Abstract

The purpose of this study is to investigate the entire evolution process of shales with various total organic contents (TOC) in order to build models for quantitative evaluation of oil and gas yields and establish methods for assessing recoverable oil and gas resources from in-situ conversion of organic matters in shale. Thermal simulation experiments under in-situ conversion conditions were conducted on Chang 73 shales from the Ordos Basin in a semi-open system with large capacity. The results showed that TOC and Ro were the key factors affecting the in-situ transformation potential of shale. The remaining oil and gas yields increased linearly with TOC but inconsistently with Ro. Ro ranged 0.75%–1.25% and 1.05%–2.3%, respectively, corresponding to the main oil generation stage and gas generation stage of shale in-situ transformation. Thus a model to evaluate the remaining oil/gas yield with TOC and Ro was obtained. The TOC of shale suitable for in-situ conversion should be greater than 6%, whereas its Ro should be less than 1.0%. Shales with 0.75% (Ro) could obtain the best economic benefit. The results provided a theoretical basis and evaluation methodology for predicting the hydrocarbon resources from in-situ conversion of shale and for the identification of the optimum “sweet spots”. The assessment of the Chang 73 shale in the Ordos Basin indicated that the recoverable oil and gas resources from in-situ conversion of organic matters in shale are substantial, with oil and gas resources reaching approximately 450 × 108 t and 30 × 1012 m3, respectively, from an area of 4.27 × 104 km2.