Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (2): 494-508.doi: 10.11743/ogg20210218

• Petroleum Geology • Previous Articles     Next Articles

Petrologic features and diagenetic evolution of fine-grained sedimentary rocks in continental lacustrine basins: A case study on the Lower Jurassic Da'anzhai Member of Yuanba area, Sichuan Basin

Yixiu Zhu1,2(), Zhenkui Jin1,2, Ke Jin3, Qiheng Guo1,2, Huan Wang1,2, Pin Lyu1,2, Xinyao Wang1,2, Yuan Shi1,2   

  1. 1. College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China
    2. State Key Laboratory of Petroleum Resources and Prospecting, Beijing 102249, China
    3. Research Institute of Exploration and Development under Liaohe Oilfield Company, PetroChina, Panjin, Liaoning 124010, China
  • Received:2020-07-23 Online:2021-04-28 Published:2021-04-21

Abstract:

Core observation, thin section identification, scanning electron microscopy (SEM) and X-ray diffraction analysis were used to finely describe the petrological characteristics and diagenesis of fine-grained sedimentary rocks as well as to discuss rock types with hydrocarbon potential and their genesis in the Lower Jurassic Da'anzhai Member of Yuanba area in the Sichuan Basin.The results show that there are three types of rocks, namely mudstone (mudstone, conchoidal shale and calcareous mudstone), siltstone and limestone (conchoidal limestone).The main mineral components are quartz, clay minerals (dominated by illite/smectitem (I/S) mixed layer, illite, kaolinite and chlorite), calcite, feldspar and pyrite; the rock assemblages are mainly conchoidal shale and mudstone interbedded with conchoidal limestone.The fine-grained rocks, currently at the B sub-stage of the mesodiagenesis, experienced compaction, cementation, dissolution, metasomasis, recrystallization of clay minerals and hydrocarbon generation from organic matters, of which, compaction and cementation were the major factors controlling the physical properties of shale and limestone.It also shows that, controlled by sedimentation and diagenesis, the organic-rich shale and the conchoidal shale are two most promising rock types for hydrocarbon reservoirs.Also as a result of diagenesis processes, the conventional reservoirs of conchoidal limestone and limestone are too tight to hold any oil or gas, but the fine-grained sedimentary rock and conchoidal shale of less tight are wonderful unconventional shale gas reservoirs.This assumption was verified in field tests during which large volume of gas flew out of conchoidal shale, but none from the adjacent conchoidal limestone.The result also suggests that rocks with well-developed laminae and micro-laminae (observed under microscope) or with siliceous and calcareous compositions of directional arrangement are potentially high-quality reservoir rocks.

Key words: diagenetic evolution, petrologic feature, fine-grained sedimentary rock, Da'anzhai Member, Yuanba area, Sichuan Basin

CLC Number: