Identification of LTAF Lithologic Traps in Western Uplift Belt of JB Block in South Sumatra Basin

Abstract

After nearly 20 years of exploration and development, the western uplift belt of JB block is currently in the stage of high maturity. With only few and small structural traps left, exploration of lithologic traps becomes the major factor to increase reserves. Based on the study on high-resolution sequence stratigraphy and the sedimentary system, the areal distribution of sandstones was studied using seismic waveform indication inversion method, and the sandstone boundary was finely characterized taking advantage of attributes of texture energy and instantaneous phase. The study shows that inversion results of seismic waveform indication are in better agreement with drilling data interpretation results etc., with higher vertical resolution, clear overlapping relationship of sand bodies and clear lateral distribution boundary. With its thickness being controlled mainly by the paleo-uplift and provenance, sand bodies are distributed in the shape of lobate and strip as a whole. Sand bodies are well developed and thicker at the lower part, but get thinner (and even pinch out) updip. The thickness of the ascending semi-cycle sandstone in LTAF Formation is 0–80 m, missing (no deposit) in the higher part of the uplift; the thickness of the descending semi-cycle sandstone is 0–120 m, overall thicker than the ascending. Eight lithologic bodies of ascending semi-cycle and 10 lithologic bodies of descending semi-cycle are developed. The lithologic bodies of descending semi-cycle have larger area than that of corresponding lithologic bodies of ascending semi-cycle, and are relatively continuous and homogeneous. The lithologic bodies are basically distributed around the palaeo-uplift. The identification of lithologic traps lays a solid foundation for follow-up evaluation and drilling in the traps, and meanwhile the identification method also provides a good reference for similar studies in other areas.