Exploration breakthrough of sandwiched shale oil in Sichuan Basin and its gas–oil geological implications: Taking Well G119H in the central Sichuan Basin as an example

The PetroChina Southwest Oil & Gasfield Company deployed a key appraisal well G119H to explore the sandwiched shale oil in the Lianggaoshan Formation in the western Gongshanmiao area, central Sichuan Basin. Recently, the well achieved a production rate of 20 t/d oil and 0.6×104 m3/d gas in test, recording a new breakthrough of lacustrine sandwiched shale oil in the basin. In order to further clarify the potential resources and exploration prospects of such shale oil in the Sichuan Basin, this paper investigates the Lianggaoshan Formation in terms of sedimentary geological setting, channel characteristics, high-quality reservoirs, and accumulation models, based on the geological and seismic data collected in the area where Well G119H is located. The results suggest that the Lianggaoshan Formation vertically develops multiple periods of lacustrine shales and delta front sand bodies overlapped under the setting of multi-phase lake basin migration. In western Gongshanmiao, the second member of Lianggaoshan Formation (Liang-2 Member) is characterized by shallow-water delta front sand body at the bottom. The sand body advances into the lake from southwest to northeast. In this member, distributary channel is the most favorable microfacies, and the dominant lithology is fine to medium-sized lithic sandstone, with an average porosity of 6.3% and a pore structure consisting of connected small pores–microthroats, where a high proportion of movable oil takes. The sandwiched shale oil in the Lianggaoshan Formation is widely distributed, with several positive factors such as thick source rocks (>10 m), good physical properties of sandstone reservoirs, and favorable source–reservoir assemblage. According to preliminary evaluation, the favorable area for sandwiched shale oil in the basin is 1.38×104 km2. Based on the existing 3D seismic data, the channel area of the Liang-2 Member is depicted to be 2 336 km2, and the sandwiched shale oil resources are estimated to be about 15×108 t. It is concluded that the exploration breakthrough by Well G119H suggests a large potential of sandwiched shale oil in the Liang-2 Member in central Sichuan Basin and further proves the solid endowment of shale oil in the Jurassic of the basin. The sandwiched shale oil in the Liang-2 Member in central Sichuan Basin is determined as a key interval of the 14th Five-Year Plan and the medium and long term incremental reserves/production. © 2024 Natural Gas Industry Journal Agency. All rights reserved.