Loose sandstone heavy oil reservoir classification evaluation method

Abstract

The invention relates to the technical field of heavy oil reservoir development, in particular to a loose sandstone heavy oil reservoir classification evaluation method, which comprises the following steps of: quantitatively depicting reservoir sand production strength in a research area by adopting a sand production index; according to the sand production boundary, a sand production grade is established by adopting an equal division method, and sand production grade evaluation is carried out on drilling wells in the research area; determining the weight of the influence of three factors including the sand production index, the crude oil viscosity and the oil saturation of the oil layer on the single well productivity; establishing a comprehensive influence factor according to the sand production index, the crude oil viscosity and the oil saturation of the oil layer, determining a reservoir comprehensive classification standard according to the comprehensive influence factor and the productivity relation chart, and performing comprehensive evaluation on the reservoir in the research area; and guiding actual production according to the sand production grade and the comprehensive evaluation result. According to the method, a theoretical basis is provided for effective utilization of the oil reservoir, perforation and reservoir transformation operation can be guided in actual production, and a reference is provided for a reservoir process transformation mode and scale.

Description

Technical Field

[0001] The invention relates to the technical field of heavy oil reservoir development, and is a classification and evaluation method for a loose sandstone heavy oil reservoir. Background Art

[0002] The medium and deep layers of the Junggar Basin have considerable heavy oil resources. The resources in the Jimusar Sag, Fudong Slope, and the Wuxia-Kebai-Hongche Fault Zone on the northwestern edge of the Junggar Basin can reach 320 million tons. The construction of medium and deep heavy oil production plays a vital role in the adjustment of the heavy oil production structure, and is also an important measure for the transformation of heavy oil to green and low-carbon development. However, due to the complexity of the main controlling factors affecting production capacity, the difficulty of reservoir classification and evaluation, the lack of supporting effective process production technology, and the difficulty of efficient development. There are the following disadvantages: ① The reservoir physical properties are poor. The rock cementation type of this type of sandstone and conglomerate reservoir is contact cementation, the degree of cementation is medium-loose, easy to sand, and the reservoir clay mineral content is high, strong water sensitivity and strong velocity sensitivity; porosity Φ: 5% to 15%, permeability K: 5×10 -3 μm 2 Up to 50×10 -3 μm 2 , which is a loose, low-permeability, low-porosity, and highly heterogeneous reservoir. ② High crude oil viscosity: density ρ: >0.934, viscosity η>50, crude oil is heavy and viscous oil, and conventional water injection gravel reservoir evaluation methods are difficult to adapt. ③ Large differences in oil layer thickness: Under the background of fluvial phase deposition, the reservoir changes rapidly laterally. ④ Deep buried oil layer: Conventional thermal oil production evaluation and production methods are difficult to adapt to the characteristics of deep viscous oil reservoirs. Summary of the invention

[0003] The present invention provides a method for classifying and evaluating a loose sandstone heavy oil reservoir, which overcomes the deficiencies of the above-mentioned prior art and can effectively solve the problem that the existing reservoir classification and evaluation methods and parameters are difficult to meet the evaluation and production needs of medium- and deep-layer loose sandstone heavy oil reservoirs.

[0004] The technical solution of the present invention is achieved by the following measures: A classification and evaluation method for a loose sandstone heavy oil reservoir is carried out according to the following steps:

[0005] The first step is to use the sand production index to quantitatively describe the sand production intensity of the reservoir in the study area;

[0006] The second step is to establish a relationship chart between the sand production index and the sand settling rate in the wellbore, determine the sand production limit, establish the sand production grade by using the equal division method according to the sand production limit, and evaluate the sand production grade of the wells in the study area;

[0007] The third step is to conduct a multi-factor correlation analysis between the sand production index, crude oil viscosity, and oil saturation of the reservoir and the single well production capacity, and determine the weights of the three factors of sand production index, crude oil viscosity, and oil saturation on the single well production capacity;

[0008] The fourth step is to calculate the comprehensive impact factor based on the sand production index, crude oil viscosity, oil saturation value and weight coefficient, establish the comprehensive classification standard of reservoirs based on the relationship chart between the comprehensive impact factor and production capacity, and conduct a comprehensive evaluation of the reservoirs in the study area;

[0009] The fifth step is to guide the actual production according to the sand production grade and comprehensive evaluation results.

