CN116575897A - A method for oxidative bursting to relieve reservoir damage in shale channeling wells - Google Patents

Abstract

The invention discloses a method for oxidizing and bursting to relieve the reservoir damage of shale pressure channeling wells. , the working fluid is mixed at the fracture connection far away from the wellbore, the hydrogen peroxide rapidly decomposes to increase the local pressure, the oxidation-reduction action releases heat and heats up, and the oxidation and dissolution removes the blockage of organic matter in the micropores, realizing the removal of damage and the increase of permeability. The invention turns harm into benefit, utilizes oxidative bursting to expand the sweep coefficient of the pressure channeling well, eliminates the damage of the channeling well, and provides a new low-cost method for controlling the channeling well of the shale.

Description

A method for oxidative bursting to relieve reservoir damage in shale channeling wells

technical field

The invention relates to a new method for production stimulation and reconstruction in the technical field of oil and natural gas exploitation, in particular to a method for removing damage to shale pressure channeling well reservoirs by oxidation and bursting.

Background technique

Hydraulic fracturing is commonly used in the development of shale gas reservoirs. Shale gas reservoirs generally have the characteristics of low porosity, tightness, and poor seepage conditions, which are difficult to develop and utilize compared with conventional gas. At present, staged hydraulic fracturing of horizontal wells is an effective means of stimulating production in shale gas reservoirs. Hydraulic fracturing breaks the rock base and opens natural fractures at the same time, forming a complex network of artificial fractures inside the gas layer, shortening the gas from the base to the fracture. The seepage distance is increased, the drainage area is increased, and the economic development of shale gas reservoirs is realized.

Large-scale hydraulic fracturing may produce pressure channeling. Affected by various factors such as the development of natural fractures and the direction of faults, volume fracturing and refracturing can easily lead to interwell channeling between new wells and old wells while communicating natural fractures and creating complex fracture networks, especially infilling. Well fracturing and old well refracturing. In a certain block of the Changning-Weiyuan shale gas demonstration area, pressure channeling between new and old wells has occurred 33 times, and the average production time of channeling adjacent wells is 477 days. The pressure channeling leads to the reduction of the hydraulic fracturing stimulation range of the fracturing well, and the fracturing fluid flows in an unexpected direction, which may form a channeling channel perpendicular to the production well, leading to problems such as wellbore sanding and blockage. Therefore, pressure channeling damage will not only cause damage to the fractured well, reduce the permeability of the reservoir, increase the generation cost, but also seriously affect the productivity of the channeling well.

At present, there are few related researches and measures on the control of channeling wells. In the fracturing construction stage, the main measures are to control the scale of fluid used, optimize the construction displacement, and temporarily plug and switch to the fracturing process. However, after the above measures are taken in a block in Xin'anbian, the pressure channeling still leads to water breakthrough in the oil well 3 kilometers away, and the recovery rate It is only 4%, which is far lower than the calibrated recovery rate of 17% for other tight oil reservoirs in this oilfield. In the post-fracture recovery stage, polymer microsphere plugging may block the seepage channel and reduce radial seepage capacity. High-strength gel plugging After the fracture, the seepage channel cannot be restored, and it is difficult to further develop the remaining oil.

Oxygen released from the decomposition of hydrogen peroxide has the potential to detonate when mixed with methane in shale gas formations. Oxidation solution has a dissolution effect on organic matter, pyrite, and other depositional environmental products in shale. The composite effect of oxidative dissolution and mixed gas explosion is used to create cracks, relieve the damage near the cracks, promote the desorption of adsorbed gas, and increase the depth of reconstruction.

Contents of the invention

The purpose of the present invention is based on the existing fracturing technology, to provide a method for oxidative bursting to relieve the damage of shale channeling well reservoir, to control the interference of fracturing fracture channeling on the production of adjacent wells, and to supplement and enhance the existing theory in accordance with. Based on the understanding of fracture channeling damage, the present invention "transforms contradictions and turns harm into benefit", considers the effect of high temperature and high pressure generated by oxidative fracturing on the transformation of gas layers, reduces the blockage of pressure channeling to fracturing wells and production wells, and forms Reasonable technical implementation countermeasures.

