Fracturing design method and device for low-permeability oil reservoir
阅读说明：本技术 低渗透油藏的压裂设计方法及装置 (Fracturing design method and device for low-permeability oil reservoir ) 是由 龙长俊 肖洁 张斌 李凝 曾志国 贾元钊 吴友梅 刘丙晓 于 2018-06-25 设计创作，主要内容包括：本发明公开了一种低渗透油藏的压裂设计方法及装置。所述方法包括：获取储集层的地质资料和测井资料、以及不同支撑剂指数条件下的无因次裂缝导流能力和无因次生产指数的关系图版；根据所述储集层的地质资料和测井资料、以及所述不同支撑剂指数条件下的无因次裂缝导流能力和无因次生产指数的关系图版,确定优化的裂缝半长的范围；利用压裂设计软件并结合所述优化的裂缝半长的范围,确定优化的压裂设计方案。利用本发明提供的低渗透油藏的压裂设计方法指导压裂施工,可有效地减缓裂缝的导流能力的递减速率,延长裂缝的有效期。(The invention discloses a fracturing design method and device for a low-permeability oil reservoir. The method comprises the following steps: acquiring geological data and logging data of a reservoir and a relation chart of dimensionless fracture conductivity and dimensionless production index under different proppant index conditions; determining the range of the optimal half-length of the fracture according to the geological data and the logging data of the reservoir and the relation chart of the non-dimensional fracture conductivity and the non-dimensional production index under the different proppant index conditions; and determining an optimized fracture design scheme by utilizing fracture design software and combining the optimized half-length range of the fracture. The fracturing design method of the low-permeability oil reservoir provided by the invention is used for guiding fracturing construction, the decreasing rate of the flow conductivity of the fracture can be effectively slowed down, and the effective period of the fracture is prolonged.)
1. A method of fracture design for a low permeability reservoir, the method comprising:
acquiring geological data and logging data of a reservoir and a relation chart of dimensionless fracture conductivity and dimensionless production index under different proppant index conditions;
determining the range of the optimal half-length of the fracture according to the geological data and the logging data of the reservoir and the relation chart of the non-dimensional fracture conductivity and the non-dimensional production index under the different proppant index conditions;
and determining an optimized fracture design scheme by utilizing fracture design software and combining the optimized half-length range of the fracture.
2. The fracture optimization design method of claim 1, wherein the determining the range of optimal fracture half-lengths from the reservoir geological data and well log data, and the relationship chart of dimensionless fracture conductivity and dimensionless production index for different proppant index conditions comprises:
a. determining the oil reservoir volume of the block reservoir layer corresponding to the single well and the volume of a propping agent required for modifying the block reservoir layer corresponding to the single well according to the geological data and the logging data of the reservoir layer;
b. selecting a proppant according to geological data and well logging data of the reservoir, and determining the permeability of the proppant;
c. selecting a proppant index according to the relation chart of the dimensionless fracture conductivity and the dimensionless production index under the condition of different proppant indexes, and calculating a first preset fracture half-length by using a proppant index method according to the fracture conductivity corresponding to the proppant index and the permeability of the proppant obtained in the step b;
d. under the condition that the volume of the proppant is equal to the volume of the fracture, calculating a second preset fracture half-length according to the proppant index selected in the step c and the fracture conductivity corresponding to the proppant index;
e. comparing whether the difference value of the first preset crack half length and the second preset crack half length is within a preset range or not according to the relation chart;
f. and if the difference value of the first preset crack half length and the second preset crack half length is not in a preset range, repeating the steps b to f, otherwise, determining the range of the optimized crack half length.
3. The fracturing optimization design method of claim 2, wherein in step c,
the formula for the proppant index is:
in the formula (I), the compound is shown in the specification,
wherein Np is proppant index, dimensionless, VfpIs the volume of the single wing crack,Unit is m3，VresVolume of block reservoir corresponding to a single well, in m3，IxFracture penetration ratio, dimensionless, CfDIs fracture conductivity, dimensionless, xf1Is the half length of the first preset crack and the unit is m, xeBlock reservoir length in m, k for a single wellfIs the permeability of the proppant, in 10-3μm2K is the matrix permeability of the block reservoir for a single well, in units of 10-3μm2。
4. The fracturing optimization design method according to claim 2, wherein in step d, when the volume of the fracture is a cuboid, the formula of the second preset fracture half-fracture length is as follows:
wherein, VfpIs the volume of the single wing crack and the unit is m3，CfDIs fracture conductivity, dimensionless, xf2The second preset half crack length is m, kfIs the permeability of the proppant, in 10-3μm2K is the permeability of the matrix in 10-3μm2，hf2Is the second predetermined crack height in m.
5. The fracture optimization design method of claim 1, wherein determining an optimized fracture design plan using fracture design software in combination with the optimized fracture half-length range comprises:
according to geological data and well logging data of a reservoir layer, simulating the relation between the accumulated yield of the single well and the half-length of the fracture in a preset time by utilizing fracturing design software and combining the range of the optimized half-length of the fracture, and determining the optimized half-length of the fracture by combining economic benefits, wherein a point value in the range of the optimized half-length of the fracture is included in data of the half-length of the fracture;
calculating the optimized average crack width and the optimized average crack height according to the optimized half crack length;
calculating the static pressure of the crack according to the half-length of the crack;
selecting pump injection parameters;
and simulating the relation between the pump injection parameters and the static pressure of the fracture within preset time, and determining an optimized fracturing design scheme.
6. The fracturing optimization design method of claim 5, wherein the pumping parameters comprise: the volume ratio of the pad fluid to the fracturing fluid, the sand-fluid ratio of the sand-carrying fluid, and the pump injection displacement.
7. The fracture optimization design method of claim 1, wherein the reservoir geological data and well log data comprise: the productivity of the reservoir, the physical and chemical properties of the rock of the reservoir, and the properties of the fluid of the reservoir.
8. The fracturing optimization design method of claim 7,
the productivity of the reservoir includes:
a category of the reservoir, a thickness of the reservoir, a side length of the reservoir, a matrix permeability of the reservoir, a temperature of the reservoir, and a pressure coefficient of the reservoir;
the physical and chemical properties of the rock of the reservoir include:
permeability, porosity, oil saturation, pore structure, cementation status, clay mineral composition, and results of susceptibility testing of the rock of the reservoir;
the properties of the fluid of the reservoir include:
the viscosity, composition, and density of the crude oil of the reservoir,
the composition, mineralization, and saturation of bound water in the formation water of the reservoir, and
the composition of the natural gas of the reservoir, and the compressibility.
9. The fracture optimization design method of any of claims 1-8, further comprising: evaluating the optimized fracture design using an orthogonal test method.
10. A fracture design device for low permeability reservoirs, comprising:
the system comprises a first acquisition module, a second acquisition module and a third acquisition module, wherein the first acquisition module is used for acquiring geological data and well logging data of a reservoir and a relation chart of dimensionless fracture conductivity and dimensionless production index under different proppant index conditions;
the second acquisition module is used for determining the optimal half-length range of the fracture according to geological data and logging data of the reservoir and a relation chart of the non-dimensional fracture conductivity and the non-dimensional production index under different proppant index conditions;
and the third acquisition module is used for determining an optimized fracture design scheme by utilizing fracture design software and combining the optimized fracture half-length range.
Technical Field
The invention relates to the technical field of oilfield exploitation, in particular to a fracturing design method and device for a low-permeability oil reservoir.
Background
Fracturing, also known as hydraulic fracturing, utilizes a fracturing fluid to form fractures with flow conductivity in a reservoir, and improves the permeability of the reservoir to increase the production of oil and gas wells.
Before fracturing construction of a low-permeability oil reservoir, determining an optimized half-length range of a crack according to geological data and well logging data of a block reservoir layer corresponding to a single well, and determining an optimized fracturing design scheme by combining the optimized half-length range of the crack with fracturing design software.
In the process of implementing the invention, the inventor finds that the related art has at least the following problems:
existing fracturing designs focus on fracturing designs for medium and high permeability reservoirs. When the existing fracturing design software is applied to fracture design of a low-permeability reservoir stratum, the matching degree of the flow conductivity of the designed fracture and the liquid supply capacity of the stratum is poor, so that the decreasing rate of the flow conductivity of the fracture generated by fracturing is high, and the effective period of the fracture is short.
Disclosure of Invention
The invention provides a fracturing design method and a fracturing design device for a low-permeability oil reservoir, which are used for solving the technical problems, effectively slowing down the decreasing rate of the flow conductivity of a fracture and prolonging the effective period of the fracture. The technical scheme is as follows:
in one aspect, an embodiment of the present invention provides a fracturing design method for a low permeability reservoir, where the method includes:
acquiring geological data and logging data of a reservoir and a relation chart of dimensionless fracture conductivity and dimensionless production index under different proppant index conditions;
determining the range of the optimal half-length of the fracture according to the geological data and the logging data of the reservoir and the relation chart of the non-dimensional fracture conductivity and the non-dimensional production index under the different proppant index conditions;
and determining an optimized fracture design scheme by utilizing fracture design software and combining the optimized half-length range of the fracture.
In an exemplary embodiment, the determining the range of optimized fracture half-lengths from the geological and well log data of the reservoir and the relational version of the dimensionless fracture conductivity and dimensionless production index for the different proppant index conditions comprises:
a. determining the oil reservoir volume of the block reservoir layer corresponding to the single well and the volume of a propping agent required for modifying the block reservoir layer corresponding to the single well according to the geological data and the logging data of the reservoir layer;
b. selecting a proppant according to geological data and well logging data of the reservoir, and determining the permeability of the proppant;
c. selecting a proppant index according to the relation chart of the dimensionless fracture conductivity and the dimensionless production index under the condition of different proppant indexes, and calculating a first preset fracture half-length by using a proppant index method according to the fracture conductivity corresponding to the proppant index and the permeability of the proppant obtained in the step b;
d. under the condition that the volume of the proppant is equal to the volume of the fracture, calculating a second preset fracture half-length according to the proppant index selected in the step c and the fracture conductivity corresponding to the proppant index;
e. according to the relation chart, comparing whether the difference value of the first preset crack half-length obtained in the step c and the second preset crack half-length obtained in the step d is within a preset range or not;
f. and if the difference value of the first preset crack half length and the second preset crack half length is not in a preset range, repeating the steps b to f, otherwise, determining the range of the optimized crack half length.
In an exemplary embodiment, in step c, the formula for the proppant index is:
in the formula (I), the compound is shown in the specification,
wherein Np is proppant index, dimensionless, VfpIs the volume of the single wing crack and the unit is m3，VresVolume of block reservoir corresponding to a single well, in m3，IxFracture penetration ratio, dimensionless, CfDIs fracture conductivity, dimensionless, xf1Is the half length of the first preset crack and the unit is m, xeBlock reservoir length in m, k for a single wellfIs the permeability of the proppant, in 10-3μm2K is the matrix permeability of the block reservoir for a single well, in units of 10-3μm2。
In an exemplary embodiment, in step d, when the volume of the crack is a rectangular parallelepiped, the formula of the second preset crack half-crack length is:
wherein, VfpIs the volume of the single wing crack and the unit is m3，CfDIs fracture conductivity, dimensionless, xf2The second preset half crack length is m, kfIs the permeability of the proppant, in 10-3μm2K is the permeability of the matrix in 10-3μm2，hf2Is the second predetermined crack height in m.
In an exemplary embodiment, the determining an optimized fracture design using fracture design software in conjunction with the optimized range of fracture half-lengths comprises:
according to geological data and well logging data of a reservoir layer, simulating the relation between the accumulated yield of the single well and the half-length of the fracture in a preset time by utilizing fracturing design software and combining the range of the optimized half-length of the fracture, and determining the optimized half-length of the fracture by combining economic benefits, wherein a point value in the range of the optimized half-length of the fracture is included in data of the half-length of the fracture;
calculating the optimized average crack width and the optimized average crack height according to the optimized half crack length;
calculating the static pressure of the crack according to the half-length of the crack;
selecting pump injection parameters;
and simulating the relation between the pump injection parameters and the static pressure of the fracture within preset time, and determining an optimized fracturing design scheme.
In an exemplary embodiment, the pumping parameters include: the volume ratio of the pad fluid to the fracturing fluid, the sand-fluid ratio of the sand-carrying fluid, and the pump injection displacement.
In an exemplary embodiment, the geological and well log data of the reservoir comprises: the productivity of the reservoir, the physical and chemical properties of the rock of the reservoir, and the properties of the fluid of the reservoir.
In an exemplary embodiment, the productivity of the reservoir comprises:
a category of the reservoir, a thickness of the reservoir, a side length of the reservoir, a matrix permeability of the reservoir, a temperature of the reservoir, and a pressure coefficient of the reservoir;
the physical and chemical properties of the rock of the reservoir include:
permeability, porosity, oil saturation, pore structure, cementation status, clay mineral composition, and results of susceptibility testing of the rock of the reservoir;
the properties of the fluid of the reservoir include:
the viscosity, composition, and density of the crude oil of the reservoir,
the composition, mineralization, and saturation of bound water in the formation water of the reservoir, and
the composition of the natural gas of the reservoir, and the compressibility.
In an exemplary embodiment, the method further comprises: evaluating the optimized fracture design using an orthogonal test method.
In an exemplary embodiment, the evaluating the optimized fracture design using an orthogonal test method comprises:
establishing an orthogonal test with the volume ratio of the pad fluid to the fracturing fluid, the average sand-fluid ratio in the sand-carrying fluid and the pump injection displacement as influence factors and with the half length of the crack, the average crack width and the average crack height as evaluation indexes;
comparing the results of the orthogonal tests to the differences of the optimized fracture design scheme;
if the results of the orthogonal tests are not significantly different from the optimized fracturing design scheme, the optimized fracturing design scheme can be used for guiding fracturing construction, otherwise, the fracturing design scheme is redesigned.
In another aspect, an embodiment of the present invention provides a fracturing design apparatus for a low permeability reservoir, where the fracturing design apparatus includes:
the first calculation module is used for obtaining geological data and logging data of a reservoir and a relation chart of the non-dimensional fracture conductivity and the non-dimensional production index under different proppant index conditions, and determining the range of the optimized fracture half-length;
and the second calculation module is used for determining an optimized fracture design scheme by utilizing fracture design software and combining the optimized fracture half-length range.
In an exemplary embodiment, the second obtaining module includes:
the first acquisition unit is used for determining the oil reservoir volume of the block reservoir layer corresponding to the single well and the volume of a propping agent required for modifying the block reservoir layer corresponding to the single well according to the geological data and the logging data of the reservoir layer;
the second acquisition unit is used for selecting a propping agent according to geological data and well logging data of the reservoir and determining the permeability of the propping agent;
the third obtaining unit is used for selecting a proppant index according to a relation chart of the dimensionless fracture conductivity and the dimensionless production index under the condition of different proppant indexes, and calculating a first preset fracture half-length by using a proppant index method according to the fracture conductivity corresponding to the proppant index and the permeability of the proppant;
the fourth obtaining unit is used for calculating a second preset fracture half-length according to the proppant index and the fracture conductivity corresponding to the proppant index under the condition that the volume of the proppant is equal to the volume of the fracture;
the judging unit is used for comparing whether the difference value of the first preset crack half length and the second preset crack half length is within a preset range or not according to the relation chart;
and a fifth obtaining unit, configured to repeatedly execute the second obtaining unit, the third obtaining unit, the fourth obtaining unit, the judging unit, and the fifth obtaining unit if the difference between the first preset half-length of the crack and the second preset half-length of the crack is not within a preset range, and otherwise, determine an optimized half-length range of the crack.