[0010] The following are further optimizations and / or improvements to the above technical solutions:

[0011] In the first step above, the sand production index is calculated by the following formula:

[0012] B=k+4μ / 3=13400ρ / Δtp 2 Formula 1

[0013] Where B is the sand production index, dimensionless; k is the bulk modulus, Pa; μ is the shear coefficient, dimensionless; ρ is the rock density, mg / cm 3 ; Δtp 2 is the longitudinal wave time difference, μS / ft.

[0014] In the second step above, the sand production limit is the maximum value of the sand production index in the sand producing wells in the study area.

[0015] In the second step above, the specific operation of establishing the sand production grade by the equal division method according to the sand production limit is as follows: through accurate statistics of the wellbore sand settling rates of multiple well repairs in the study area, a relationship chart between the sand production index and the sand settling rate is established, and the boundary linear fitting is performed to determine the sand production rate boundary. For areas where the reservoir sand production index is less than the sand production limit, the equal division method is used, and three sand production grades are divided according to the sand production limit.

[0016] The three sand production levels divided according to the sand production boundaries are respectively weak sand production section, moderate sand production section and strong sand production section.

[0017] In the fourth step above, the comprehensive impact factor is calculated according to the following formula:

[0018] K=A*N1+B*N2+C*N3 Formula 2

[0019] Where A is the oil saturation of the oil layer, B is the sand production index, C is the viscosity of the crude oil, and N1, N2, and N3 are coefficients.

[0020] In the fifth step mentioned above, in actual production, the perforation operation is guided according to the sand production grade, and the perforation avoids the strong sand production section, which fundamentally reduces the risk of sand production in the oil layer; the sand control strength is evaluated according to the sand production index, and the reservoir transformation ideas are judged based on the comprehensive evaluation results to guide the selection of construction displacement and fracturing scale.

[0021] The present invention establishes a comprehensive classification and evaluation method for medium-deep loose low-permeability sandstone heavy oil reservoirs. According to the characteristics of medium-deep loose sandstone heavy oil reservoirs, the method takes into account multiple factors such as reservoir sand production and crude oil viscosity, improves the accuracy of reservoir classification and evaluation, provides a theoretical basis for the effective utilization of oil reservoirs, can guide perforation and reservoir transformation operations in actual production, and provide a reference for the method and scale of reservoir process transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Attached Figure 1 It is a flow chart of the technical solution of the present invention.

[0023] Attached Figure 2 This is a relationship diagram between the cumulative oil production and sand production index of the oil producing wells in the North 10 well area in Example 8 of the present invention.

[0024] Attached Figure 3 This is a sand classification chart for the Toutunhe Formation reservoir in the North 10 well area in Example 8 of the present invention.

[0025] Attached Figure 4 This is a fitting relationship diagram between the comprehensive impact factor K of a single well in the North 10 well area and the initial (self-flowing) production capacity in Example 8 of the present invention. DETAILED DESCRIPTION

[0026] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0027] The present invention will be further described below in conjunction with embodiments:

[0028] Example 1: The loose sandstone heavy oil reservoir classification evaluation method is carried out according to the following steps:

[0029] The first step is to use the sand production index to quantitatively describe the sand production intensity of the reservoir in the study area;

[0030] The second step is to establish a relationship chart between the sand production index and the sand settling rate in the wellbore, determine the sand production limit, establish the sand production grade by using the equal division method according to the sand production limit, and evaluate the sand production grade of the wells in the study area;

[0031] The third step is to conduct a multi-factor correlation analysis between the sand production index, crude oil viscosity, and oil saturation of the reservoir and the single well production capacity, and determine the weights of the three factors of sand production index, crude oil viscosity, and oil saturation on the single well production capacity;

[0032] The fourth step is to calculate the comprehensive impact factor based on the sand production index, crude oil viscosity, oil saturation value and weight coefficient, establish the comprehensive classification standard of reservoirs based on the relationship chart between the comprehensive impact factor and production capacity, and conduct a comprehensive evaluation of the reservoirs in the study area;

[0033] The fifth step is to guide the actual production according to the sand production grade and comprehensive evaluation results.

