RU2326230C1 - Method for pay isolation at casing cementing - Google Patents

Abstract

FIELD: oil producing industry.

SUBSTANCE: invention is referred to oil producing industry, in particular to technology of well site construction and it is intended for well cementing drilled on oil, gas and water. The method for isolation of a pay at the casing cementing includes a running with a saddle on a bottom-hole of a casing string, equipped with the device for pay isolation in the form of the back pressure valves which have been placed at the pay base surface level, landing of oil well tubings with a trailer nipple, an injection in tubular annulus of calculated quantity of a working substance with a gravity equal to the gravity of a cement mortal, landing of oil well tubings prior pressure-tight interplay of a nipple with a saddle, an injection of a cement mortal and its pushing through by chaser in annular room of a casing string, hermetic sealing of internal room of a tubing string, an injection in tubular annulus of calculated quantity of chaser, dissociation of annular room of a hole and its development, as a working substance a cement mortal with hollow members is used, space filled by hardened at chilling by water or by a sandy-oil mixture, after a cement-slurry thickening and withstanding before fusion of specified water or a sandy-oil mixture under the influence of exterior factors the opening and a depression purification are carried out.

EFFECT: reliable isolation of a pay, extension of functionality due to realisation of the specified method at down hole performance with a pay having high injection capacity.

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Description

The invention relates to the oil industry, in particular to the technology of well construction, and is intended for fastening wells drilled for oil, gas and water.

The well-known "Method of selective isolation of the reservoir when cementing the production string of pipes in the well" (US Pat. RU No. 2087674, ЕВВ 33/14, publ. Bull. No. 23 from 08/20/97,), including installation on the production string before lowering it into the well of the upper and lower packer units with the possibility of their placement under the sole and above the top of the reservoir, flushing the column after its descent, sealing the annular space by opening the packer units and pumping the cement, while the top packer unit is installed the cementing sleeve is poured, and annular space is sealed first under the sole of the productive formation by opening the lower packer unit, and then above the roof of the productive formation, while the cement mortar is first pumped under the lower packer unit under pressure, and then through the cementing sleeve.

The disadvantage of this method is the low reliability of isolation of the reservoir in cases where the walls of the well are complicated by uneven cavity in the installation interval of the packers, in addition, it is difficult to ensure the guaranteed operation of two packers, which does not exclude the penetration of cement into the interval of the reservoir, it should also be noted that that for the implementation of the method requires complex fixtures and additional designs, which requires a highly skilled staff, and this together leads to additional material costs.

Also known is the "Method of selective isolation of the reservoir during cementing of the production string" (US Pat. RU No. 2135740, ЕВВ 33/14, publ. Bull. No. 24 from 08/27/99), including the descent into the well of a casing equipped with a device for isolation reservoir, placing the specified device in the well against the reservoir and communicating the annulus of the well above and below the interval of the reservoir through the bypass channels in the apparatus, separation of the annulus of the well and subsequently f cementing the annulus above and below the reservoir, and the productive reservoir is separated by injection into the interval against the reservoir before or after the casing of the viscoelastic mixture is lowered, after which the viscoelastic mixture column is fixed against the reservoir, and subsequent cementing is performed along the bypass channel of the device for isolation and annulus of the well.

The disadvantages of this method are low efficiency and high material costs due to the fact that bypass channels are used, which lead: firstly, to reduce the internal passage of the casing string, which complicates the further use of this well - additional milling of the inner diameter of the casing will be required, or the use of non-standard equipment for work inside the well in the interval of the reservoir and below it; secondly, the development of this well is complicated, as perforation in the interval of the productive formation is difficult; thirdly, it increases the metal consumption of this device, in addition, the use of a packer does not guarantee a tight fit to the wellbore complicated by uneven cavity, which leads to leaching of the viscoelastic mixture or, due to the difference in density with the cement mortar, to “float” or “flooding” "Of this mixture, all this in total leads to incomplete isolation of the reservoir, which reduces the efficiency of using this method.

