Characteristics and Significance of Triple Natural Gas Peak Relay Generation of Source Rocks in Bohai Sea Area

Abstract:

The Bohai Sea area of the Bohai Bay Basin is an important direction in oil and gas exploration at present and in the future. Understanding of the generation pathway，mechanism， and potential of natural gas at Bohai Sea area is beneficial for developing the natural gas generation theory and guideing petroleum exploration in the Bohai Bay Basin. Through the simulation experiment of typical source rocks in Liaozhong Sag of the Bohai Sea area， the generation characteristics of main source rocks in the Bohai Sea area are studied， and the generation model of main source rocks in the Bohai Sea area is established. Based on the analysis of typical hydrocarbon accumulation mechanism， the accumulation regularity of different types of natural gas is identified， and the potential and direction of natural gas are discussed. The results show that Type II1 and Type II2 hydrocarbon source rocks of the third member of the Shahe Formation in the Bohai Sea area have the characteristics of triple peak relay gas generation. The Ro of the three gas generation peaks is 1.0% （①）， 1.5 % （②） and 2.7 % （③）， respectively. The three gas generation peaks show intermittent relay gas generation characteristics. The total gas production of the three gas generation stages has a Peak③≈Peak② >Peak①； Natural gas reservoirs generated at Peak ① and Peak ② stages are generally developed in Liaozhong Sag of the Bohai Sea area， among them， Peak① mainly shows atmospheric pressure oil and gas accumulation in the slope zone close to the source rock， and Peak② mainly shows overpressure condensate gas accumulation in the uplift zone. The natural gas formed by Peak ③ is only found at local well points. It shows that the deep source rocks in Liaozhong Sag have entered Peak ③ stage and have the potential to form large over-mature gas reservoirs.