High-energy shoals and the controls of the gas enrichment in northern Fuling,Chongqing

The intraplatform high-energy shoal reservoirs occur on a wide range of scales in the Permian to Triassic carbonate rocks in the Sichuan Basin. The present paper deals,in terms of well logs and seismic data for the Changxing and Feixianguan Formations,with the characteristics and criteria for the recognition of the intraplatform high-energy shoal reservoirs in the marine strata in the Fuling region,Chongqing. Lithologically,the intraplatform high-energy shoal reservoirs in the Changxing Formation are dominated by sparry bioclastic limestones with partial dolomitization and dissolution pores and fissures. The electrical measurements include V<6100m/s and GR<36API. The seismic reponses are indicated by low-frequency,moderate to weak amplitudes and slightly hummocky seismic reflection configurations in the topmost part and chaotic seismic reflection configurations in the inner part of the reservoirs. In the Feixianguan Formation,Fuling region,multiple phases of oolitic shoals have greater thickness and widespread occurrence,and thus have excellent potential of oil and gas exploration. The main controlling factors include multiple stacking of high-energy shoal reservoirs, favourable diagenetic reworking such as dolomitization and dissolution,development of structural fissures/cracks.