The closest in technical essence and the achieved result to the proposed one is the "Method of isolating the reservoir during cementing of the casing" (US Pat. RU No. 2234593, ЕВВ 33/14, publ. Bull. No. 23 from 08/20/2004), including the descent into casing well equipped with a device for isolating the reservoir, injecting cement into the annulus of the casing, pushing the cement with squeezing fluid and disengaging the annulus of the well, while lowering the casing into the bottom hole is equipped with a saddle, then the tubing string with the end nipple is lowered, before the casing is cemented, the calculated amount of the hydrophobic composition with a density equal to the density of the cement mortar is pumped into the annulus, then the nipple is inserted into the saddle, and then the cement mortar is pushed into the casing fluid annular space, at the end of cementing, the inner space of the tubing string is sealed, and into the annulus ivayut calculated amount of displacement fluid, and as a device for producing formation isolation using check valves disposed at the level of the producing formation of the sole.

The disadvantage of this method is the use of a hydrophobic fluid with a density equal to the density of the cement mortar, the use of which is associated with accurate measurements directly on the well of the density of the cement used, calculation of the ingredients that make up the hydrophobic preparation, which requires highly skilled and highly paid workers with a limited time limit of up to " setting "cement mortar, and with a slight violation of the technology of preparation, the hydrophobic liquid will "Migrate" into the cement slurry in the annulus is upward or downward, respectively, at low or high density, which may lead to emergency situations, such as crossflow. Also, this method cannot be used if the reservoir is highly receptive, since the hydrophobic fluid will be crushed into the reservoir by a column of cement mortar.

The technical problem is to create such a method for isolating the reservoir during cementing of the production string, which, being efficient and reliable, was not expensive at the same time, with the possibility of working in wells with a highly-productive reservoir.

The technical problem is solved by isolating the reservoir during cementing of the casing string, lowering into the well with a saddle on the bottom of the casing string, equipped with a device for isolating the reservoir in the form of check valves located at the bottom level of the reservoir, lowering the tubing string with an end nipple, injection into the annular space of the calculated amount of the working agent with a density equal to the density of the cement mortar, the descent of the tubing string to tight the interaction of the nipple with the seat, pumping cement mortar and pushing it with squeezing fluid into the annulus of the casing string, sealing the inner space of the tubing string, injecting the calculated amount of squeezing fluid into the annulus, uncoupling the annulus of the well and its development.

What is new is that a cement slurry with hollow elements filled with water or a sand-oil mixture hardened during cooling is used as a working agent; after the cement solution has hardened, it is held until the water or sand-oil mixture melts under the influence of external factors and an autopsy and depression cleaning are performed .

Also new is the fact that ice or a sand-oil mixture is used as a composition in hollow elements.

This set of distinctive features leads to the reliability of isolation of the reservoir and the economic efficiency of the application of this method, being simple and affordable. The use of a working agent in the form of a dispersed system, where hollow elements filled with a destructible composition are used as a dispersed substance in a cement solution, does not allow the cement mortar to mix or dissolve in it, and the fact that the working agent has a density approximately equal to the density of the cement mortar allows to exclude packer devices, which, due to their unreliability, resulted in low-quality formation isolation in the prototype. As hollow elements can be used tubes filled with a composition in the form of ice to reduce the total density of the dispersed system or sand-oil mixture to increase the total density. The injection of the working agent after filling the annular space of the well with cement mortar guarantees the penetration of the working agent into the interval of the reservoir and eliminates its mixing under the influence of external factors, since there will be no extraneous external influences due to the completion of the injection of cement into the annulus. And due to the lack of packers and the use of simple devices - check valves, a saddle located at the bottom of the well, and an end nipple on the tubing string to isolate the reservoir, in this method, the desired result is achieved and material costs are reduced.

Figure 1, 2, 3, 4 shows the principle of the proposed method.

Figure 1 schematically shows the stage: filling the annulus with a hydrophobic composition.

