A fracturing process pretreatment method for ensuring the success rate of shale oil fracturing construction

Abstract

The present application relates to the technical field of shale oil fracturing construction, and particularly relates to a fracturing construction process pretreatment method for ensuring the success rate of shale oil fracturing construction. The method comprises the following steps: performing acid squeezing treatment on shale oil mud before fracturing; based on material erosion theory and a fracture fluid flow model, a dynamic optimization adjustment model of fracturing construction parameters in the low sand ratio slug stage is established; the rock core elastic modulus and Poisson's ratio of the reservoir are measured through indoor rock mechanics experiments; the viscosity and density of the fracturing fluid are measured; the elastic modulus, Poisson's ratio and diameter of the proppant particles are obtained; the obtained parameters are brought into the model in step 2, and the proppant concentration and the fracturing fluid viscosity that can ensure the maximum ER erosion efficiency are obtained in combination with the sand carrying performance of the fracturing fluid. Through effective channel establishment technology and fracture widening and filtration reduction technology, the success rate of shale oil well fracturing construction can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of shale oil fracturing construction, and particularly relates to a fracturing process pretreatment method for ensuring the success rate of shale oil fracturing construction. BACKGROUND

[0002] The shale oil reservoir geological conditions are unique, clay minerals develop, the average content is 35.6%, the permeability is less than 0.01*10 -3 μm 2 , horizontal foliation layer develops, vertical fractures are opened along the principal stress direction in the fracturing process, and multiple horizontal fractures along the foliation surface are opened, forming a complex network fracture in the shape of a Chinese character 'feng'. At present, the shale oil reservoir reconstruction mainly adopts the fracturing mode of close cutting + large-displacement injection of slickwater gel liquid + combined proppant slug + continuous addition, the composite reconstruction mode of high-viscosity main fracture and low-viscosity foliation opening, and the longitudinal development degree and fracture complexity of the reservoir are improved. However, the success rate of shale oil fracturing construction in the same block as before is only 78.6%, and the main reasons for the low success rate of construction are as follows: first, the clay minerals develop in the shale oil reservoir of Gulong, and the nano-scale pores are mainly formed, which causes small displacement and high pressure during construction, and the construction is difficult; second, the foliation layer develops in the shale oil reservoir of Gulong, and the complex fracture in the shape of a Chinese character 'feng' is easily formed near the wellbore during construction, which leads to fast filtration of fracturing fluid, large fracture corner, narrow fracture width, easy sanding, and difficult sanding, and the construction is difficult. SUMMARY

[0003] The purpose of the present application is to provide a fracturing process pretreatment method for ensuring the success rate of shale oil fracturing construction, so as to overcome the defects of the existing shale oil fracturing construction process, such as continuous sanding difficulty, excessive fracturing fluid, and high risk of sand plugging and overpressure, which cause low success rate of construction.

[0004] In order to achieve the above-mentioned purpose, the present application provides a fracturing process pretreatment method for ensuring the success rate of shale oil fracturing construction, comprising the following steps:

[0005] Step 1. Pre-fracturing acid squeezing treatment is performed on shale oil mud;

[0006] Step 2. Based on the material erosion theory and the in-slit fluid flow model, a low sand ratio slug stage construction parameter dynamic optimization adjustment model is established;

[0007] Step 3. The rock core elastic modulus and Poisson's ratio of the reservoir are measured through indoor rock mechanics experiments;

[0008] Step 4. The viscosity and density of the fracturing fluid are measured;

[0009] Step 5. The elastic modulus, Poisson's ratio and diameter of the proppant particles are obtained;

[0010] Step 6. The parameters obtained in step 3, step 4 and step 5 are brought into the model in step 2, and the sand-carrying performance of the fracturing fluid is combined to obtain the concentration of the proppant and the viscosity of the fracturing fluid that can ensure the maximum ER erosion efficiency.

[0011] Preferably, it further comprises:

[0012] Step 7. The results obtained in step 6 guide the adjustment of the concentration of the proppant and the viscosity of the fracturing fluid on site.

[0013] Preferably, the model in step 2 is specifically:

[0014]

[0015] Wherein: ER is the erosion efficiency; E1 is the proppant elastic modulus; E2 is the reservoir elastic modulus; v1 is the Poisson's ratio of the proppant; v2 is the Poisson's ratio of the reservoir; p is the density of the fracturing fluid; R is the diameter of the proppant; m is the viscosity of the fracturing fluid; Q is the fracturing construction discharge; A is the total perforation cross-sectional area; is the operating pressure difference; C is the concentration of the proppant; d is the fracture width.

