Low-pressure low-permeability oil layer alternate injection reverse self-displacement pressure-driving method and system

Abstract

The invention discloses a low-pressure low-permeability oil layer alternate injection reverse self-displacement pressure flooding method and system, and relates to the technical field of petroleum reservoir transformation and yield increase, and the method comprises the steps that an oil flooding system is injected into a low-pressure low-permeability oil layer until the formation pressure coefficient of the low-pressure low-permeability oil layer rises to a first preset threshold value; high-viscosity fracturing fluid is injected into the low-pressure and low-permeability oil layer until the fracturing crack length of the low-pressure and low-permeability oil layer is increased to a second preset threshold value; an oil displacement system and high-viscosity fracturing fluid are alternately injected into the low-pressure and low-permeability oil layer until the formation pressure coefficient rises to a third preset threshold value and the fracturing fracture length increases to a fourth preset threshold value; and the soaking time is determined based on the geological parameters of the low-pressure and low-permeability oil layer and the total amount of injected liquid, and soaking is conducted on the production well of the low-pressure and low-permeability oil layer based on the soaking time. The technical problem that the yield stabilizing effect is not ideal in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of oil reservoir transformation and production increase, and in particular to a method and system for alternating injection into low-pressure and low-permeability oil layers and replacing pressure drive with reverse self-drive. Background Art

[0002] my country's low-pressure and low-permeability oil reservoirs have rich reserve resources. However, due to the limitations of reservoir conditions and engineering technology, their development effect is poor, and the characteristics of low energy and low liquid are prominent. The main reason is that the reservoir seepage difficulties lead to slow pressure transmission and poor liquid supply, making the injection and production problems more significant. It is urgent to find new ways to supplement energy and improve recovery rates.

[0003] In response to the many problems existing in low-pressure and low-permeability reservoirs, the current pressure-driven transformation is mainly used in areas with a complete injection-production well network. Most of them inject oil-displacing liquids at a high speed and in large quantities through injection wells, and then shut down the wells to wait for the pressure to spread before starting production in production wells. For areas with imperfect injection-production well networks, the current pressure-driven transformation mainly adopts the transformation measures of injecting a large amount of pressure-driven liquid in the early stage and adding sand for fracturing in the later stage. The overall impact range is limited and the stable production effect is not ideal. Summary of the invention

[0004] The purpose of the present invention is to provide a method and system for alternately injecting reverse self-drive and pressure-displacing into low-pressure and low-permeability oil layers in order to solve at least one of the above technical problems.

[0005] In the first aspect, an embodiment of the present invention provides a method for alternating injection of reverse self-displacing pressure drive into a low-pressure and low-permeability oil layer, which is applied to a low-pressure and low-permeability oil layer; comprising: injecting an oil displacement fluid system into the low-pressure and low-permeability oil layer until the formation pressure coefficient of the low-pressure and low-permeability oil layer rises to a first preset threshold value and then stops; injecting a high-viscosity fracturing fluid into the low-pressure and low-permeability oil layer until the length of the fracture in the low-pressure and low-permeability oil layer increases to a second preset threshold value and then stops; the high-viscosity fracturing fluid carries supporting materials and debonding agents; alternately injecting the oil displacement fluid system and the high-viscosity fracturing fluid into the low-pressure and low-permeability oil layer until the formation pressure coefficient rises to a third preset threshold value and the length of the fracture increases to a fourth preset threshold value and then stops; determining a shut-in time based on the geological parameters of the low-pressure and low-permeability oil layer and the total amount of injected liquid, and shutting in the production well of the low-pressure and low-permeability oil layer based on the shut-in time.

[0006] Furthermore, the oil displacement fluid system includes an oil displacement agent, a drag reducing agent and a clay stabilizer.

[0007] Furthermore, the oil displacement agent content in the oil displacement fluid system is 0.15%-0.35%, the drag reducer content is 0.15%-0.25%, and the clay stabilizer content is 0.2%-0.3%.

[0008] Furthermore, the high-viscosity fracturing fluid includes HPG, a bactericide, a clay stabilizer, a drainage aid, an emulsifier, a temperature resistance enhancer and a cross-linking agent.

