Water reduction and oil production increase method and completion structure for horizontal wells in dual-medium reservoirs

Abstract

The present invention discloses a method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir and a completion structure. The method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir comprises the following steps: S1, determining the filling pressure; S2, injecting a filling fluid with microparticles into the annular space between the horizontal well and the oil layer in which it is located, until the pressure in the annular space reaches the filling pressure, and at the same time fracturing the oil layer to form a tree root-shaped fracture cluster in the oil layer; S3, maintaining the filling pressure, and continuously injecting the filling fluid until the microparticles fill the annular space and the fracture cluster. In the present invention, by combining fracturing with microparticle filling, the oil production of the horizontal well is further increased without substantially increasing the water production and the production pressure difference, thereby achieving reducing water and increasing oil production.

Description

Technical Field

[0001] The invention relates to the technical field of oil and natural gas exploitation, and in particular to a method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir and a completion structure for the horizontal well of a dual-medium oil reservoir. Background Art

[0002] Dual-medium reservoirs refer to reservoirs composed of two of the three media: matrix (pore structure), fractures, and caves. They are generally composed of matrix and fractures or matrix and caves. For example, reef limestone reservoirs are mainly composed of matrix and microfracture system, in which the matrix permeability is relatively low, generally less than 200mD, and due to geological effects, discontinuous microfractures are developed with uncertainty, and the fracture width is 0.01-2mm. Its permeability is relatively high relative to the matrix, and most of them are fractures with larger angles, thus forming a fracture pore type reservoir. For bottom water fractured reef limestone reservoirs, water production problems are usually more serious. Taking a bottom water reservoir as an example, if Figure 1 As shown in the figure, the horizontal well section 1, oil layer 2, natural fracture 3, oil-water interface 4 and bottom water 5 are shown. The thickness of the oil layer D1 is 50-100m, the thickness of the bottom water D2 is greater than 30m, the viscosity of oil is 50-100 centipoise, and the viscosity of water is about 0.6 centipoise, so the oil-water viscosity ratio of the two is greater than 100. In the production process of fractured reef limestone reservoirs, water production will seriously affect the production of the oil field. The reasons are as follows: due to the pressure difference between the fracture and the bottom water, the conductivity of the fracture is very strong. Usually, the conductivity of a 0.5-2mm wide fracture is equivalent to the conductivity of the matrix with a permeability of 100-400m and a permeability of 0.2D. Assuming that there is such a fracture within an average wellbore distance of 200m, the water content of the well will reach 50%. During the production process, after the oil in the fracture is produced, water will flow along the fracture, and the oil in the matrix above the oil layer is difficult to be used. Since the oil-water viscosity ratio is greater than 100, the water content is further increased, so that the water content quickly reaches more than 90%. Due to the existence of large-angle fractures, water appeared on the day the well was opened, even though the oil layer is 50 to 100 meters thick. The water content of the adjustment well was as high as 80% on the day it was opened and put into production. The water content rose to 90% after one month and 95% after two months. At the same time, due to the crossflow of water in the wellbore, the production pressure difference decreased, and the oil production dropped significantly.

[0003] In order to control water and increase oil production in dual-media reservoirs, the existing technologies use chemical methods and isolation and water control methods. The chemical method mainly plugs the relatively high permeability zone of the reservoir near the wellbore, but the plugging range is difficult to control, and the effectiveness and sustainability are poor. For example, if chemical plugging agents are injected into the dual-media reservoir, not only is it difficult to ensure the plugging of the cracks, but it is also easy to block the matrix, resulting in reduced production capacity and a negative impact on production results. The isolation and water control method mainly plays the role of isolating the annulus, inhibiting annular crossflow, and balancing the horizontal well supply profile to a certain extent, but it is limited to the horizontal wellbore, and has limited effect on the reservoir near the wellbore. Moreover, once the packer encounters wellbore expansion, its effect will be greatly reduced. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir and a completion structure for a horizontal well of a dual-medium oil reservoir in view of the defects of the above-mentioned prior art.

[0005] The technical solution adopted by the present invention to solve the technical problem is: to provide a method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir, comprising the following steps:

[0006] S1. Determine the filling pressure;

[0007] S2, injecting a filling fluid containing particles into the annular space between the horizontal well and the oil layer, until the pressure in the annular space reaches the filling pressure, and fracturing the oil layer to form a tree root-like fracture cluster in the oil layer;

[0008] S3. Maintain the filling pressure and continue to inject the filling liquid until the particles fill the annular space and the fracture clusters.

[0009] Preferably, the extension length of the fracture cluster in the lateral direction is less than or equal to the oil drainage radius;

[0010] The extension length of the fracture cluster in the longitudinal direction is 1 / 5-2 / 5 of the thickness of the oil layer.

[0011] Preferably, in step S2, the volume concentration of the microparticles in the filling liquid is 1-5%;

[0012] The density of the microparticles is 1.03-1.06 g / cm3 and the particle size is 40-100 meshes.

[0013] Preferably, in step S1, the filling pressure is 1.05-1.1 times the fracture pressure of the formation fracture.

[0014] Preferably, the method for determining the formation fracture pressure is as follows:

[0015] Continue to inject water into the annular space around the horizontal well, record the injection pressure, and obtain the liquid absorption index of the formation where the horizontal well is located according to the following formula:

[0016] I=Q / (P W -P)

[0017] Where I is the liquid absorption index, Q is the amount of water injected, P W is the bottom hole pressure of the horizontal well, P is the reservoir pressure, and P W The difference between and P is the formation pressure difference;

[0018] A curve is drawn with the liquid absorption index as the ordinate and the formation pressure difference as the abscissa. The point where the liquid absorption index suddenly drops is determined on the curve, and its abscissa value is the rupture pressure of the formation fracture.

[0019] Preferably, in step S1, the method for determining the filling pressure is: through a triaxial stress experiment, the Young's modulus, shear modulus and Poisson's ratio of the rock are measured, and a relationship curve between the formation fracture pressure and the fracture depth is measured and drawn; the formation fracture pressure when the fracture depth is 1 / 5-2 / 5 of the rock sample thickness is selected as the filling pressure.

[0020] Preferably, in step S1, the filling pressure is determined by empirical statistics: in the same reservoir area, different filling pressures are used for trial production; and the filling pressure value with the best oil-increasing effect is selected as the filling pressure of the oil wells in the reservoir area.

[0021] The present invention also provides a dual-medium oil reservoir horizontal well completion structure, comprising a horizontal well arranged in an oil layer, and a root-like fracture cluster formed in the oil layer by fracturing; an annular space is arranged between the horizontal well and the oil layer, and the fracture cluster is connected to the annular space; the annular space and the fracture cluster are both filled with microparticles.

[0022] Preferably, the extension length of the fracture cluster in the transverse direction is ≤ the oil drainage radius; and the extension length of the fracture cluster in the longitudinal direction is 1 / 5-2 / 5 of the thickness of the oil layer.

[0023] Preferably, the density of the microparticles is 1.03-1.06 g / cm3 and the particle size is 40-100 mesh.

[0024] In the present invention, by combining fracturing with microparticle filling, the oil volume of the horizontal well is further increased without substantially increasing the water production and the production pressure difference, thereby achieving water reduction and oil increase.

[0025] Among them, first, make full use of the good conductivity of the particles to increase the flow performance of the oil; second, use lightweight and low-concentration controlled pressure filling to make the length of the crack cluster more uniform; third, the process is simple, saves materials, and has high economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0027] Figure 1 It is a schematic diagram of the cross-sectional structure of an existing bottom water oil reservoir;

[0028] Figure 2 It is a schematic cross-sectional structure diagram of a dual-medium reservoir horizontal well completion structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0030] refer to Figure 2 A method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir according to an embodiment of the present invention comprises the following steps:

[0031] S1. Determine the filling pressure.

[0032] The filling pressure is used to fracture the matrix of the reservoir in the near-wellbore zone of the horizontal well 10 , and to form a tree-root-like fracture cluster 20 in the matrix.

[0033] Alternatively, a first method for determining the filling pressure is as follows: the filling pressure is 1.05-1.1 times the fracture pressure of the formation fracture.

[0034] Among them, the method for determining the formation fracture pressure is as follows:

[0035] Continue to inject water into the annular space around the horizontal well and record the injection pressure, which includes the bottom hole pressure and the oil layer pressure. The liquid absorption index of the oil layer where the horizontal well is located is obtained according to the following formula:

[0036] I=Q / (P W -P)

[0037] Where I is the liquid absorption index, Q is the amount of water injected, P W is the bottom hole pressure of the horizontal well, P is the reservoir pressure, and P W The difference between P and P is the formation pressure difference.

