西南石油大学学报(自然科学版) ›› 2017, Vol. 39 ›› Issue (3): 47-56.DOI: 10.11885/j.issn.1674-5086.2016.01.28.02

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Comprehensive Classification and Evaluation of Low Permeability Reservoirs Based on the Identification of Complex Lithological Characteristics

NIU Tao, WANG Hui, HU Xiaoqing, ZHANG Yukun, GAO Yufei   

  1. CNOOC Research Institute, Chaoyang, Beijing 100028, China
  • Received:2016-01-28 Online:2017-06-01 Published:2017-06-01

Abstract: The SHA1 and SHA2 reservoirs of the Q oil field have widely-developed mixed sedimentary rocks composed of terrestrial debris and lacustrine carbonates. The mixing of these sediments in varying degrees and forms has resulted in a variety of lithological combinations; as a whole, the SHA1 and SHA2 reservoirs are low-porosity/low-permeability reservoirs. In view of the complex lithology and low porosity/permeability of this oil field, the data obtained from rock cores, casting sheets, cathodoluminescence and elemental capture spectroscopy (ECS) logging were used to establish a comprehensive evaluation method for low permeability reservoirs based on the identification of complex lithological characteristics. This method uses 7 evaluative parameters including lithological characteristics, effective thickness, permeability, porosity, displacement pressure, median radius, and sorting coefficient, in which displacement pressure, median radius, and the sorting coefficient are the structural parameters of microscopic pore throats which are obtained via mercury porosimetry. An analytic hierarchy process was then used to obtain the weights of each parameter and the comprehensive evaluative parameters of the reservoir, under constraints applied by the reservoirs' geological conditions. Based on this method of evaluation, the reservoirs in this region were classified into three types; in particular, the lithology of Type I reservoirs is mainly composed of silkites and oolitic sandstones with well-developed dissolution pores, high levels of pore connectivity, and have excellent deliverability test results. Hence, this is the "sweet spot" of these low-permeability reservoirs.

Key words: reservoir, mixed sedimentary rock, pore types, pore structure, comprehensive evaluation

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