Method for optimizing mixing amount of clay stabilizer for low-permeability tight reservoir

Abstract

The invention relates to the technical field of oil-gas field development and reservoir protection, in particular to a low-permeability tight reservoir clay stabilizer mixing amount optimization method, which comprises the following steps: firstly, enabling a rock sample and clay stabilizer solutions with different concentration gradients to generate imbibition to obtain nuclear magnetic signal peak areas corresponding to different imbibition moments; obtaining a liquid inlet amount change rate K sequence and a permeability change rate K sequence; then obtaining a first weight coefficient alpha and a second weight coefficient beta; and finally, calculating a comprehensive decision index CDI sequence. Taking the concentration of the clay stabilizer solution corresponding to the permeability change rate K less than or equal to the maximum permeability damage threshold value Kmax and the minimum value of the comprehensive decision index CDI as the optimal clay stabilizer concentration; according to the method, accurate and differentiated optimization of the mixing amount of the clay stabilizer is achieved, the defects of an existing static evaluation method are overcome, and the method has important significance for protecting a low-permeability tight reservoir and improving the recovery ratio.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development and reservoir protection, and particularly relates to a clay stabilizer dosage optimization method for low-permeability tight reservoirs. BACKGROUND

[0002] In low-permeability tight oil and gas reservoirs, high-content sensitive clay minerals such as illite and illite / montmorillonite mixed layer are generally developed. In the process of drilling and completion, fracturing reconstruction and injection-production development, the invasion of external working fluid can easily induce the physical and chemical effects of clay mineral hydration, dispersion and migration, resulting in the blockage of micro-pore throat structure of the reservoir and the significant attenuation of effective permeability, which eventually seriously restricts the productivity and development benefit of oil and gas wells. The industry standard "SY / T 5358-2010 Evaluation Method for Reservoir Sensitivity Flow Experiment" provides an authoritative water sensitivity damage degree classification basis for evaluating the sensitivity of the reservoir (such as no damage when water sensitivity index Dw≤5%, weak damage when 5%<Dw≤30%, etc.).

[0003] Currently, the industry generally uses the process technology of adding clay stabilizer to inhibit the reservoir damage caused by clay minerals. However, the existing evaluation methods and optimization strategies for stabilizer concentration still have the following key bottlenecks, which cannot be fully integrated with the scientific evaluation system embodied in the above standard: (1) Static evaluation dimension: the existing technology mainly relies on static evaluation indexes such as anti-swelling rate test and core flow experiment endpoint permeability damage rate, lacks dynamic process characterization of fluid invasion, imbibition and damage evolution, and cannot reflect the real-time migration and interaction mechanism of working fluid in micro-nano pore throat, resulting in significant deviation in determining the critical concentration of stabilizer; (2) Insufficient lithology adaptation capability: low-permeability tight reservoirs have strong lithology and physical property heterogeneity. Different types of cores (such as fine sandstone, siltstone and mudstone) have essential differences in mineral composition, pore structure and clay occurrence state, and should have different needs for stabilizer concentration. However, the existing method generally ignores the constraint of reservoir geological characteristics, often provides a single and empirical concentration recommendation, and lacks quantitative description of the lithology-concentration response relationship; (3) Decision-making process relies on subjective experience: the existing concentration recommendation is mostly based on the data provided by suppliers or field operation experience, lacks a standardized, reproducible and clear mechanism experimental evaluation system that can be connected with standards such as "SY / T 5358-2010" as a decision-making support, which easily leads to the deviation of the added concentration from the optimal range, and the phenomena of insufficient stabilization or excessive injection of chemical agents, which not only cannot effectively protect the reservoir, but also can induce secondary damage and significantly increase the development cost.

