Design method of tight oil horizontal well oil washing energy storage expansion huff and puff enhanced recovery

Abstract

The present application belongs to the field of evaluation and research of tight gas reservoirs, and particularly relates to a design method for improving recovery ratio of tight oil horizontal well oil washing energy storage expansion stimulation, which comprises the following steps: S1, selecting a nano surfactant system suitable for the target tight oil horizontal well matrix pore and pore size; S2, designing partial parameters of the oil washing slug; S3, designing partial parameters of the energy storage slug; S4, designing partial parameters of the expansion slug; and S5, designing the soaking time. The present application realizes the secondary reconstruction and production increase of the depleted tight oil horizontal well through the combination of oil washing, energy storage and expansion, and improves the recovery ratio of the tight oil horizontal well. The present application has been applied to 8 wells in the Honggang and Qian'an tight oil blocks of Jilin Oilfield, and good application effects have been achieved, which shows obvious effects of liquid and oil increase, and has high practicability.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas field development, and in particular relates to a design method for improving the recovery rate of a tight oil horizontal well by washing oil, storing energy, expanding capacity and throughput. Background Art

[0002] Tight oil horizontal well development in the Jilin Oilfield relies on volumetric fracturing to generate production, with a subsequent depletion-based approach primarily employed. Initial production is high, but stability is poor and production declines rapidly. Pumping begins after 14-31 months of self-flow, and in the first year after the stable production period, fluid production declines by 25%-30%, while oil production declines by 15%-16%. The dynamic fluid level declines (wells below 1000 m in 43%), daily oil production decreases (wells below 3 tons in 25%), and formation depletion occurs (flowback rate is 244%). Existing technologies primarily replenish energy after the horizontal well is fracturing and depleted for a period of time, i.e., in the middle and late stages of its lifecycle, by injecting water or gas. The reservoir has low effective permeability, an average pore throat radius below 500 nm, and low movable fluid saturation. The fluid systems used for fracturing, such as guar gum, slick water, and conventional surfactants, are all micron-sized, making effective access to matrix pores difficult. The injection pressure in small pores is high, and the reservoir migration capacity is poor. Therefore, how to combine the physical properties of tight oil reservoirs, how to wash out the crude oil in the micropores and carry it out of the well, and how to maximize the overall effect of tight oil layers have become the key and difficulty of improving the recovery rate of horizontal wells in tight oil reservoirs.

[0003] Currently, commonly used methods for enhancing oil recovery in tight oil horizontal wells rely on water injection, CO2 injection, and fracturing to increase reservoir energy. These methods, through prolonged well shut-in, achieve dialysis replacement of the reservoir matrix, ultimately increasing oil production, and have generally achieved some success. Water injection and CO2 injection primarily target the original fracture spaces, failing to further expand the treatment target. Natural dialysis replacement, using water and CO2 as media, has poor replacement effectiveness and efficiency, resulting in insufficient oil production capacity. Water injection and CO2 injection, based on single or multi-well asynchronous methods, primarily target existing fracture channels and spaces, easily forming ineffective circulation pathways, ultimately limiting the improvement in recovery. Simply using fracturing as a method to further expand the swept volume can achieve the effect of further expanding the swept volume. However, for tight oil horizontal wells with severe depletion, a large amount of liquid is needed to replenish the energy of the original reservoir. The early injection by fracturing has been proved by field applications to be mainly focused on the expansion and filling of the original cracks. It is difficult to open new cracks and further expand the swept volume. Under the premise of achieving the basic goal of achieving an original formation pressure of more than 1.0 for energy storage, the liquid consumption is high and the cost is high, and the effect of improving the recovery rate and the economic benefits are poor.

[0004] Based on this, there is an urgent need to study a method based on a three-dimensional well network to improve the dialysis capacity of horizontal wells, increase reservoir energy, and further increase the transformation volume to control decline, extend the stable production period and improve the recovery rate. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention, based on integrated oil washing, energy storage, and capacity expansion technology, aims to further enhance the matrix dialysis replacement capacity and further increase the target well's stimulation volume. This design method utilizes a well-in-place throughput method to effectively enhance oil recovery in tight oil horizontal wells that lack effective energy replenishment. The method utilizes a 0.3-0.5% high-concentration nano-infiltration nonionic surfactant system to effectively penetrate the basal pores and ducts of the tight oil reservoir, reducing oil-water interfacial tension and increasing the capillary count, thereby enhancing matrix dialysis replacement capacity. A 0.05-0.1% low-concentration nano-infiltration nonionic surfactant system is used for energy replenishment, completing reservoir energy replenishment with a low-cost system. This system effectively improves oil washing capacity in the original volume fractures while achieving energy replenishment. A 0.1-0.3% medium-concentration nano-infiltration nonionic surfactant system is used for temporary plugging and diversion fracturing, further increasing the reservoir stimulation volume based on the original volume fracturing stimulation. The highly efficient surfactant system further expands the swept volume, achieving the desired effect of enhancing oil recovery in tight oil horizontal wells through throughput. At the same time, this method can be applied to a single well, and can also be carried out simultaneously with multiple wells using parent and child wells. On the basis of the above effects, effective interference of multiple wells can be achieved, and on the basis of the above effects, the displacement effect of multiple wells can be achieved.

