Control of facies/potential on hydrocarbon accumulation: a geological model for lacustrine rift basins

Abstract

The formation and distribution of hydrocarbon accumulations are jointly controlled by “stratigraphic facies” and “fluid potential”, which can be abbreviated in “control of facies/potential on hydrocarbon accumulation”. Facies and potential control the time-space distribution of hydrocarbon accumulation macroscopically and the petroliferous characteristics of hydrocarbon accumulation microscopically. Tectonic facies and sedimentary facies control the time-space distribution. Lithofacies and petrophysical facies control the petroliferous characteristics. Favorable facies and high porosity and permeability control hydrocarbon accumulation in the lacustrine rift basins in China. Fluid potential is represented by the work required, which comprises the work against gravity, pressure, interfacial energy and kinetic energy. Hydrocarbon migration and accumulation are controlled by the joint action of multiple driving forces, and are characterized by accumulation in the area of low potential. At the structural high, low geopotential energy caused by buoyancy control anticlinal reservoir. The formation of lithological oil pool is controlled by low interfacial energy caused by capillary force. Low compressive energy caused by overpressure and faulting activity control the formation of the faulted-block reservoir. Low geopotential energy of the basin margin caused by buoyancy control stratigraphic reservoir. The statistics of a large number of oil reservoirs show that favorable facies and low potential control hydrocarbon accumulation in the rift basin, where over 85% of the discovered hydrocarbon accumulations are distributed in the trap with favorable facies and low potentials. The case study showed that the prediction of favorable areas by application of the near source-favorable facies-low potential accumulation model correlated well with over 90% of the discovered oil pools’ distribution of the middle section of the third member of the Shahejie Formation in the Dongying Depression, Bohai Bay Basin.