[0016] Preferably, the pre-fracturing acid squeezing treatment of the shale oil mudstone in step 1 specifically comprises:

[0017] The fracturing pump truck injects 5m 3 of the acid treatment fluid into the shale reservoir through the wellbore at a discharge of 0.6m 3 / min.

[0018] Preferably, in step 4, the viscosity and density of the fracturing fluid are measured by a high-temperature and high-pressure rheometer and a fracturing fluid density instrument.

[0019] The present application has the following beneficial effects: through the effective channel establishment technology and the fracture expansion and filtration reduction technology, the success rate of shale oil well fracturing construction (the success rate of construction: the construction fluid volume is not more than 120% of the designed fluid volume, and the actual sand addition amount is equal to the designed sand addition amount) can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a fracturing process pretreatment method flowchart for ensuring the success rate of shale oil fracturing construction;

[0021] Fig. 2a and 2b are scanning electron microscope photos before and after acid treatment of the Gulong shale core in the laboratory;

[0022] Figure 3 is a pre-fracturing acid squeezing construction curve;

[0023] Figure 4 is a pretreatment effect and continuous sand addition construction curve. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0025] As shown in Figure 1 , the present embodiment provides a fracturing construction process pretreatment method for ensuring the success rate of shale oil fracturing construction, specifically comprising:

[0026] Step S1, pre-fracturing acid squeezing treatment is performed on shale oil argillaceous matter.

[0027] The effective channel establishment technology is used to improve the permeability of the formation and reduce the construction pressure.

[0028] In view of the characteristics that the shale oil reservoir physical property is special and the argillaceous content is high, which leads to less liquid inlet channel, small displacement, and high pressure during fracturing, pre-fracturing acid squeezing treatment is performed, the dissolution of acid is used (as shown in FIGS. 2a and 2b), the permeability of the formation is improved, and the expansion of clay minerals is inhibited.

[0029] The specific measures for pre-fracturing acid squeezing treatment are as follows: the fracturing pump truck injects 5m 3 acid treatment fluid into the shale reservoir through the wellbore at a displacement of 0.6m 3 / min, and the effect after the measures is as shown in Figure 3 .

[0030] The acid treatment fluid is prepared according to the following components and percentages: hydrochloric acid: 36.8%; hydrofluoric acid: 2.4%; corrosion inhibitor: 1.9%; cleanup agent: 0.1%; clay stabilizer: 0.9%, and the rest is water.

[0031] It should be noted that the corrosion inhibitor, cleanup agent, and clay stabilizer can be any mature and purchasable agent on the market.

[0032] Step S2, a low-sand-ratio slug stage construction parameter dynamic optimization adjustment model is established based on the material erosion theory and the in-fracture fluid flow model.

[0033]

[0034] In the formula: ER is the erosion efficiency; E1 is the proppant elastic modulus; E2 is the reservoir elastic modulus; v1 is the proppant Poisson's ratio; v2 is the reservoir Poisson's ratio; p is the fracturing fluid density; R is the proppant diameter; m is the fracturing fluid viscosity; Q is the fracturing construction displacement; and A is the total perforation cross-sectional area. C is the proppant concentration; d is the fracture width.

[0035] Step S3, the elastic modulus and Poisson's ratio of the reservoir core are measured by indoor rock mechanics experiment;

[0036] Step S4, the viscosity and density of the fracturing fluid are measured;

[0037] Step S5, the elastic modulus, Poisson's ratio and diameter of the proppant particles are obtained;

[0038] The elastic modulus and Poisson's ratio of the reservoir core are measured by indoor rock mechanics experiment; the viscosity and density of the fracturing fluid are measured by high temperature and high pressure rheometer and fracturing fluid density instrument; the elastic modulus, Poisson's ratio and diameter of the proppant particles are provided by the third party proppant manufacturer, which are the data of the existing materials that can be queried.

