Reverse mixed carbon dioxide pre-fracturing pump injection design method

Abstract

The invention provides a reverse mixed carbon dioxide pre-fracturing pump injection design method, which belongs to the technical field of horizontal well fracturing, and comprises the following steps: acquiring basic parameters of a target oil reservoir, and determining reservoir transformation requirements; according to the target oil reservoir transformation requirement, a reservoir transformation design scheme is determined through numerical simulation, and fracturing transformation parameters of the target area body are determined; according to the target oil reservoir transformation requirement, the reverse mixing pump injection technology is optimized; carbon dioxide pre-construction parameters are optimized according to indoor experiments and numerical simulation; and constructing a reverse mixed carbon dioxide pre-fracturing pump injection program by utilizing the fracturing transformation parameters, the reverse mixed pump injection process and the carbon dioxide pre-construction parameters. According to the method, the carbon dioxide pre-fracturing construction difficulty is reduced, and the carbon dioxide pre-fracturing yield increasing effect is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of horizontal well fracturing, and in particular relates to a reverse mixed carbon dioxide pre-fracturing pump injection design method. Background Art

[0002] The sandstone reservoir has poor permeability, and the horizontal well depletion development method has a rapid energy decline and low recovery rate. At the same time, the reservoir is highly heterogeneous, the water drive effect is poor, and it is not suitable for well network injection and production development. 2 Under downhole conditions, it can be converted into a supercritical state, with ultra-low interfacial tension, strong fluidity and diffusivity, and can effectively affect tight reservoirs. Combined with hydraulic fracturing, CO 2 Pre-energy storage fracturing can reduce crude oil viscosity, replenish formation energy, increase production and recovery rate on the basis of hydraulic fracturing, and at the same time can better control fracturing costs. It is an important development direction for the efficient development of Mahu tight oil.

[0003] Due to the complex rock mechanical properties of conglomerate, it is difficult to initiate fractures. At the same time, the hydraulic fractures are relatively complex and tortuous, showing strong near-wellbore friction. 2 The front fracturing pump design strengthens the above characteristics, coupled with CO 2 The high friction of the fluid has shown extremely high construction difficulty in field practice, long fracturing construction period, and the amount of fracturing fluid used has greatly exceeded the designed amount, significantly increasing the capacity construction period and fracturing cost. 2 The return is obvious, and the production effect has not met expectations, indicating that CO 2 The oil displacement effect has not been fully exerted.

[0004] Conglomerate CO 2 Pre-storage fracturing lacks reasonable construction technology and construction parameters, and cannot fully play the role of CO 2 There are two main problems in increasing production potential. First, due to the complex rock mechanical properties of conglomerate, the crack expansion varies greatly. How to achieve CO 2 Balanced injection; second, based on effective injection, what kind of pumping parameters can be used for specific areas to achieve the best production increase effect. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a reverse mixed carbon dioxide pre-fracturing pumping design method. The technical problem to be solved by the present invention is how to reduce the difficulty of carbon dioxide pre-fracturing construction and improve the production increase effect of carbon dioxide pre-fracturing.

[0006] In order to solve the above technical problems, the present invention provides a reverse mixed carbon dioxide pre-fracturing pump injection design method, comprising step S1: obtaining basic parameters of the target reservoir and determining the reservoir transformation requirements;

[0007] Step S2: According to the transformation requirements of the target reservoir, the reservoir transformation design scheme is determined through numerical simulation, and the fracturing transformation parameters of the main body of the target area are determined;

[0008] Step S3: Optimizing the reverse mixing pumping process according to the target reservoir transformation requirements;

[0009] Step S4: Optimizing carbon dioxide pre-construction parameters according to indoor experiments and numerical simulations;

[0010] Step S5: construct a reverse mixing carbon dioxide pre-fracturing pumping program using the fracturing stimulation parameters, reverse mixing pumping process and carbon dioxide pre-construction parameters.

[0011] Furthermore, in step S1, the basic parameters of the target reservoir include the target reservoir type, oil layer distribution, temperature, pressure and fluid characteristics, lithology, physical properties, rock mechanical properties and geological parameters related to the development of natural fractures.

[0012] Furthermore, in step S2, the fracturing transformation parameters include perforation technology, fracturing materials, stage cluster design, fracturing scale, carbon dioxide injection amount and carbon dioxide injection method.