[0009] Furthermore, the HPG content in the high-viscosity fracturing fluid is 0.35%-0.55%, the bactericide content is 0.1%-0.3%, the clay stabilizer content is 0.3%-0.5%, the drainage agent content is 0.1%-0.3%, the emulsifier content is 0.1%-0.3%, the temperature resistance enhancer content is 0.3%-0.5%, and the cross-linking agent content is 0.3%-0.4%.

[0010] Furthermore, the oil displacement liquid system and the high-viscosity fracturing liquid are alternately injected into the low-pressure and low-permeability oil layer, comprising: injecting the oil displacement liquid system into the low-pressure and low-permeability oil layer so that the formation pressure coefficient of the low-pressure and low-permeability oil layer increases by 0.05-0.1 and then stopping; and then injecting the high-viscosity fracturing liquid into the low-pressure and low-permeability oil layer so that the length of the fracture of the low-pressure and low-permeability oil layer increases by 30m-50m and then stopping, thereby alternately injecting.

[0011] Furthermore, the calculation formula for the soaking time includes:

[0012]

[0013] Where, t is the soaking time, Q is the total amount of injected liquid, μ is the viscosity of the displacement fluid, L is the length of the fracture, H is the height of the fracture, Ф is the reservoir porosity, and K is the total amount of injected liquid. m is the matrix permeability; P1 is the fracture pressure after fracturing; P2 is the matrix pressure, and a is the unit conversion factor.

[0014] In a second aspect, an embodiment of the present invention further provides a low-pressure and low-permeability oil layer alternating injection reverse self-displacing pressure drive system, which is applied to low-pressure and low-permeability oil layers; it comprises: a first injection module, a second injection module, an alternating injection module and a well shut-in module; wherein the first injection module is used to inject an oil displacement fluid system into the low-pressure and low-permeability oil layer until the formation pressure coefficient of the low-pressure and low-permeability oil layer rises to a first preset threshold and then stops; the second injection module is used to inject a high-viscosity fracturing liquid into the low-pressure and low-permeability oil layer until the length of the fracture of the low-pressure and low-permeability oil layer increases to a second preset threshold and then stops; the high-viscosity fracturing liquid carries supporting materials and gel breakers; the alternating injection module is used to alternately inject the oil displacement fluid system and the high-viscosity fracturing liquid into the low-pressure and low-permeability oil layer until the formation pressure coefficient rises to a third preset threshold and the length of the fracture increases to a fourth preset threshold and then stops; the well shut-in module is used to determine the well shut-in time based on the geological parameters of the low-pressure and low-permeability oil layer and the total amount of injected liquid, and shut-in the production well of the low-pressure and low-permeability oil layer based on the well shut-in time.

[0015] The present invention provides a method and system for alternating injection and reverse self-displacement pressure drive in low-pressure and low-permeability oil layers. The method increases the effective distance of deoiling liquid and increases the length of supporting fractures through alternating injection. After the alternating injection is completed, the pump is stopped and the well is soaked to promote the liquid to diffuse into the formation and cause oil-water imbibition and displacement. This can not only replenish formation energy, but also improve the reverse self-displacement production capacity of the oil layer, thereby alleviating the technical problem of unsatisfactory stable production effect in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 A flow chart of a method for alternately injecting reverse self-drive and pressure-drive into a low-pressure and low-permeability oil layer provided by an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of alternately injecting an oil displacement fluid system and a high-viscosity fracturing fluid into a low-pressure and low-permeability oil layer provided by an embodiment of the present invention;

[0019] Figure 3 A schematic diagram of a low-pressure and low-permeability oil layer alternating injection reverse self-drive displacement pressure drive system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Embodiment 1

[0022] Figure 1 This is a flow chart of a method for alternately injecting reverse self-drive and pressure-drive into a low-pressure and low-permeability oil layer according to an embodiment of the present invention. The method is applied to low-pressure and low-permeability oil layers. Figure 1 As shown, the method specifically comprises the following steps:

[0023] Step S102, injecting the oil displacement fluid system into the low-pressure and low-permeability oil layer until the formation pressure coefficient of the low-pressure and low-permeability oil layer rises to a first preset threshold value and then stops.

