Originai Gas in-place(OGIP) of lower Silurian and Lower Cambrian Black Shale in the South China

Wang, Feiyu; Meng, Xiaohui; He, Zhiyong
China University of Petroleum, Beijing, China.

The assessment of shale gas resource potential in China are undergoing in recent years to find favorable plays and areas for exploration and production. The lower Silurian Longmaxi Formation and lower Cambrian black Shale are assigned to be two the most favorable intervals, which are widespread distributed in the Upper and Middle and Yangtze region, south China, and the most shale gas exploration activities in China were focused in these two favorable intervals in recent years. The TOC, organic matter maturity, thickness, shale porosity, gas contents and composition are through documented for these two black shale intervals to construct the refined geological model, based on data from the 89 wells and outcrops in the Upper and Middle and Yangtze region, Geochemical screen analysis indicate that organic matter rich(TOC more than 2%) black shale intervals are confined to bottom part of lower Silurian(15-110m) and lower Cambrian(40-150m), all analyzed shale sampled are in the phase of overmature (VRo or VRE range 2.2%-4.8%), and shale porosity range 3% to 6%, Shale gas include free gas in pores, adsorbed gas in the solid organic matter, solution gas in the residual oil and water. P-T conditions control the partitioning between adsorbed gas, solution gas and free gas. The algorithm of free gas, adsorbed gas and solution gas in shale have been designed to quantify the spatial distribution of original gas in-place(OGIP) in Trinity 3D petroleum system modeling software. OGIP variation of lower Silurian and lower Cambrian black shale have been preliminary established according to the present available geological framework and source rock data, calibrated with the a few limited measured data of gas content. Most calculation value of OGIP range from 2 to 5.5 cubic meters per ton rocks. We recognize that overmature phase of shales in this region, which result in the lower porosity and free gas content of shale, may be the unfavorable factor for shale gas.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012