Advances in the basic study of lacustrine shale evolution and shale oil accumulation

Abstract

This manuscript provides a review of the recent advances in the study of fundamental processes and geological drivers involved in the lacustrine shale deposition, burial diagenesis, thermal maturation and in-situ oil accumulation, aimed at identifying key problem areas for future study. A survey of relevant literature on the sedimentology of fine-grained sediments reveals that paleoclimate changes on the global scale and tectonic evolution on the basinal scale have played a significant role in the formation of organic rich shales. Due to the strong heterogeneity in the mixed deposition of fine-grained sediments in the lacustrine setting, multiscale integration of different grain sequence sedimentary rocks is vital in the modeling of the lacustrine shale oil reservoirs. Techniques and methodologies are generally mature for characterizing and describing micropores and microfractures at various scales in the lacustrine shales. However, the current understanding of the dynamic processes in the shale diagenesis is incompatible with the high demand for predicting the key shale attributes as an effective shale oil reservoir. The processes involved in the thermal maturation, hydrocarbon generation and expulsion, as well as the physical status of oils in a shale, are generally well understood. The next logic step would be the application of these knowledges to tailor our methodologies for the classification and evaluation of shale oil resources in different tectonostratigraphic settings. While progresses have been made fairly recently in the physical constraints of the multi-phase and multiscale non-Darcy flows in the lacustrine shale, it is highly desirable to gain a better understanding of the likely modes, as well as associated temporal and spatial consequences, of hydrocarbon flows across different shale lithofacies. As the basic study of shale oil accumulation mechanisms has lagged behind the industry drilling activity, it is necessary to expedite the basic study in order to develop suitable protocols, parameters and laboratory tools for core area and "sweet-spots" delineation in a lacustrine shale play.

Keywords

• lacustrine shale oil
• accumulation mechanism
• fine-grained sediments
• flow mechanism
• resource assessment