[0024] Optionally, the first preset threshold includes 0.05-0.1.

[0025] Step S104, injecting high-viscosity fracturing liquid into the low-pressure and low-permeability oil layer until the length of the fracture in the low-pressure and low-permeability oil layer increases to a second preset threshold value and then stops; the high-viscosity fracturing liquid carries the supporting material and the gel breaker.

[0026] Optionally, the supporting material includes ceramsite and quartz sand.

[0027] Optionally, the second preset threshold includes 60m.

[0028] Step S106, alternately injecting the oil displacement fluid system and the high-viscosity fracturing fluid into the low-pressure and low-permeability oil layer until the formation pressure coefficient rises to a third preset threshold and the fracture length increases to a fourth preset threshold.

[0029] Optionally, the third preset threshold includes 1.1.

[0030] Step S108, determining the shut-in time based on the geological parameters of the low-pressure and low-permeability oil layer and the total amount of injected liquid, and shut-in the production well of the low-pressure and low-permeability oil layer based on the shut-in time.

[0031] Specifically, the oil displacement fluid system includes an oil displacement agent, a drag reducing agent and a clay stabilizer.

[0032] In an optional implementation provided in an embodiment of the present invention, the content of the oil displacement agent in the oil displacement fluid system is 0.15%-0.35%, the content of the drag reducer is 0.15%-0.25%, and the content of the clay stabilizer is 0.2%-0.3%. Among them, the oil displacement agent is an anionic, cationic or non-ionic surfactant, which has the performance of reducing surface interfacial tension and changing the wettability of the rock surface. It should be noted that the contents in the embodiments of the present invention are all mass percentages.

[0033] In an optional implementation provided in the embodiment of the present invention, the interfacial tension of the oil displacement fluid system is 0.001 mN / m-0.01 mN / m, and the injection displacement is 5.0 m 3 / min-8.0m 3 / min, injection volume 800m 3 -1500m 3 .

[0034] Specifically, the high-viscosity fracturing fluid includes hydroxypropyl guar (HPG), a fungicide, a clay stabilizer, a drainage aid, an emulsifier, a temperature resistance enhancer and a cross-linking agent.

[0035] In an optional implementation provided in an embodiment of the present invention, the HPG content in the high-viscosity fracturing fluid is 0.35%-0.55%, the bactericide content is 0.1%-0.3%, the clay stabilizer content is 0.3%-0.5%, the drainage agent content is 0.1%-0.3%, the emulsifier content is 0.1%-0.3%, the temperature resistance enhancer content is 0.3%-0.5%, and the cross-linking agent content is 0.3%-0.4%.

[0036] In an optional implementation provided by an embodiment of the present invention, the base fluid viscosity of the high-viscosity fracturing fluid is 30mPa·s-60mPa·s, the cross-linking time is 150s-200s, the shear resistance is 60mPa·s-100mPa·s under the condition of 90℃-150℃, the viscosity of the debonding fluid is 2mPa·s-4mPa·s, the residue content is 200mg / L-300mg / L, and the anti-swelling rate is 80%-95%; the supporting material is 40 / 70 mesh + 20 / 40 mesh ceramsite, the compressive grade is 52MPa, and the crushing rate is 5%-6%; the construction displacement is 5.0m 3 / min-8.0m 3 / min, sand addition ratio 5%-40%, fracturing fluid volume 300m 3 -600m 3 , sand adding amount 40m 3 -80m 3 .

[0037] Figure 2 Schematic diagram of alternately injecting a displacement fluid system and a high-viscosity fracturing fluid into a low-pressure, low-permeability oil layer according to an embodiment of the present invention. Figure 2 As shown, step S106 also includes the following steps:

[0038] The oil displacement fluid system is injected into the low-pressure and low-permeability oil layer so that the formation pressure coefficient of the low-pressure and low-permeability oil layer increases by 0.05-0.1 and then stops. Then, a high-viscosity fracturing fluid is injected into the low-pressure and low-permeability oil layer so that the length of the fracture in the low-pressure and low-permeability oil layer increases by 30m-50m and then stops. The injection is repeated alternately.