[0034] Example 2: As an optimization of the above example, in the first step, the sand production index is calculated by the following formula:

[0035] B=k+4μ / 3=13400ρ / Δtp 2 Formula 1

[0036] Where B is the sand production index, dimensionless; k is the bulk modulus, Pa; μ is the shear coefficient, dimensionless; ρ is the rock density, mg / cm 3 ; Δtp 2 is the longitudinal wave time difference, μS / ft.

[0037] Based on the comparison of various interpretation methods, the present invention selects the sand production index to quantitatively characterize the sand production intensity of the reservoir. The larger the sand production index B is, the greater the rock strength and stability are, and it is not easy to produce sand. Otherwise, it is easy to produce sand.

[0038] Embodiment 3: As an optimization of the above embodiment, in the second step, the sand production limit is the maximum value of the sand production index in the sand producing wells in the study area.

[0039] Example 4: As an optimization of the above example, in the second step, the specific operation of establishing the sand production grade by using the equal division method according to the sand production limit is as follows: through accurate statistics of the wellbore sand settling rates of multiple well repairs in the study area, a relationship chart between the sand production index and the sand settling rate is established, and the boundary linear fitting is performed to determine the sand production rate boundary. For areas where the reservoir sand production index is less than the sand production limit, the equal division method is used, and 3 sand production grades are divided according to the sand production limit.

[0040] Embodiment 5: As an optimization of the above embodiment 4, three sand production levels are divided according to the sand production boundary, namely, weak sand production section, moderate sand production section and strong sand production section.

[0041] Embodiment 6: As an optimization of the above embodiment, in the fourth step, the comprehensive impact factor is calculated according to the following formula:

[0042] K=A*N1+B*N2+C*N3 Formula 2

[0043] Where A is the oil saturation of the oil layer, B is the sand production index, C is the viscosity of the crude oil, and N1, N2, and N3 are weight coefficients respectively.

[0044] Example 7: As an optimization of the above example, in the fifth step, in actual production, the perforation operation is guided according to the sand production level, and the perforation avoids the strong sand production section, which fundamentally reduces the risk of sand production in the oil layer; the sand control strength is evaluated according to the sand production index, and the reservoir transformation idea (mainly fracturing or mainly sand control) is judged according to the comprehensive evaluation results to guide the selection of construction displacement and fracturing scale.

[0045] The present invention provides a reservoir classification evaluation method for loose sandstone heavy oil reservoirs in medium and deep layers. The method aims at the sand production problem of oil reservoirs, compares a variety of interpretation methods, and selects a sand production index to quantitatively characterize the sand production intensity of the reservoir. A multi-factor correlation analysis is performed on the three influencing factors of oil well sand production, crude oil viscosity and oil saturation of the oil layer. According to the comprehensive classification standard of reservoirs combined with actual conditions, the reservoirs are divided into three categories. The method of the present invention is used to carry out reservoir classification evaluation and prediction in the region, and the degree of consistency of production capacity prediction is high, which provides a theoretical basis for the effective use of oil reservoirs. According to the evaluation results of the present invention, combined with the logging interpretation and further combined with the simulation of the characteristic parameters of the geostatistical inversion, the distribution rules of various oil layers in the study area on the plane can be further grasped. In actual production, the perforation and reservoir transformation operations are guided. According to the comprehensive classification of the reservoir, the quality of the reservoir can be intuitively determined, and a reference can be provided for the reservoir process transformation method and scale.

