Abstract

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Title:: Reservoir Space Types of Oligocene Xiaganchaigou Formation from Well S3-1 in Yingxi Area of Qaidam Basin, China

Author(s):: HUANG Cheng-gang; CUI Jun; GUAN Xin; CHANG Hai-yan; YANG Sen; HUI Yuan-yuan; WU Liang-yu; WU Li-rong; 1. Key Laboratory of Reservoir Description of CNPC, Lanzhou 730020, Gansu, China; 2. Northwest Branch of Research Institute of Petroleum Exploration and Development, PetroChina, Lanzhou 730020, Gansu, China; 3. Research Institute of Exploration and Development, Qinghai Oilfield Company, PetroChina, Dunhuang 736202, Gansu, China; 4.School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, Sichuan, China

Keywords:: intercrystalline pore of dolomite; dissolution pore; Xiaganchaigou Formation; extra low porosity-extra low permeability; kinetics barrier; penecontemporaneous metasomatism; Yingxi oilfield; Qaidam Basin

Abstract:: In recent years, there is important discovery for oil and gas exploration of Oligocene Xiaganchaigou Formation in Yingxi area of Qaidam Basin. However, the main reservoir space types have been debated over. Based on core observation and systematically study of the micro petrological and structural characteristics of Well S3-1, the main reservoir space types were concluded. The results show that the main reservoir space types are intercrystalline pores of dolomite rather than dissolution pores. The main evidences include that the dark layers with high deposition rate are difficult for exposure and dissolution; dolomite is one of the most important minerals in rocks; under the field emission scanning electron microscope, the angular intercrystalline pores widely develop; because of the crystallization of salt minerals, not dissolution, the pores and holes observed in core are all in the fractures under the polarized microscope; the physical characteristic is “extra low porosity-extra low permeability”; the displacement pressure is high, the pore throat radius is small, and the efficiency of mercury withdrawal is very low; the characteristics under fluorescence microscopy is whole. Oil-bearing matrix porosity widely develop, so that it is one of the main control factors of large oilfield with high and stable yield in Yingxi area; the results have important guide for the further exploration.