Development trend of marine shale gas reservoir evaluation and a suitable comprehensive evaluation system

At present, shale gas exploration and development in China is faced with some problems, such as the imperfect evaluation system of reservoir effectiveness and the limitations of reservoir evaluation system on efficient development of shale gas. In order to improve the content and the standard of reservoir evaluation, this paper analyzed the shortcomings and challenges in the static evaluation of shale gas reservoirs on the basis of existing reservoir evaluation, and established a method for evaluating shale gas reservoir effectiveness and a scheme for classifying pore systems. Then, the dynamic evaluation parameters after shale fracturing and their effects on drainage and production measures were discussed. In addition, the potential evaluation parameters of "automatic mitigating water blocking" were studied, and a comprehensive reservoir evaluation system of "static–dynamic" combination was established. And the following research results were obtained. First, new challenges to the shale gas reservoir evaluation are emerged as the lack of in-depth study on "reservoir effectiveness, dynamic evaluation parameter system after fracturing and drainage and production measures after fracturing", which leads to the serious lag of existing shale gas reservoir evaluation system behind production. Second, the evaluation of reservoir effectiveness is mainly presented as the evaluation on the lower limit of effective porosity, and is embodied in the influence of clay bound water and unconnected pores on the development of shale gas. Third, the development of shale gas reservoir evaluation follows the trend of refining the static reservoir evaluation parameters, defining the potential evaluation indexes of "automatic mitigating water blocking" and establishing the reservoir comprehensive evaluation system of "static–dynamic" combination. Fourth, a post-frac dynamic evaluation system is determined for the potential evaluation indexes of "automatic mitigating water blocking" (e.g., wettability, water imbibition retention capacity, water imbibition expansion mode, expansion rate, and water imbibition cracking capacity). Fifth, a reservoir evaluation idea is put forward that "static evaluation of shale gas reservoir is the foundation and postfrac dynamic evaluation is the complement", and a comprehensive reservoir evaluation system is established of "static–dynamic" combination suitable for the evaluation of marine shale gas reservoirs in China.