[0046] Example 8: The loose sandstone heavy oil reservoir classification evaluation method is used to evaluate the oil reservoir in the North 10 well area of ​​Xinjiang Oilfield. The specific operations are as follows:

[0047] Data collation and preparation: The required data include: tight reservoir rock properties, oil layer resistivity, logging characteristic parameters, production well parameters and target well production history. The rock properties include reservoir permeability, porosity, and oil saturation; the production well parameters include drilling, fracturing and completion parameters; the target well production history includes the initial daily oil production of the block, the average daily oil production in the first year, etc.

[0048] Taking the Jurassic Toutunhe Formation reservoir in the North 10 well area of ​​Xinjiang Oilfield as an example, combined with the production situation of a single well on site, the lower the sand production of a single well, the smaller the impact of formation sand on production, the longer the production time, and the higher the cumulative oil production of a single well in one year. The one-year cumulative oil production and sand production index show that the sand production index is consistent with the actual sand production of a single well on site (see Figure 1 ).

[0049] Sand production is considered to be the main factor affecting productivity, and the sand production index is used to quantitatively characterize the sand production intensity of the reservoir. The study determined that the sand production limit of the well area is 2.96, that is, B < 2.96 is prone to sand production. Through the precise statistics of the sand settling rate of 12 well repairs in 10 wells (95% of the total number of wells) in the well area, a relationship chart between the sand production index and the sand settling rate was established ( Figure 3 ).like Figure 3As shown in the figure, quantitative evaluation of sand production is carried out through boundary linear fitting. The upper boundary oblique line represents the maximum value of sand production rate under specific sand production index conditions. The sand production limit (i.e. the maximum value of reservoir sand production index in the current sand production well) is determined by the boundary data points. When the reservoir sand production index is greater than the sand production limit, there is no sand production. When the reservoir sand production index is less than the sand production limit, the equal division method is used to divide the sand production into three grades (weak sand production section, moderate sand production section, and strong sand production section, respectively). The results are shown in Table 1. This chart can be used to evaluate the reservoir sand production grade of all wells in the entire area.

[0050] During the oil testing and production test of the Toutunhe Formation reservoir in the North 10 well area, some oil wells produced serious sand. The high viscosity of crude oil and the large difference in oil content have a comprehensive impact on the effective use of reserves. Through the multivariate linear regression method, it was determined that the main factor affecting production capacity is sand production in the oil well, followed by oil content and crude oil viscosity. The weights of the three factors on the single well production capacity are 0.6012, 0.2027, and 0.1961 respectively. Introducing the comprehensive influencing factor K, the calculation formula of the comprehensive influencing factor is:

[0051] K=A*N1+B*N2+C*N3(N1=0.2027, N2=0.6012, N3=0.1961)

[0052] The comprehensive influencing factor K was fitted with the initial self-flowing capacity of the oil well, which showed that the comprehensive influencing factor K had a high correlation with the initial self-flowing capacity of the oil well, with a correlation coefficient of 0.724 (see Figure 3 ). According to the comprehensive influencing factor K, the comprehensive classification standard of reservoirs is established (see Table 2), and the comprehensive classification evaluation standard of Toutunhe Formation reservoirs in Bei 10 well area is established.

[0053] On the basis of reservoir sand production grade evaluation and comprehensive reservoir evaluation, we selectively select perforation sections, optimize transformation measures, predict oil well productivity, and determine production increase targets and potential based on single well productivity prediction and actual production conditions.

[0054] The present invention avoids the shortcoming of low logging interpretation accuracy caused by existing reservoir classification, and further quantitatively characterizes the sand production intensity of the reservoir in combination with the actual sand production situation on site, and screens out high-quality reservoirs; the present invention is used to transform the reservoir in a targeted manner based on the result of reservoir classification, and the oil well production rate reaches more than 80%, with good results; the method of the present invention is used to predict the oil production capacity of a single well oil layer, calculate the theoretical production capacity of the oil well, compare it with the current actual production situation of the oil well, and verify it in field applications, with an error within ±10%.

