Geological Structure Characteristics And The Influence On Hydrocarbon Accumulation In Jizhong Depression

Geological data, seismic data, log and resource evaluation data are used to contrasted andresearched the geological structure characteristic of twelve main depressions of Jizhongsubbasin, then the control mechanization of geological structure for sedimentation areresearched among those classical depressions, on this basis, hydrocarbon accumulationelements of all Jizhong depressions were researched and contrasted, finally, the hydrocarbonaccumulation differences and the main controlling factors were researched and contrasted.According to the hydrocarbon accumulation differences, twelve Jizhong secondarydepressions are divided to rich-oil depression, oil depression, and poor-oil depression, andthese twelve depressions are further divided to eastern depression play and western depressionplay by distribution pattern, on the base of geological structure and feature contrasted, thispaper come to a conclusion that the most beneficial depression is the inherited half grabenstructureⅡ, such as Raoyang depression, followed by the half graben structure Ⅰ,and thedeclined structure is the worst. Influenced by fracture cutting and bedrock tilting effect, thecharacteristics of eastern depression play’s multi-subsags, multi-buried hill, multi-slope andvarious structural styles are obvious, the four more features are beneficial for hydrocarbonexpulsion, migration and accumulation, in contrast, the western depressions play have fourless features which are not conducive to hydrocarbon accumulation.Based on contrast of the fracture development characteristics of the whole study area, mystudy shows that the fracture system of Jizhong eastern depressions play was extensive, andacted in many times in Cenozoic era, basin edge fractures were main fracture styles in westerndepressions play and the main active stage was from Pretertiary to early Paleogene. Typicalcontrol concave fractures are selected to analyze the fracture’s control function on theformation of the depression geological structure, and based on the analysis of structureformation and evolution to study the geological structure and tectonic zone’s influences ondepositional systems, then research the law of the migration of the depocenter, this papercome to a conclusion that Jizhong depression’s East-West zonation, North-South division tectonic pattern and the differences of various depressions’ structural characteristics are themain reasons for Jizhong depositional system’s evolution, in detail, the sedimentary system ofLanggu-Baxian-Raoyang depression play is the best, followed by Shenxian-Shulu-Jinxiandepression play, and the depressions of western play are the worst.The elements of hydrocarbon formation and accumulation are researched and controlledon the basis of deposition research, confirmed the differences of hydrocarbon formation andaccumulation of different depressions, As a whole, eastern zone is better than western zonewhile central zone is better than others.Based on the contrast of different depression’s geological characteristics and the elementsof hydrocarbon information and accumulation, my research shows that oil and gasaccumulation is obviously influenced by tectonic framework and structural characteristics.The most important form of hydrocarbon accumulation is that buried hill as the main body ofhydrocarbon accumulation, and exist popularly in eastern area, with the whole law ofEast-rich oil and West-poor oil, the central oil-rich and north-south oil and gassimultaneously; Influenced by tectonic zone and different source-reservoir-cap assemblage,oil and gas accumulation layer as well as the trap type show the law of order andcomplement and diversity; and this area have the characteristic of surrounding subsagsgather oil which is controlled by main hydrocarbon generation sags. In addition, the rate ofdeposition in eastern large-scale half graben depressions is always quick, which lead to thepopularity of uncompaction, and the overpressure begin to appear, based on some study, myresearch showed that the relativity between the overpressure and the hydrocarbon enrichmentdegree in different depressions is close.