Quantitative evaluation on the effectiveness of fault-block traps in the K Gas Field, Xihu Sag of East China Sea Shelf Basin

Fault-block gas reservoirs are dominated in the K Gas Field, Xihu Sag, East China Sea Shelf Basin. Research on the effectiveness of fault-block traps is lacking. A quantitative method for the evaluation on the effectiveness of fault-block traps has been developed in the study. Based on the core test, logging and geophysical data, detailed depiction and trap effectiveness research were conducted on the pools of the gas field. Anticline traps, lithological traps and mudstone-correspondent traps are effective traps with high probability of reservoir formation, while sandstone-correspondent traps are the least effective with 35% probability of effective traps. Twenty-one drilling wells in the K Gas Field show that when the fault displacement pressure is less than the reservoir displacement pressure, the trap is non-effective, which matches the result 92% of traps without oil and gas. On the contrary, the trap is effective, which matches the result 100% of gas reservoirs. The discrimination diagram of fault-block trap effectiveness can quickly identify trap effectiveness and contribute to fault-block oil and gas exploration in K Gas Field. The method has a wide application potential for the exploration of fault-block reservoirs in other areas.