[0013] Furthermore, in step S3, the reverse mixing pumping process is optimized according to the indoor large rock sample hydraulic fracturing test and the proppant migration numerical simulation, and the optimization of the reverse mixing pumping process includes optimizing the fracturing material dosage, step sand ratio setting, stage fracturing fluid type, injection displacement, spacer fluid dosage and the number of front segment plugs.

[0014] Furthermore, in step S4, optimizing the carbon dioxide pre-placement construction parameters includes optimizing the carbon dioxide injection sequence, the carbon dioxide injection displacement, and the pre-placement liquid ratio parameters.

[0015] Furthermore, in step S4, the indoor large rock sample carbon dioxide fracturing test and numerical simulation and the regional early carbon dioxide pre-fracturing pilot test construction are analyzed to determine the carbon dioxide injection displacement.

[0016] Furthermore, in step S5, the reverse mixed carbon dioxide pre-fracturing pumping procedure includes test squeezing (squeezing acid, replacing acid, stopping pumping and soaking acid), the first pre-fluid, pumping carbon dioxide, the second pre-fluid, slugging sand, continuous sand carrying and displacement fluid stages.

[0017] Furthermore, the trial extrusion includes squeezing acid, replacing acid and stopping the pump to soak the acid.

[0018] Furthermore, in the trial squeeze phase: inject fracturing fluid of set viscosity into the target layer to limit the pressure and increase the displacement.

[0019] Furthermore, in the sand-carrying stage, sand-carrying fluid is injected into the target layer and proppant is continuously added; in the displacement fluid stage, displacement fluid is injected into the target layer.

[0020] The present invention provides a reverse mixing carbon dioxide pre-fracturing pumping design method, which comprehensively considers the influence of carbon dioxide rock breaking and migration mechanism and pumping technology on oil recovery efficiency during fracturing, and forms a set of carbon dioxide pre-fracturing reverse mixing pumping procedures through numerical simulation and field practice to guide carbon dioxide pre-fracturing production increase.

[0021] The present invention has the following beneficial effects:

[0022] (1) Provides CO 2 The pre-fracturing pump injection design method can effectively solve the CO 2 Problems with pre-fracturing production enhancement construction. Through field construction verification, the pump injection design method has a 100% compliance rate for sand addition, and an average production increase of 33.3% compared with the comparison wells, which fully proves the effectiveness of this method.

[0023] (2) It is universal for conglomerate reservoirs. This method can be used to construct a pumping program suitable for different reservoirs, which can be extended to other conglomerate tight oil blocks to effectively increase crude oil production and recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic flow diagram of a reverse mixed carbon dioxide pre-fracturing pump injection design method of the present invention.

[0025] Figure 2 It is a schematic diagram of numerical simulation of proppant migration in a reverse mixed carbon dioxide pre-fracturing pump injection design method of the present invention; Figure 2 (a) is a schematic diagram of the setting of the digital model crack tortuosity; Figure 2 (b) is a schematic diagram of the proppant volume fraction distribution under different tortuosity conditions.

[0026] Figure 3 It is a production simulation schematic diagram of different carbon dioxide injection sequences in a reverse mixed carbon dioxide pre-fracturing pump injection design method of the present invention.

[0027] Figure 4 It is a schematic diagram of an embodiment of a reverse mixed carbon dioxide pre-fracturing pump injection design method of the present invention; Figure 4 (a) is a schematic diagram of carbon dioxide pre-injection fracturing analysis; Figure 4 (b) is a schematic diagram of the sweep range of different carbon dioxide front displacement rates, where x is the sweep distance in the direction perpendicular to the crack, and y is the sweep distance along the crack.

[0028] Figure 5The invention discloses a reverse mixed carbon dioxide pre-fracturing pump injection design method for CO2 with different pre-fluid and sand-carrying fluid ratios. 2 Distribution diagram.

[0029] Figure 6 This is a comparison chart of cumulative production of different proportions of pre-fluid and sand-carrying fluid in a reverse mixed carbon dioxide pre-fracturing pump injection design method of the present invention; Figure 6 (a) is a graph showing the relationship between cumulative oil production and time; Figure 6 (b) in the figure is a curve diagram showing the relationship between cumulative oil production and time.

