Adaptability analysis and optimization of log suite for uncased wellbores of shale gas reservoirs: A case study of Sichuan Basin, China

Abstract

Significant progress has been made in the exploration and development of unconventional gas resources in China since the beginning of the 21st century. With a rapid increase in yield, the exploration and development of shale gas have been upgraded to a level of national strategy. Logging is one of the core technologies in gas exploration and development. However, logging technologies face the challenges of complex geological conditions and well casing environment, high temperature, high pressure, and strong heterogeneity. Despite the rich experience accumulated, unified understanding and implementation specifications are yet to be established for shale gas well logging. Given the analysis and comparison of the effectiveness and adaptability of logging technologies at different stages of shale gas exploration and development for the Sichuan Basin, this study optimizes the log suite to meet the demand for high-efficiency exploration and development of shale gas. According to the adaptability analysis of shale gas log suite, the mandatory logging items of exploratory wells should include caliper log (CAL), natural gamma ray spectrometry (NGS) log, spontaneous potential (SP) log, directional survey, borehole compensated sonic log, litho-density log (LDL), compensated neutron log (CNL), dual laterolog-microspherically focused log/dual induction-laterolog log/array induction log, temperature log, elemental capture spectroscopy (ECS) log, formation microimager (FMI) log, and array sonic log. The log suite of appraisal wells is almost the same as that for exploratory wells, excluding the ECS log and micro-resistivity scanning imaging. Meanwhile, for the logging of horizontal/highly-deviated holes, the log suite of vertical wells should be referred to according to specific well conditions.