[0004] Therefore, there is an urgent need in the art to develop a clay stabilizer dosage optimization method that can simulate real formation environment, real-time characterize fluid dynamic imbibition behavior, and integrate multi-source geological information, to establish a scientific, precise, and universal concentration decision-making paradigm that is consistent with industry standards, and to provide key technical support for efficient and safe development of low permeability and tight reservoirs. SUMMARY

[0005] The purpose of the present application is to overcome the above-mentioned defects of the prior art, and to provide a low permeability and tight reservoir clay stabilizer dosage optimization method based on dynamic imbibition characterization. The method monitors the whole imbibition process in real time through nuclear magnetic resonance technology, and innovatively proposes the dynamic evaluation parameter of "liquid intake rate of change", thereby realizing the precise and scientific optimization of the clay stabilizer dosage for different lithological reservoirs.

[0006] The technical solution of the present application is: A low permeability and tight reservoir clay stabilizer dosage optimization method, the method being as follows: The rock sample is subjected to imbibition with clay stabilizer solutions of different concentration gradients, the peak area of nuclear magnetic signal corresponding to different imbibition times is obtained, and then the liquid intake rate of change K sequence and the permeability rate of change ΔK sequence corresponding to the clay stabilizer solutions of different concentration gradients are obtained; the first weight coefficient α and the second weight coefficient β are obtained according to the mean value, standard deviation and coefficient of variation of the liquid intake rate of change K sequence and the permeability rate of change ΔK sequence; and then the comprehensive decision index CDI sequence corresponding to the clay stabilizer solutions of different concentration gradients is calculated; the permeability rate of change ΔK of the clay stabilizer solution corresponding to the minimum value of the comprehensive decision index CDI is less than or equal to the maximum permeability damage threshold ΔK max , and the concentration of the clay stabilizer solution corresponding to the minimum value of the comprehensive decision index CDI is the optimal clay stabilizer concentration; The specific solving process of the comprehensive decision index CDI is as follows: CDI = α (K / K0) + β (△K / △K max ) Formula 1 In the formula, α is the first weight coefficient; β is the second weight coefficient; K is the liquid intake rate of change; K0 is the liquid intake rate of change when the concentration of the clay stabilizer solution is 0; △K is the permeability rate of change; △K max is the maximum permeability damage threshold.

[0007] The specific solving process of the first weight coefficient α and the second weight coefficient β is as follows: α = CV K / (CV K + CV △K ) Formula 2 β = CV △K / (CV K + CV△K ) Formula 3 CV K =σ K / μ K Formula 4 CV △K =σ △K / μ △K Formula 5 In the formula, CV K is the coefficient of variation of the liquid inflow rate K; σ K and μ K are the standard deviation and mean value of the liquid inflow rate K, respectively; CV △K is the coefficient of variation of the permeability rate ΔK; σ △K and μ △K are the standard deviation and mean value of the permeability rate ΔK, respectively.

[0008] The specific solving process of the liquid inflow rate K is as follows: K = [(A tmax -A dry ) - (A tcritical -A dry )] / (A tmax -A dry ) Formula 6 In the formula, A dry is the peak area of the nuclear magnetic signal of the rock sample before wicking; A tmax is the peak area of the nuclear magnetic signal at the stable time point tmax of wicking; and A tcritical is the peak area of the nuclear magnetic signal at a specific time point tcritical in the initial stage of wicking.

[0009] The specific different concentration gradients are 0%, 0.1%, 0.3%, 0.5%, 0.7% and 1.0%, and the specific different wicking times are 0 h, 2 h, 6 h, 12 h, 24 h, 48 h and 72 h.

[0010] The specific time point tcritical in the initial stage of wicking is 2 h after the start of wicking, and the stable time point tmax of wicking is 72 h after the start of wicking.

[0011] The specific solving process of the permeability rate ΔK is as follows: ΔK = |K0-K i | / K0 × 100% Formula 7 In the formula, K i is the permeability at a certain time point after the start of wicking.

[0012] The maximum permeability damage threshold value ΔK max is 30%.