[0030] Figure 7 It is a schematic diagram of a reverse mixing pumping program of a reverse mixing carbon dioxide pre-fracturing pumping design method of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0033] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0034] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In order to better understand the purpose, structure and function of the present invention, a reverse mixed carbon dioxide pre-fracturing pump injection design method of the present invention is further described in detail below in conjunction with the accompanying drawings.

[0036] Embodiment 1:

[0037] like Figure 1 As shown, the present invention provides a reverse mixed carbon dioxide pre-fracturing pump injection design method, comprising the following steps:

[0038] Step S1: Obtain the basic parameters of the target reservoir and determine the reservoir transformation requirements.

[0039] Step S2: According to the transformation requirements of the target reservoir, the reservoir transformation design scheme is determined through numerical simulation, and the fracturing transformation parameters of the main body of the target area are determined.

[0040] Step S3: Optimize the reverse mixing pumping process according to the target reservoir transformation requirements.

[0041] Step S4: Optimize carbon dioxide pre-construction parameters based on indoor experiments and numerical simulations.

[0042] Step S5: construct a reverse mixing carbon dioxide pre-fracturing pumping program using the fracturing stimulation parameters, reverse mixing pumping process and carbon dioxide pre-construction parameters.

[0043] Embodiment 2:

[0044] like Figure 1 As shown, the present invention provides a reverse mixed carbon dioxide pre-fracturing pump injection design method, comprising the following steps:

[0045] Step S1: Obtain the basic parameters of the target reservoir and determine the reservoir transformation requirements.

[0046] Step S2: According to the transformation requirements of the target reservoir, the reservoir transformation design scheme is determined through numerical simulation, and the fracturing transformation parameters of the main body of the target area are determined.

[0047] Step S3: Optimize the reverse mixing pumping process according to the target reservoir transformation requirements.

[0048] Step S4: Optimize carbon dioxide pre-construction parameters based on indoor experiments and numerical simulations.

[0049] Step S5: construct a reverse mixing carbon dioxide pre-fracturing pumping program using the fracturing stimulation parameters, reverse mixing pumping process and carbon dioxide pre-construction parameters.

[0050] This embodiment is different from the first embodiment in that:

[0051] In step S1, the basic parameters of the target reservoir include geological parameters such as target reservoir type, oil layer distribution, temperature, pressure and fluid characteristics, lithology, physical properties, rock mechanical properties, natural fracture development, and engineering characteristics such as early fracturing conditions and understanding.

[0052] In the step S2, the geological characteristics of the target reservoir are mainly analyzed. According to the transformation requirements of the target reservoir, the reservoir transformation design scheme is determined through preliminary practical analysis and numerical simulation. The fracturing transformation parameters include perforation technology, fracturing materials, stage cluster design, fracturing scale, carbon dioxide injection amount and carbon dioxide injection method.

[0053] In step S3, the reverse mixing pumping process is optimized according to the previous development practice, indoor large rock sample hydraulic fracturing test, and proppant migration numerical simulation. The optimization of the reverse mixing pumping process includes optimizing the amount of fracturing material, the step sand ratio setting, the type of stage fracturing fluid, the injection displacement of each stage, the amount of spacer fluid and the number of front slugs.

[0054] In step S4, optimizing the carbon dioxide pre-placement construction parameters includes optimizing the carbon dioxide injection sequence, the carbon dioxide injection displacement, and the pre-placement liquid ratio parameters.

[0055] In step S5, the reverse mixed carbon dioxide pre-fracturing pumping procedure includes test squeeze (squeezing acid, replacing acid, stopping pumping and soaking acid), first pre-fluid, pumping carbon dioxide, second pre-fluid, slugging sand, continuous sand carrying and displacement fluid stages. The specific parameters of each stage are determined according to the design results of steps S1 to S4.

[0056] Embodiment 3:

[0057] The reservoir of this embodiment is located in the oil reservoir of the Upper Wuerhe Formation of the Permian System in the South Well Area of ​​the Fifth District of the Mahu Oilfield in the Junggar Basin.

[0058] In step S1, the block reservoir type, reservoir characteristics, temperature and pressure system, fluid properties, reservoir sensitivity, oil test and production test conditions, rock mechanical properties, natural fracture development conditions, previous fracturing conditions, development history data and other information are collated and analyzed to determine the reservoir transformation needs and principles.