In an exemplary embodiment, the third obtaining module includes:
a sixth obtaining unit, configured to determine an optimized fracture half-length by using fracture design software and combining the optimized fracture half-length range, simulating a relationship between the cumulative yield of the single well and the fracture half-length within a preset time and combining economic benefits according to geological data and well logging data of a reservoir, where a point value in the optimized fracture half-length range is included in the data of the fracture half-length;
a seventh obtaining unit, configured to calculate an optimized average crack width and an optimized average crack height according to the optimized half-length of the crack;
the eighth acquisition unit is used for calculating the static pressure of the crack according to the half length of the crack;
the selection unit is used for selecting the pumping parameters;
and the ninth acquisition unit simulates the relation between the pump injection parameters and the fracture static pressure in preset time and determines an optimized fracturing design scheme.
In an exemplary embodiment, the fracture design apparatus further comprises:
and the checking module is used for evaluating the optimized fracturing design scheme by using an orthogonal test method.
In an exemplary embodiment, the verification module includes:
the orthogonal test unit is used for establishing an orthogonal test which takes the volume ratio of the pad fluid to the fracturing fluid, the average sand-fluid ratio in the sand carrying fluid and the pump injection displacement as influence factors and takes the half length of a crack, the average crack width and the average crack height as evaluation indexes,
the second judgment unit is used for comparing the result of the orthogonal test with the difference of the optimized fracturing design scheme obtained by the third acquisition module;
and the tenth acquiring unit is used for repeating the first acquiring module, the second acquiring module, the third acquiring module and the verifying module if the result of the orthogonal test is not significantly different from the optimized fracturing design scheme acquired by the third acquiring module, wherein the optimized fracturing design scheme acquired by the third acquiring module can be used for guiding fracturing construction.
The technical scheme provided by the embodiment of the invention has the beneficial effects that:
because the relationship chart of the dimensionless fracture conductivity and the dimensionless production index under the condition of different proppant indexes reflects the matching degree of the fracture conductivity and the stratum permeability, the method is suitable for low-permeability oil reservoirs, medium-permeability oil reservoirs and high-permeability oil reservoirs, and therefore, the fracturing design method of the low-permeability oil reservoirs of the embodiment of the invention firstly obtains geological data and well logging data of reservoir layers and the relationship chart of the dimensionless fracture conductivity and the dimensionless production index under the condition of different proppant indexes; and determining the half-length range of the optimized fracture according to geological data, logging data and a relation chart of the non-dimensional fracture conductivity and the non-dimensional production index under different proppant index conditions, and finally determining an optimized fracturing design scheme by combining fracturing design software, so that the fracturing construction is guided by the optimized fracturing design scheme, the decreasing rate of the conductivity of the fracture can be effectively slowed down, and the effective period of the fracture is prolonged.
Drawings
FIG. 1 is a flow chart illustrating a method for fracture design of a low permeability reservoir in accordance with an exemplary embodiment of the present invention.
FIG. 2 is a flow
FIG. 3 is a flow
FIG. 4 is a plot of cumulative production for a single well versus half-length of the fracture.
FIG. 5 is a plot of static fracture pressure versus average sand-to-fluid ratio.
Figure 6 is a plot of hydrostatic pressure of the fracture versus the volume ratio of pad fluid to fracturing fluid.
FIG. 7 is a graph of fracture static pressure versus pump displacement.
FIG. 8 is a graph of fracture half-length versus volume ratio of pad fluid to fracturing fluid, average sand-fluid ratio, and pumping capacity.
FIG. 9 is a plot of average fracture width versus the volume ratio of pad fluid to fracturing fluid, average sand-fluid ratio, and pumping capacity.
FIG. 10 is a plot of average fracture height versus volume ratio of pad fluid to fracturing fluid, average sand-fluid ratio, and pumping capacity.
FIG. 11 is a block diagram of a fracture design apparatus for a low permeability reservoir in accordance with an exemplary embodiment of the present invention.
FIG. 12 is a block diagram illustrating a second acquisition module in a fracture design apparatus for a low permeability reservoir in accordance with an exemplary embodiment of the present invention.
FIG. 13 is a block diagram of a third acquisition module in a fracture design apparatus for a low permeability reservoir in accordance with an exemplary embodiment of the present invention.
Detailed Description
In order to make the technical solutions and advantages of the present invention clearer, the following will describe embodiments of the present invention in further detail with reference to the accompanying drawings.
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the invention, as detailed in the appended claims.
For the convenience of a reader to quickly understand the technical scheme provided by the embodiment of the invention, before introducing the fracturing design method of the low-permeability reservoir provided by the embodiment of the invention, the fracturing construction operation is simply introduced first.
When the fracturing construction is carried out, a high-viscosity pad fluid is injected from a shaft of an oil-gas well to a reservoir layer at the bottom of the well by utilizing a ground high-pressure pump connecting pipeline. When the rate of injection of the pad fluid exceeds the rate of absorption of the reservoir, high fluid pressures develop across the reservoir. When the hydraulic pressure exceeds the pressure required for rock fracture of the reservoir, the reservoir fractures, forming fissures. Continuously injecting a pad fluid into the reservoir, and gradually extending the crack; then injecting a sand-carrying fluid into the reservoir from the well bore to continue the fracture, and retaining the proppant in the sand-carrying fluid in the fracture to keep the fracture open; and then, injecting a displacement fluid into the reservoir from the well bore, so that the sand-carrying fluid in the well bore completely flows into the fracture under the action of hydraulic pressure, and the proppant therein is retained in the fracture as much as possible to form the fracture with certain length, width and height and flow conductivity. The crack is communicated with the shaft to form an oil and gas channel and improve the yield of the oil and gas well.
