Well Logging Evaluation of“Three Quality”of Jurassic Tight Gas Sandstone Reservoirs in Kuqa Depression

In order to unravel the tight gas reservoir characteristics and establish the well log evaluation methods of Jurassic tight gas reservoirs in Kuqa depression, core observation, rock physics experiment, conventional logging and image log data were used to unravel the“seven relations”of lithology, physical property, electrical property, oil-gas bearing property, brittleness, source rock properties and in-situ stress of Jurassic Ahe Formation tight sandstone gas reservoir in monocline zone of northern Kuqa depression. The logging interpretation model of porosity, permeability and gas saturation was established, and well logging calculation model of TOC (total organic carbon), brittleness index as well as triaxial in-situ stress profile were established respectively. Then the logging methods of source rock property, reservoir quality and engineering quality are established based on the research of“seven relations”. The results show that the lithology of Ahe Formation mainly includes conglomerate, medium-coarse sandstone and mudstone. The reservoir spaces are mainly intergranular dissolution pore, intragranular dissolution pore, micro-fractures and micro-pores. The typical gas-bearing interval is characterized by low gamma ray (<60 API), high resistance (> 10 Ω·m) and high acoustic time difference (>70 μs/ft). The source rock quality was characterized by TOC content calculated by logging, and four reservoir quality types were classified according to physical property test, mercury injection test and the degree of fracture development. The engineering quality was identified and classified mainly by brittleness index and in-situ stress. Finally, the logging evaluation results of“three qualities”were applied to the evaluation and prediction of single well productivity, which is in good agreement with the actual well test, and the results were testified in the eight intervals of seven wells including DB 101 and other wells. © 2024 China University of Geosciences. All rights reserved.