[0013] The technical effect of the present application is that: The present application combines the liquid influx rate K and the permeability change rate AK by constructing the comprehensive decision index CDI. The increase of the liquid influx rate K value reflects that the clay stabilizer delays the initial absorption process of the fluid and inhibits the rapid hydration and swelling of the clay. The decrease of the permeability change rate AK value indicates that the permeability damage is reduced and the reservoir percolation capacity is protected. The present application realizes the precision and differentiation optimization of the clay stabilizer dosage, overcomes the shortcomings of the existing static evaluation method, and has important significance for protecting the low permeability and tight reservoir and improving the recovery rate. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The flowchart of the low permeability and tight reservoir clay stabilizer dosage optimization method of the present application. DETAILED DESCRIPTION

[0015] A low permeability and tight reservoir clay stabilizer dosage optimization method, the method is as follows, The rock sample is subjected to imbibition with clay stabilizer solutions of different concentration gradients. The concentration of the clay stabilizer solution is 0%, 0.1%, 0.3%, 0.5%, 0.7% and 1.0%. The nuclear magnetic signal peak area at 0h, 2h, 6h, 12h, 24h, 48h and 72h after imbibition is obtained, wherein the nuclear magnetic signal peak area corresponding to 0h is the nuclear magnetic signal peak area A of the rock sample before imbibition. dry The nuclear magnetic signal peak area corresponding to 2h is A tcritical The nuclear magnetic signal peak area corresponding to 72h is A tmax The liquid influx rate K sequence and the permeability change rate AK sequence corresponding to the clay stabilizer solutions of different concentration gradients are calculated by the nuclear magnetic signal peak areas at different time points of imbibition. The first weight coefficient a and the second weight coefficient b are calculated according to the mean value, standard deviation and coefficient of variation of the liquid influx rate K sequence and the permeability change rate AK sequence. Then, the comprehensive decision index CDI sequence corresponding to the clay stabilizer solutions of different concentration gradients is calculated. The permeability change rate AK is less than the maximum permeability damage threshold AK max And the concentration of the clay stabilizer solution corresponding to the minimum value of the comprehensive decision index CDI is the optimal clay stabilizer concentration.

[0016] Specific experimental cases A low permeability and tight reservoir clay stabilizer dosage optimization method, the method is as follows.

[0017] ​Step 1: Drill a standard core column (diameter 2.5 cm, length 5.0 cm) from the core section of the target oilfield low-permeability tight reservoir. After washing the oil with chloroform extraction and washing with ethanol to remove salt, the standard core column is dried to constant weight in a constant temperature oven at 60-80°C as a rock sample. The following steps are used for lithology classification: Analyze the logging data in the area to obtain the natural gamma GR value of the core corresponding depth point; analyze the particle size distribution of the core by casting thin section + image analysis system; accurately divide according to the lithology classification standard: Fine sandstone: GR value = 38 API, median particle size 0.12 mm (> 0.0625 mm), thin section identification shows that the fine sandy content is 68%; Siltstone: GR value = 62 API, median particle size 0.045 mm (0.0156-0.0625 mm), silt content 63%; Mud shale: GR value = 104 API, median particle size 0.008 mm (< 0.0156 mm), argillaceous content 58%.

[0018] Take mud shale as an example in the subsequent steps.

[0019] Step 2: Preparation of clay stabilizer with different concentration gradients; A commercially available quaternary ammonium salt clay stabilizer is selected, and its performance is detected in the laboratory as follows: Molecular weight: 850 daltons (satisfies <1000 daltons requirement); Anti-swelling rate: 94% (satisfies ≥85% requirement); Temperature resistance: 155°C (satisfies ≥140°C requirement); Three times of water washing and erosion resistance: 96% (satisfies ≥90% requirement); Use the slick water fracturing fluid formula used in the field as the base fluid, and obtain the supernatant after gel breaking and filtration. Use a precision electronic balance (accuracy 0.0001 g) and a pipette to add stabilizers to the supernatant to prepare 1000 mL of series clay stabilizer solutions with concentrations of 0%, 0.1%, 0.3%, 0.5%, 0.7%, and 1.0%, respectively, and ultrasonic oscillation to mix them uniformly.

