Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (1): 98-106, 123.doi: 10.11743/ogg20210109

• Petroleum Geology • Previous Articles     Next Articles

Division of shale lithofacies associations and their impact on fracture network formation in the Silurian Longmaxi Formation, Sichuan Basin

Cheng Shen1,2(), Lan Ren2, Jinzhou Zhao2, Mingpei Chen3   

  1. 1. Shale Gas Research Institute under Southwest Oil & Gas Field Branch Company Ltd., PetroChina, Chengdu, Sichuan 610041
    2. State Key Laboratory of Oil and Gas Reservoir Geology and Exploration, Southwest Petroleum University, Chengdu, Sichuan 610500, China
    3. Beijing Science and Technology Innovation Research Center, Beijing 100744, China
  • Received:2018-11-26 Online:2021-02-28 Published:2021-02-07

Abstract:

A commercial development of shale gas reservoirs largely depends on the effect of hydraulic fracturing.However, shale of different lithofacies associations responds differently to the treatment.The study used the Silurian Longmaxi Formation shale in the Sichuan Basin as an example to conduct a division of lithofacies associations and an analysis on the impact of the associations upon fracture networks.The roles of mineral composition, physical properties, beddings and bedding-parallel fractures of the shale in the formation of fracture networks were analyzed and then integrated with characterization of crops, cores and stimulation effect of hydraulic fracturing in the shale to define the association divisions.The results show that there are four types of lithofacies associations in the shale.Type Ⅰ association (FA1) is obviously the result of diagenesis modification and contains well-developed calcite-filled fractures, which can be activated preferentially to generate fracture networks but are also likely to confine the expansion of fractures during the earlier stage of fracturing.Type Ⅱ (FA2) shows evident signs of sedimentary control and tends to contain interbeds of promising gas reservoirs with crackable reservoirs.Type Ⅲ (FA3) and Type Ⅵ (FA4) are dominated by terrigenous components in comparison and are difficult to crack to from fracture networks.In all, FA1 and FA2 are the potential sweet spots for fracturing.The study is of theoretical support and on-site guiding significance to target formation selection and scheme design in fracturing.

Key words: shale lithofacies association, diagenesis, fracturing, fracture, reservoir, Longmaxi Formation, Sichuan Basin

CLC Number: