Logging-lithology identification methods and their application: A case study on Chang 7 Member in central-western Ordos Basin, NW China

Abstract

Abstract: Based on the different logging responses in lithologic, electric, physical and radioactive properties of the seventh member of the Yanchang Formation (Chang 7 Member) in the central-western Ordos Basin, two innovative logging-lithology identification methods have been developed, i.e. cross-plot method and Vsh–TOC method. The former method can be used to identify sandstones, siltstones, mudstones and tuffs by crossing the well logs with lithology, while the latter method can be used to identify sandstones, siltstones, mudstones and high-organic shale through calculating the shale content (Vsh) and organic carbon content (TOC). By comparing the calculation results with test results and core samples, both methods are determined to have accuracy above 86%. Results of lithology identification for 240 wells within the study area were used to generate planar and cross sections. It is indicated that shales are widely and continuously developed at the top of the Chang 7 Member in the study area and reduce upwards; sandstones are distributed in the northern, eastern and northeastern parts of the study area, as well as the southern and southwestern parts. As time goes by, the isolate sand bodies in the central part of the study area increased both in area and quantity, and eventually formed the large distribution in Chang 7₁.

Key words: Ordos Basin, Yanchang Formation, Chang 7 Member, logging-lithology identification

Cheng Dawei, Yuan Xuanjun, Zhou Chuanmin, Tan Cong, Wang Mengshi. Logging-lithology identification methods and their application: A case study on Chang 7 Member in central-western Ordos Basin, NW China[J]. China Petroleum Exploration, 2016, 21(5): 117-126.

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