[0020] Step 3: Dynamic imbibition experiment and nuclear magnetic resonance monitoring; Place the rock sample in the reaction chamber of a high temperature and high pressure imbibition instrument (such as the American Temco HNP-100 type), and set the experimental conditions to simulate the actual formation environment: temperature: 60.0±0.5°C; confining pressure: 20.0±0.2 MPa; fluid salinity: 80000±200 mg / L (simulate formation water); The series of clay stabilizer solution is injected into the reaction chamber to ensure complete immersion of the rock sample. The T2 spectrum data of the rock sample is accurately collected at 0h, 2h, 6h, 12h, 24h, 48h, 72h after the start of imbibition by using a low-field nuclear magnetic resonance analyzer (such as Suzhou Nuomei MesoMR23-060H-I type). The parameter settings of the low-field nuclear magnetic resonance analyzer are as follows: the main frequency is 23MHz, the waiting time TW is 3000ms, the echo time TE is 0.2ms, and the scanning number NS is 64.

[0021] Step 4: Calculation of the liquid injection rate change K (taking the concentration of the clay stabilizer solution as 0.7% as an example): The nuclear magnetic signal peak area A of the rock sample before imbibition dry =3102.263, the nuclear magnetic signal peak area A of the rock sample at 2h after the start of imbibition 2h =4076.663, and the nuclear magnetic signal peak area A of the rock sample at 72h after the start of imbibition 72h =7450.201. K=[(A tmax -A dry )-(A tcritical -A dry )] / (A tmax -A dry )=[(7450.201-3102.263)-(4076.663-3102.263)] / (7450.201-3102.263)=77.57%. The liquid injection rate change K corresponding to the series of clay stabilizer solutions is calculated in turn, and the calculation results are shown in Table 1. Table 1 Calculation results of the liquid injection rate change K corresponding to the series of clay stabilizer solutions .

[0022] Step 5: Calculation of the permeability change rate ΔK: The calculation formula is: ΔK=|K0-K i | / K0×100%; the permeability change rate ΔK corresponding to the series of clay stabilizer solutions is calculated in turn, and the calculation results are shown in Table 2. Table 2 Calculation results of the permeability change rate ΔK corresponding to the series of clay stabilizer solutions ; Among them, the damage degree evaluation is obtained according to SY / T 5358-2010; the maximum permeability damage threshold ΔK max =30% is set according to the upper limit of weak damage set in SY / T 5358-2010.

[0023] Step 6: Calculation of the first weight coefficient α and the second weight coefficient β; The series of clay stabilizers corresponding to the liquid volume change rate K sequence is specifically [41.48, 60.02, 62.36, 69.29, 77.57, 78.00], and the standard deviation σ K ≈13.71, the mean μ K =64.79, the coefficient of variation CV K of the liquid volume change rate K is σ K / μ K =13.71 / 64.79≈0.2115; The series of clay stabilizers corresponding to the permeability change rate ΔK sequence is specifically [39.32, 31.70, 35.39, 29.60, 21.45, 21.50], and the standard deviation σ △K ≈7.19, the mean μ △K =29.83, the coefficient of variation CV △K of the permeability change rate ΔK is σ △K / μ △K =7.19 / 29.83≈0.2411; The calculation results are α=CV K / (CV K +CV △K )=0.2115 / (0.2115+0.2411)≈0.467, and β≈0.533.

[0024] Step 7: Calculation of comprehensive decision index CDI (taking the concentration of clay stabilizer solution as 0.7% as an example): CDI=α(K / K0)+ β(△K / △K max )=0.467×(77.57 / 41.48)+0.533×(21.45 / 30)=1.254; The calculation results of the comprehensive decision index CDI corresponding to the series of clay stabilizer solutions are shown in Table 3; Table 3 Calculation results of the comprehensive decision index CDI corresponding to the series of clay stabilizer solutions ; According to the condition that the permeability change rate ΔK≤30 and the minimum value of the comprehensive decision index CDI corresponds to the optimal clay stabilizer concentration, it is determined that 0.7% is the optimal clay stabilizer concentration.