[0039] Step S6, the parameters in steps S3-S5 are brought into the low sand ratio slug stage construction parameter dynamic optimization adjustment model, and the proppant concentration and the fracturing fluid viscosity that can ensure the maximum ER erosion efficiency are obtained by combining the fracturing fluid sand carrying performance currently used in Daqing underground;

[0040] Step S7, according to the result obtained in step S6, the proppant concentration and the fracturing fluid viscosity are adjusted on site.

[0041] The sand ratio of the sand adding sand ratio reel controller is adjusted by adjusting the sand ratio of the sand mixing truck, and the thickening agent ratio is adjusted by the mixing truck, the shale oil fracturing construction pretreatment is carried out, after the pretreatment by the method, the construction difficulty of the subsequent continuous sand adding construction stage is greatly reduced, and the effect after the measure is adopted is as shown in Figure 4 .

[0042] Reference Figure 4 , Gupian 34 well is located in Qijia Gulong depression of Songliao basin, and the construction started in June 2021, the third segment construction pretreatment stage adopts the method of the embodiment, the fracturing fluid with a viscosity of 40 mPa·s is pumped into the formation at 5% and 7% sand ratio, the construction pressure is reduced from 62.5 MPa to 56.4 MPa, the pressure drop is significant, it is confirmed that the method can be used to erode and polish the near wellbore fracture, reduce the friction resistance in the fracture, and lay a good foundation for the subsequent continuous sand adding construction.

[0043] Table 1 Comparison of shale oil well fracturing construction scale and completion before and after the measure

[0044]

[0045] The field test was carried out in a shale oil well in Qijia Gulong Sag of Songliao Basin in 2021, compared with before 2021, the construction success rate is increased from 78.6% to more than 90%, the average sand completion rate is also increased from 92.11% to more than 95%, the sand plugging risk is significantly reduced, the application effect is remarkable, the purpose of improving the construction success rate and ensuring the construction scale is achieved.

[0046] In addition, Guye 34 well is located in Qijia Gulong Sag of Songliao Basin, and the construction started in June 2021, the third segment construction pretreatment stage adopts the method S1 in the patent, and the acid is squeezed for 5m 3 with a displacement of 0.6m 3 / min, the construction displacement is increased to 7.4m 3 / min (at this time the acid has not entered the formation), after the acid completely enters the reservoir, the displacement is increased to 13m 3 / min, and the pressure is only 64.0MPa, which improves the permeability of the formation and solves the problem of small shale oil fracturing displacement and high pressure, and the effect is remarkable.

[0047] The beneficial effects of the pretreatment method for ensuring the success rate of shale oil fracturing construction are as follows:

[0048] 1. For the characteristics of special shale oil reservoir physical properties and high argillaceous content, which leads to less liquid inlet channel, small displacement and high pressure during fracturing, the acid squeezing treatment before pressure is carried out to improve the permeability of the formation and inhibit the swelling of clay minerals.

[0049] 2. Control the fracture morphology near the wellbore, create a good main fracture near the wellbore, and reduce the difficulty of continuous sanding construction.

[0050] 3. Control the fluid loss in the fracture, and realize the control of near and expansion of far.

[0051] 4. Using the pretreatment method of the application, the shale oil reservoir fracturing success rate in Qingshankou Formation of Qijia Gulong Sag in Songliao Basin in 2021 can be increased from 78.6% to more than 90%.

[0052] Finally, it should be pointed out that: the above-mentioned is only the preferred embodiment of the present application, and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A pre-treatment method for fracturing process to ensure the success rate of shale oil fracturing operation, characterized in that, The application comprises the following steps: Step 1. Pre-fracturing acid squeezing treatment is carried out on shale oil mudstone; Step 2. A dynamic optimization adjustment model for construction parameters of a low sand ratio slug stage is established based on material erosion theory and a model for fluid flow in a fracture, and the model is specifically as follows: ； ER = E1 / E2 * (v1-v2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2)2) * (1- (R / 2 ​ ​ ​ ​ 2. The pre-treatment method of hydraulic fracturing process to ensure the success rate of shale oil fracturing operation as claimed in claim 1, characterized in that, ​ ​ 3. The pre-treatment method of frac process to ensure the success rate of shale oil fracturing operation as claimed in claim 1, wherein, ​ A fracturing pump truck injects 5m 3 of acid treatment fluid through the wellbore at a rate of 0.6m 3 / min.

4. The pre-treatment method of frac process to ensure the success rate of shale oil fracturing operation as claimed in claim 1, wherein, ​

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