A method for predicting solid phase invasion damage of deep compact oil and gas reservoirs

Abstract

This invention discloses a method for predicting solid phase invasion damage in deep tight oil and gas reservoirs, belonging to the field of oil and gas reservoir development technology. The method includes the following steps: A mathematical model of suspended colloid migration in porous media is established based on the mass balance of suspended and retained particles, the expression for particle capture rate, and Darcy's law; the variables in the mathematical model of suspended colloid migration in porous media are made dimensionless; the above dimensionless mathematical model of suspended colloid migration in porous media is solved to obtain a drilling fluid damage prediction model for tight oil and gas reservoirs; and the damage status of the oil and gas reservoir is determined based on the drilling fluid damage prediction model. This invention provides a basis for the selection of sealing materials for fractured reservoirs, proposes a series of evaluation methods for the performance parameters of sealing materials, and can timely and effectively control leakage problems.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of drilling fluid loss control, and particularly relates to a solid phase invasion damage prediction method for deep tight oil and gas reservoirs. BACKGROUND

[0002] In the drilling process, a series of induced cracks and extended cracks are generated due to pressure fluctuation or drill tool vibration, and drilling fluid inevitably enters the formation, wherein the solid phase can be retained in the reservoir pores and adsorbed on the crack wall, thereby affecting the permeability of the formation around the well. In order to deal with the drilling fluid loss, which is the most serious reservoir damage mode in the drilling and completion process, how to effectively predict and control the loss damage of the working fluid is the core problem of reservoir protection in fractured oil and gas reservoirs.

[0003] At present, the working fluid loss control method in the drilling process mainly adds plugging materials to the drilling fluid to form a plugging layer with certain compression resistance and pressure bearing capacity by bridging, filling and dense accumulation in the cracks. The field loss control operation lacks underground vision, mainly relying on trial and error method and experience method, lacks regular cognition and theoretical guidance, and cannot realize timely, targeted and efficient loss control.

[0004] For loss damage, the migration of suspended particles is an important factor affecting the loss damage: when the suspended particles migrate, the permeability of the subsequent reservoir will be reduced, thereby causing damage to the reservoir. However, the problem is rarely considered in the study of drilling fluid loss damage, resulting in low accuracy of the final result and little guiding significance for actual production. SUMMARY

[0005] To solve the problem of drilling fluid loss in deep tight oil and gas reservoirs, the present application provides a time and space evolution prediction method for drilling fluid loss damage zone in deep tight oil and gas reservoirs, and the technical scheme of the present application is as follows.

[0006] A solid phase invasion damage prediction method for deep tight oil and gas reservoirs, comprising the following steps:

[0007] S1, according to the mass balance of suspended particles and retained particles, the particle capture rate and Darcy's law, a mathematical model of suspended colloidal migration in porous media is established and dimensionless is carried out;

[0008] S2, the dimensionless model is solved to obtain a pressure drop model;

[0009] S3, according to Darcy's law and the pressure drop model, the damage condition of the oil and gas reservoir is judged.

[0010] The present application has the beneficial effect that the related parameters of the suspended particles are considered, so that the prediction result of the damage to the reservoir after the drilling fluid loss is more accurate. DETAILED DESCRIPTION

[0011] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solutions of the present application are described in detail as follows, but cannot be understood as limiting the implementable scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0012] The present application is further described below in combination with embodiments.

[0013] S1, according to the mass balance of suspended particles and retained particles, particle capture rate and Darcy's law, a mathematical model of suspended colloids migration in porous media is established and is dimensionless;

[0014] The specific model of suspended colloids migration in porous media established is as follows:

[0015]

[0016]

[0017]

[0018] The initial and boundary conditions are:

[0019] t=0: c=s=0

[0020] x=0: c=c 0 (4)

[0021] Where, φ is the porosity, U is the Darcy flow rate, c is the suspended concentration, σ is the retained concentration, σ m is the maximum retained concentration corresponding to all the empty sites captured by the packed particles, λ0 is the filtration coefficient, p is the pressure, k is the permeability, μ is the water viscosity, β is the reservoir damage, x is the position in the radial direction, and t is the time.

[0022] Wherein, the suspended concentration is defined as the number of particles per unit volume of fluid; the retained concentration is equal to the number of particles per unit volume of rock; the filtration coefficient λ is the probability of particles being captured per unit length of its trajectory; the radial direction refers to the shortest distance between a point and the wellbore.

[0023] The variables of the suspended colloids migration model in porous media are dimensionless as follows:

[0024]

[0025] The model is converted into the following dimensionless form:

[0026]

[0027]

[0028]

[0029] Initial and boundary conditions:

[0030] T=0: C=S=0 (9)

[0031] x=0: C=1,

[0032] where k0 is the permeability of the wellbore, p0 is the pressure at the wellbore, C is the dimensionless suspended concentration; S is the dimensionless retained concentration; X is the dimensionless radial position; P is the dimensionless pressure; T is the dimensionless time; S m is the dimensionless value of the maximum retained concentration corresponding to all the voids captured by the packing particles; f(c) is the nonlinear suspension function.

[0033] For 0 < T < X, the model has:

[0034]

[0035] C(X,T) = S(X,T) = 0 (12)

[0036] The model is meaningless in this interval, so we consider the 0 < X < T region below.

[0037] For the above nonlinear suspension function f(c), the embodiments of the present application provide a variety of suspension functions to facilitate users to obtain suitable models:

[0038] For the dimensionless suspension function, the properties of f(c) are:

[0039] f(0) = 0, f'(0) = 1 (13)

[0040] Considering the second-order Taylor expansion form of the suspension function at c = 0 and satisfying (13), the expression of f(c) is:

[0041] f(c) = c + bc 2 (14)

[0042] Considering the double suffix Margules expression of the non-ideal solution activity coefficient, the expression of f(c) is:

[0043]

[0044] where the interaction parameter A is an empirical coefficient usually obtained by fitting experimental data. By substituting formula 15 into formula 24 and then substituting formula 24 into formula 31, and combining the measured pressure drop data, the value of A can be obtained.

[0045] Equation (15) for the traditional filtration model A = 0, then:

[0046] f(c) = c (16)

[0047] S2, solve the above dimensionless mathematical model of colloidal migration in porous media, get tight oil and gas layer drilling fluid damage prediction model;

[0048] Solving the dimensionless mathematical model of colloidal migration in porous media includes the following steps:

[0049] S21, solve the dimensionless suspension concentration

[0050] Introducing a new independent variable τ:

[0051] τ = T-X (17)

[0052] The range 0 < X < T becomes: X > 0, τ > 0; but the boundary condition (10) when X = 0 remains unchanged.

[0053] Substitute τ into equations (11) and (7) to get:

[0054]

[0055]

[0056] When τ = 0, S = 0:

[0057]

[0058]

[0059] Expression (21) can be written as:

[0060]

[0061] By equations (18) and (19) can be obtained:

[0062]

[0063] The expression of the concentration is:

[0064]

[0065] Substitute (24) into (23) to get:

[0066]

[0067] By the method of characteristics change the order of derivatives in equation (25) and combine the integral boundary conditions (10) in x to get:

[0068]

[0069]

[0070] Dividing the obtained variable in ordinary differential equation (26) by, the solution C(X, τ) is obtained.

[0071] S22, solving the reserved concentration

[0072] From formula (27)

[0073]

[0074] Where C(X, 0) is given by expressions (21) and (22), take the derivative of both sides of equation (28) with respect to X:

[0075]

[0076] Considering the reserved concentration expression (24), the expression of Riemann invariant is obtained

[0077]

[0078] Determine the solution S(X, T).

[0079] S3, judging the damage of oil and gas layer according to the damage prediction model of drilling fluid of dense oil and gas layer.

