Saturation Calculation Model With Variable Rock-Electrical Parameters for Tight Sandstone Reservoirs: A Case Study of the Shihezi Formation (8th Member) in Western Sulige Gas Field

doi:10.19657/j.geoscience.1000-8527.2021.183

Abstract

Abstract:

Tight sandstone reservoirs are one of the major regions for oil and gas exploration. Due to the characteristics of low porosity and permeability, complex pore structure, and strong heterogeneity in rock electrical parameters, logging interpretation process for tight sandstone reservoirs is different from that of conventional reservoirs. When interpreting tight sandstone reservoirs with the Archie formula, strong heterogeneity would lead to changes in the rock electrical parameters a, b, m and n with different reservoirs. In this study, a saturation model is established by using the variable rock electrical parameters for the tight sandstone reservoir in the Shihezi Formation (8^th member) in the western Sulige gas field. According to the rock-electrical experiment on 25 cores, we found that the relationship between cementation coefficient m and lgϕ is a quadratic function, the relationship between m and lithology coefficient a is a power function, and the irreducible water saturation S_wb has major influence on the saturation index n. Therefore, based on the analysis of porosity, irreducible water saturation and pore structure index, the saturation model with variable rock electrical parameters is established by integrating the various influence factors. The results show that the accuracy of this method is higher than that of the traditional Archie formula, which is effective for interpreting complex pore structure sandstone reservoirs.

Key words: tight sandstone, Archie formula, variable rock-electric parameter, saturation model, Sulige gas field

CLC Number:

TE122.2

LU Junhui, ZHANG Xiaoli, YANG Zhen, LI Yajun, WANG Xiaolin, ZHAO Xi. Saturation Calculation Model With Variable Rock-Electrical Parameters for Tight Sandstone Reservoirs: A Case Study of the Shihezi Formation (8^th Member) in Western Sulige Gas Field[J]. Geoscience, 2022, 36(04): 1131-1137.

Figures/Tables 11

Fig.1 Diagram of formation factors and porosity (a) and diagram of lgF and lgϕ (b)

Fig.2 m and lgϕ diagram

Fig.3 a and m diagram

Fig.4 Relationship between resistivity index and water saturation

Fig.5 Relationship between porosity and saturation index

Fig.6 Relationship between porosity structure index and saturation index

Fig.7 Relationship between bound-water saturation and saturation index

Fig.8 Relationship between natural gamma and median grain diameter

Fig.9 Relationship between experimental bound water saturation and calculated bound water saturation

Fig.10 Comparison of water saturation calculated by variable rock electric paramneters in Well S1 with that calculated by nuclear magnetic logging

Table 1 Analysis and comparison of water saturation error in Well S1

深度/m	综合解释结论	核磁含水饱和度	传统Archie公式计算含水饱和度			变岩电参数模型计算含水饱和度
深度/m	综合解释结论	核磁含水饱和度	计算值	绝对误差	相对误差/%	计算值	绝对误差	相对误差/%
3 619.0~3 621.7	气层	0.359	0.424	0.064	20.4	0.335	-0.024	5.7
3 621.7~3 628.0	气水同层	0.443	0.503	0.059	16.6	0.434	-0.009	8.2
3 635.9~3 639.0	干层	0.396	0.524	0.128	31.5	0.385	-0.011	10.6
3 639.0~3 641.4	差气层	0.315	0.438	0.122	28.6	0.343	0.027	6.9

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