Abstract

Traditional isothermal adsorption experiments often fail to accurately estimate the adsorption capacity of reservoirs with rapidly changing lithology. Temperature, pressure, and mineral composition can influence the adsorption capacity of shale reservoirs. We have examined the influence of these factors on the amount of gas adsorbed in samples from well Yu-88. Samples consist of marine-continental transitional coal-bearing strata from the Upper Paleozoic Shanxi-Taiyuan Formation of the Ordos Basin of China. Shales occur as frequently interbedded, thin, and single layers that exhibit large cumulative thickness and rapid changes in mineral composition. Our experiments on samples B1 and B2 indicated that Langmuir constant VL varied inversely with temperature, but Langmuir pressure PL did not. The PL exhibits good correlation with illite as well as illite/smectite content but did not clearly correlate with the total organic carbon (TOC). The VL correlated positively with TOC and negatively with illite/smectite content. These relationships enabled modeling of VL, PL, and mineral composition. Novel step-by-step modeling methods of well logs generated optimized estimates for well-log parameters including mineral composition. According to the actual temperature of the reservoir, we corrected the Langmuir constant VL. We calculated a profile for the amount of gas adsorbed in shale intervals of well Yu-88. Comparisons with experimental values indicate relatively high reference values.

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