A method for acidizing reconstruction design of clay type shale reservoir

Abstract

A design method for acidizing clay-type shale reservoirs is presented. The technical approach is based on the characteristics of clay-type shale reservoirs and lithology, fully leveraging the advantages of bedding planes to maintain the rock framework, clear bedding planes, and connect pores while simultaneously preventing swelling and promoting large-scale acidizing. The design method uses quartz, feldspar, and clay minerals as the rock framework, primarily incorporating calcite, dolomite, siderite, and pyrite from dissolved bedding planes. A bedding plane acidizing injection parameter design method is established, using the portion of HCl-soluble rock on the dissolved bedding planes as the basis for dosage design. The upper limit for injection pressure is defined as reservoir fracturing, and the upper limit for injection volume at this pressure is also defined. The overall goal is to achieve deep acid treatment, forming effective acid etching trenches to improve bedding permeability and thus transforming clay-type shale reservoirs. This invention has achieved good oil production and fluid increase results in field trials during shale oil development.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development, specifically relating to a design method for acidizing stimulation of clay-type shale reservoirs. Background Technology

[0002] With the increasing proportion of unconventional reservoirs in exploration and development, shale reservoir exploration and development in Jilin Oilfield has become the main replacement resource for the next stage. Currently, in the clay-type shale oil reservoirs being developed in the oilfield, the shale exhibits well-developed bedding, poor matrix properties, and clay mineral content reaching 50-60%. Conventional fracturing stimulation methods suffer from problems such as proppant embedding, low conductivity, long post-fracturing oil breakthrough periods, and severe sand production, resulting in poor overall performance. Therefore, the key to effectively stimulating clay-type shale reservoirs lies in how to combine the characteristics of the clay-type shale rock and reservoir to effectively create high-conductivity seepage channels while reducing clay expansion and migration.

[0003] Currently, literature review shows that existing shale reservoir stimulation methods mainly rely on large-scale proppant fracturing. This method aims to increase the scale of proppant addition and injection volume to form highly conductive propped fractures and other fractures. However, due to the high clay mineral content in clay-type shale reservoirs, the proppant is severely embedded, making it difficult to establish effective propped fractures. This results in problems such as long oil production cycles and severe sand production after fracturing, leading to poor overall stimulation effects. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a design method for acidizing stimulation of clay-type shale reservoirs, comprising the following steps:

[0005] S1. The theoretical basis for acidizing stimulation is determined by the bedding shape, porosity and permeability level, and rock composition distribution of shale reservoirs.

[0006] S2. Determine the main rock skeleton components of the shale reservoir, namely quartz, feldspar, and clay minerals, and the content of soluble components, mainly calcite, dolomite, siderite, and pyrite, to obtain the proportion and distribution pattern of the rocks that can be reflected.

[0007] S3. Based on the characteristics of rock bedding distribution in shale reservoirs, clarify the number of bedding units per meter or the distribution law of bedding permeability in shale reservoirs, and obtain the number of acid fluids entering the bedding units per unit thickness or the proportion of acid fluids that can enter the permeability level per unit thickness.

[0008] S4. Based on the laboratory experimental data of rock bedding and acid reaction in shale reservoirs, determine the proportion of rocks that can participate in acid-rock reaction, and define it as the contactable reaction coefficient.

[0009] S5. Introduce the above parameters, such as the proportion of reactive rock, the ratio of bedding density / permeability level, and the contactable reaction coefficient, into the acidizing dosage design formula to obtain the dosage design formula for the main acidizing slug.

[0010] S6. Determine the acid reaction time through indoor experiments to obtain the minimum acid injection rate, ensuring that the acid system can penetrate deep into the reservoir for dissolution.

[0011] The beneficial effects of this invention are as follows: Through analysis and understanding of the lithological characteristics of clay-type shale reservoirs, a large-scale acidizing stimulation technology approach was determined, which fully utilizes the advantages of bedding planes, maintains the rock skeleton, clears rock bedding, connects pores, and simultaneously prevents swelling and promotes oil washing. The amount of HCl-soluble rock on the bedding planes is used as the basis for dosage design, with reservoir fracturing as the upper limit for injection pressure and injection volume at this pressure. The overall goal is to achieve deep acid treatment, form effective acid etching trenches, effectively improve bedding permeability, and achieve effective stimulation of clay-type shale reservoirs. This invention has achieved good application results in 9 field test wells in Jilin Oilfield shale oil, demonstrating significant increases in fluid volume and oil production, and possesses high practicality. Attached Figure Description

[0012] Figure 1 This is a basic theoretical model diagram of shale reservoir production enhancement provided by the present invention;

[0013] Figure 2 This invention provides a diagram showing the content and distribution of rock composition in shale reservoir acidification modification.

[0014] Figure 3 This is a diagram showing the permeability distribution of shale reservoirs at different levels, provided by this invention.