[0055] In summary, the present invention establishes a comprehensive classification and evaluation method for medium-deep loose sandstone heavy oil reservoirs based on the characteristics of medium-deep loose sandstone heavy oil reservoirs, taking into account various factors such as reservoir sand production and crude oil viscosity. The present invention provides a theoretical basis for the effective use of oil reservoirs, can guide perforation and reservoir transformation operations in actual production, and provide a reference for the method and scale of reservoir process transformation.

[0056] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

[0057] Table 1

[0058]

[0059] Table 2

[0060] Method Name Class I (good) Category II (moderate) Class III (poor) Comprehensive Impact Factor Method (≥10.54) (9.04-10.54) (6.04-9.04)

Claims

1. A classification and evaluation method for loose sandstone heavy oil reservoirs, characterized in that Follow these steps: The first step is to use the sand production index to quantitatively describe the sand production intensity of the reservoir in the study area; The second step is to establish a relationship chart between the sand production index and the sand settling rate in the wellbore, determine the sand production limit, establish the sand production grade by using the equal division method according to the sand production limit, and evaluate the sand production grade of the wells in the study area; The third step is to conduct a multi-factor correlation analysis between the sand production index, crude oil viscosity, and oil saturation of the reservoir and the single well production capacity, and determine the weights of the three factors of sand production index, crude oil viscosity, and oil saturation on the single well production capacity; The fourth step is to calculate the comprehensive impact factor based on the sand production index, crude oil viscosity, oil saturation value and weight coefficient, establish the comprehensive classification standard of reservoirs based on the relationship chart between the comprehensive impact factor and production capacity, and conduct a comprehensive evaluation of the reservoirs in the study area; The fifth step is to guide the actual production according to the sand production grade and comprehensive evaluation results.

2. The method for classifying and evaluating a loose sandstone heavy oil reservoir according to claim 1, characterized in that In the first step, the sand production index is calculated by the following formula: B=k+4μ / 3=13400ρ / Δtp 2 formula 1 Where B is the sand production index, dimensionless; k is the bulk modulus, Pa; μ is the shear coefficient, dimensionless; ρ is the rock density, mg / cm 3 ; Δtp 2 is the longitudinal wave time difference, μS / ft.

3. The method for classifying and evaluating a loose sandstone heavy oil reservoir according to claim 1 or 2, characterized in that In the second step, the sand production limit is the maximum value of the sand production index among the sand producing wells in the study area.

4. The method for classifying and evaluating a loose sandstone heavy oil reservoir according to any one of claims 1 to 3, characterized in that In the second step, the specific operation of establishing the sand production grade by the equal division method according to the sand production limit is as follows: through the accurate statistics of the wellbore sand settling rate of multiple well repairs in the study area, a relationship chart between the sand production index and the sand settling rate is established, and the boundary linear fitting is performed to determine the sand production rate boundary. For areas where the reservoir sand production index is less than the sand production limit, the equal division method is used, and three sand production grades are divided according to the sand production limit.

5. The method for classifying and evaluating a loose sandstone heavy oil reservoir according to claim 4, characterized in that The three sand production levels divided according to the sand production boundary are weak sand production section, moderate sand production section and strong sand production section.

6. The method for classifying and evaluating a loose sandstone heavy oil reservoir according to any one of claims 1 to 5, characterized in that In the fourth step, the comprehensive impact factor is calculated according to the following formula: K=A*N1+B*N2+C*N3 Formula 2 Where A is the oil saturation of the oil layer, B is the sand production index, C is the viscosity of the crude oil, and N1, N2, and N3 are weight coefficients respectively.

7. The method for classifying and evaluating a loose sandstone heavy oil reservoir according to any one of claims 1 to 6, characterized in that In the fifth step, in actual production, the perforation operation is guided according to the sand production grade, and the perforation is avoided in the strong sand production section, which fundamentally reduces the risk of sand production in the oil layer; the sand control strength is evaluated according to the sand production index, and the reservoir transformation ideas are judged based on the comprehensive evaluation results to guide the selection of construction displacement and fracturing scale.

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