Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (2): 294-301.doi: 10.11743/ogg20190208

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Quality differences between dolomite and tight sandstone reservoirs

Wei Xinshan1,2, Chen Juanping1,2, Lyu Qiqi3, Zhao Xiaohui1,2, Jia Ya'ni1,2   

  1. 1. Exploration and Development Institute of Changqing Oilfield Branch Company, PetroChina, Xi'an, Shaanxi 710018, China;
    2. National Engineering Laboratory of Exploration and Development of Low Permeability Oil/Gas Fields, Xi'an, Shaanxi 710018, China;
    3. Hubei Cooperative Innovation Center of Unconventional Oil and Gas, Yangtze University, Wuhan, Hubei 430100, China
  • Received:2018-01-08 Revised:2018-11-30 Online:2019-04-28 Published:2019-01-23

Abstract: The quality parameters of dolomite and tight sandstone reservoirs are a randomly distributed continuum.Their pore structures and physical parameters are complex and changeable,and are thus hard to be characterized.With the help of techniques such as thin section casting,mercury injection,nuclear magnetic resonance(NMR),and measurements of porosity and permeability,and a large number of data for natural gas exploration and development,we focused the study on analyzing and comparing the macroscopic and microscopic characteristics of the parameters of the reservoir quality.Results show that the quality parameters of dolomite and tight sandstone reservoirs are normally distributed in a pyramidal data structure.The proportion of conventional reservoirs is generally ranging from 15% to 20%,which are the "sweet spots" of the sandstone or tight dolomite reservoirs.The microscopic pores are well developed with good pore-throat connectivity and uniform distribution in the tight sandstone reservoirs.The reservoir porosity and permeability are of good relationship,showing relatively high porosity and low permeability.The tight dolomite reservoirs,however,are characterized by unfavorable factors including poor pore-throat connectivity and poor relationship of porosity and permeability,while having certain favorable factors of its kind including relatively high permeability,low irreducible water saturation,low displacement pressure,and better development of fracture networks.These favorable factors keep the natural gases flow well in tight dolomite reservoirs,indicating great potentials for the exploration and development of hydrocarbons.Carbonate deposits are well developed in China,so the exploration of tight dolomite gas reservoirs and study on their accumulation conditions should be strengthened.

Key words: sandstone, dolomite, reservoir quality, tight reservoir, natural gas, Jingbian gas field, Sulige gas field, Ordos Basin

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