[0015] Figure 4 This invention provides a diagram showing the actual proportion of rock species involved in acid-rock reactions, i.e., the contact reaction coefficient. Detailed Implementation

[0016] A design method for acidizing stimulation of clay-type shale reservoirs includes the following steps:

[0017] S1. The theoretical basis for acidizing stimulation is determined by the bedding shape, porosity and permeability level, and rock composition distribution of shale reservoirs.

[0018] S2. Determine the main rock skeleton components of the shale reservoir, namely quartz, feldspar, and clay minerals, and the content of soluble components, mainly calcite, dolomite, siderite, and pyrite, to obtain the proportion and distribution pattern of the rocks that can be reflected.

[0019] S3. Based on the characteristics of rock bedding distribution in shale reservoirs, clarify the number of bedding units per meter or the distribution law of bedding permeability in shale reservoirs, and obtain the number of acid fluids entering the bedding units per unit thickness or the proportion of acid fluids that can enter the permeability level per unit thickness.

[0020] S4. Based on the laboratory experimental data of rock bedding and acid reaction in shale reservoirs, determine the proportion of rocks that can participate in acid-rock reaction, and define it as the contactable reaction coefficient.

[0021] S5. Introduce the above parameters, such as the proportion of reactive rock, the ratio of bedding density / permeability level, and the contactable reaction coefficient, into the acidizing dosage design formula to obtain the dosage design formula for the main acidizing slug.

[0022] S6. Determine the acid reaction time through indoor experiments to obtain the minimum acid injection rate, ensuring that the acid system can penetrate deep into the reservoir for dissolution.

[0023] The calculation in step S2 is as follows:

[0024] S21, Percentage of HCl-soluble matter in rock (γ) CaCO3 The calculation formula is as follows:

[0025] γ CaCO3 =100% - Quartz % - Clay minerals % - Feldspar %

[0026] The calculation in step S3 is as follows:

[0027] S31. The proportion of permeability in higher stratification layers, ξ, is calculated using a reference value of ≥0.1mD, as follows:

[0028] ξ = ξ1 + ξ2 + ξ3 + ξ4 + ...

[0029] In the formula: ξ: the proportion of permeability with higher stratification; ξ1, ξ2, ξ3, ξ4: the proportion of permeability ≥ 0.1 mD;

[0030] The calculation in step S5 is as follows:

[0031] S51. The formula for calculating the amount of acid used is as follows:

[0032] Pre-fluid calculation formula: V 前 =πr 2 ×φ×h

[0033] Formula for calculating the main acid:

[0034] Post-filling fluid calculation formula: V 顶 =2-3 times V 井筒

[0035] In the formula: V前 Pre-acid plug dosage, m 3 V 处 Acidification dosage, m 3 V 后 Rear slug usage, m 3 r: processing radius, m; h: reservoir thickness, m; Φ: reservoir permeability; γ CaCO3 : Percentage of HCl-soluble matter in rocks, % (including calcite, dolomite, siderite, and pyrite); β CaCO3 : Solubility of HCl per unit volume, m 3 / m 3 ; θ: Accessible reactivity coefficient (determined by laboratory tests); ξ: Percentage of higher permeability in the stratification layer (%), with ≥0.1mD as the reference value;

[0036] The calculation in step S6 is as follows:

[0037] S61. The formula for calculating acid injection displacement is as follows:

[0038] V 处 / t 酸液反应时间 ≤Q 排量 <Q P破裂压力

[0039] In the formula: t 酸液反应时间 : Slow-rate acid reaction time (min); Q 排量 Injection displacement m 3 / min; Q P破裂压力 Injection rate (m) during reservoir fracturing 3 / min;

[0040] like Figure 1 As shown, taking Well Cha 35 as an example, Well Cha 35 is located in the northern part of the Changling Depression, bordered by Liangjing Oilfield to the east, Qian'an Oilfield to the south, and Haituozi Oilfield to the west. The area has full 3D seismic coverage. The target formation of this well is the Qingyi shale formation, consisting of layers Bu 8, Bu 7, Bu 6, Bu 4, and Bu 3, which are shale oil reservoirs. Acidizing stimulation design for shale oil production will be carried out.

[0041] The specific implementation process is as follows:

[0042] The first step is to analyze the bedding shape, porosity and permeability distribution, and rock distribution of the shale core of the target layer in the well to understand the theoretical basis for acidizing stimulation of the target layer.

[0043] The second step involves analyzing the rock composition of the target layer. The composition is as follows: clay minerals comprise 20-30% quartz and feldspar; clay minerals comprise 40-60%; calcite and iron ore comprise 10-30%. Calculations determine that the reactant rock comprises approximately 12%. See details... Figure 2 .

[0044] The third step, combining the shale reservoir permeability distribution map, calculated that the percentage of bedding planes accessible to acid fluid is 7.7%; see details. Figure 3 .

[0045] The fourth step involved combining acid etching experiments with the target layer core samples in the laboratory, determining the contactability coefficient to be 0.066–0.1; see details below. Figure 4 .