[0039] Specifically, in the embodiment of the present invention, the displacement fluid system is first injected into the low-pressure and low-permeability oil layer, and the formation pressure coefficient is stopped after rising by 0.05-0.1, and then the construction is stopped when the high-viscosity fracturing fluid is injected into the low-pressure and low-permeability oil layer for the first time, and the construction is stopped when the length of the fracture increases to 60m, and then the displacement fluid system and the high-viscosity fracturing fluid are injected alternately, wherein each alternation condition is that the formation pressure coefficient rises by 0.05-0.1, and the fracture length increases by 30m-50m, until the formation pressure coefficient rises to 1.1 and the fracture length increases to the fourth preset threshold, and then the above-mentioned alternating injection process is stopped. The fourth preset threshold is a threshold set according to design requirements.

[0040] Finally, the soaking time is optimized according to the geological parameters and the total amount of injected liquid, so that the liquid injected into the oil layer can fully replace the crude oil in the porous medium. Specifically, the calculation formula for soaking time includes:

[0041]

[0042] Where, t is the soaking time, s; Q is the total amount of injected liquid, m 3 ; μ is the viscosity of the displacement fluid, mpa.s; L is the length of the fracture, m; H is the height of the fracture, m; Ф is the reservoir porosity, %; K m is the matrix permeability, μm 2 ; P1 is the fracture pressure after fracturing, MPa; P2 is the matrix pressure, MPa; a is the unit conversion factor, 1×10 -3 .

[0043] For example, after optimized calculation, the well-keeping time is 10 to 30 days.

[0044] From the above description, it can be seen that the embodiment of the present invention provides a method for alternating injection of reverse self-displacing pressure drive in low-pressure and low-permeability oil layers. In the process of reservoir transformation in areas with imperfect injection and production well networks, by repeatedly injecting oil-displacing liquid and sand fracturing into oil production wells at high pressure and high displacement and large liquid volume, the effective action distance of the oil-displacing liquid, the reservoir pressure coefficient and the length of the artificial fractures of sand fracturing are effectively increased under the same construction scale, the adsorption and retention of the oil-displacing liquid near the wellbore are reduced, and ultimately the maximum release of reservoir production capacity is achieved.

[0045] Embodiment 2

[0046] Figure 3 Schematic diagram of a low-pressure and low-permeability oil layer alternate injection reverse self-drive displacement pressure drive system provided by an embodiment of the present invention, the system is applied to low-pressure and low-permeability oil layers. Figure 3 As shown, the system includes: a first injection module 10 , a second injection module 20 , an alternating injection module 30 and a soaking module 40 .

[0047] Specifically, the first injection module 10 is used to inject the oil displacement liquid system into the low-pressure and low-permeability oil layer until the formation pressure coefficient of the low-pressure and low-permeability oil layer rises to a first preset threshold value and then stops;

[0048] The second injection module 20 is used to inject high-viscosity fracturing liquid into the low-pressure and low-permeability oil layer until the length of the fracture in the low-pressure and low-permeability oil layer increases to a second preset threshold value and then stops; the high-viscosity fracturing liquid carries the supporting material and the gel breaker;

[0049] The alternate injection module 30 is used to alternately inject the oil displacement fluid system and the high-viscosity fracturing fluid into the low-pressure and low-permeability oil layer until the formation pressure coefficient rises to a third preset threshold value and the fracture length increases to a fourth preset threshold value;

[0050] The well shut-in module 40 is used to determine the well shut-in time based on the geological parameters of the low-pressure and low-permeability oil layer and the total amount of injected liquid, and shut-in the production well of the low-pressure and low-permeability oil layer based on the well shut-in time.

