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| Source-rock-derived diagenetic evolution and origin of calcareous interlayer in reservoirs of well N1 in the northern Qaidam Basin |
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WANG Aiguo1,2, WANG Zhenliang1,2, LENG Xiangang3, WU Xiaoning3, PU Lei3, YUAN Xu4, HUI Tao4, ZHAO Jian5
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(1.National ＆ Local Joint Engineering Research Center for Carbon Capture and Sequestration Technology, Xi 'an 710069, China;2.Department of Geology in Northwest University, Xi 'an 710069, China;3.Changqing Oilfield Company, PetroChina, Xi 'an 710021, China;4.Shaanxi Yanchang Petroleum International Exploration and Development Engineering Company Limited, Xi 'an 710075, China;5.Qinghai Oilfield Company, CNPC, Dunhuang 736202, China)
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| Abstract: |
| Taking well N1 in the northern Qaidam Basin as an example, the formation of one type of calcareous interlayer in burial diagenetic stage was investigated using microscopic observation and geochemical analysis. The results show that the calcareous interlayers in the sandstone reservoir of well N1 are thermal degraded by the source rocks as calcite cementation (Ca1 and Ca2), which contain minor bitumen-stained kaolinite. The corrosion of adjacent porous interlayers is strong, and the residual calcite, kaolinite, as well as two episodes of bitumen (Hy1, Hy2) can be observed. The calcareous interlayers are not generated by direct precipitation of calcite, but it is a result of diagenetic evolution (Kaolinite-Hy1-Ca1-dissolution/kaolinite-Hy2-Ca2) which is controlled by two epiosodes of hydrocarbon generation and expulsion in source rocks. In other words, the calcareous interlayers in well N1 results from the superposition of early-stage dissolution-generated Ca1-type and late-stage Ca2-type calcareous interlayers. |
| Key words: Qaidam Basin diagenesis diagenetic evolution calcareous interlayers |
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