[0080] As a specific embodiment of the present application, step S5 comprises the following steps:

[0081] S31, according to different suspension functions (14), (15) and (16), it is obtained c(x, t) in table 1 after being brought into formula 24, and s(x, t) in table 1 after being brought into formula 30;

[0082] Table 1 reserved concentration and suspended concentration of different suspension functions

[0083]

[0084]

[0085] S32, according to different suspended concentration expressions, the corresponding pressure drop expression is obtained;

[0086] The pressure gradient expression in equation (8) combined with the integral from zero to x in x obtains the pressure drop through the core:

[0087] ΔP(X, T) = X + βφc 0 ∫0 X S(X, T)dx (31)

[0088] S33, taking the ratio of the pressure drop at t time and the initial pressure drop as a dimensionless pressure drop;

[0089]

[0090] S34, according to Darcy's law, the ratio of the initial permeability and the permeability at t time can be obtained through the dimensionless pressure drop, and the damage degree of the drilling fluid can be predicted by observing the change of the permeability.

[0091]

[0092] Through formula 32, the change of the pressure drop at a certain point in the reservoir over time can be calculated; and according to formula 33, it can be known that the change of the pressure drop and the change of the permeability are inversely proportional, when the pressure drop at a point in the reservoir gradually rises, the permeability at the point gradually decreases. The change of the permeability is often used by the person skilled in the art to judge the damage degree of the reservoir, therefore, the damage degree of the reservoir can be judged through formula 33.

[0093] At the same time, finally according to the actual situation, when the suspension function shown in formula 15 is used, the final prediction result is more accurate.

[0094] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of the change or replacement within the technical range disclosed by the embodiments of the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for predicting solid invasion damage in deep, tight oil and gas formations, comprising: The method comprises the following steps: S1, establishing a mathematical model of suspended colloidal migration in a porous medium according to the mass balance of suspended particles and retained particles, particle capture rate and Darcy's law, and dimensionless the mathematical model; the mathematical model of suspended colloidal migration in the porous medium is as follows: Wherein, the initial and boundary conditions of the model are: t=0: c=σ=0 x = 0: c = c 0 where φ is the porosity, U is the Darcy velocity, c is the suspended concentration, σ is the retention concentration, σ m is the maximum retention concentration corresponding to all the voids captured by the packing particles, λ0is the filtration coefficient, p is the pressure, k is the permeability, μ is the viscosity of the water laden, β is the reservoir damage coefficient; x is the position in the radial direction, t is the time, c 0 is the suspended concentration at the boundary S2, solving the dimensionless model to obtain a pressure drop model; S3, judging the damage condition of the oil and gas layer according to Darcy's law and the pressure drop model.

2. The method of claim 1, wherein, In S1, the dimensionless mathematical model of suspended colloidal migration in the porous medium is as follows: Initial and boundary conditions: T=0: C=S=0 X = 0: C = 1, where C is the dimensionless suspension concentration; S is the dimensionless retention concentration; X is the dimensionless radial position; P is the dimensionless pressure; T is the dimensionless time; S m is the dimensionless value of the maximum retention concentration corresponding to all voids captured by the packing particles; f(c) is a non-linear suspension function.

3. The method of claim 2, wherein, The where A is an interaction parameter, obtained by fitting the experimental data obtained.

4. The method of claim 2, wherein, The S3 comprises: S31, the dimensionless retention concentration is: where λ0is the filtration coefficient; σ m is the maximum retention concentration corresponding to all the voids captured by the filler particles, c 0 is the concentration of the suspension at the boundary, and φ is the porosity. S32, the pressure drop expression is calculated as: In the formula, Δp(x, t) is the pressure drop at position x at time t; S(x, t) is the retention concentration at position x at time t; S33, calculating the dimensionless pressure drop as: where J(t) is the dimensionless pressure drop; S34, according to Darcy's law, the following model is obtained: In the formula, J(t) is the dimensionless pressure drop, and k(x, t) is the permeability at position x at time t. Through the model, the permeability reduction of a point in the reservoir at different times can be determined, and the damage of drilling fluid leakage to the reservoir can be determined.

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