Study on simulation of reservoir-controlling of fault-unconformity composite transport in Chengbei Fault Zone

Abstract Due to the multi-phase tectonic movements in Chengbei Fault Zone, a superimposed pattern of Paleozoic buried hill and Cenozoic fault-step slope was developed on the North China platform. The fault–unconformity composite transport played a vital role in the oil and gas supply for the underlying buried hill and the distal high slope, resulting in the accumulation forming of multi-layer multi-type oil and gas. On the basis of seismic and well logging data, the characteristics of fault–unconformity composite transport in Chenghai buried hill and southern high slope were determined. And the reservoir-controlling mechanisms of fault–unconformity composite transport were revealed through oil and gas filling simulation experiments under different transport conditions. The results showed that the composite transport of fault and unconformity in buried hill zone was beneficial to the forming of large-scale reservoirs, and the dominant thick reservoirs or even negative tectonics under unconformity with abundant oil source were the main hydrocarbon accumulation area. As to the forming of reservoirs in the high slope, the key was the lithology configurations around the unconformity of “upper sand and lower mud” and “upper gravel and lower mudstone”. With the help of fault, the composite transport enables long-distance migration of oil and gas from the northern source rocks in Shahejie Formation, leading to hydrocarbon accumulation above the unconformity of Guantao Formation and even in the structural trough of southern high slope. These results revealed that fault–unconformity composite transport was helpful to hydrocarbon accumulation on a large scale, and even negative tectonics in buried hill below unconformity or structural troughs in high slope above unconformity are potential to form reservoirs. This provides a useful reference for theoretical research on reservoir forming in fault basins and a beneficial guidance for oil exploration in similar areas to a certain extent.