Mechanism of Bubble Point Pressure and Gas-oil Ratio Changing with Depth in Complex Structural Reservoirs

Reservoir bubble point pressure and gas-oil ratio are important parameters for the scheme design of oilfield development and calculation for reservoir elastic reserves. However, their change laws are complex. At present, there are few studies on the mechanism of bubble point pressure and gas oil ratio changing with depth, which is an urgent problem to be solved in the exploration and development of oil and gas fields. This study focuses on the variation mechanism of bubble point pressure and gas-oil ratio with depth under different tectonic movement conditions in the process of reservoir formation of complex structural reservoirs. When the buried depth of the reservoir is small, the crude oil from bottom to top will be in an unsaturated state (bubble point pressure is less than the formation pressure) to a saturated state (bubble point pressure is greater than the formation pressure), and there will be a gas cap at the top of the oil layer. When the buried depth of the reservoir is large, the formation pressure of the reservoir from bottom to top is greater than the bubble point pressure, and the crude oil of the reservoir is in a single-phase state. A series of tectonic movements will occur in the process of reservoir formation of complex structural reservoirs, which will affect the state of oil and gas in the reservoir. In this study, under the three conditions of complex structural reservoirs including no tectonic movement, tectonic uplift, and tectonic subsidence, the change in bubble point pressure and gas-oil ratio with depth was analyzed respectively. Finally, the mechanism of bubble point pressure and gas-oil ratio changing with depth in complex structural reservoirs is obtained. This study can provide theoretical guidance for reservoir reserve research and development scheme design.