[0059] In step S2, according to the target reservoir transformation requirements, the reservoir transformation design scheme is determined through numerical simulation, and the main fracturing parameters of the target area are determined as follows: using the bridge plug cluster perforation fracturing process, the construction displacement is 10-12m 3 / min, cluster spacing 35m, 2 clusters per section, single seam sand volume 50m 3 , carbon dioxide is injected in intervals, and the injection volume of a single stage is 200-250t. Small-size quartz sand is used as the proppant, and low-, medium-, and high-viscosity variable viscosity fracturing fluid is used as the fracturing fluid.

[0060] In step S3, the reverse mixing pumping process is optimized based on the reservoir transformation plan according to the previous fracturing conditions of the target area or blocks with similar reservoir conditions. Figure 2As shown in the figure, based on the early development practice, indoor large rock sample hydraulic fracturing test, and proppant migration numerical simulation, it is determined to adopt low viscosity test squeeze, high viscosity seam opening + low viscosity slippery water plug sand addition + low, medium and high viscosity slippery water continuous sand carrying reverse mixing pumping process. The early construction of the target area is relatively difficult. In the pumping procedure, the amount of high viscosity seam opening is increased, the sand lifting ratio step is reduced during continuous sand carrying, the sand concentration when switching to medium and high viscosity during continuous sand carrying is reduced, and the maximum sand concentration during continuous sand carrying is reduced. The acid treatment process is selected to reduce the risk of sand plugging and ensure safe sand addition. In the early fracturing construction of the target area, the reduction of construction pressure by multiple plugs in the pre-stage is not obvious, so the number of pre-stage plugs is reduced.

[0061] In step S4, Figure 3 As shown, ① determine the injection sequence of carbon dioxide. Carry out numerical simulation of carbon dioxide injection: Scheme 1 first injects part of the fracturing fluid to open a complete fracture, then injects carbon dioxide, and then continues fracturing; Scheme 2 uses carbon dioxide to open a 25m fracture, and then continues fracturing. The results show that although Scheme 2 cannot diffuse to a deeper position after dispersion and the carbon dioxide concentration in the affected area is low, carbon dioxide can interact with more crude oil within the entire fracture length to play a viscosity-reducing role. From the simulation of production effects, it can be seen that the production increase effect of injecting fracturing fluid first is better than that of injecting carbon dioxide first. It is determined to inject fracturing fluid to create fractures first and then inject liquid carbon dioxide.

[0062] ② Determine the carbon dioxide injection displacement. Figure 4 As shown, indoor large rock sample carbon dioxide fracturing test was carried out, numerical simulation and early carbon dioxide pre-fracturing pilot test construction analysis were carried out in a certain area. According to indoor experiments, increasing the carbon dioxide displacement can increase the number of bedding fractures opened. Among the 7 groups of rock samples fracturing with liquid carbon dioxide, except for one group of unopened bedding fractures, the three rock samples with a displacement of 100mL / min opened an average of 1.7 bedding fractures, and the three rock samples with a displacement of 300mL / min opened an average of 3 bedding fractures; according to numerical simulation and MaHW1320 well fracturing practice, 3m 3 / min or more can make the cracks continue to extend and increase the affected range. The friction resistance of carbon dioxide injection is relatively high. Under the condition of meeting the pressure limit, the displacement should be increased as much as possible to increase the crack length and the effective distance of carbon dioxide. According to the regional conditions and on-site equipment conditions, the pre-placement carbon dioxide displacement is determined to be 4m 3 / min.

[0063] ③Optimize the pre-fluid ratio. Figure 5 As shown, numerical simulation of carbon dioxide injection and production is carried out to clarify the optimal pre-liquid ratio.

[0064] According to the injection numerical simulation, as the ratio of pre-fluid: sand-carrying fluid increases, the distribution of carbon dioxide changes from a nearly elliptical shape to a spindle shape, with little increase in height and extending along the fracture in width. When the ratio of sand-carrying fluid is 1:9, carbon dioxide is only distributed near the perforation point after the injection of pre-fluid; when the ratio of pre-fluid: sand-carrying fluid is greater than 5:5, the distribution of carbon dioxide remains basically unchanged.

[0065] like Figure 6 As shown in the figure, according to the production numerical simulation, as the ratio of pre-pad fluid to sand-carrying fluid increases, the cumulative production increases first, and then decreases after reaching 6:4. The ratio of pre-pad fluid to sand-carrying fluid is determined to be 6:4.