Concrete technical scheme of the present invention is as follows:

A method for releasing damage to shale channeling well reservoirs by oxidative bursting, comprising:

For the fracturing wells (frac wells) and production wells (frustration wells) that have already produced fracturing and channeling, establish a chemical reaction system between the wells, inject hydrogen peroxide solution and displacement fluid into the frac wells, and inject Catalytic decomposition liquid and replacement liquid, when the hydrogen peroxide solution and the catalytic decomposition liquid meet in the pressure-through crack, a chemical reaction occurs to generate a large amount of oxygen. In hydraulic fractures, due to the low solubility of oxygen, it is difficult to dissolve in water, so air bubbles will form and rise rapidly, thereby producing the effect of partial bursting. During the bursting process, oxygen can quickly diffuse into the surrounding fractures, oxidize the organic matter and minerals in them, make them decompose to produce more gas and other chemical substances, and generate a large amount of heat energy and high-pressure gas, thereby blowing the surrounding rocks Loose and broken. These reactions also oxidize and decompose sediment and clay minerals, thereby increasing the size, complexity and density of fractures. This can further expand the scope of hydraulic fractures, improve the permeability and gas production capacity of fractures.

The reaction rate of the hydrogen peroxide solution and the catalytic decomposition liquid depends on the concentration and temperature of the oxidizing agent and reducing agent in the liquid, so it is necessary to design the ratio, dosage, and injection pressure of the liquid to achieve the best oxidative detonation effect.

As a preferred technical solution, the concentration of the hydrogen peroxide solution is 10%-20%, a small amount of dilute hydrochloric acid is added to make the pH 4.0, the injection pressure is lower than the fracture pressure of the formation, and greater than the pore pressure of the formation, so as to avoid excessive hydrogen peroxide entering the fractured well The fracture network system leads to excessive oxidation reaction and secondary damage to the reservoir. The method of gradually increasing the concentration of the oxidizing solution can be adopted, and parameters such as pressure and flow can be monitored at the same time to ensure that the injection fluid is evenly distributed in the fracture network system. The injection amount of hydrogen peroxide solution is related to the volume of the reservoir to be damaged, and the injection amount is calculated according to the following formula:

In the formula: V ₁ is the volume of hydrogen peroxide solution, m ³ ; P _f is the formation fracture pressure, Pa; φ _f is the porosity of reservoir fractures; V _O is the volume of the reservoir to be damaged, m ³ ; Z is the gas Compressibility factor; R is molar gas constant, 8.314J/(mol·K); T is formation temperature, K; ρ is hydrogen peroxide density, 1.463×10 ³ kg/m ³ ; c is hydrogen peroxide concentration.

As a preferred technical solution, the catalytic decomposition liquid is mineralized water containing sodium hydroxide or manganese dioxide, the salinity and water type are consistent with formation water, and the injection pressure is less than formation fracture pressure and greater than formation pore fracturing, avoiding Excessive alkaline fluid enters the fracture network system of the fractured well and damages the shale reservoir. The injection flow rate of the channeling well needs to match the injection flow rate of the fracturing well to ensure that the two fluids are evenly distributed in the fracture network system of the fracturing well, and the injection volume of the catalytic decomposition liquid is the same as that of hydrogen peroxide:

V ₂ =V ₁

In the formula: V ₁ is the volume of hydrogen peroxide solution, m ³ ; V ₂ is the volume of catalytic decomposition solution, m ³ .

As a preferred technical solution, the displacement fluid is high-viscosity slick water, which is used to squeeze hydrogen peroxide solution and catalytic decomposition liquid from the wellbore into the depth of the fracture, so that hydrogen peroxide can be decomposed away from the wellbore to protect the integrity of the wellbore. It is related to the effective volume of the wellbore and the volume of the ellipsoidal hydraulic fracture. Calculate the injection volume of the displacement fluid according to the following formula:

In the formula: V ₃ is the displacement fluid volume, m ³ ; H is the height of the main hydraulic fracturing fracture, m; W is the width of the main hydraulic fracturing fracture, m; L is the half length of the main hydraulic fracturing fracture, and V _well is the wellbore Effective volume, m ³ .

