CN106547034A - A kind of method for calculating compact reservoir rock brittleness index - Google Patents

Abstract

The invention provides a method for rapidly calculating rock brittleness based on well logging data, which is used to realize the rapid calculation of rock brittleness of tight reservoirs under formation conditions and promote the efficient development of tight oil and gas reservoirs. This method mainly starts from the perspective of rock fracture form and fracture fracture energy, and is based on the principle that the more complex the rock fracture form, the smaller the fracture fracture energy, and the greater the rock brittleness index. Using Young's modulus and dilation angle to reflect the ability of rock to resist deformation and the rate of deformation respectively, the brittle characteristics of rock can be well described. characteristics of the stage. The gray relational theory is used to calculate the weight coefficients of Young's modulus and dilation angle, and thus a new method for calculating rock brittleness index is established. This method is a calculation method for quickly predicting brittleness index based on well logging data, which improves the rationality of rock brittleness evaluation and promotes the efficient development of tight oil and gas reservoirs.

Description

A Method for Calculating Brittleness Index of Tight Reservoir Rocks

Technical field:

The invention relates to the field of unconventional oil and gas exploration and development, in particular to a method for calculating the brittleness index of tight reservoir rocks based on logging data.

Background technique:

my country's tight oil and gas reserves are abundant and have good development potential, but the development is difficult. Inspired by the effective development of shale gas reservoirs, fracture network fracturing has been practiced in tight oil and gas reservoirs. In fracture network fracturing, rock brittleness is an important parameter to judge the ability of reservoir fracturing to form fracture network. At present, the mineral brittleness index and dynamic rock mechanics parameters most widely used in oil and gas development in the petroleum industry to calculate rock brittleness are summaries of the shale gas fracturing experience in the United States. The rock brittleness in the field of rock mechanics is mainly calculated based on the stress-strain curve and mechanical characteristics of rock laboratory tests, which is not combined with the field of oil and gas development, so it is difficult to be used in field applications. Therefore, tight oil and gas fracturing urgently needs a rock brittleness calculation method based on rock brittleness mechanical performance and convenient field application.

Invention content:

Aiming at the shortcomings of the rock brittleness calculation methods currently used in tight oil and gas fields, the present invention proposes a method for quickly calculating the rock brittleness index based on rock fracture energy, fracture shape and logging data, so as to realize the rock brittleness of tight reservoirs under formation conditions The rapid calculation of the method provides a basis for the design of fracturing schemes for tight reservoirs.

The microscopic fracture energy and macroscopic fracture form of rock are the specific manifestations of rock brittleness. A method for calculating the brittleness index of tight reservoir rock proposed by the present invention uses Young's modulus and dilation angle to respectively reflect the ability of rock to resist deformation and the rate of deformation, and has a good principle of describing the brittleness characteristics of rock. A new calculation method for rock brittleness is established by assigning corresponding weights to the two parameters, and the parameter values for calculating the brittleness index are obtained by using well logging data. The present invention mainly comprises the following steps:

1. Well logging data preparation. Well logging data include full-wave train acoustic logging or dipole acoustic and natural gamma ray logging data, at least including shear wave time difference, compressional wave time difference, density, porosity, and natural gamma ray logging curves of the fractured interval;

2. Calculate the Young's modulus E, Poisson's ratio ν, and internal friction angle of the rock by using the transverse wave transit time, longitudinal wave transit time, density curve, and natural gamma ray curve The shale content V _sh profile is calculated by formulas (1)-(5):

In the formula, E _d is the dynamic Young's modulus, v _d is the dynamic Poisson's ratio, ρ is the density, V _t is the longitudinal wave velocity, V _s is the shear wave velocity, is the internal friction angle, φ is the porosity, SH is the relative value of natural gamma ray, GR, GR _max and GR _min are the natural gamma ray value of the target layer, the natural gamma value of the pure mudstone formation, and the natural gamma ray value of the pure lithology formation, respectively. Ma value, V _sh is shale content, GCUR is an empirical coefficient related to age, 3.7 for old formations, 2 for new formations.

3. Calculate the rock compressive strength and confining pressure profile by using the rock mechanical characteristic parameters obtained in step 2 and the shale content profile, and use formulas (6) and (7) to calculate respectively:

σ _c =(0.0045+0.0035V _sh )E _d (6)

In the formula, _σc is the compressive strength of the rock, _Pc is the confining pressure, H is the depth of the reservoir, and α is the effective stress coefficient.

When the shale content V _sh >0.8, the effective stress coefficient α=0.6; when the shale content V _sh <0.2, the effective stress coefficient α=0.9; when the shale content 0.2<V _sh <0.8, the effective stress coefficient

4. Utilize the rock compressive strength that step 3 obtains and the confining pressure to calculate the dilation angle profile of the rock, calculate with formula (8);

where ψ is the dilation angle of the rock, is the internal friction angle, σ _c is the rock compressive strength, and P _c is the confining pressure.

5. Establish a new rock brittleness index evaluation method using the two parameters of Young's modulus and dilation angle, and calculate the weight coefficients of Young's modulus and dilation angle through gray relational theory;

6. Using the Young's modulus obtained in step 2, the dilation angle obtained in step 4, and the weight coefficient obtained in step 5, calculate the rock brittleness index profile, and use formula (9) to calculate the rock brittleness index B _I .

B _I =W ₁ E _n +W ₂ ψ _n (9)

In the formula, B _I is the brittleness index, E _n is the normalized Young’s modulus, ψ _n is the normalized dilation angle, W ₁ is the weight of Young’s modulus, W ₂ is the dilation angle account for weight.

Among them, the calculation formulas of E _n and ψ _n are as follows:

In the formula, E, E _max , and E _min are the Young's modulus at any point in the formation, the maximum Young's modulus of the fractured interval formation, and the minimum Young's modulus of the fractured interval formation; ψ, ψ _max , ψ _min Respectively, the dilation angle at any point in the formation, the maximum dilation angle of the formation in the fractured interval, and the minimum dilatation angle in the formation in the fractured interval.

Compared with the existing method for calculating the rock brittleness index, the present invention has the following beneficial effects: the present invention proposes a calculation method for rapidly predicting the brittleness index by utilizing logging data based on the fracture energy and fracture form of the rock, and the brittleness of the rock Combined with the fracture pattern of rocks in laboratory experiments, it provides a more intuitive judgment for the brittleness of underground rocks, provides a basis for the optimization of fracturing schemes for tight oil and gas reservoirs, and is conducive to improving the fracturing effect of tight oil and gas.

Description of drawings:

Fig. 1 is a block diagram of steps for calculating rock brittleness in the present invention.

Fig. 2 is a schematic diagram of well logging data of a tight oil reservoir in the Dagang Oilfield of the present invention from 4050m to 4065m

Fig. 3 is a schematic diagram of the brittleness index profile of the 4050m-4065m well section of the tight oil reservoir calculated according to the method of the present invention

detailed description:

Below the implementation method of the present invention is described in further detail, specifically as follows:

Taking a tight oil reservoir in the Kong 2 Member of Dagang Oilfield as an example, the buried depth of the reservoir is 4050-4065m, and the average formation pressure of this well section is 45MPa. Taking the buried depth of 4050m as an example, the method of the present invention is used to calculate the brittleness index.

1. According to step 1, prepare the shear time difference, longitudinal wave time difference, density, porosity and natural gamma ray logging curve of the fracturing section, and the logging data are shown in Figure 2;

2. Calculate the Young’s modulus, Poisson’s ratio, internal friction angle, and shale content of the rock by using the relevant logging data, and calculate the Young’s modulus, Poisson’s ratio, internal friction angle, and shale content at the buried depth of 4050m through the formulas (1)-(5) in step 2. The modulus is E=36580.5MPa, Poisson's ratio is v=0.258, and the internal friction angle is The shale content is V _sh =0.209;

3. According to the formulas (6)-(7) in step 3, the rock compressive strength at the buried depth of 4050m is calculated to be σ _c =191.44MPa, and the confining pressure is P _c =59.85MPa, according to the formula in step 4 (8) The calculated dilation angle of the rock is Ψ=5.69°;

4. According to the weight coefficients of Young's modulus and dilation angle calculated in step 5, the weight coefficients of these two parameters are 0.426 and 0.574 respectively, and according to the formula (9)-(11) in step 6, the rock at the buried depth of 4050m is obtained The brittleness index was B _I =0.824.