Figure 2 schematically shows the stage: injection of cement into the annulus.

Figure 3 schematically shows the stage: the injection of hydrophobic fluid into the interval of the reservoir by pumping the squeezing fluid into the annulus and completing the process of isolating the reservoir.

Figure 4 schematically shows the stage: flushing equipment from the remnants of a hydrophobic fluid and cement mortar.

The method is carried out in the following sequence (combined with an example of a specific implementation).

Before the casing 1 is lowered (see Fig. 1) into the well 2, the interval of the productive formation 3 is determined from geophysical data and the design of the casing 1 is assembled so that the device 4 for isolating the productive formation 3 is located against or slightly higher (about 1 meter) of the sole 5 of the productive formation 3 of the well 2, taking into account the placement on the bottom of the well 2 of the standard shoe 6 with the check valve 7 and the seat 8 of the well 2. In our particular case, the role of the device 4 for isolating the productive formation 3 is played by check valves ( Example, a spring-loaded ball covering the hole in the casing) placed along the perimeter of the casing 1 at the same level and with the same opening modes (~ 2 MPa). After lowering the casing 1, the tubing string 9 with the end nipple 10 having sealing elements 11 is lowered into it to the bottom, which, when the nipple 10 is inserted into the saddle 8, prevents unauthorized flow of liquids from the annulus into the annulus. Then, the tubing string 9 is raised by about 1-2 meters — a distance allowing the nipple 10 to exit the seat 8, and the calculated amount of working agent 12 is pumped into the annulus between the casing string 1 and the tubing string 9 (dispersed system, where as a dispersed substance in cement mortar use hollow elements filled with a destructible composition) with a density approximately equal to the density of cement mortar 13. The calculated amount of working agent 12 is determined by the formula {1}:

where V is the volume of the injected working agent, m ³ ;

d ₁ - the inner diameter of the casing string, m;

h is the interval of the well from the bottom to the bottom of the reservoir, m;

D is the diameter of the drilled well, m;

d ₂ - the outer diameter of the casing string, m;

N - the interval of the reservoir, m;

α = 1-1,05 - coefficient determined by geophysical exploration and taking into account the complexity of the well by caverns.

For example: Romashkinskoye field well. No. 24543 (NGDU Aznakaevskneft),

borehole diameter D = 215.6 mm = 0.2156 m; casing outer diameter d ₂ = 146.1 mm = 0.1461 m; casing inner diameter d ₁ = 132.1 mm = 0.1321 m; geophysical coefficient and taking into account the complexity of the well by caverns α = 1.01;

artificial slaughter - 1748 m, the bottom of the reservoir - 1699 m, the roof of the reservoir - 1693 m, i.e.

reservoir interval H = 6 m; interval from the bottom to the bottom of the reservoir h = 49 m

Hence:

Then (see Fig. 2), the tubing string 9 is lowered to the end of the nipple 10 in the saddle 8 and unloaded to the bottom of the well 2, after which cementing is carried out in a standard way until cement mortar 13 appears (using cement of the PTsT grade GOST 1581-96 with density 1 , 7-1.9 kg / cm ³ ) at the wellhead 2. Upon completion of cementing (see FIG. 3), the interior of the tubing string 9 is sealed with a wellhead valve 14 and the estimated amount of displacement fluid 15 is pumped into the annulus, the volume of which is less than or equal to the volume of the annulus and 2 wells in the productive formation interval 3.

The estimated amount of squeezing fluid 15 is determined by the formula {2}:

where V ₁ - the volume of injected squeezing fluid, m ³ ;

D is the diameter of the drilled well, m;

d ₂ - the outer diameter of the casing string, m;

N - the interval of the reservoir, m

α = 1-1,05 - coefficient determined by geophysical exploration and taking into account the complexity of the well by caverns.

