RU2121566C1 - Method of killing the development wells - Google Patents

Abstract

FIELD: oil producing industry, in particular, killing of development wells in carrying out of repair jobs. SUBSTANCE: method includes injection into well annular space, with open tubing of viscoelastic compound in volume equalling that of annular space and tubing; closing of tubing at wellhead and injection of viscoelastic compound through annular space in volume of well below tubing, then injection through annular space of killing fluid with density determined by the expression given in the invention description. Should pressure at wellhead do not rise above test pressure of casing, killing fluid with closed tubing as wellhead is injected in volume of annular space, tubing is opened, and killing fluid in volume of tubing is injected; tubing is closed and excessive pressure is built up at the wellhead within the values indicated in the invention description. Then well is shut-in for process holding, if wellhead pressure rises above test pressure, killing fluid is injected through annular space with tubing opened at wellhead, in volume of annular space and tubing, tubing is closed, excessive pressure is built up at wellhead, well is closed and let stand. 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 reservoir pressure with a hydrostatic column of kill fluid.

 Closest to the invention in technical essence is a method of killing production wells, when a viscoelastic composition is pumped into tubing, and then into the annular space and after technological soaking, killing fluid (for example, saline) is pumped through the annular space of the well in the well volume - a prototype [2].

 The disadvantage of this method is the impossibility of its use in wells equipped with rod and electric spring pumps, because in their layouts there is a check valve that does not allow injection of a viscoelastic composition through tubing from the wellhead.

 The purpose 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 жидкость глушения, кг/м³;
P_пл - пластовое давление, кг/м²;
h_нкт - глубина спуска насосно-компрессорных труб, м;
Н - глубина залегания кровли продуктивного пласта, м;
γ - плотность вязкоупругого состава, кг/м³;
τ₀ - предельное напряжение сдвига вязкоупругого состава, кг/м²;
d - внутренний диаметр обсадных труб скважины, м.Before leaving the well for technological shutdown create excess pressure at the wellhead from the condition
P _od ≥ P _y ≥ (0.05 - 0.15) P _pl ,
where P _y - overpressure at the wellhead, kg / m ² ;
P _ODA - pressure test wells, kg / m ² ;
P _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 ;
P _PL - reservoir pressure, kg / m ² ;
h _tubing - the depth of the descent of the tubing, m;
N - the depth of the roof of the reservoir, m;
γ is the density of the viscoelastic composition, kg / m ³ ;
τ ₀ - ultimate shear stress of viscoelastic composition, kg / m ² ;
d is the 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, and 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 flow of formation fluid into the wellbore is to create a hydrostatic column of fluid that balanced 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, the viscoelastic composition is pumped through 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 electric submersible pumps, the prototype method has limited use. It is applicable when a knockdown valve is installed in the underground equipment line-up and 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 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 downhole 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. Well N 31174 bush 1284 of the Samotlor field DAO-OT "Nizhnevartovskneft" has:
- production casing 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 m ≈ 8.94 mm; oppressed at 209 kg / cm ² ;
- underground equipment: ETsN-5-125 on tubing with a diameter of 73 mm in the interval 0-195 m and 60 mm in the interval 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 map of isobars), the actual reservoir pressure determined directly by the method of 235 kg / cm ² ;
- injectivity of the well 500 m ³ / day at an overpressure of 70 kg / cm ² ;
- the well was put into operation on January 17, 1987. During the period from 01.87 to 02.31.93, 11 underground repairs and 1 overhaul were carried out. From 02.31.93 the well is idle. Repeated killing with salt solutions of different densities of 1.11-1.18 g / cm ³ did not give a positive result.

 03/26/96 started killing the well according to 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 tubing was closed and another 7 m ^{3 of} viscoelastic composition was pumped through the annular space (well volume below the tubing).

где Р_пл = 235•10³ кг/м²,
h_нкт = 1440 м,
Н = 1779 м,
γ = 900 кг/м³,
d = 0,153 м,
τ₀ = 39 кг/м², \
ρ = 1,180 кг/м³.Then they started to inject saline, the density of which was determined from the expression:

where R _pl = 235 • 10 ³ kg / m ² ,
h _tubing = 1440 m,
H = 1779 m,
γ = 900 kg / m ³ ,
d = 0.153 m
τ ₀ = 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 our 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 _n = 51 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 water cut of 65% to Q _n = 42 t / day.

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

Example 2. Well N 37058 bush 1228 Samotlor field DAO-OT "Nizhnevartovskneft" has:
- production casing with a diameter of 168.3 mm, lowered to a depth of 2300 m with a wall thickness of 9 mm;
- pressed to 150 kg / cm ² ;
- underground equipment: tubing pipes 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 (12/06/94);
- injectivity of the well 80 m ³ / day at an overpressure of 120 kg / cm ² .

Since 1993, the well has been idle awaiting underground repairs. The well exhibits an aerosol P _kp = 70 kg / cm ² .

где Р_пл = 232000 кг/м²;
h_нкт = 1550 м,
Н = 2252 м,
γ = 600 кг/м³,
τ₀ = 16 кг/м²,
d = 0,15 м,
ρ = 1140 кг/м³.October 26, 1993 began killing wells 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 viscoelastic composition, while the pressure at the wellhead rose to 160 kg / cm ² . We opened tubing at the wellhead 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 P _PL = 232000 kg / m ² ;
h _tubing = 1550 m
H = 2252 m
γ = 600 kg / m ³ ,
τ ₀ = 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} saline with a density of 1.14 g / cm ^{3 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 production wells, which includes injecting a viscoelastic composition into the annular space of the wells when the tubing is closed at the mouth, pumping the killing fluid through the annular space into the volume of the annular space and tubing, and technological shutter speed, characterized in that before injecting the viscoelastic of the composition into the annular space when the tubing is closed at the mouth of the tubing displaces the wellbore fluid at the wellhead by injecting a viscoelastic composition into the annular space when the tubing is open at the mouth with the subsequent injection of a viscoelastic composition 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 for technological shutter speed . 2. The method according to claim 1, characterized in that the excess pressure P _at the wellhead is created from the condition
P _od ≥ P _y ≥ (0.05 - 0.15) P _pl ,
where P _OPR - pressure testing wells, kg / m ² ;
P _PL - reservoir pressure, kg / m ² . 3. The method according to claims 1 and 2, characterized in that the density ρ of the kill fluid is determined from the expression

where P _PL - reservoir pressure, kg / m ² ;
h _nk.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 is the inner diameter of the well casing, m  4. The method according to 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 killing fluid when the tubing is open at the mouth in the tubing volume pipes.  5. The method according to 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.