[0066] In step S5, Figure 7 As shown, the CO2 pre-fracturing pumping procedure is determined according to the optimization results of step S1 to step S4, including test squeeze (squeezing acid, replacing acid, stopping pumping and soaking acid), first pre-fluid, pumping CO2, second pre-fluid, slugging sand, continuous sand carrying, and displacement fluid stages.

[0067] The details are as follows:

[0068] Preparation stage: Use low-viscosity fracturing fluid for cyclic pressure testing, pushing the bridge plug and pushing it into the seat;

[0069] Trial squeeze phase: inject low-viscosity fracturing fluid into the target layer to limit the pressure and increase the displacement; when the displacement does not reach the threshold, stop the pump, squeeze the acid, and then proceed to the next step; when the displacement reaches the threshold, proceed directly to the next step;

[0070] Stop pumps and switch processes;

[0071] Pre-CO 2 Phase: Injecting liquid CO into the target layer 2 ;

[0072] Stop pumps and switch processes;

[0073] First pre-fluid stage: injecting a first pre-fluid into the target layer, wherein the first pre-fluid is a high-viscosity fracturing fluid;

[0074] Second pre-fluid stage: injecting a second pre-fluid into the target layer; the second pre-fluid is a low-viscosity fracturing fluid;

[0075] Sand-carrying fluid stage: injecting sand-carrying fluid into the target layer and continuously adding proppant, wherein the sand-carrying fluid is a medium- or high-viscosity fracturing fluid;

[0076] Displacement fluid stage: Displacement fluid is injected into the target layer, and the displacement fluids are high-viscosity fracturing fluid and low-viscosity fracturing fluid, respectively.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A reverse mixed carbon dioxide pre-fracturing pump injection design method, characterized in that: include Step S1: Obtain basic parameters of the target reservoir and determine reservoir transformation requirements; Step S2: According to the transformation requirements of the target reservoir, the reservoir transformation design scheme is determined through numerical simulation, and the fracturing transformation parameters of the main body of the target area are determined; Step S3: Optimizing the reverse mixing pumping process according to the target reservoir transformation requirements; Step S4: Optimizing carbon dioxide pre-construction parameters according to indoor experiments and numerical simulations; Step S5: construct a reverse mixing carbon dioxide pre-fracturing pumping program using the fracturing stimulation parameters, reverse mixing pumping process and carbon dioxide pre-construction parameters.

2. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 1, characterized in that: In step S1, the basic parameters of the target reservoir include the target reservoir type, oil layer distribution, temperature, pressure and fluid characteristics, lithology, physical properties, rock mechanical properties and geological parameters related to the development of natural fractures.

3. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 2, characterized in that: In step S2, the fracturing transformation parameters include perforation technology, fracturing materials, stage cluster design, fracturing scale, carbon dioxide injection amount and carbon dioxide injection method.

4. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 3, characterized in that: In step S3, the reverse mixing pumping process is optimized according to the indoor large rock sample hydraulic fracturing test and the proppant migration numerical simulation, and the optimization of the reverse mixing pumping process includes optimizing the fracturing material dosage, the step sand ratio setting, the stage fracturing fluid type, the injection displacement, the spacer fluid dosage and the number of front slugs.

5. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 4, characterized in that: In step S4, optimizing the carbon dioxide pre-placement construction parameters includes optimizing the carbon dioxide injection sequence, the carbon dioxide injection displacement, and the pre-placement liquid ratio parameters.

6. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 5, characterized in that: In step S4, the indoor carbon dioxide fracturing test and numerical simulation and the regional early carbon dioxide pre-fracturing pilot test construction are analyzed to determine the carbon dioxide injection displacement.

7. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 6, characterized in that: In step S5, the reverse mixed carbon dioxide pre-fracturing pumping procedure includes test squeezing, first pre-fluid, pumping carbon dioxide, second pre-fluid, slugging sand, continuous sand carrying and displacement fluid stages.

8. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 7, characterized in that: The trial extrusion includes squeezing acid, replacing acid and stopping the pump to soak acid.

9. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 7, characterized in that: Trial squeeze phase: inject fracturing fluid of set viscosity into the target layer to limit the pressure and increase the displacement.

10. The reverse mixed carbon dioxide pre-fracturing pump injection design method according to claim 7, characterized in that: Sand carrying stage: inject sand carrying fluid into the target layer and continuously add proppant; displacement fluid stage: inject displacement fluid into the target layer.

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