Heterogeneous Characteristics of Hydrocarbon Migration: Observations, Controlling Factors, and Consequences

Xiaorong Luo¹, Likuan Zhang¹, Qianjin Liao², Dunqing Xiao², Junqing Su², Shuqin Yuan², and Changhua Yu^2
1Institute of Geology and Geophysics,Chinese Academy of Sciences, Beijing, China
²Research Center of Exploration and Development, Dagang Oilfield Company, CNPC, Tianjin, China

Carriers are important linkages for hydrocarbon migration and accumulation in a petroleum system. Oil and gas migrate commonly along narrow and zigzag pathways in porous media, even in those “homogeneous” media at a macro-scale. A migration simulator based on percolation theory, which couples the fluid potential as driving force with capillary pressure as resistance, may satisfactorily explain migration processes in heterogeneous media. In macro-scale homogeneous carriers, migration pathways are generally perpendicular to equal-potential lines, but locally the pathways are irregular because of the influence of micro-heterogeneity. The irregularity of these pathways depends on the difference between competing driving force and capillary pressure. When numerous pathways formed in a migration-accumulation system, the flux of migrating hydrocarbons varies among these pathways. In macro-scale heterogeneous carriers, the irregularity of migration pathways are exacerbated. Hydrocarbons tend to migrate in carriers where the hydraulic conductivity is relatively large. For example, when two carriers of different conductive capacities abut against an open fault, hydrocarbons fill the fault opening first, then find the carrier with the least resistance to migrate. These pathways differ from those predicted by fluid potential.

Faults and fluvial sand-bodies combine to form extremely heterogeneous carriers in the Oligocene petroleum system in Chengbei Step-Fault Zone, Bohaiwan Basin, China. The migration behavior in this system was studied by classifying the carrier-fault pathway combinations into 14 types. The simulation results show that the discovered oil accumulations are clearly associated with dominant pathways.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas