Source-to-sink System and Reservoir Property Variation of the Second Member of Liushagang Formation in the Southern Steep Slope, Wushi Sag

doi:10.19657/j.geoscience.1000-8527.2018.06.05

Abstract

Abstract:

In recent years, the southern steep slope of the Wushi Sag has become an important oil-gas exploration target in the Beibuwan Basin, in which the second member of the Liushagang Formation is considered as the main target layer. To identify the distribution pattern of sand and favorable reservoirs, we conducted detailed source-to-sink and fracture system analyses, discussed the coupled fracture-provenance deposition controls and the main factors of favorable reservoir distribution, based on comprehensive analyses of drilling and seismic data. The results reveal an obvious lake retreat in the middle bed of the Liushagang Formation second member, which developed a fan delta system. The slope-break and F7 fault zone likely controlled the development of medium-large fan delta systems in this area, and we have summarized three types of structurally deposition control patterns. Parent lithologic differences are likely the main cause for the reservoir dissolution. The main parent rock type in the central and western districts is magnetite granite. Its sediments contain less stable minerals such as K-feldspar, which formed dissolved pores and improved the physical properties of the reservoir. The above analysis shows that the central and western districts are favorable exploration areas due to the large fan delta development and good reservoir physical properties.

Key words: Wushi Sag, the second member of Liushagang Formation, source-to-sink system, sedimentary system, reservoir property variation, dissolution

CLC Number:

TE122

HE Weijun, XU Wanxing, LIU Juan, LIU Fang, JIAO Xiangyan. Source-to-sink System and Reservoir Property Variation of the Second Member of Liushagang Formation in the Southern Steep Slope, Wushi Sag[J]. Geoscience, 2018, 32(06): 1161-1172.

Figures/Tables 10

Fig.1 Structural outline and division of tectonic units at the Wushi Sag

Fig.2 Distribution and activity analysis of F7 fault at the Wushi Sag

Fig.3 Characteristics of heavy mineral assemblages, parent-rock types and paleocurrent direction of drill holes in the study area

Fig.4 Seismic cross section of the northern margin of the Liusha Bulge (location shown in Fig.1)

Fig.5 Grain-size probability curves (a) and C-M diagram (b) of the fan delta of the Liushagang Formation second member

Fig.6 Characteristics of sidewall core and resistivity imaging of well W17-5b

Fig.7 Seismic cross section of the fan delta in the southern steep slope, Wushi Sag (location shown in Fig.1)

Fig.8 Development pattern and sand-controlling model of F7

Fig.9 RMS amplitude and sedimentary facies map of the Liushagang Formation second member in the southern steep slope, Wushi Sag

Fig.10 Reservoir physical characteristics of the Liushagang Formation second member in the southern steep slope, Wushi Sag

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