Similarly, the method of the present invention can be used to calculate the brittleness index profile of tight reservoir rocks with a buried depth of 4050-4065m, and the results are shown in Figure 3.

Claims (5)

1. a kind of method for calculating compact reservoir rock brittleness index, comprises the following steps：

(1) Well logging Data prepares.Well-log information includes that full wave train acustic logging or dipole acoustic and natural gamma are surveyed Well data, at least including shear wave slowness, compressional wave time difference, density, porosity, Natural Gamma-ray Logging Curves；

(2) calculate the Young mould of rock using shear wave slowness, compressional wave time difference, density, porosity, gamma ray curve respectively Amount, Poisson's ratio, internal friction angle, shale content；

(3) the rock-mechanics property parameter and shale content section obtained using step (2) be calculated compressive strength of rock and Confined pressure section；

(4) compressive strength of rock for being obtained using step (3) and the dilative angle section of calculating of surrounding rock pressure rock；

(5) new rock brittleness index number evaluation method is set up using Young's modulus and dilative angle the two parameters, closed by grey The weight coefficient of connection theoretical calculation Young's modulus and dilative angle；

(6) weight coefficient that the dilative angle and step (5) that the Young's modulus that obtains with step (2), step (4) are obtained is obtained, It is calculated rock brittleness index profile.

2. the Forecasting Methodology according to the above-mentioned compact reservoir rock brittleness index of claim 1, it is characterised in that：The step (2) Young's modulus, Poisson's ratio, internal friction angle in, the computing formula of shale content are：

In formula, E_dFor kinetic Youngs modulus, ν_dFor dynamic Poisson's ratio, ρ is density, V_tFor velocity of longitudinal wave, V_sFor shear wave velocity,For Internal friction angle, φ is porosity, and SH is natural gamma relative value, GR, GR_max、GR_minRespectively target zone natural gamma value, pure The natural gamma value of the natural gamma value of mudstone stratum, pure lithologic character stratum, V_shFor shale content, GCUR is the Jing relevant with the age Coefficient is tested, old stratum takes 3.7, and new stratum takes 2.

3. the Forecasting Methodology according to the above-mentioned compact reservoir rock brittleness index of claim 1, it is characterised in that：The step (3) compressive strength of rock and calculating of surrounding rock pressure formula in be：

σ_c=(0.0045+0.0035V_sh)E_d (6)

In formula, σ_cFor the compression strength of rock, P_cFor confined pressure, depth of the H for reservoir, α are effective stress coefficient.

As shale content V_shDuring ＞ 0.8, effective stress factor alpha=0.6；As shale content V_shDuring ＜ 0.2, effective stress factor alpha =0.9；As 0.2 ＜ V of shale content_shDuring ＜ 0.8, effective stress coefficient

4. the Forecasting Methodology according to the above-mentioned compact reservoir rock brittleness index of claim 1, it is characterised in that：The step (4) the dilative angle computing formula in is：

In formula, dilative angles of the ψ for rock,For internal friction angle, σ_cFor compressive strength of rock, P_cFor confined pressure.

5. the Forecasting Methodology according to the above-mentioned compact reservoir rock brittleness index of claim 1, it is characterised in that：The step (6) the rock brittleness index B in_IComputing formula be：

B_I=W₁E_n+W₂ψ_n (9)

In formula, B_IFor brittleness index, E_nFor normalized Young's modulus, ψ_nFor normalized dilative angle, W₁Shared by Young's modulus Weight, W₂The weight shared by dilative angle.

Wherein, E_nAnd ψ_nComputing formula it is as follows：

In formula, E, E_max, E_minThe respectively Young's modulus of stratum arbitrfary point, stratum maximum Young's modulus, stratum minimum Young mould Amount；ψ, ψ_max, ψ_minRespectively the dilative angle of stratum arbitrfary point, stratum maximum dilative angle, stratum minimum dilative angle.