The following exemplary embodiments are individually set forth in detail with respect to how fractures having high conductivity and long life are created to maximize oil and gas well production and economic efficiency.
In one aspect, the embodiment of the invention provides a fracturing design method for a low-permeability oil reservoir. Referring to fig. 1, fig. 1 is a flow chart illustrating a method for designing a fracture of a low permeability reservoir according to an exemplary embodiment of the present invention. As shown in fig. 1, the method includes:
101: acquiring geological data and logging data of a reservoir and a relation chart of dimensionless fracture conductivity and dimensionless production index under different proppant index conditions;
102: determining the range of the optimal half-length of the fracture according to the geological data and the logging data of the reservoir and the relation chart of the non-dimensional fracture conductivity and the non-dimensional production index under the different proppant index conditions;
103: and determining an optimized fracture design scheme by utilizing fracture design software and combining the optimized half-length range of the fracture.
The working principle of the fracturing design method of the low-permeability oil reservoir provided by the invention is as follows:
because the relationship chart of the dimensionless fracture conductivity and the dimensionless production index under the condition of different proppant indexes reflects the matching degree of the fracture conductivity and the stratum permeability, the method is suitable for low-permeability oil reservoirs, medium-permeability oil reservoirs and high-permeability oil reservoirs, and therefore, the fracturing design method of the low-permeability oil reservoirs of the embodiment of the invention firstly obtains geological data and well logging data of reservoir layers and the relationship chart of the dimensionless fracture conductivity and the dimensionless production index under the condition of different proppant indexes; and determining the half-length range of the optimized fracture according to geological data and logging data of a reservoir and a relation chart of the non-dimensional fracture conductivity and the non-dimensional production index under different proppant index conditions, and finally determining an optimized fracturing design scheme by combining fracturing design software, so that the optimized fracturing design scheme guides fracturing construction, the decreasing rate of the conductivity of the fracture can be effectively slowed down, and the effective period of the fracture is prolonged.
It is noted that reservoirs with a matrix permeability of 50mD or less are generally referred to in the art as low permeability reservoirs.
In an exemplary embodiment of the invention, the geological and well log data of the reservoir comprises: the productivity of the reservoir, the physical and chemical properties of the rock of the reservoir, and the properties of the fluid of the reservoir. Wherein the productivity of the reservoir comprises: the type of the reservoir (such as clastic, carbonate, and volcanic), the thickness of the reservoir, the length of the side of the reservoir, the matrix permeability of the reservoir, the temperature of the reservoir, and the pressure coefficient of the reservoir, among others; the physical and chemical properties of the rock of the reservoir include: permeability, porosity, oil saturation, pore structure, cementation, clay mineral composition, and results of susceptibility tests (rate-, water-, salt-, acid-, and alkali-sensitive), etc., of the rock of the reservoir; the properties of the fluid of the reservoir include: the viscosity, composition, and density of the crude oil of the reservoir, the composition, mineralization, and saturation of bound water in the formation water of the reservoir, and the composition, compressibility, and the like of the natural gas of the reservoir.
For a specific implementation form of
1021: determining the oil reservoir volume of the block reservoir layer corresponding to the single well and the volume of a propping agent required for modifying the block reservoir layer corresponding to the single well according to the geological data and the logging data of the reservoir layer;
it should be noted that, in order to calculate the reservoir volume of the reservoir, a person skilled in the art generally regards the reservoir as a rectangular parallelepiped with a square cross section, and therefore, the block reservoir corresponding to a single well can also be regarded as a rectangular parallelepiped with a square cross section, and then the block reservoir corresponding to the single wellThe reservoir volume of a reservoir may be expressed as:
The volume of the proppant required for modifying the reservoir zone of the block corresponding to the single well can refer to the volume of the proppant required for modifying the adjacent oil and gas wells, and can also be determined according to geological data and logging data of the reservoir zone, which is not described herein again.
1022: selecting a proppant according to geological data and well logging data of the reservoir, and determining the permeability of the proppant;
the specific operation of
Since the permeability of the proppant is a key factor affecting fracture conductivity, it is desirable to determine the permeability of the proppant. The permeability of the proppant can be determined by one skilled in the art using an instrument that measures the permeability of the proppant.
1023: selecting a proppant index according to the relation chart of the dimensionless fracture conductivity and the dimensionless production index under the condition of different proppant indexes, and calculating a first preset fracture half-length by using a proppant index method according to the fracture conductivity corresponding to the proppant index and the permeability of the proppant;
in
in the formula (I), the compound is shown in the specification,
wherein Np is proppant index, dimensionless, VfpIs the volume of the single wing crack and the unit is m3，VresVolume of block reservoir corresponding to a single well, in m3，IxFracture penetration ratio, dimensionless, CfDIs fracture conductivity, dimensionless, xf1Is the half length of the first preset crack and the unit is m, xeBlock reservoir length in m, k for a single wellfIs the permeability of the proppant, in 10-3μm2K is the matrix permeability of the block reservoir for a single well, in units of 10-3μm2。
It can be seen that the proppant index method selected by the present invention is the proppant index method of Econoamides et al that responds to the degree of matching between fracture length and fracture conductivity. The proppant index method considers the influence of the Darcy seepage on the fracture length and the fracture conductivity, so that the proppant index method is suitable for the fracturing design of low-permeability oil reservoirs.
