550 m, N 2252 m, γ = 600 kg / m ³ , τ _o = 16 kg / m ² , d 0.15 m, ρ = 1140 kg / m ³ .

The tubing was closed at the mouth, and another 0.2 m ^{3 of} brine with a density of 1.14 g / cm ^{2 was} pumped into the annular space. The pressure at the wellhead was 150 kg / m ² , closed the annular space and left the well for technological exposure.

 After venting the well does not show.

Claims (5)

 1. The method of killing a production well, which includes injecting a viscoelastic composition into the annular space of the well when the tubing is closed at the mouth, injecting the killing fluid through the annular space into the volume of the annular space and tubing, and holding the process, characterized in that before viscoelastic injection of the composition into the annular space when the tubing is closed at the mouth, the well fluid is displaced at the wellhead by injection of a viscoelastic composition and into the annular space when the tubing is open at the mouth and then the viscoelastic composition is pumped through the annular space when the tubing is closed in the well volume below the tubing, then the kill fluid is injected and the well is shut with overpressure at the wellhead excerpt. 2. The method according to p. 1, characterized in that the excess pressure at the wellhead is created from the condition
P _od ≥ P _y ≥ (0.05 0.15) P _pl ,
where P is _the overpressure at the wellhead, wells, kg / m ² ;
P _{about p r} pressure testing of wells, kg / m ² ;
R _{p l} reservoir pressure, kg / m ² . 3. The method according to claim 1 or 2, characterized in that the density of the kill fluid is determined from the expression

where ρ is the density of the kill fluid, kg / m ³ ;
R _{p l} reservoir pressure, kg / m ² ;
h _{n to t the} depth of the descent of the tubing, m;
H the depth of the roof of the reservoir, m;
γ is the density of the viscoelastic composition, kg / m ³ ;
τ _o - ultimate shear stress of viscoelastic composition, kg / m ² ;
d inner diameter of the well casing, m  4. The method according to one of claims 1 to 3, characterized in that the killing fluid is pumped into the annular space when the tubing is closed at the mouth in the volume of the annular space, followed by the injection of the killing fluid when the tubing is open at the mouth in the tubing volume compressor pipes.  5. The method according to one of claims 1 to 3, characterized in that the kill fluid is pumped into the annular space when the tubing is open at the mouth in the volume of the tubing and the annular space.