Characterization of carrier formation for hydrocarbon migration:concepts and approaches

The occurrence of secondary hydrocarbon migration in basins depends on the correlation between driving force under natural geological conditions and the resistance of carriers,which controls the formation process and special distribution of hydrocarbon accumulations.Previously quantitative studies on the driving force of hydrocarbon migration have been nearly perfect,whereas studies on migration paths remain still in qualitative level.Based on our recent-years attempts at quantitatively analyzing migration paths,we examined the study scale of hydrocarbon migration in actual basins and its maneuverability,used ideas and methods engaged in characterizing reservoirs in oilfield development as reference and proposed a concept on the carrier formation in order to achieve a quantitative characterization of hydrocarbon migration carriers.The carrier formation is defined as a stratum that has a certain thickness,is located beneath a regional seal and may include all the carriers that have microscopic pore space and permeability.These carrier formation are geometrically linked together from a macroscopic perspective and capable of a fluid dynamic connectivity with each other when hydrocarbon migration and accumulation occur.Based on actual situations of terrestrial basins in China,we summarized all the analytical methods for the connectivity of sandstone carriers and proposed a basic working procedure to set up models for sandstone carriers.Finally,we established a methodology to characterize them quantitatively with conventional property parameters,which should include the following 5 steps: ①to determine the thickness and domains of carrier intervals;②to delineate sand-body properties in carrier formations;③to analyze the geometric connectivity among sand bodies in carrier formations;④to examine the hydraulic connectivity among sand bodies in carrier formations;⑤to quantitatively characterize the transporting capability of carrier formations.The permeability seems to be the best parameter in the quantitative characterization of carrier formations from a perspective of setting up a carrier framework composed of various carriers.