Prediction of Favorable Zones in Low-Permeability Reservoirs Based on Classification of Diagenetic Facies：A Case Study of the Yan-9 Member in the H65 Block，Ordos Basin

doi:10.7657/XJPG20260404

Abstract

Abstract:

There is a close relationship between diagenetic facies and distribution of high-quality reservoirs. Logging interpretation of diagenetic facies is crucial for predicting favorable zones in low-porosity and low-permeability reservoirs. The diagenetic facies were classified after analyzing the data of cast thin sections, scanning electron microscopy (SEM), high-pressure mercury intrusion (HPMI), and physical property tests. Using logging data, the diagenetic facies were classified across the study area from the prospective of coring wells, full hole of individual wells, and target intervals by integrating the Fisher discriminant method with the dominant facies method. On this basis, the favorable zones were predicted. The results show that the ninth member of the Lower Jurassic Yan’an formation (Yan-9 member) in the H65 block of the southern Tianhuan depression, is represented by low-porosity and low-permeability, fine-pore and fine-throat reservoirs. These reservoirs are dominated by lithic quartz sandstone, with low cement content. The storage space is mostly composed of feldspar dissolved pores-intergranular pores, with uneven distribution of pore throats and poor connectivity. In the diagenetic transformation stage, compaction led to a significant reduction in porosity, by a rate up to 44.57%, thus being the main destructive factor. In contrast, dissolution improved the porosity only by 3.01%, suggesting a limited contribution to the optimization of pore throat connectivity and the expansion of storage space. Six types of diagenetic facies are identified in the study area, including intergranular pore facies, feldspar dissolved pore-intergranular pore facies, feldspar dissolved pore facies, kaolinite cementation facies, carbonate cementation facies, and mechanical compaction facies. Based on the classification of diagenetic facies by using the Fisher discriminant method across the study area, it is believed that the central and central-southern parts of the study area hold favorable conditions of diagenetic facies for oil and gas accumulation, and thus can be considered as the targets for subsequent exploration. The results demonstrate that the Fisher discriminant method is highly accurate in classifying diagenetic facies, thereby facilitating the prediction of favorable zones in low permeability reservoirs.

Key words: Ordos Basin, Tianhuan depression, Yan’an formation, reservoir, diagenetic facies, Fisher discriminant method, favorable zone prediction

CLC Number:

TE112.23

LIU Ting, WEI Tao, DUAN Xiaochen, CHEN Yulongzhuo, WU Dezhi, ZHU Yushuang. Prediction of Favorable Zones in Low-Permeability Reservoirs Based on Classification of Diagenetic Facies：A Case Study of the Yan-9 Member in the H65 Block，Ordos Basin[J]. Xinjiang Petroleum Geology, 2026, 47(4): 416-424.

Figures/Tables 12

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Table 2.

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Table 3.

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层位	粒间孔面孔率		粒间溶孔面孔率		长石溶孔面孔率		岩屑溶孔面孔率		晶间孔面孔率		总面孔率
层位	平均值	占比	平均值	占比	平均值	占比	平均值	占比	平均值	占比	总面孔率
延9₁小层	7.4	76.8	0.4	3.9	1.4	14.3	0.3	2.9	0.2	2.1	9.7
延9₂小层	4.8	57.1	0	0	2.6	31.0	0.6	7.1	0.4	4.8	8.4
延9段	6.1	67.8	0.2	2.2	2.0	22.2	0.4	4.4	0.3	3.3	9.0

成岩相类型	自然伽马/API	声波时差/（μs·m^-1）	补偿中子/%	密度/（g·cm^-3）	电阻率/（Ω·m）
粒间孔相	23.1~41.0（31.4）	226.7~249.0（236.4）	15.0~16.9（15.8）	2.33~2.42（2.35）	11.6~13.5（12.7）
长石溶孔-粒间孔相	33.3~37.1（34.6）	229.7~239.1（234.1）	15.1~16.6（16.0）	2.35~2.42（2.38）	10.0~12.5（11.3）
长石溶孔相	33.2~55.9（42.5）	217.3~237.5（233.3）	10.3~18.5（15.2）	2.36~2.41（2.39）	8.3~10.7（9.0）
高岭石胶结相	35.7~62.3（50.8）	225.0~232.9（230.0）	9.9~15.3（12.6）	2.29~2.38（2.37）	4.3~6.7（5.0）
碳酸盐胶结相	39.5~45.8（42.7）	227.7~231.3（229.5）	12.2~13.8（12.5）	2.36~2.45（2.40）	6.8~12.5（10.6）
机械压实相	51.6~74.9（65.5）	222.3~228.9（226.2）	9.1~12.5（10.5）	2.34~2.43（2.37）	5.5~10.1（7.2）

成岩相类型	Fisher判别函数
粒间孔相	F1=0.579q_API+16.121Δt-10.283${\varphi }_{N}$+2 777.046ρ+30.904R_t-5 210.233
长石溶孔-粒间孔相	F2=0.407q_API+15.822Δt-9.617${\varphi }_{N}$+2 803.496ρ+31.92R_t-5 213.65
长石溶孔相	F3=0.529q_API+16.299Δt-10.599${\varphi }_{N}$+2 795.477ρ+31.089R_t-5 289.77
高岭石胶结相	F4=0.387q_API+15.606Δt-9.49${\varphi }_{N}$+2 712.607ρ+30.139R_t-4 940.17
碳酸盐胶结相	F5=0.463q_API+15.788Δt-9.607${\varphi }_{N}$+2 769.833ρ+30.829R_t-5 120.637
机械压实相	F6=0.711q_API+16.326Δt-11.104${\varphi }_{N}$+2 779.619ρ+31.453R_t-5 262.03