Uncovering the Potential of Thin, Tight Gas Reservoirs in Sichuan Basin, China - New Development Campaign Using New LWD Imaging Technology and Innovative Interpretation Workflows

Abstract

ABSTRACT Located in central China, the Sichuan basin holds the biggest gas reserve in the country. Tight gas reservoir (limestone, dolomite, and tight sand) development has been taking place since early 1992. Since then, relatively thicker gas reservoirs have been commonly developed, and more challenging, very thin reservoirs are now being targeted. Long horizontal drilling combined with multistage hydraulic fracturing is planned. However, the management of the subsurface uncertainties appears as the biggest challenge. Located in a major compressional tectonic area, the geological province presents reverse/thrust faults and high structural dip uncertainty. Lateral property changes in the dolomite target reservoir and a stratigraphic thickness of the reservoir that varies from 1 m to 2 m add to the difficulty. To overcome these challenges and to enhance reservoir understanding, advanced logging-while-drilling acquisition and real-time transmission of high-resolution electrical borehole images, azimuthal gamma ray, and multidepth measurement of formation resistivity were deployed in a recently completed gas well. Based on these data and advanced techniques, structural features including dips, faults, and fractures could be clearly identified in real time while drilling and helped the team to: 1) accurately geosteer the well and significantly reduce the probability of erroneous lateral placement and 2) optimize the completion design and planning of the hydraulic fracturing staging and segmentations. Completed in 2011, the well represents the first successful completion in the thin, tight gas reservoir; a 1095-m horizontal section was drilled with 91% net-to-gross and the gas production was recorded at 123 700 m3/d, exceeding the set production goal of the well by 33%. This particular success is proving that a thin, tight gas reservoir can be profitably developed. Several subsequent wells have been planned to be drilled in different target zones in the Sichuan basin.