[0046] Fifth, substitute the above parameters into the acid calculation equation to obtain the dosage of different slugs, where the main acid dosage is 600m³. 3 ;

[0047] Step 6: Considering the slow-reaction acid system has a reaction time of over 10 hours, the final injection rate is determined to be 1-2 m³ / h. 3 / min;

[0048] Shale reservoir acidizing stimulation technology, based on the analysis and understanding of clay-type shale reservoirs and their lithological characteristics, has established a technical approach that fully leverages the advantages of bedding planes. This has resulted in a large-scale acidizing stimulation technology that maintains the rock framework, unblocks rock bedding, connects pores, and prevents swelling while promoting oil washing. Using quartz, feldspar, and clay minerals as the rock framework, and primarily calcite, dolomite, siderite, and pyrite in the dissolution bedding, a bedding plane acidizing stimulation injection parameter design method has been established. This method defines reservoir fracturing as the upper limit for injection pressure, and the upper limit for injection volume at this pressure. The overall goal is to achieve deep acid treatment, form effective acid etching trenches, effectively improve bedding permeability, and achieve effective stimulation of clay-type shale reservoirs. Based on this technical approach, this invention establishes a shale oil acidizing stimulation injection parameter optimization design method, aiming to effectively guide the design of shale oil acidizing stimulation schemes.

[0049] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A design method for acidizing stimulation of clay-type shale reservoirs, characterized in that, Includes the following steps: S1. The theoretical basis for acidizing stimulation is determined by the bedding shape, porosity and permeability level, and rock composition distribution of shale reservoirs. S2. Determine the main rock skeleton components of the shale reservoir, namely quartz, feldspar, and clay minerals, and the content of soluble components, mainly calcite, dolomite, siderite, and pyrite, to obtain the proportion and distribution pattern of the rocks that can be reflected. The calculation in step S2 is as follows: S21, Percentage of HCl-soluble matter in rock (γ) CaCO3 The calculation formula is as follows: γ CaCO3 =100% - Quartz % - Clay minerals % - Feldspar % S3. Based on the characteristics of rock bedding distribution in shale reservoirs, clarify the number of bedding units per meter or the distribution law of bedding permeability in shale reservoirs, and obtain the number of acid fluids entering the bedding units per unit thickness or the proportion of acid fluids that can enter the permeability level per unit thickness. The calculation in step S3 is as follows: S31. The proportion of permeability in higher stratification layers, ξ, is calculated using a reference value of ≥0.1mD, as follows: ξ = ξ1 + ξ2 + ξ3 + ξ4 + ... In the formula: ξ is the proportion of the layered structure with higher permeability; ξ1, ξ2, ξ3, and ξ4 are the proportions of the permeability ≥ 0.1 mD; S4. Based on the laboratory experimental data of rock bedding and acid reaction in shale reservoirs, determine the proportion of rocks that can participate in acid-rock reaction, and define it as the contactable reaction coefficient. S5. Introduce the above parameters, such as the proportion of reactive rock, the proportion of bedding density / permeability level, and the contactable reaction coefficient, into the acidizing dosage design formula to obtain the dosage design formula for the main acidizing slug. The calculation in step S5 is as follows: S51. The formula for calculating the amount of acid used is as follows: Pre-fluid calculation formula: Formula for calculating the main acid: Post-filling fluid calculation formula: In the formula: V 前 Pre-acid plug dosage, in m³ 3 V 处 Acidification modification dosage, unit is m 3 V 顶 Rear slug usage, unit is m 3 V 筒 Wellbore volume, in meters (m³) 3 r: processing radius, in meters; h: reservoir thickness, in meters (m); Φ: Reservoir permeability; γ CaCO3 : Percentage of HCl-soluble matter in rocks, in %; β CaCO3 HCl solubility per unit volume, expressed in m³. 3 / m 3 ; θ: Accessible reaction coefficient; ξ: Percentage of higher permeability in stratification (%), with ≥0.1mD as the reference value; S6. Determine the acid reaction time through indoor experiments to obtain the minimum acid injection rate, ensuring that the acid system can penetrate deep into the reservoir for dissolution. The calculation in step S6 is as follows: S61. The formula for calculating acid injection displacement is as follows: V 处 / t 酸液反应时间 ≤Q 排量 <Q P破裂压力 In the formula: t 酸液反应时间 Q represents the slow-reaction acid reaction time, expressed in minutes. 排量 The injection displacement is expressed in meters (m). 3 / min; Q P破裂压力 This refers to the injection rate during reservoir fracturing, expressed in m³. 3 / min.

2. The acidizing stimulation design method for clay-type shale reservoirs according to claim 1, characterized in that, The accessible reaction coefficient is between 0.066 and 0.

1.

3. The acidizing stimulation design method for clay-type shale reservoirs according to claim 1, characterized in that, The amount of the main acid used is 600m. 3 .

4. The acidizing stimulation design method for clay-type shale reservoirs according to claim 1, characterized in that, Considering that the acid reaction time in the slow-release acid system is over 10 hours, the final injection displacement is determined to be 1-2 m³ / h. 3 / min.

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