Characteristics of S-type strike-slip transform zone and its control on lateral sealing of shallow oil and gas in Bozhong 8-4 Oilfield

The neotectonic movement in Bohai Sea of is very intensive, forming a unique strike-slip structural system and shallow reservoir formation in the Bozhong Sag. Previous studies focused mostly on the demonstration of strike-slip movement and the discussion on the types of strike-slip transform zone, and there is a lack of detailed research on the role of reservoir controlling by the strike-slip transform zone. We studied the characteristics of S-type strike-slip transform zone in Bozhong 8-4 Oilfield and its control on the lateral sealing of oil and gas using seismic data and oilfield cases. Results show that the main fault in the Bozhong 8-4 Oilfield is an S-type strike-slip transform system, in which pressure-releasing belt and pressure-boosting belt are developed. In the pressure releasing belt, the strata are steep and traps are poorly developed, which is the filling zone of oil and gas from deep to shallow. The pressure-boosting belt is characterized by gently-dipping strata, clear anticline shape, and dense low-amplitude nose-like faults and faulted-block traps, forming oil and gas accumulation rooms. Meanwhile, we proposed the strike-slip fault sealing index with which the lateral sealing ability of the strike-slip transform belt could be quantitatively characterized. According to the statistics of nearly 20 oilfields, the value of the strike-slip fault sealing index at 4 can be regarded as the critical point of the lateral sealing of the strike-slip fault. The research results provide a new method and idea for exploration in shallow oil and gas under sand-rich background.