Organic porosity evaluation of Lower Cambrian Niutitang Shale in Qiannan Depression, China

摘要

Qiannan Depression was selected as a study case to confirm the contribution of organic pores (microscale and nanoscale pores within organic grains in shale) formed by hydrocarbon generation to shale gas reservoir space. Using the material balance principle combined with chemical kinetics methods, an evaluation model of organic porosity for shale gas reservoirs was established. The results indicate that there are four important model parameters to consider when evaluating organic porosity in shale: the original organic carbon (w(TOC0)), the original hydrogen index (I-H0), the transformation ratio of generated hydrocarbon (F(R-o)) and the organic pore compression coefficient (C). The organic porosity of carbonaceous shale in the middle and lower part of the Niutitang Formation in the Cy1 well is from 0.68 to 5.24%, and the average value is 3.01%.