A Novel Approach for the Sweet Spots Prediction of Shale Oil – A Case Study on the Es3L Sub-Member of Bonan Sag, Jiyang Depression, China

Abstract

The key to improving the efficiency of shale oil exploration and development is the sweet spots identification since the high heterogeneity of shale reservoirs. This paper propose an evaluation model of shale oil sweet spots index (SPI) based on the movable oil content and the fracability of the shale reservoir to identify the sweet spots in shale oil plays prospects. The movable oil content was evaluated by the combination of the total shale oil content and the shale oil mobility model. The fracability of the shale reservoir was estimated coupled by the rock brittleness and mechanics.

We took the Es3^L sub-member of Bonan sag as an example. Based on the Leco, pyrolysis, X-Ray diffraction, porosity and saturation testing experiments and the well logging of well L69, the organic heterogeneity logging evaluation model was established to predict the residual oil content firstly, such as TOC, S₁, porosity and oil saturation. According to the residual oil content, we calculated the total shale oil content by the light and heavy hydrocarbon correction techniques. The shale oil mobility model was established by two methods, the first one is the kerogen and mineral adsorption model, the other is the mass-volume conservation method using the molecular simulation technology, and the evaluation results by two methods are consistent well. In addition, the inorganic heterogeneity logging evaluation model was also established to predict the brittleness mineral content (siliceous and calcareous minerals) and the mechanics parameters so as to evaluate fracability of the shale reservoir, the higher brittleness mineral content and the lower Young’s modulus, the easier the fracturing of the shale reservoir. Then, other wells of Bonan sag were applied using the above model, and the lower limit value of the shale oil sweet spots index was set as 0.1 based on the relationship between the sweet spots index and the shale oil production. Finally, the distribution of the sweet spots in the study area is determined.

Shale oil sweet spots index evaluation model is a comprehensive manifestation of organic sweet spots and inorganic sweet spots. It takes the shale oil mobility and shale fracturing into account and has practical significance for the exploration and development of shale oil. At the same time, with the advantages of logging high resolution, the shale oil sweet spots index evaluation model is feasible in the identification and prediction of the favorable area of shale oil.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018