Multi-parameters logging identifying method for sand body architectures of tight sandstones: A case from the Triassic Chang 9 Member, Longdong area, Ordos Basin, NW China

Abstract

Due to its huge production potential, tight sandstone reservoirs are the most promising exploration target in the Upper Triassic Yanchang Formation, Ordos Basin. Although tight sandstone reservoirs have received much attention in recent years, their strong internal heterogeneity makes the identification of petrologically superior sandbodies a great challenge. Based on cores, structural analysis, sedimentary microfacies analysis, lithologic analysis and other analytical tests and conventional logging curves, the characteristics of sand body architectures of the Member Chang 9 tight sandstones of the Triassic Yanchang Formation in Longdong area are described and summarized and the criteria for identification of sand body architecture by conventional logging curves are established. The sand body architectures in the Chang 9 tight sandstones were classified into five types: smooth cylinder-shaped architecture, laminaed cylinder-shaped architecture, smooth bell-shaped architecture, laminaed bell-shaped architecture, and finger-shaped architecture. The response characteristics of different sand body architectures were summarized through analyzing the logging curves, and single sand body, relative center of gravity, capacity of argillaceous laminae development, and homogeneity of argillaceous laminae characterizing were used to quantitatively characterize the sand body architectures, thus the criteria for identification of different sand body architectures by logging were established. The vertical identification and classification of sand body architectures in a single well was then accomplished by processing the log data from each well using proposed method, and the results of sand body architectures identification tally well with the results of formation testing. The workflow proposed based on the multi-phases and step-by-step progressive, can be applied in the Ordos Basin and other tight sandstones to improve the accuracy and reduce the economic cost of hydrocarbon exploration.