1024: under the condition that the volume of the proppant is equal to the volume of the fracture, calculating a second preset fracture half-length according to the proppant index and the fracture conductivity corresponding to the proppant index;
in
Vfp＝hf2wp2xf2③
wherein, VfpIs the volume of the single wing crack and the unit is m3，CfDIs fracture conductivity, dimensionless, xf2The second preset half crack length is m, kfIs the permeability of the proppant, in 10-3μm2K is the permeability of the matrix in 10-3μm2，hf2For the second predetermined crack height in m, wp2The width of the second predetermined slit is m.
It should be noted that the second predetermined crack height hf2May be approximately equal to the thickness of the block reservoir to which a single well corresponds.
1025: comparing whether the difference value of the first preset crack half length and the second preset crack half length is within a preset range or not according to the relation chart;
1026: and if the difference value of the first preset crack half length and the second preset crack half length is not in a preset range, repeating the
When the difference between the first preset fracture half-length obtained in
For a specific implementation form of
1031: according to geological data and well logging data of a reservoir layer, simulating the relation between the accumulated yield of the single well and the half-length of the fracture in a preset time by utilizing fracturing design software and combining the range of the optimized half-length of the fracture, and determining the optimized half-length of the fracture by combining economic benefits, wherein a point value in the range of the optimized half-length of the fracture is included in data of the half-length of the fracture;
since the effective life of a fracturing design is typically 3 years, the preset time may be 3 years.
1032: calculating the optimized average crack width and the optimized average crack height according to the optimized half crack length;
in
wherein, wpTo optimize the average crack width, m; vfpIs the volume of the single wing crack and the unit is m3，CfDIs fracture conductivity, dimensionless, kfIs the permeability of the proppant, in 10-3μm2K is the permeability of the matrix in 10-3μm2，hfIs the crack height in m.
In calculating the optimized average fracture width, the reservoir thickness is approximately equal to the average fracture height.
1033: calculating the static pressure of the crack according to the half-length of the crack;
in
According to the related parameters, the static pressure of the fracture is related to the well head pumping pressure, the bottom hole pressure, the on-way friction resistance of the fracturing fluid, the closing pressure of the fracture and the like, wherein the bottom hole pressure is generated by the well head pumping pressure, the well head pumping pressure is in direct proportion to the pumping displacement and the viscosity of the fracturing fluid, the on-way friction resistance of the fracturing fluid is in inverse proportion to the pumping displacement, and the on-way friction resistance of the fracturing fluid is in inverse proportion to the viscosity of the fracturing fluid, so that the net pressure of the fracture can be controlled by regulating the pumping displacement and the viscosity of the fracturing fluid.
1034: selecting pump injection parameters;
the fracturing fluid includes a pad fluid, a sand-carrying fluid, and a displacement fluid. The sand-carrying fluid is usually a pad fluid added with a proppant, and the volume ratio of the proppant to the sand-carrying fluid is the sand-fluid ratio.
The pumping parameters include: the volume ratio of the pad fluid to the fracturing fluid, the sand-fluid ratio of the sand-carrying fluid, and the pump injection displacement. Ideally, at the end of pumping, the pad fluid is just lost into the formation and the proppant enters the fracture, providing sufficient conductivity to the fracture. Excess pad fluid can cause excessive fracture propagation, which narrows the average fracture width and reduces the fracture conductivity due to the determined amount of proppant, while excess pad fluid can cause greater damage to the reservoir. The average sand-to-fluid ratio is related to the viscosity of the sand-to-fluid and the fluid-carrying capacity of the sand-to-fluid, and influences the on-way friction resistance of the sand-to-fluid in the fracturing fluid according to the content of the parameters related to the static pressure of the fracture. Therefore, the volume ratio of pad to fracturing fluid, the average sand-fluid ratio in the sand-carrying fluid, and the pump-out volume are key factors in the optimized fracturing design.
1035: and simulating the relation between the pump injection parameters and the static pressure of the fracture within preset time, and determining an optimized fracturing design scheme.
The final determined optimized fracture design may include: the fracturing fluid flow rate is optimized by optimizing the half-length of the fracture, optimizing the average fracture width, optimizing the average fracture height, optimizing the average sand-liquid ratio, optimizing the ratio of the pad fluid to the fracturing fluid, optimizing the pump injection capacity and the like.
In the embodiment of the present invention, after
Step 104 includes the steps of:
1041: establishing an orthogonal test with the volume ratio of the pad fluid to the fracturing fluid, the average sand-fluid ratio in the sand-carrying fluid and the pump injection displacement as influence factors and with the half length of the crack, the average crack width and the average crack height as evaluation indexes;
1042: comparing the results of the orthogonal tests to the differences in the optimized fracture design plan obtained in
1043: if the results of the orthogonal tests are not significantly different from the optimized fracture design obtained in
Each of the steps in the exemplary embodiments described above will be embodied in a fracturing design test for XL10-163x wells.