For an example we take the same well: Romashkinskoye field of a well. No. 24543 (NGDU Aznakaevskneft),

borehole diameter D = 215.6 mm = 0.2156 m; casing outer diameter d ₂ = 146.1 mm = 0.1461 m; reservoir interval H = 6 m; geophysical coefficient and taking into account the complexity of the well by caverns α = 1.01;

Hence:

As a result, the check valves 4 will open and the working agent 12 will fill the annular space of the well 2 in the interval of the productive formation 3. After that (see Fig. 4), the tubing string 9 with the end nipple 10 is raised 2-5 meters to exit the nipple 10 from the seat 8 , the inner space of the tubing string 9 is depressurized and the remains of the cement slurry 13 and working agent 12 are washed out from the in-tube space of the well 2 by reverse circulation of the squeezing fluid 15.

The estimated amount of hydrophobic composition 12 when injected into the annular space is the sum of the volume necessary to fill the in-pipe space of the well 2 from the bottom to the check valves 4, and the volume necessary to isolate the reservoir 3 in the annulus of the well 2. And the estimated amount of displacement fluid 15 is pumped into the annular space of the well 2 for extrusion through the check valves 4 of the same volume of the working agent 12 into the annular space of the well 2, necessary for isolating the product su- layer 3.

At the final stage, the tubing string 9 with the nipple 10 is removed from the well 2 (not shown in FIG.). After holding a time sufficient for hardening the cement slurry 13 (≈1 day), additional holding time (0.5 days) is provided for guaranteed melting of ice in the hollow element of working agent 12. Then, development of well 2 is carried out by any known methods.

The use of a dispersion composition as a working agent 12, where hollow elements filled with the composition are used as the dispersed substance in the cement mortar 13, allows you to pre-prepare the dispersed composition of the desired density by first lowering the hollow elements in water (to reduce the total density) or in sand and oil mixture (to increase the total density) to fill the cavities. Then the hollow elements are sifted out of the water or mixture and are rapidly cooled until the composition hardens in their cavities. Further, the hollow elements with the substance inside are delivered in thermally insulated containers to the well and without loss of time at the time of mixing are added to the cement mortar, which is pumped into the well 2 in the interval of the productive formation 3. Since the dimensions of the hollow elements are significant compared to the pores of the productive formation 3, then they are guaranteed not to be crushed into the reservoir 3. Moreover, the presence of a large amount of dispersed substance in the working agent 12 virtually eliminates the possibility of forcing cement solution 13 in the interval of the productive formation 3, excluding the calcination of the formation 3 with cement mortar 13 and the movement of the working agent 12 in another interval of the well 2 even with a slight discrepancy between the densities of the working agent 12 and cement mortar 13. After "setting" of the cement mortar 13 and destruction and / or dissolution of the substance in the cavities of the hollow elements, after opening the formation and pressure treatment, the working agent 12 becomes permeable to the oily fluid extracted from the reservoir 3 of the well 2.

The technical and economic effect of the proposed method for isolating the reservoir during cementing of the casing is due to the simplicity and accessibility of the tools used, which ensure reliability and comparative low cost, significantly reduce material costs and expand functionality due to the possibility of working in wells with highly receptive reservoir.

Claims (1)

A method of isolating a productive formation during cementing of a casing string, including a descent into a well with a saddle at the bottom of a casing string, equipped with a device for isolating a productive formation in the form of check valves located at the bottom of the productive formation, lowering a string of tubing with an end nipple, pumping annulus of the estimated amount of the working agent with a density equal to the density of the cement slurry, the descent of the tubing string to tight interaction n Ippel with a saddle, pumping cement mortar and pushing it with squeezing fluid into the annulus of the casing string, sealing the inner space of the tubing string, injecting the calculated amount of squeezing fluid into the annulus, uncoupling the well annulus and developing it, characterized in that as working agent use a cement mortar with hollow elements filled with hardened by cooling with water or sand-oil mixture, after hardening grout and exposure to melt said water or oil-sand mixture under the influence of external factors autopsy is performed and a depression treatment.

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