[0051] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0052] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for alternating injection into low-pressure and low-permeability oil layers, characterized in that: Applicable to low pressure and low permeability reservoirs; including: Injecting an oil displacement fluid system into the low-pressure and low-permeability oil layer until the formation pressure coefficient of the low-pressure and low-permeability oil layer rises to a first preset threshold value and then stops; Injecting a high-viscosity fracturing fluid into the low-pressure and low-permeability oil layer until the length of the fracture in the low-pressure and low-permeability oil layer increases to a second preset threshold value, and then stopping; the high-viscosity fracturing fluid carries a supporting material and a breaker; Alternately injecting the oil displacement fluid system and the high-viscosity fracturing fluid into the low-pressure and low-permeability oil layer until the formation pressure coefficient rises to a third preset threshold value and the fracture length increases to a fourth preset threshold value; The shut-in time is determined based on the geological parameters of the low-pressure and low-permeability oil layer and the total amount of injected liquid, and the production well of the low-pressure and low-permeability oil layer is shut-in based on the shut-in time.

2. The method according to claim 1, characterized in that: The oil displacement fluid system comprises an oil displacement agent, a drag reducing agent and a clay stabilizer.

3. The method according to claim 2, characterized in that: The oil displacement agent content in the oil displacement liquid system is 0.15%-0.35%, the drag reducer content is 0.15%-0.25%, and the clay stabilizer content is 0.2%-0.3%.

4. The method according to claim 1, characterized in that: The high-viscosity fracturing fluid comprises HPG, a bactericide, a clay stabilizer, a drainage aid, an emulsifier, a temperature resistance enhancer and a cross-linking agent.

5. The method according to claim 4, characterized in that: The high-viscosity fracturing fluid contains 0.35%-0.55% HPG, 0.1%-0.3% fungicide, 0.3%-0.5% clay stabilizer, 0.1%-0.3% drainage aid, 0.1%-0.3% emulsifier, 0.3%-0.3% temperature enhancer and 0.3%-0.4% crosslinker.

6. The method according to claim 1, characterized in that: Alternatingly injecting the oil displacement fluid system and the high-viscosity fracturing fluid into the low-pressure and low-permeability oil layer comprises: The oil displacement fluid system is injected into the low-pressure and low-permeability oil layer so that the formation pressure coefficient of the low-pressure and low-permeability oil layer increases by 0.05-0.1 and then stopped. Then, the high-viscosity fracturing fluid is injected into the low-pressure and low-permeability oil layer so that the length of the fracture in the low-pressure and low-permeability oil layer increases by 30m-50m and then stopped, and the injection is alternately performed.

7. The method according to claim 1, characterized in that: The calculation formula of the soaking time includes: Where, t is the soaking time, Q is the total amount of injected liquid, μ is the viscosity of the displacement fluid, L is the length of the fracture, H is the height of the fracture, Ф is the reservoir porosity, and K is the total amount of injected liquid. m is the matrix permeability; P1 is the fracture pressure after fracturing; P2 is the matrix pressure, and a is the unit conversion factor.

8. A low-pressure and low-permeability oil layer alternate injection reverse self-drive pressure drive system, characterized in that: Applicable to low-pressure and low-permeability oil layers; including: a first injection module, a second injection module, an alternating injection module and a soaking module; wherein, The first injection module is used to inject the oil displacement fluid system into the low-pressure and low-permeability oil layer until the formation pressure coefficient of the low-pressure and low-permeability oil layer rises to a first preset threshold value and then stops; The second injection module is used to inject high-viscosity fracturing liquid into the low-pressure and low-permeability oil layer until the length of the fracture of the low-pressure and low-permeability oil layer increases to a second preset threshold value; the high-viscosity fracturing liquid carries supporting materials and breaker; The alternate injection module is used to alternately inject the oil displacement fluid system and the high-viscosity fracturing fluid into the low-pressure and low-permeability oil layer until the formation pressure coefficient rises to a third preset threshold and the fracture length increases to a fourth preset threshold; The well shut-in module is used to determine the well shut-in time based on the geological parameters of the low-pressure and low-permeability oil layer and the total amount of injected liquid, and shut-in the production well of the low-pressure and low-permeability oil layer based on the well shut-in time.

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