The beneficial effects are:

(1) Relieve the damage near the fractures. After the shale is oxidized, the stress sensitivity is reduced, and the organic colloidal substances in the micro-nano pores and fractures are decomposed to prevent their deposition and accumulation from blocking the oil and gas flow channels;

(2) Improving the permeability of the base block. The injection of hydrogen peroxide will generate a large number of free radicals and oxygen molecules, which can oxidize the organic matter and hydrocarbons in the reservoir, thereby increasing the permeability of the reservoir and improving productivity, promoting desorption, and finally improving recovery factor;

(3) The construction is safe and environmentally friendly. Oxidative bursting is based on the understanding of existing fractures. It can quickly pump liquid into the fracture, and preliminarily judge the liquid injection volume and bursting range to protect the integrity of the wellbore;

(4) Utilize the channeling fractures to expand the producing degree of the reservoir. Oxidative bursting forms new bursting fractures and dissolution pores and fractures at the fracture channeling place, which improves the gas supply capacity of the matrix-fractures and makes the high-permeability channelization between wells It is an efficient channel for oil and gas seepage.

Description of drawings

In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the specific embodiments or the prior art. Throughout the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, elements or parts are not necessarily drawn in actual scale.

Fig. 1 is a schematic diagram of the injection sequence of the oxidative bursting working fluid in a shale pressure channeling well according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of pressure channeling caused by hydraulic fracturing according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of oxidative bursting to relieve shale pressure channeling well reservoir damage according to an embodiment of the present invention;

In the figure, a-pressure well; b-channeling well; c-hydrogen peroxide solution and displacement fluid; d-catalytic decomposition liquid and displacement fluid; e-oxidation burst induced in channeling reservoir; f-hydraulic fracture; g-induced fracture; h-reservoir stimulation volume; i-burst fracture.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below, obviously, the described embodiments are only some 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 persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relationship between the components in a certain posture (as shown in the drawing). If the specific posture changes, the directional indication will also change accordingly.

In addition, in the present invention, descriptions such as "first", "second" and so on are used for description purposes only, and should not be understood as indicating or implying their relative importance or implicitly indicating the quantity of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the invention.

The present invention will be described further in conjunction with accompanying drawing now.

As shown in Figure 1, according to the present invention, the slug flow method is adopted to simultaneously inject working fluid into the pressure flow well and the channeling well, the pressure flow well is injected with hydrogen peroxide solution and the replacement fluid in sequence, and the channeling well is sequentially injected with catalytic decomposition liquid, replacement fluid liquid.

As shown in Fig. 2, according to the embodiment of the present invention, pressure channeling leads to reduction in volume of reservoir stimulation, water breakthrough in channeling wells, and measures for both channeling wells and channeling wells are simultaneously carried out by oxidation bursting.

As shown in FIG. 3 , after oxidation burst is induced according to the present invention, burst fractures are created to increase the volume of reservoir stimulation, and remove damage to the reservoir near the fractures.

In the figure, a-pressure well; b-channeling well; c-hydrogen peroxide solution and displacement fluid; d-catalytic decomposition liquid and displacement fluid; e-oxidation burst induced in channeling reservoir; f-hydraulic fracture; g-induced fracture; h-reservoir stimulation volume; i-burst fracture.

Taking a shale oil well in Yanchang Formation, Xin'an, northern Shaanxi as an example, the working fluid dosage was designed. The specific dosage and working principle of each working fluid are as follows:

(1) Hydrogen peroxide solution

The concentration of hydrogen peroxide solution is 10%-20%, add a small amount of hydrochloric acid to make the pH value around 4.0, and the dosage is calculated by the following formula:

In the formula: V ₁ is the volume of hydrogen peroxide solution, m ³ ; P _f is the formation fracture pressure, Pa; φ _f is the porosity of reservoir fractures; V _O is the volume of the reservoir to be damaged, m ³ ; Z is the gas Compressibility factor; R is molar gas constant, 8.314J/(mol·K); T is formation temperature, K; ρ is hydrogen peroxide density, 1.463×103kg/m ³ ; c is hydrogen peroxide concentration.

The formation fracture pressure is 29.3MPa, the reservoir fracture porosity is 9%, the reservoir damage volume to be removed is 1000m ³ , the gas compression factor is 1.2, the formation temperature is 337K, and the hydrogen peroxide concentration is 10%. The calculated amount of hydrogen peroxide solution is 335m ³ .

