Reservoir Characteristics of Permian Lower He 8 Member in Longdong Area, Ordos Basin

doi:10.19657/j.geoscience.1000-8527.2021.04.028

Abstract

Abstract:

The Longdong area is a new natural gas exploration zone in the Upper Paleozoic Ordos Basin. The Permian Lower Shihezi Formation (lower He 8 gas member) is the main gas-producing layer. The local deposition, reservoir and accumulation are relatively complex, and the level of understanding in the natural gas exploration is relatively low. Combining logging data, core observation, thin-section, physical properties and other data, we investigated the petrological characteristics, physical properties, and pore structural characteristics of the lower He 8 reservoir of the Lower Shihezi Formation in the southwestern Ordos Basin, and we discuss the main controlling factors on the reservoir performance. The results show that the reservoir sandstones of the lower He 8 are dominated by quartz sandstone and lithic quartz sandstone. Arkose content is low, suggestive of a high-energy and distal-source environment. During diagenesis, sandstone reservoirs may have undergone intense compaction and pressure dissolution, and the clastic particles and lithic fragments are interlocked with each other, accompanied by different degrees of quartz regrowth, and the disappearance of large number of primary intergranular pores. The pore types include mainly micro-sized intragranular pores and rock chip-dissolved pores. The reservoir physical properties are controlled by both the sedimentary facies and diagenesis. Sedimentary facies fundamentally control the reservoir physical properties. The sand-body structure has an important impact on the reservoir physical properties. The physical properties of the cut-type single sand-body are relatively good, followed by the spliced sand-body, and then by isolated single sand-body. Compaction is the main reason for the densification of the layer physical properties. Hydromica is the primary factor for the densification of the reservoir due to cementation. The degree of reservoir dissolution is low and the improving effect on the reservoir quality is limited. Our results provide a reliable geological basis and scientific basis for the further exploration and development of the lower He 8 reservoir at Longdong.

Key words: reservoir characteristics, reservoir physical properties, lower He 8 reservoir, major controlling factor, Ordos Basin

CLC Number:

TE122.2

CUI Gaixia, WEI Qinlian, XIAO Ling, WANG Song, HU Rong, WANG Chonghuan. Reservoir Characteristics of Permian Lower He 8 Member in Longdong Area, Ordos Basin[J]. Geoscience, 2021, 35(04): 1088-1097.

Figures/Tables 15

Fig.1 Map showing the study area at Longdong, Ordos Basin

Fig.2 Distribution characteristics of reservoir rock types in the lower section of He 8 at Longdong

Fig.3 Reservoir rock types in the lower section of He 8 at Longdong

Fig.4 Pie chart of interstitial content of reservoirs in the lower section of He 8 at Longdong

Fig.5 Histogram of reservoir pore types in the lower section of He 8 at Longdong

Fig.6 Micro-pore characteristics of reservoirs in the lower section of He 8 at Longdong

Fig.7 Sandstone pore structure types of reservoirs in the lower section of He 8 at Longdong

Fig.8 Distribution frequency map of reservoir porosity and permeability in the lower section of He 8 at Longdong

Fig.9 Relations between porosity and permeability of the lower He 8 reservoir at Longdong

Table 1 Relations between sedimentary microfacies and reservoir physical properties of the lower He 8 reservoir at Longdong

沉积亚相	沉积微相	岩性	沉积构造	孔隙度/%	渗透率/10^-3 μm²
三角洲平原	分流河道	细砂岩,中上部由粉砂岩和泥质粉砂岩组成	板状、槽状交错层理	9.6	0.53
三角洲平原	分流间洼地	粉砂岩,泥质粉砂岩	水平层理、沙纹层理	5.63	0.06
三角洲前缘	水下分流河道	细砂到中粗砂岩	槽状层理、沙纹层理、板状层理及平行层理等	10.58	0.54
三角洲前缘	分流间湾	泥岩、粉砂质泥岩	水平层理、波状层理	3.83	0.023
浅湖亚相	浅湖砂坝	浅灰色中、细粒砂岩	波状层理、浪成砂纹层理、斜波状交错层理以及搅动变形层理、虫孔等	8.63	0.48
浅湖亚相	浅湖泥	深灰、灰黑色泥岩及粉砂质泥岩	微波状层理、水平层理及互层型层理发育	3.46	0.05

Fig.10 Reservoir lithology-physical relations of the lower He 8 reservoir at Longdong

Fig.11 Scatter plot of pore-permeability relations of sand-bodies with different structures

Fig.12 Relations between intergranular volume and cement content of reservoirs in the lower section of He 8 at Longdong

Fig.13 Relations between the content of various cement types and borehole ratio in the lower section of He 8 at Longdong

Fig.14 Relations between the dissolved pore content and borehole ratio of various reservoir types in the lower section of He 8 at Longdong

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