Shiyou shiyan dizhi (Jan 2022)
Geological characteristics and seismic fine description of different types of sand bodies in Jurassic Shaximiao Formation in central Sichuan Basin
Abstract
Sand bodies in the Jurassic lacustrine-fluvial sedimentary system in the Sichuan Basin are realistic objects of shallow tight oil and gas exploration and development. Due to the influence of sedimentary microfacies, sand bodies have geological characteristics such as type diverse, variable lithology, significant thickness variation, and strong heterogeneity. Therefore, the fine description and prediction of different types of sand bodies is the current bottleneck for exploration and development. Based on the classification of various sand group types of the 1st member of Jurassic Shaximiao Formation, reservoir analysis was carried out, logging and geophysical response characteristics were concluded, and fine identification and spatial prediction were made by time-sharing window. Results show that: (1) The 1st member of Shaximiao Formation can be divided into 5 sand groups, among which the 1st sand group is mainly littoral-shallow lacustrine sheet sand and beach bar sand, and the 2nd to 5th sand groups are delta front facies channel-plain channel; (2) The average porosity of channel sand is 4.68%, which is significantly higher than that of bottom sheet sand (3.1%). The physical properties of the Ⅰ channel are the best, followed by the Ⅳ, Ⅱ, and Ⅲ channels. (3) The prediction standard of channel sand is: natural gamma < 65 API, and the prediction standard of sheet sand locates between 65 and 75 API. In sand body prediction, for sheet sands (beach bars), the study time window is extracted to be within 0-20 ms, and for river channels, the study time window is in the range of 20-100 ms upwards from the bottom of the Shaximiao Formation. Finally, a set of methods suitable for fine description and prediction of different types of sand bodies in the lacustrine-fluvial sedimentary system was established.
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