(2) Catalytic decomposition liquid

The catalytic decomposition liquid is mineralized water containing manganese dioxide or sodium hydroxide, the water type and salinity are compatible with the reservoir, and the dosage is the same as hydrogen peroxide solution, 335m ³ .

(3) Displacement fluid

The displacement fluid is high-viscosity slick water, which is used to squeeze the hydrogen peroxide solution and catalytic decomposition liquid from the wellbore into the deep fracture, so that the hydrogen peroxide can be decomposed far away from the wellbore to protect the integrity of the wellbore. related to the crack volume.

In the formula: V ₃ is the displacement fluid volume, m ³ ; H is the height of the main hydraulic fracturing fracture, m; W is the width of the main hydraulic fracturing fracture, m; L is the half length of the main hydraulic fracturing fracture, and V _well is the wellbore Effective volume, m ³ .

The height of the main hydraulic fracturing fracture is 20m, the width of the main hydraulic fracturing fracture is 0.03m, the half length of the main hydraulic fracturing fracture is 260m, and the effective volume of the wellbore is 40m ³ . The channeling wells were injected with 203m ³ of displacement fluid.

The designed amount of hydrogen peroxide solution is 335m ³ , the amount of catalytic decomposition liquid is m ³ , and the amount of displacement fluid is m ³ (203m ³ for press wells and channeling wells), totaling 1076m ³ , which can contact damage within 1000m ³ of fracture channeling.

The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be applied to the foregoing embodiments Modifications to the technical solutions described in the examples, or equivalent replacement of some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention, and they shall cover Within the scope of the claims and description of the present invention.

Claims (4)

1. A method for releasing shale pressure channeling well reservoir damage by oxidation bursting, characterized in that: comprising: For the two adjacent wells where pressure channeling occurred, the fracturing wells were injected with hydrogen peroxide solution and displacement fluid in sequence, and the production wells were injected with catalytic decomposition fluid and displacement fluid in sequence, and injected into the pressure channeling layer in a slug manner; , the hydrogen peroxide solution and the catalytic decomposition liquid are mixed at the fracture passage far away from the wellbore, the hydrogen peroxide decomposes rapidly to increase the local pressure, the oxidation-reduction reaction generates heat, induces oxidation burst, forms secondary fractures and relieves nearby damage; after the well is opened , a small amount of residual working fluid is flowed back to the surface through the hydraulic fracture-wellbore, and is treated by gas-water separation in the surface pipe network; if the channeling distance is long, the injection amount of the displacement fluid can be controlled to achieve multiple oxidation bursts at different positions. 2. A method for oxidizing and bursting to relieve shale pressure channeling well reservoir damage, characterized in that: a hydrogen peroxide solution design method is provided: the concentration of the hydrogen peroxide solution is 10%-20%, and a small amount of acid solution is added to make the pH value at Around 4.0, design the calculation equation for the injection volume of hydrogen peroxide solution: In the formula, V _l is the volume of hydrogen peroxide solution, m ³ ; P _f is the formation fracture pressure, Pa; φ _f is the porosity of reservoir fractures; V _O is the volume of the reservoir to be damaged, m ³ ; Z is the gas Compressibility factor; R is molar gas constant, 8.314J/(mol·K); T is formation temperature, K; ρ is hydrogen peroxide density, 1.463×10 ³ kg/m ³ ; c is hydrogen peroxide concentration. 3. A method for oxidative bursting to relieve shale pressure channeling well reservoir damage according to claim 1 and claim 2, characterized in that: the catalytic decomposition liquid is mineralized water containing manganese dioxide or sodium hydroxide, Water type and salinity are compatible with the reservoir. 4. A method for oxidative bursting to relieve shale pressure channeling well reservoir damage according to claim 1 and claim 2, characterized in that: the displacement fluid is high-viscosity slick water, which is used to displace hydrogen peroxide solution 1. The catalytic decomposition liquid is squeezed into the deep fracture from the wellbore to decompose hydrogen peroxide far away from the wellbore to protect the integrity of the wellbore. The injection volume is related to the effective volume of the wellbore and the volume of the hydraulic fracture.