Novel energy-increasing and plug-removing method for shale oil exploitation

Abstract

The invention relates to a novel energy-increasing and plug-removing method for shale oil exploitation, which comprises the following steps of: (1) firstly, injecting prepad fluid from an oil sleeve ring space, wherein the injection flow is 10m < 3 > / h, the injection pressure is not more than 20MPa, and the injection temperature is not lower than 50 DEG C; (2) after the prepad fluid is injected, associated gas is injected from an oil sleeve ring space, the injection flow is 50000 m < 3 > / h, the injection pressure is not higher than 20 MPa, and the injection temperature is not lower than 70 DEG C; and (3) after the associated gas is injected, soaking is started, the associated gas is fully dissolved, and soaking is conducted for 15-20 days. And the single-well oil production of the shale oil well is effectively improved, the exploitation benefit is improved, and sustainable development is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil production in oilfields, and particularly to a new method for enhancing energy and removing blockages in shale oil exploitation. Background Art

[0002] The shale reservoir has a relatively high clay content. However, due to the deep burial and high temperature of the reservoir, a large amount of clay minerals are transformed into illite, forming secondary quartz, and the brittleness increases, which provides advantageous conditions for the effective exploitation of shale oil. Due to the brittle nature of shale and the development of bedding planes, after large-scale volume fracturing, the rock is severely broken, generating a large number of fine clay particles. As production continues in the later stage, these fine clay particles will gradually migrate towards the near-well area and form larger particle clusters in the form of bridging, blocking the effective pores and fractures around the bottom hole, reducing the reservoir permeability, forcing the oil well production to decrease, and prematurely entering the stage of well blowout cessation.

[0003] In addition, shale oil wells mainly exploit shale oil layers. Usually, horizontal well drilling and large-scale volume fracturing are used to increase the single-well production, and mainly rely on the natural energy depletion of the formation for exploitation. Due to the low permeability and strong water sensitivity of the shale oil reservoir, the single-well production decreases rapidly, and conventional water flooding cannot be used to supplement energy, resulting in generally low recovery rates of shale oil wells. As shale oil wells are continuously exploited, some heavy components of crude oil will continuously deposit around the near wellbore. This is an inevitable actual situation in the production process of all oil wells, and this phenomenon is more likely to occur in shale oil, mainly because as the formation pressure continuously decreases, when it is lower than the saturation pressure, the crude oil gradually degasses, the viscosity of the oil increases, and the fluidity becomes worse. In this way, the pore permeability around some near wellbores will deteriorate year by year, which is also an important reason for the reduction of oil well production. Summary of the Invention

[0004] In order to solve the problems existing in the background art, the present invention provides a new method for enhancing energy and removing blockages in shale oil exploitation. This method effectively improves the single-well oil production of shale oil wells, improves the exploitation efficiency, and realizes sustainable development.

[0005] The technical solution provided by the present invention is: a new method for enhancing energy and removing blockages in shale oil exploitation, including the following steps, (1), First, inject a preflush fluid from the annulus between the tubing and the casing. The injection flow rate is 10 m 3 / h, the injection pressure does not exceed 20 MPa, and the injection temperature is not lower than 50 °C; The injection volume V of the preflush fluid: It is calculated from the selected treatment radii a and b, the empirical coefficient e = 1.5, the reservoir porosity φ, and the horizontal section length L. The calculation formula is as follows: V = eπabφL; (2), After the injection of the preflush fluid is completed, inject associated gas from the annulus between the tubing and the casing. The injection flow rate is 50000 m 3 / h, the injection pressure shall not exceed 20 MPa, and the injection temperature shall not be lower than 70 °C. The injection volume V of associated gas: It is calculated from the selected treatment radii a and b, reservoir porosity φ, horizontal section length L, oil saturation m, and solution gas-oil ratio y. The calculation formula is as follows: V = πabφLmy, where the solution gas-oil ratio y is obtained from the fitting curve of the dissolution experiment of shale oil under different pressure conditions. (3) After injecting the associated gas, start the shut-in well to allow sufficient dissolution to occur. The shut-in time is 15 - 20 days.

[0006] The above-mentioned preflush fluid includes 15% ammonium chloride, 1% triethylene glycol, 0.5% fluorocarbon surfactant, and the balance is water, and the above components are in terms of mass percentage.

[0007] The beneficial effects of the present invention are as follows: Since the natural productivity of shale oil wells is low, the decline is rapid, and the mining efficiency deteriorates year by year, it is urgent to study the method for increasing the production of shale oil wells. On the one hand, this application can solve the problem of reservoir plugging in the near-wellbore area. On the other hand, it can increase the formation energy, reduce the viscosity of crude oil, and improve the oil-water displacement relationship. Through the above two synergistic effects, it can effectively increase the single-well oil production of shale oil wells, improve the mining efficiency, and achieve sustainable development. Description of the Drawings

[0008] Figure 1 It is the exponential fitting curve of the solution gas-oil ratio of associated gas under different pressure conditions; Figure 2 It is the linear fitting curve of the solution gas-oil ratio of associated gas under different pressure conditions; Figure 3 It is the logarithmic fitting curve of the solution gas-oil ratio of associated gas under different pressure conditions; Figure 4 It is the polynomial fitting curve of the solution gas-oil ratio of associated gas under different pressure conditions; Figure 5 It is the power fitting curve of the solution gas-oil ratio of associated gas under different pressure conditions. Detailed Embodiments

[0009] The present invention will be further described below with reference to the drawings and examples: Example: A new method for enhancing energy and removing plugging in shale oil exploitation includes the following steps: (1) First, inject the preflush fluid from the annulus space between the tubing and the casing. The injection volume V of the preflush fluid is 950 m 3 : The injection flow rate is 10 m 3 / h, and the average injection pressure is maintained at 18.5 MPa, and the injection temperature is 50 °C; The injection volume V of the preflush fluid: It is calculated from the selected treatment radii a and b, empirical coefficient e = 1.5, reservoir porosity φ, and horizontal section length L. The calculation formula is as follows: V = eπabφL; The preflush fluid comprises 15% ammonium chloride, 1% triethylene glycol, 0.5% fluorocarbon surfactant and the balance water, and the above components are in terms of mass percentage.