101: obtaining geological data and logging data of a reservoir in the west willow area of the northwest China oil field and a relation chart version of the dimensionless crack conductivity and the dimensionless production index under different proppant index conditions;
the
the
the step 1023-1024 may be embodied by calculating the first preset fracture half-length and the second preset fracture half-length according to the relationship chart of the non-dimensional fracture conductivity and the non-dimensional production index under different proppant indexes, the formula ①, the
TABLE 1 comparison of the first and second predetermined fracture half-lengths
Proppant index (N)p)
Fracture conductivity (C)fd)
First predetermined crack half length/m
Second predetermined half crack length/m
0.1
1.6
35
342.3
1
2.5
88.5
273.9
8
9.1
131.3
143.5
9
10
132.8
136.9
10
10.3
137.9
134.9
The detailed description of the above steps 1025-1026 may be: as can be seen from Table 1, when the first predetermined half-length of the crack is 137.9m and the second predetermined half-length of the crack is 134.9m, the difference between the first predetermined half-length of the crack and the second predetermined half-length of the crack is less than 5cm, and thus, the optimal half-length of the crack is determined to be in the range of 134m to 145 m.
The
The
the steps 1033-1035 can be embodied as follows: the volume ratio of the pad fluid to the fracturing fluid, the average sand-fluid ratio in the sand-carrying fluid and the pump-out displacement are selected according to experience, and the relationship between the volume ratio of the pad fluid to the fracturing fluid, the average sand-fluid ratio in the sand-carrying fluid and the pump-out displacement and the static pressure of the crack is simulated, which is respectively shown in fig. 5, 6 and 7.
According to the results shown in fig. 5, the optimized volume ratio of the pad fluid to the fracturing fluid is 45-50%;
according to the results shown in fig. 6, the optimized average sand-to-liquid ratio is 21% -23%;
according to the results shown in FIG. 7, the optimized pump displacement is 4.75-5.0m3/min。
The step 104 may be embodied as: and (3) carrying out an orthogonal test by taking the volume ratio of the pad fluid to the fracturing fluid, the average sand-fluid ratio and the pump injection displacement as influence factors and taking the half length of the crack, the average crack width and the average crack height as evaluation indexes.
The volume ratio of the pad fluid to the fracturing fluid, the average sand-fluid ratio and the pump injection displacement are used as influence factors, the half length of a crack, the average crack width and the average crack height are used as evaluation indexes, and 5 horizontal orthogonal tests with 3 factors are established and are detailed in table 2.
TABLE 2L25(53) Influence factor level meter
Level of
Pump displacement/m3/min
Average sand to fluid ratio/%)
Volume ratio of pad fluid to fracturing fluid%
1
4.00
21
30
2
4.25
23
35
3
4.50
25
40
4
4.75
27
45
5
5.00
29
50
The results of the orthogonal experiments are detailed in fig. 8, 9 and 10:
in FIG. 8, the fracture half-length gradually increases as the pumping capacity increases, and is greater than 4.75m at the pumping capacity3After/min, the increase amplitude decreases; the half-length of the crack gradually decreases with the increase of the average sand-to-liquid ratio; the half length of the fracture gradually increases along with the increase of the volume ratio of the pad fluid to the fracturing fluid, and the fracture tends to be stable after the volume ratio of the pad fluid to the fracturing fluid is more than 45%;
in fig. 9, the average fracture width gradually increases as the pump displacement and the volume ratio of pad to fracturing fluid increases; the average fracture width does not show obvious variation trend along with the increase of the average sand-liquid ratio;
in fig. 10, the average fracture height gradually decreases as the pump displacement and the volume ratio of pad to fracturing fluid increases; as the average sand to fluid ratio increases, the average fracture width shows a tendency to increase first and then decrease, and reaches a maximum when the average sand to fluid ratio is about 25%;
the orthogonal test shows that the pump injection displacement is 4.75m3And/min, the average sand-to-fluid ratio is 23%, and the volume ratio of the pad fluid to the fracturing fluid is 45%, which is included in the optimized fracturing design scheme.
Analysis of variance was performed based on the results of the orthogonal test, and the results are shown in tables 3, 4 and 5.
TABLE 3 analysis of variance table for half-length of crack
Influencing factor
Sum of squares of deviation
Degree of freedom
F ratio
Critical value of F
Significance of
Displacement of pump
61.686
4
0.733
2.78
Average sand-to-liquid ratio
5.842
4
0.069
2.78
Volume ratio of pad fluid to fracturing fluid
431.626
4
5.13
2.78
*
As can be seen from table 3, the volume ratio of pad fluid to fracturing fluid has a significant effect on the half-length of the fracture. And determining that the volume ratio of the optimized pad fluid to the fracturing fluid is 45-50% by combining the results shown in FIG. 8, and selecting that the volume ratio of the optimized pad fluid to the fracturing fluid is 45% for fracturing construction.
TABLE 4 ANOVA TABLE OF MEASURED CRACK WIDTH
Influencing factor
Sum of squares of deviation
Degree of freedom
F ratio
Critical value of F
Significance of
Displacement of pump
0.003
4
0.391
3.26
Average sand-to-liquid ratio
0.001
4
0.13
3.26
Volume ratio of pad fluid to fracturing fluid
0.019
4
2.478
3.26
As can be seen from table 4, the pump shot displacement, average sand-to-fluid ratio, and the volume ratio of pad to fracturing fluid did not have a significant effect on the average fracture width.
