A Novel Evaluation Method of Double Sweet Spots in Shale Oil Reservoirs: A Case Study

This paper mainly studied the effects of eight parameters including Young's modulus, formation brittleness, internal friction angle, fracture energy, fracture toughness, porosity, permeability, and clay content on the double sweet spots of shale oil reservoirs. We calculated the double sweet spot indexes comprehensively. Further, the double sweet spot index profiles were imported into the Petrel software to obtain the correlation diagram of the double sweet spot index versus the well depth for a single-well and the three-dimensional model of the double sweet spots in the target block. Double sweet spot evaluation was conducted on shale oil reservoirs in Jiyang Depression. The results show that the double sweet spot layers of FY1-X well are located at the depth of 4034∼4160m and 4556∼4686m. The double sweet spot layers of well FY1-Y are located at 4883∼5043m, 5121∼5280m, and 5394∼5717m depth. The double sweet spot index of this block is between 0 and 1.41. In the middle of the block, the double sweet spot index is almost 0, while in the southwest and northeast of the block, the double sweet spot index is greater than 1, which is considered as a double sweet spot area. 1. INTRODUCION Shale oil refers to thermogenic petroleum resources occurring in shale formation mainly in free state, supplemented by adsorbed state and dissolved state. It includes the oil in the pores and fractures of shale, as well as the oil resources in the adjacent layers and interlayers of tight carbonate rocks or clastic rocks in shale formations. (Zhang et al., 2012) The technical recoverable resources of continental shale oil in China are 4.352 billion tons, ranking third in the world. Shale oil resources have become the focus and hot spot in current petroleum exploration and development research. Shale oil sweet spot refers to the relatively rich area of shale oil that can be extracted under current technical conditions. The evaluation of shale oil double sweet spots is of great help to the exploitation of shale oil resources. The efficient development of paleogene shale oil in Jiyang Depression of Bohai Bay is a major strategic measure to ensure national energy security. However, the high reservoir heterogeneity of shale oil in Jiyang Depression and complex distribution of favorable properties results in low recovery efficiency and reservoir productivity without design optimization of fracturing and construction parameters. Therefore, a dual-sweet spot evaluation model suitable for shale oil reservoir is established to provide strong support for efficient development of shale oil and optimization of fracturing construction parameters.