[0038] A curve is drawn with the liquid absorption index as the ordinate and the formation pressure difference as the abscissa. The point where the liquid absorption index suddenly drops is determined on the curve, and its abscissa value is the rupture pressure of the formation fracture.

[0039] Alternatively, a second method for determining the filling pressure is to measure the Young's modulus, shear modulus and Poisson's ratio of the rock through a triaxial stress test, and to draw a curve of the relationship between the formation fracture rupture pressure and the fracture depth; the formation fracture rupture pressure when the fracture depth is 1 / 5-2 / 5 of the rock sample thickness is selected as the filling pressure.

[0040] Alternatively, a third method for determining the filling pressure is determined through empirical statistics: in the same reservoir area, different filling pressures are used for trial production; the filling pressure value with the best oil increase effect is selected as the filling pressure of the oil wells (i.e., horizontal wells) in the reservoir area.

[0041] S2. Inject the filling fluid containing the particles 40 into the annular space 30 between the horizontal well 10 and the oil layer 100 until the pressure in the annular space 30 reaches the filling pressure, and at the same time, fractur the oil layer 100 to form a root-like fracture cluster 20 in the matrix of the oil layer 100.

[0042] The volume concentration of the microparticles 40 in the filling liquid is 1-5%. The density of the microparticles 40 is 1.03-1.06 g / cm3, and the particle size is 40-100 mesh. Alternatively, the microparticles 40 can be a polymer material such as polyethylene, high-density polyethylene, polypropylene, polyvinyl chloride or styrene divinylbenzene cross-linked copolymer.

[0043] In this step, the particles 40 are brought into the annular space 30 outside the horizontal well 10 by the injection of the filling fluid, and the filling pressure determined in step S1 is reached by increasing the injection pressure. At the same time, the oil layer is fractured by the filling pressure to form a tree root-shaped fracture cluster 20, and the filling fluid also carries the particles 40 into the fracture cluster 20.

[0044] Since natural fractures may exist in the oil layer 100 , the fracture clusters 20 may be formed on the natural fractures through fracturing with filling pressure.

[0045] In the oil layer 100, the fracture cluster 20 can be extended as much as possible in the horizontal direction to improve the diversion effect of the fracture cluster 20. Preferably, the horizontal extension length of the fracture cluster 20 is ≤ the oil drainage radius; the vertical extension length of the fracture cluster 20 is 1 / 5-2 / 5 of the thickness of the oil layer 100, so that the fracture cluster 20 will not extend to connect to the bottom water 200 below the oil layer 100. The horizontal and vertical extension lengths of the fracture cluster 20 can be controlled by setting the filling pressure.

[0046] During the filling process, due to the low strength of the dual-medium reservoir, it is easy to be broken by fracturing under a certain pressure. The annular space 30 outside the horizontal well 10 has a strong conductivity, which is equivalent to an isobaric body, and the pressure difference between the fluid in the wellbore and the bottom water is a constant. Since the pressure difference in each section of the horizontal well 10 is the same, the cracks in the entire well section will be evenly distributed. Moreover, the length of the cracks is the same. Once the cracks in some places in the dual-medium reservoir become longer and the leakage volume increases, the pressure in the crack cluster 20 drops, and the extension of the crack cluster 20 will stop. In this way, under a certain pressure, the penetration length of each crack cluster 20 is basically the same, which can be accurately controlled within the range of 1 / 5-2 / 5 of the thickness of the oil layer 100.

[0047] In the present invention, the fracture cluster 20 may be in a straight comb-like forked shape, or in an irregular tree root shape formed by natural splitting according to the matrix structure of the oil layer 100 .

[0048] In addition, a flow control screen 50 is provided in the horizontal well 10. After the filling fluid carrying the particles 40 is injected into the annular space 30 and the fracture cluster 20, the filling fluid flows into the interior of the horizontal well 10 through the flow control screen 50 and flows back out, while the particles 40 remain in the annular space 30 and the fracture cluster 20, filling the annular space 30 and the fracture cluster 20.