TABLE 5 ANOVA TABLE OF MEASURED CRACK HEIGHT
Influencing factor
Factors of the fact
Sum of squares of deviation
Degree of freedom
F ratio
Critical value of F
Significance of
Displacement of pump
Discharge capacity
13.35
4
2.873
2.78
*
Average sand-to-liquid ratio
Sand ratio
0.178
4
0.038
2.78
Volume ratio of pad fluid to fracturing fluid
Pre-liquid ratio
14.166
4
3.049
2.78
*
As can be seen from Table 5, the pump displacement and the volume ratio of the pad fluid to the fracturing fluid have a significant effect on the average fracture height, and in combination with the results shown in FIGS. 8 and 10, it was determined that the optimized volume ratio of the pad fluid to the fracturing fluid was 45% to 50%, and the optimized pump displacement was 4.75 to 5.0m3Min, since greater pumping capacity results in greater wellhead pumping pressure and bottom hole pressure, the maximum pressure that the pumping equipment can withstand, the maximum pressure that the string in the wellbore can withstand, and the critical pressure of the reservoir must be considered. In the fracturing construction process, the bottom hole pressure generated by the wellhead pumping pressure is lower than the critical pressure of a reservoir stratum, so that the condition that the fracturing construction is out of control due to overlarge average crack height is avoided, and therefore, the optimized pumping displacement can be selected to be 4.75m3And performing fracturing construction at/min.
Although the sand fluid ratio has no significant effect on the fracture half-length, average fracture width, and average fracture height according to the results of the orthogonal tests. However, according to the results of fig. 10, as the average sand-to-fluid ratio increases, the average fracture width tends to increase first and then decrease, and thus, it is determined that the optimized average sand-to-fluid ratio is 21% to 23%, and the optimized average sand-to-fluid ratio of 23% may be selected for fracture construction.
The daily liquid production of XL10-163x well after fracturing is 14.2m3The daily crude oil yield is 11.73 t. After crude oil production in XL10-163x well for 350 days, the daily liquid production per well is 11.75m3The daily crude oil yield was 8.74 t.
Comparative experiments between XL10-163x wells and XL10-123x wells
XL10-123x wells are adjacent to XL10-163x wells, the reservoir properties of the XL10-123x wells are the same, the side length of the range of a single well control reservoir is the same, the matrix permeability is the same, and the volume of proppant required for reconstruction is the same. And (3) applying FracpropT fracturing design software to carry out fracturing design on the XL10-123x well and guiding fracturing construction. The daily liquid production of XL10-123x well after fracturing is 9.31m3The daily crude oil yield was 5.59 t. It can be seen that for the reservoirs of low permeability reservoirs with the same properties, the crude oil yield is different by adopting the fracturing design method of the embodiment and the existing fracturing design method. The daily oil production of XL10-163x wells after fracturing is significantly higher than that of XL10-123x wells after fracturing.
Therefore, the fracturing design method of the low-permeability oil reservoir provided by the embodiment is used as a guide to perform fracturing construction, the flow conductivity of the generated crack is good, the decreasing rate of the flow conductivity of the crack is correspondingly reduced, and compared with the existing fracturing optimization design method, the fracturing design method of the low-permeability oil reservoir provided by the embodiment can achieve a better yield increase effect.
On the other hand, the embodiment of the invention also provides a fracturing design device for the low-permeability oil reservoir. Referring to fig. 11, fig. 11 is a block diagram of a fracture design apparatus for a low permeability reservoir according to an exemplary embodiment of the present invention. As shown in fig. 11, the fracture designing apparatus includes:
the
a second obtaining
referring to fig. 12, fig. 12 is a block diagram of a second obtaining module in a fracture design device for low permeability reservoirs according to an exemplary embodiment of the present invention. As shown in fig. 12, the second obtaining
the first obtaining
a second obtaining
a third obtaining
a fourth obtaining
a determining
a fifth obtaining
And a third obtaining
Referring to fig. 13 for the specific structure of the third obtaining
a sixth obtaining unit 301, configured to determine an optimized fracture half-length by using fracture design software and combining the optimized fracture half-length range, simulating a relationship between the cumulative yield of the single well and the fracture half-length within a preset time and combining economic benefits according to geological data and well logging data of a reservoir, where a point value in the optimized fracture half-length range is included in the data of the fracture half-length;
a seventh obtaining unit 302, configured to calculate an optimized average crack width and an optimized average crack height according to the optimized half-length of the crack;
an eighth obtaining unit 303, configured to calculate a fracture static pressure according to the fracture half-length;
a selection unit 304 for selecting a pumping parameter;
the ninth obtaining unit 305 simulates a relationship between the pumping parameter and the fracture static pressure within a preset time, and determines an optimized fracturing design scheme.
In an exemplary embodiment, the fracture design apparatus further comprises:
and the
The
the orthogonal test unit 401 establishes an orthogonal test using the volume ratio of the pad fluid to the fracturing fluid, the average sand-fluid ratio in the sand-carrying fluid, and the pump-injection displacement as influence factors, and using the half length of the fracture, the average fracture width, and the average fracture height as evaluation indexes,
a second judging unit 402, which compares the result of the orthogonal test with the difference of the optimized fracturing design scheme obtained by the third obtaining
the tenth obtaining unit 403, if the result of the orthogonal test is not significantly different from the optimized fracturing design scheme obtained by the third obtaining
The above description is only for facilitating the understanding of the technical solutions of the present invention by those skilled in the art, and is not intended to limit the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
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