[0025] According to the above steps, the optimal concentrations of clay stabilizer solutions corresponding to fine sandstone, siltstone and mud shale are obtained, and the results are shown in Table 4. Table 4 Final results of clay stabilizer content optimization for different lithology ; Further, it is obtained that the concentration of clay stabilizer solution corresponding to fine sandstone is 0.3%, the concentration of clay stabilizer solution corresponding to siltstone is 0.5%, and the concentration of clay stabilizer solution corresponding to mud shale is 0.7%.

Claims

1. A method for optimizing the dosage of a clay stabilizer for low-permeability tight reservoirs, characterized in that, The method is as follows: The rock sample is subjected to wicking with clay stabilizer solutions of different concentration gradients, nuclear magnetic signal peak areas corresponding to different wicking times are obtained, and then a sequence of liquid intake rate K corresponding to the clay stabilizer solutions of different concentration gradients and a sequence of permeability rate change ΔK are obtained; according to the mean value, standard deviation and coefficient of variation of the sequence of liquid intake rate K and the sequence of permeability rate change ΔK, a first weight coefficient α and a second weight coefficient β are obtained; then a sequence of comprehensive decision indexes CDI corresponding to the clay stabilizer solutions of different concentration gradients is calculated; when the permeability rate change ΔK is less than or equal to the maximum permeability rate damage threshold ΔK max , and the concentration of the clay stabilizer solution corresponding to the minimum value of the comprehensive decision index CDI is the optimal clay stabilizer concentration. The specific solving process of the comprehensive decision index CDI is as follows: CDI = a (K / K0) + β (ΔK / ΔK max ) Equation 1 In the formula, α is the first weight coefficient; β is the second weight coefficient; K is the liquid inlet rate change rate; K0 is the liquid inlet rate change rate when the concentration of the clay stabilizer solution is 0; AK is the rate of permeability change; AK max is the maximum permeability damage threshold.

2. The method according to claim 1, wherein, The specific solving process of the first weight coefficient α and the second weight coefficient β is as follows: a = CV K / (CV K + CV △K ) Equation 2 β = CV △K + CV K + CV △K Equation 3 CV K =σ K / μ K Formula 4 CV △K =σ △K / μ △K Formula 5 wherein: CV K is the coefficient of variation of the flow rate variation K; σ K , μ K are the standard deviation and the mean of the flow rate variation K, respectively; CV △K is the coefficient of variation for the rate of change of permeability; σ △K , μ △K are the standard deviation and mean, respectively, of the rate of change of permeability.

3. The method according to claim 1, wherein the method is characterized by, The specific solving process of the liquid inlet rate change rate K is as follows: K = [(A tmax - A dry ) - (A tcritical - A dry )] / (A tmax - A dry ) Equation 6 In the formula: A dry is the peak area of the nuclear magnetic signal of the rock sample before infiltration; A tmax is the peak area of the nuclear magnetic signal at the stable time point tmax of infiltration; A tcritical is the peak area of the nuclear magnetic signal at a specific time point tcritical in the early stage of infiltration.

4. The method according to claim 3, wherein the method is characterized by, The different concentration gradients are specifically 0%, 0.1%, 0.3%, 0.5%, 0.7%, and 1.0%; and the different infiltration times are specifically 0 h, 2 h, 6 h, 12 h, 24 h, 48 h, and 72 h.

5. The method according to claim 4, wherein the method is characterized by, The specific time point tcritical in the initial infiltration stage is 2 h after the start of infiltration, and the stable infiltration time point tmax is 72 h after the start of infiltration.

6. The method of claim 1, wherein the method is characterized by, The specific solving process of the permeability change rate ΔK is as follows: AK = | K0 - K i | / K0 x 100% Equation 7 In the formula: K i is the permeation rate at a certain time point after the start of imbibition.

7. The method of claim 1, wherein the method is characterized by, the maximum permeability damage threshold AK max is 30%.

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