[0049] S3. Maintain the filling pressure and continue to inject the filling liquid until the particles 40 fill the annular space 30 and the fracture cluster 20 (that is, until the injection volume is close to zero).

[0050] After completion, the injection of the filling liquid is stopped, and the total volume of the particles 40 filled in the annular space 30 and the fracture cluster 20 is 1.5-2.5 times the volume of the annular space 30, achieving overfilling.

[0051] The dual-medium reservoir horizontal well completion structure of one embodiment of the present invention can achieve the above-mentioned water reduction and oil production increase. Figure 2 As shown, the dual-medium reservoir horizontal well completion structure includes a horizontal well 10 disposed in an oil layer 100 and a root-shaped fracture cluster 20 formed in the oil layer 100 by fracturing.

[0052] An annular space 30 is provided between the horizontal well 10 and the oil layer 200 , and the fracture cluster 20 is connected to the annular space 30 .

[0053] The horizontal extension length of the fracture cluster 20 is ≤ the oil drainage radius. The vertical extension length H2 (also the depth) of the fracture cluster 20 is 1 / 5-2 / 5 of the thickness H1 of the oil layer 100, so that the fracture cluster 20 will not extend to connect to the bottom water 200 below the oil layer 100.

[0054] The fracture cluster 20 is formed in the oil layer 100 by filling pressure fracturing and is located around the horizontal well 10, so the fracture cluster 20 can also be understood as artificial fracturing. Since there are natural fractures in the oil layer 100, the fracture cluster 20 can be formed on the natural fractures by filling pressure fracturing. The extension length of the fracture cluster 20 in the horizontal and vertical directions can be controlled by setting the filling pressure.

[0055] The fracture cluster 20 may be in a straight comb-like forked shape, or in an irregular tree root shape formed by natural splitting according to the matrix structure of the oil layer 100 .

[0056] In particular, the annular space 30 and the fracture clusters 20 are filled with particles 40 .

[0057] The density of the microparticles 40 is 1.03-1.06 g / cm3 and the particle size is 40-100 mesh. Alternatively, the microparticles can be made of polymer materials such as polyethylene, high-density polyethylene, polypropylene, polyvinyl chloride or styrene divinylbenzene cross-linked copolymer.

[0058] Since the particles 40 are of granular structure, in order to inject them into the annular space 30 and the fracture cluster 20, as described in the above water reduction and oil production enhancement method, the particles 40 are brought into and filled in the annular space 30 and the fracture cluster 20 by injecting a filling fluid. The volume concentration of the particles 40 in the filling fluid is 1-5%.

[0059] The total volume of the particles 40 filled in the annular space 30 and the crack cluster 20 is 1.5-2.5 times the volume of the annular space 30, thereby achieving overfilling.

[0060] Furthermore, the well completion structure of the present invention further comprises a flow control screen 50 disposed in the horizontal well 100. The flow control screen 50 is an ICD screen or an AICD screen.

[0061] After the particles 40 are injected into the annular space 30 by injecting the filling fluid, the filling fluid carries the particles 40 into the annular space 30 and the fracture cluster 20, and the filling fluid flows into the interior of the horizontal well 100 through the flow control screen 50 and flows back out, while the particles 40 remain in the annular space 30 and the fracture cluster 20 to fill the annular space 30 and the fracture cluster 20.

[0062] The present invention is further described below through specific applications.

[0063] In a fractured reef limestone oil field, there are a large number of natural fractures, the oil layer thickness is 70 meters, there is a lot of bottom water, the crude oil viscosity is 100 centipoise, the formation water viscosity is 0.7 centipoise, the oil-water viscosity ratio is 143, the horizontal section wellbore diameter is 6 inches, and the horizontal section length is 1000 meters.

[0064] The well was initially completed with an open hole, and the water content increased rapidly. After three months of production, the water content reached 95%, with a daily liquid production of 400 cubic meters, a daily oil production of 7 cubic meters, and a production pressure difference of 0.5 MPa.

