Applications of petroleum geochemistry to exploration and reservoir management

Petroleum migration pathways through a basin are determined by the three-dimensional distribution of discontinuous sealing surfaces, which are usually parallel to bedding. The petroleum migrates below the sealing surface, taking the structurally most advantageous route. The three-dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper. Application of the model to the Paris and Williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models. Pathways form a dense network overlying generating areas in the central parts of basins. Toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing-surface morphologies. Eventually, these pathways may reach the surface as seepages. It is important to integrate surface outcrops of migration routes (surface seepages) into migration modeling. Deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal, fault juxtaposition, or cross-formational seals such as salt intrusions. Deflection of pathways also occurs where there are hydrodynamic conditions in response to topography-driven groundwater flow. Zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies, or juxtaposition to nonsealing strata by faults. Vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture. Reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool. It assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion.

Petroleum Migration Pathways and Charge Concentration: A Three-Dimensional Model

Petroleum migration and accumulation in the Bozhong sub-basin, Bohai Bay basin, China: Significance of preferential petroleum migration pathways (PPMP) for the formation of large oilfields in lacustrine fault basins

Abstract Numerous works have been published during recent years discussing the occurrence and effects of chromatographic processes with respect to petroleum migration. ‘Geochromatography’ has been, and still remains, a controversial topic. Based on the principles and conventions of separation science a definition of geochromatography is proposed, followed by a discussion of the relevance and potential occurrence of chromatographic type fractionation effects during primary and secondary petroleum migration. The evaluation of the relevant literature suggests that chromatographic processes in natural systems involving liquid mobile phase can result only in compound class fractionation (saturates, aromatics, polars) whereas molecular fractionation may be expected to occur with gaseous mobile phases. Problems associated with the recognition, experimental verification and quantification of geochromatography are discussed in detail.

Geochromatography in petroleum migration: a review

Invasion percolation and secondary migration: experiments and simulations

Experimental data suggest that the secondary migration of oil in porous, permeable sediments probably occurs, in most circumstances, along restricted pathways or conduits. These conduits are formed after the oil has reached a high enough saturation in the reservoir rock for the buoyancy of the oil to overcome the capillary pressure in the pore throats. The oil probably moves vertically until it reaches the top of the reservoir interval. The oil then moves updip along the top of the reservoir interval via a narrow, restricted pathway until it reaches the trap and begins to accumulate. Depending on the area of the original oil saturation at the bottom of the reservoir unit and the structural geometry, multiple conduits may form, along which the oil may flow. Because these conduits are limited in diameter, the amount of oil lost during secondary migration could be limited to the irreducible oil saturation left behind in the conduit, provided no small-scale traps exist along the path to the main trap. Rates of oil movement are very rapid in a geologic context, suggesting that the timing of primary migration is a good indicator of the timing of secondary migration.

Michael J. Anderson

Papers

Secondary Migration of Oil: Experiments Supporting Efficient Movement of Separate, Buoyant Oil Phase Along Limited Conduits: GEOLOGIC NOTE