According to the overall division of fault sealing evaluation and the actual requirements of the study area, the evaluation set is determined as follows:
V = {good, better, worse, worse}
According to the fault sealing evaluation standard, the fuzzy subset of evaluation index Xi to V is Ri=(ri 1, ri2, ri3, ri4).
Reservoir characteristics and fine reservoir description: taking Lao 45 1 block in Laohekou Oilfield as an example.
The fuzzy subset composed of n indicators is:
Among many evaluation factors, the difference of each evaluation factor's contribution to V must be considered, so it is necessary to determine a weighted fuzzy subset for n indicators: w = {w 1, w2, w3, ... ……Wi), and satisfy:
Reservoir characteristics and fine reservoir description: taking Lao 45 1 block in Laohekou Oilfield as an example.
Then the evaluation set:
V=W R=(b 1，b2，b3，b4)
Corresponding to b 1: good; B2: Better; B3: poor; B4； Pity.
Normalization:
Reservoir characteristics and fine reservoir description: taking Lao 45 1 block in Laohekou Oilfield as an example.
Finally, the membership values of four evaluation grades are obtained, and the evaluation grade is determined according to the maximum membership degree.
According to the main factors affecting fault sealing and the research degree of Lao 45 1 block, * * evaluation factors (X 1-X8) are selected and their values are determined (Table 3- 13 ~ Table 3- 19). According to the research purpose, the selection of indicators is mainly aimed at Sha 2.
Coefficient 1(x 1)- ratio of mudstone to total thickness;
Factor 2(x2)- the ratio of mudstone to sandstone thickness;
Factor 3(x3)- fracture dip angle;
Factor 4(x4)- Fracture mechanical properties (tensile value 0.2, tensile value 0.35, torsion value 0.5, compression value 0.8, compression value1.0);
Factor 5 (X5)-the matching relationship between fault occurrence and stratum occurrence (normal fault value is 0.5, inverse normal fault value is 0.9, and arc inverse normal fault value is1.0);
Factor 6(X6)- The value is 0.3 when matched, 0.7 when unmatched, and 1.0 when unmatched.
Factor 7(X7)—— Profile lithology configuration (sandstone and mudstone configuration 1.0, sandstone and sandy mudstone configuration 0.75, sandstone and argillaceous sandstone configuration 0.5, sandstone and sandstone configuration 0).
Factor 8(X8)—— Mudstone pollution factor, SSF >；; 0.2≤SSF≤4 at 4 o'clock and 0.5 at SSF.
Table 3- 13 Data Sheet of Sand and Mud or Mud-Sand Thickness Ratio of Main Fractures in Lao 45 1 Block
Table 3- 14 Lithologic Configuration of Main Fault Sections in Lao 45 1 Block
Table 3- 15 Lithologic Configuration of Main Fault Sections in Lao 45 1 Block
Table 3- 16 Data Table of Dip Angle Change of Main Faults in Lao 4 15 Block
Table 3- 17 Matching relationship between main fault active period and hydrocarbon migration period in Lao 45 1 block
Table 3- 18 Main fracture mechanical properties of Lao 4 15 block (current stress action)
Table 3- 19 Lao 45 1 Block Relationship between Main Fault Occurrence and Formation Occurrence Structure
According to the analysis of fault structure, stress state and oil and gas geological characteristics in the study area, the evaluation standard of this area is determined as shown in Table 3-20.
Table 3-20 Evaluation Criteria for Fault Sealing
On the basis of comprehensive analysis of the influence degree of various indicators and factors on the fracture sealing in the study area, we give weight to eight indicators according to their importance and meet them, as shown in Table 3-2 1.
Table 3-2 1 Weight of evaluation index
On the basis of the above data analysis, the fuzzy comprehensive evaluation program is used for calculation, and the evaluation results are as follows (Table 3-22):
Table 3-22 Comprehensive Evaluation Results of Fault Sealing in Lao 45 1 Block by Fuzzy Mathematics
Through the comprehensive evaluation of the main fault sand bodies in Lao 45 1 block, it is concluded that the sand bodies to the east of Lao 45 1 ~ 3, to the south of Lao 45 1, 2,4 ~ 6, and to the east of Lao 45 fault 650. Some sand bodies such as No.4, No.5 and No.6 of Lao 45 1 Jingnan fault failed to accumulate oil and gas due to improper attitude configuration; Well No.3 of Lao 45 South Fault, Lao 3 1 South Fault 1 Well and Lao 45 1 South Fault No.3 have good sealing performance. No.4 sand body of Lao 45 1 well east 1 fault, No.3 1 well south1sand body, No.2 sand body south of Lao 45 well and No.4 sand body east of Lao 45 well have poor fracture sealing. No.2 and No.3 sand bodies in the east fault of Lao 45 well have the worst sealing property.
It should be noted that the quantitative evaluation of fault sealing by using fuzzy mathematics and other calculation methods is still in the trial and exploration stage, and its research methods need to be gradually improved. At the same time, the method of fuzzy mathematics is the comprehensive effect of various factors, which determines that there is a strong subjectivity in the process of using this method to distinguish. It is inevitable that different people will have certain differences in the selection of various factors because of their different mastery of information and depth of understanding of research fields. In addition, due to the objective differences in research fields and the differences in researchers' own understanding, the contributions of various factors to the calculation results will inevitably vary greatly. Only when the geological understanding of the work area is mature enough and the evaluation results are actually compared can we finally approach the expected goal of quantitative evaluation of fault sealing.