[0006] The present invention aims to provide a method for designing a tight oil horizontal well through oil washing, energy storage, and capacity expansion to enhance oil recovery. To achieve the above-mentioned object, the present invention provides a method for developing tight oil horizontal well through oil washing and energy storage to enhance oil recovery based on a single well and a three-dimensional well pattern, wherein the method comprises:

[0007] S1 Optimize the nanosurfactant system suitable for the matrix pore size and pore size of the target tight oil horizontal well. Based on the principle of "entry, washing depth, travel distance, and flow out", the use range of different concentrations of the nanosurfactant system is determined based on the dialysis, oil washing, and surface tension evaluation experiments of the target well core and oil products. Based on the characteristics of the tight oil horizontal wells in Jilin Oilfield and the relationship between the pore radius and throat radius distribution of cores with different permeabilities, the diameter of the liquid system should be as small as possible. The liquid system has good oil washing efficiency and good wettability improvement effect. The liquid system has good resistance to formation core adsorption, and the active ingredients can play a role at the oil-water interface as much as possible. The mixture of the liquid system and crude oil should be able to pass through the throat smoothly and flow out.

[0008] The parameters of the S2 oil wash slug are designed to inject a certain volume of high-concentration nanosurfactant system. This step reduces the oil-water interfacial tension, increases the capillary number, improves the dialysis and replacement capacity of the energy storage front matrix, and simultaneously realizes a partial energy storage function.

[0009] (1) Dosage design method:

[0010]

[0011] Q1: amount used in the oil washing stage; Q0: cumulative oil production, t; PO: crude oil density, g / cm 3 ; B0: crude oil volume coefficient; Q 累产 : Cumulative liquid production of a single well, t; Q 压裂液 : Fracturing fluid injection volume, m 3 ; B w : Volume coefficient of water, 1.001 (constant); δ: Oil washing front coefficient, 0.33-0.5;

[0012] (2) Injection speed design:

[0013] Using CMG software, we simulated and analyzed the injection volume and pressure changes during oil washing, energy storage, and expansion based on history matching. During the oil washing phase, as the injection rate increased, the injection time decreased, but the total injection volume increased slightly. Simulations of well shutoff after energy storage at different injection rates revealed little change in formation pressure before and after shutoff. The maximum injection rate was used without reservoir pressure opening.

[0014] The S3 energy storage segment plug parameter design injects a large amount of low-concentration nanosurfactant system for energy replenishment, effectively improving the oil washing capacity in the original volume fracture fracture while achieving energy replenishment. The dosage design principle is based on the reservoir liquid deficit, and at the same time ensures that the reservoir pressure is ≥ the original formation pressure after the injection is completed;

[0015] (1) Dosage design method:

[0016]

[0017] Q2: Amount used in the energy storage stage; Q1: Amount used in the oil washing stage; Q0: Cumulative oil production, t; PO: Crude oil density, g / cm 3 ; B0: crude oil volume coefficient Q 累产 : Cumulative liquid production of a single well, t; Q 压裂液 : Fracturing fluid injection volume, m 3 ; B w : Volume coefficient of water, 1.001 (constant); δ: Oil washing front coefficient, 0.33-0.5;

[0018] (2) Injection speed design:

[0019] Using CMG software, based on history matching, simulations of injection volume and pressure changes during oil washing, energy storage, and expansion were conducted. Simulations of well shutoff after energy storage at different injection rates revealed that bottomhole pressure changes increased with increasing injection rate. Simulations of expansion after low-displacement energy storage indicated that higher injection rates reduced the total time required to reach the target pressure. The pressure diffusion ranges varied similarly across different injection rates, but lower injection rates resulted in more uniform formation pressure distribution. Taking the construction period into consideration, a moderate energy storage displacement was optimal.

[0020] The parameters of the S4 expansion segment plug are designed to inject a certain volume of medium-concentration nanosurfactant system by temporarily plugging and switching to sand fracturing. This further increases the reservoir stimulation volume based on the original volume fracturing stimulation, and further expands the swept volume with the high-efficiency surfactant system.

[0021] Combined with the geological reservoir characteristics of the target well and the characteristics of the adjacent wells, the fracture length and fracture height range of the target well during the expansion phase are determined. Combined with the on-site well conditions, the fracturing technology and materials are determined. The injection volume, injection rate and sand addition amount during the expansion phase are determined using PT software.

[0022] The S5 soaking time design uses a temporary plugging method to switch to sand fracturing and inject a certain volume of medium-concentration nano-surfactant system. This further increases the reservoir stimulation volume based on the original volume fracturing stimulation, and further expands the swept volume with a high-efficiency surfactant system.

[0023]

[0024] ΔL is half the distance from the fracture network to the matrix center, m; фm is porosity, %; μ is liquid viscosity, mPa.s; Km is matrix permeability, mD; ΔP is driving pressure, MPa; G is starting pressure gradient, MPa / m.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The advantage of the present invention is that it can achieve secondary transformation and production improvement of depleted tight oil horizontal wells through a combination of oil washing, energy storage, and capacity expansion, thereby improving the recovery rate of tight oil horizontal wells. The surfactant system required by this invention can enter the nano-matrix pores of tight oil to achieve efficient oil washing; the effective recovery of reservoir energy and dialysis replacement under the surfactant system are achieved in the energy storage plug; in the capacity expansion stage, the transformation volume of the tight oil horizontal well is further expanded by adopting the method of efficient temporary plugging and diverting fracturing (sand fracturing); in the later stage, the recovery rate of the tight oil horizontal well is improved through a reasonable well shut-in and oil production system. This invention has been tested on 8 wells in the Honggang and Qian'an tight oil blocks of Jilin Oilfield, and has achieved good application results, showing obvious effects of increasing fluid and oil, and has high practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention provides an understanding of reservoir matrix pore distribution;

[0028] Figure 2 The particle size distribution of the nano surfactant system provided by the present invention;

[0029] Figure 3 The present invention provides a mechanism for energy storage, oil washing, capacity expansion and throughput of tight oil horizontal wells.

[0030] Figure 4 The present invention provides CMG software simulation injection speed optimization during the energy storage stage;

[0031] Figure 5 The expansion stage provided by the present invention is combined with the optimization design of crack length and height parameters;

[0032] Figure 6 This is a soaking time calculation model provided by the present invention. DETAILED DESCRIPTION

[0033] In order to make the technical means adopted by the present invention and the objectives achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0035] Example 1:

[0036] Well Example 1: Nano-increased nonionic surfactant (ZY-2#) with a high concentration of 0.3%, a medium concentration of 0.2%, and a low concentration of 0.1% is selected as the main surfactant system for oil washing; the total deficit of this well according to geological reserve calculation is 10,000m 3 ; By calculating the amount of oil wash plug 3300m 3 (0.3% ZY-2#); 6300m of slug 3 (0.1% ZY-2#); for capacity expansion, high-strength temporary plugging agent + multi-size temporary plugging balls and sand fracturing are used; the slickwater variable displacement design is 10-12-14m 3 / min, single-stage sand volume 100m 3 , 4 clusters are opened in a single section, the half-slit length of each cluster is 105m, the support seam height is 20m, and the total liquid volume in the optimization expansion stage is 7000m 3 , total sand volume is 680m3.

[0037] Example 2:

[0038] Well Case 2: ZY-2# nano surfactant high concentration 0.3%, medium concentration 0.2%, and low concentration 0.1% are preferred as the main surfactant system for oil washing; the total deficit of this well is 6000m3 according to geological reserve calculation.3 ; By calculating the amount of oil wash plug 3000m 3 (0.3% ZY-2#); slug 3000m 3 (0.1% ZY-2#); expansion adopts high-strength temporary plugging agent + multi-size temporary plugging ball temporary plugging fracturing (without adding sand), slick water variable displacement design 10m 3 / min, the length of each cluster half-fracture is 100m, the support fracture height is 15m, and the total liquid volume in the optimization expansion stage is 4500m 3 .

[0039] Although some embodiments of the present invention have been described herein, those skilled in the art will appreciate that modifications may be made to the embodiments herein without departing from the spirit of the present invention. The above embodiments are merely exemplary and should not be used as limitations on the scope of the present invention.

Claims

1. A design method for improving oil recovery by washing, storing, expanding and throughput of tight oil horizontal wells, characterized by: The following steps are involved: S1. Based on a nanosurfactant system suitable for the matrix pore size and pore size of the target tight oil horizontal well, and based on dialysis, oil washing, and surface tension evaluation experiments on target well cores and oil products, determine the range of different concentrations of the nanosurfactant system. The nanosurfactant system has good oil washing efficiency and improves wettability. It has good resistance to formation core adsorption, and the active ingredients can be maximized at the oil-water interface. The mixture of the nanosurfactant system and crude oil can smoothly pass through the throat and flow out. S2. Design the parameters of the oil wash slug, including dosage and injection speed, and inject a certain volume of high-concentration nanosurfactant system; S3. Design parameters for the energy storage slug, including dosage and injection rate. Inject a large amount of low-concentration nanosurfactant system for energy replenishment. This effectively improves the oil washing capacity in the original volume of the fractured fracture while achieving energy replenishment. The dosage design principle is based on the reservoir liquid deficit. At the same time, ensure that the reservoir pressure after injection is ≥ the original formation pressure. S4. Design the parameters of the expansion slug, inject a certain volume of medium-concentration nanosurfactant system by temporarily plugging and switching to sand fracturing. This will further increase the reservoir stimulation volume based on the original volume fracturing stimulation, and further expand the swept volume with the high-efficiency surfactant system. Combined with the geological reservoir characteristics of the target well and the characteristics of the adjacent wells, the fracture length and fracture height range of the target well during the expansion phase are determined. Combined with the on-site well conditions, the fracturing technology and materials are determined. The injection volume, injection rate and sand addition amount during the expansion phase are determined using PT software. S5. Design the soaking time and inject a certain volume of medium-concentration nano-surfactant system by temporarily plugging and switching to sand fracturing. On the basis of the original volume fracturing transformation, further increase the transformation volume of the reservoir and further expand the swept volume with a high-efficiency surfactant system.

2. The design method for enhancing oil recovery by washing, storing, expanding and throughput of tight oil horizontal wells according to claim 1 is characterized in that: The design method of the dosage in step S2 is: , Q1: amount used in the oil washing stage; Q0: cumulative oil production, t; ρ0: crude oil density, g / cm 3 ; B0: crude oil volume coefficient; Q 累产 : Cumulative liquid production of a single well, t; Q 压裂液 : Fracturing fluid injection volume, m 3 ; B w : Volume coefficient of water, 1.001; δ: Oil washing front coefficient, 0.33-0.

5.

3. The design method for enhancing oil recovery by washing, storing, expanding and throughput of tight oil horizontal wells according to claim 1 is characterized in that: The injection rate design method described in step S2 is: using CMG software to carry out simulation analysis of oil washing, energy storage and expansion injection volume and pressure changes based on historical matching. In the oil washing stage, as the injection rate increases, the injection time decreases, but the total injection volume increases slightly. A simulation study of well shut-in after energy storage at different injection rates is carried out. The formation pressure does not change much before and after shut-in, and the maximum injection rate is used without pressurizing the reservoir.

4. The design method for enhancing oil recovery by washing, storing, expanding and throughput of tight oil horizontal wells according to claim 1 is characterized in that: The design method of the dosage in step S3 is: , Q2: amount used in the energy storage stage; Q1: amount used in the oil washing stage; Q0: cumulative oil production, t; ρ0: crude oil density, g / cm 3 ; B0: crude oil volume coefficient; Q 累产 : Cumulative liquid production of a single well, t; Q 压裂液 : Fracturing fluid injection volume, m 3 ; B w : Volume coefficient of water, 1.001; δ: Oil washing front coefficient, 0.33-0.

5.

5. The design method for enhancing oil recovery by washing, storing, expanding and throughput of tight oil horizontal wells according to claim 1 is characterized in that: The injection rate design method described in step S3 is as follows: CMG software is used to conduct simulation analysis of injection volume and pressure changes for oil washing, energy storage, and capacity expansion based on history matching. A simulation study of well shutoff after energy storage at different injection rates is conducted. As the injection rate increases, the bottomhole pressure change before and after well shutoff increases. The simulation study of capacity expansion after low-displacement energy storage shows that the higher the injection rate, the shorter the total time required to reach the target pressure. The pressure diffusion range is not much different at different injection rates, but the lower the injection rate, the more uniform the formation pressure distribution. Taking the construction period into consideration, a moderate energy storage displacement is preferably selected.

6. The design method for enhancing oil recovery by washing, storing, expanding, and throughput of a tight oil horizontal well according to claim 1, wherein: The soaking time in step S5 is calculated according to the following formula: , t——well soaking time, d; ΔL——half the distance from the fracture network to the matrix center, m; φ m ——porosity, %; μ——liquid viscosity, mPa.s; K m ——matrix permeability, mD; Δp——driving pressure, MPa; G——starting pressure gradient, MPa / m.

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