[0010] Treat the area near the wellbore with preflush fluids such as ammonium chloride and glycol solution to improve the permeability of the area near the wellbore. Generally, the shale oil reservoir contains more than 5% carbon dioxide gas components. When carbon dioxide fully combines with the injected ammonium chloride solution, a hydrochloric acid environment with a certain concentration will be formed in the reservoir. Clay has a swelling reduction effect in an acidic environment. In this way, some bridged clay particles will decompose from the formed particle clusters, which can improve the pore conditions near the wellbore. In addition, the spent triethylene glycol solution has a strong water absorption function, which can take away some of the bound water in the swelling clay, accelerate the swelling reduction and decomposition of clay particles, further reduce the swelling of clay when encountering water. The exfoliated clay fine particles will finally flow out of the wellbore with the shale oil fluid, improving the permeability near the wellbore and increasing the oil well production. The fluorocarbon surfactant mainly reduces the viscosity of downhole crude oil and forms foam under water-bearing conditions to improve the huff and puff effect. The fluorocarbon surfactant plays a viscosity reduction role when encountering oil and a profile control role when encountering water. The following is the indoor experiment situation.

[0011] Change of core permeability before and after treatment with preflush fluid Table 1

[0012] (2) After the injection of the preflush fluid is completed, 855,000 cubic meters of associated gas is injected from the annulus between the tubing and the casing. The injection flow rate is 50000m 3 / h, and the average injection pressure is maintained at 18.5 MPa, and the injection temperature is 70 °C. The injection volume V of the associated gas: It is calculated from the selected treatment radii a and b, the porosity φ of the oil reservoir, the horizontal section length L, the oil saturation m and the solution gas-oil ratio y. The calculation formula is as follows: V = πabφLmy, where the solution gas-oil ratio y can be obtained from the fitting curve of the dissolution experiment of shale oil under different pressure conditions.

[0013] Injecting the associated gas produced from shale oil can play an obvious role in viscosity reduction and volume expansion, increasing the oil production per well. The specific injection volume is designed by the following method. Under high-pressure conditions, associated gas is easily dissolved in underground crude oil, and the dissolved gas volume mainly depends on the formation pressure. Determine the solution gas-oil ratio under each pressure condition through indoor experiments, and then perform multi-mode fitting. The higher the fitting degree, the higher the prediction accuracy. The fitting curve is as Figure 1 - Figure 5 shown. Through 5 modes of fitting, and the fitting degree R 2 of the polynomial fitting curve is the highest at 0.9888, indicating that this formula has the highest accuracy. Finally, the polynomial formula is selected for fitting: So apply y = 0.1786x 2The dissolved gas-oil ratio of associated gas is calculated by the formula +4.0929x - 1, where x is the formation pressure in MPa.

[0014] (3) After injecting the associated gas, shut-in the well to allow sufficient dissolution to occur for 20 days.

[0015] Dissolution experiment of shale oil under different pressure conditions Table 2

[0016] The designed treatment radius of the preflush fluid for Well Ye-1 is 1 m, the horizontal section length of this well is 2000 m, the porosity is 0.1, and the designed injection volume of the preflush fluid is 950 m³. The designed treatment radius of the associated gas is 5 m, the remaining oil saturation is 30%, the current formation pressure is 21.8 MPa, and the designed injection volume of the associated gas is 850,000 m³. 950 m³ of the preflush fluid containing 15% ammonium chloride and 1% triethylene glycol was actually injected on site 3 , after 10 days of shut-in, 855,000 m³ of the oilfield associated gas was injected. The average injection pressure was maintained at about 18.5 MPa. After 20 days of shut-in, the well was opened for production, with an average daily oil increase of 3.5 tons and a cumulative oil increase of 850 tons. The effect of the stimulation measure is obvious.

Claims

1. A new method for shale oil production energy enhancement and blockage removal, comprising the following steps: (1) First, inject the pre-fluid into the oil casing annulus space at a flow rate of 10m 3 / h, the injection pressure shall not exceed 20MPa, and the injection temperature shall not be lower than 50℃; The amount of pre-fluid injection V is calculated by the selected treatment radius a and b, the empirical coefficient e=1.5, the reservoir porosity φ, and the horizontal section length L. The calculation formula is as follows: V=eπabφL; (2) After the injection of the pre-fluid is completed, the associated gas is injected from the oil-casing annulus at a flow rate of 50,000 m 3 / h, injection pressure shall not exceed 20MPa, injection temperature shall not be lower than 70℃, The associated gas injection volume V is calculated by the selected treatment radius a and b, the oil layer porosity φ, the horizontal section length L, the oil saturation m and the dissolved gas-oil ratio y. The calculation formula is as follows: V=πabφLmy, where the dissolved gas-oil ratio y is obtained by fitting the curve of the shale oil dissolution experiment under different pressure conditions; (3) After injecting the associated gas, start to keep the well shut for 15-20 days to allow it to fully dissolve.

2. A new method for shale oil production energy enhancement and blockage removal according to claim 1, characterized in that: The pre-fluid includes 15% ammonium chloride, 1% triethylene glycol, 0.5% fluorocarbon surfactant and the balance water, wherein the above components are calculated by mass percentage.

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