[0065] The specific process and parameters of the present invention are as follows: a water control screen with an outer diameter of 4 inches is lowered, and the lowering length is 1000 meters. The filling pressure is determined by the clean water test method: Under normal circumstances, the liquid production index of the reservoir is constant at 8MPa. When the clean water test exceeds 8MPa, the liquid production index begins to rise, so this point is used as the critical pressure point for the opening of near-wellbore fractures. When the filling pressure exceeds the critical pressure, cracks will be generated near the wellbore. During the filling operation, the filling pressure is increased by 10% on the basis of the critical pressure, so that the cracks extend to a certain depth. Once the pressure is released, they will no longer extend, and the cracks that have not been opened will still be generated under the high pressure of the wellbore, thereby generating tree root-shaped fracture clusters. Later, through indoor research, for fractured reef limestone with a permeability of 500 millidarcy, when the filling pressure exceeds the critical pressure by 10%, the fracture extension length is about 12 meters. During the implementation of the project, the concentration of the filling fluid used was 3%, and the true density of the particles was 1.03-1.06g / cm 3 , the particle size of the filling particles is 40-100 mesh, and the annular space volume is 10m 3 , overfilling volume is 2.5 times (based on the annular volume, the annular volume divided by the total filling volume).

[0066] After the project was put into production, the daily liquid production was 300 cubic meters per day and the daily oil production was 50 cubic meters per day, which was 7 times that before water control. The production pressure difference was 4.5 MPa, which was 9 times that before water control. The reason for the reduction of water and increase of oil production is that, on the one hand, the tree root-like fracture clusters connected to the oil layer were generated due to the oversaturated filling near the well. These fracture clusters were in full contact with the matrix of the oil layer, and the length of the fracture clusters was controlled within the range of 1 / 5-2 / 5 of the thickness of the matrix. The permeability of the particles with a particle size of 40-100 mesh filled in the fracture clusters was about 80D, which was about 400 times the permeability of the matrix of about 0.2D. This greatly increased the fracture conductivity and more oil flowed into the wellbore; on the other hand, some particles blocked the fractures of the connected bottom water, achieving the effect of reduction of water.

[0067] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir, characterized in that: The following steps are involved: S1. Determine the filling pressure; S2, injecting a filling fluid containing particles into the annular space between the horizontal well and the oil layer, until the pressure in the annular space reaches the filling pressure, and fracturing the oil layer to form a root-like fracture cluster in the oil layer, wherein the extension length of the fracture cluster in the horizontal direction is ≤ the oil drainage radius, and the extension length of the fracture cluster in the vertical direction is 1 / 5-2 / 5 of the thickness of the oil layer; S3. Maintain the filling pressure and continue to inject the filling liquid until the particles fill the annular space and the fracture clusters.

2. The method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir according to claim 1, characterized in that: In step S2, the volume concentration of the microparticles in the filling liquid is 1-5%; The density of the microparticles is 1.03-1.06 g / cm3 and the particle size is 40-100 meshes.

3. The method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir according to any one of claims 1 to 2, characterized in that: In step S1, the filling pressure is 1.05-1.1 times the fracture pressure of the formation.

4. The method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir according to claim 3, characterized in that: The method for determining the formation fracture pressure is as follows: Continue to inject water into the annular space around the horizontal well, record the injection pressure, and obtain the liquid absorption index of the formation where the horizontal well is located according to the following formula: I=Q / (P w -P) Where I is the liquid absorption index, Q is the amount of water injected, P W is the bottom hole pressure of the horizontal well, P is the reservoir pressure, and P W The difference between and P is the formation pressure difference; A curve is drawn with the liquid absorption index as the ordinate and the formation pressure difference as the abscissa. The point where the liquid absorption index suddenly drops is determined on the curve, and its abscissa value is the rupture pressure of the formation fracture.

5. The method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir according to any one of claims 1 to 2, characterized in that: In step S1, the method for determining the filling pressure is: through a triaxial stress test, the Young's modulus, shear modulus and Poisson's ratio of the rock are measured, and a curve of the relationship between the formation fracture pressure and the fracture depth is measured and drawn; the formation fracture pressure when the fracture depth is 1 / 5-2 / 5 of the rock sample thickness is selected as the filling pressure.

6. The method for reducing water and increasing oil production in a horizontal well of a dual-medium oil reservoir according to any one of claims 1 to 2, characterized in that: In step S1, the filling pressure is determined by empirical statistics: in the same reservoir area, different filling pressures are used for trial production; The filling pressure value with the best oil-increasing effect is selected as the filling pressure of the oil wells in the reservoir area.

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