Research On Vertical Structure Of Mesozoic Uncomformity And Hydrocarbon Accumulation Mechanism, Jiyang Depression

The characteristics of Mesozoic unconformity in Jiyang Depression and its effect on oil-gas migration and accumulation was researched by using seismic, well logging, geochemistry and other data. The study on physical modeling experiments could help to understand hydrocarbon migration and accumulation process along unconformity by constructing the effective unconformity models, to systematically and visually analyze forming process and mechanism of strata reservoir, and to provide theoretical basis for future subtle reservoir exploration.The types of Mesozoic uncomformity in Jiyang Depression were almost truncated-onlap uncomformities, which could form the truncated strata reservoirs or overlap strata reservoirs combining with the microscopic constitution of the uncomformity, such as the stratigraphic contact relationships of sand-sand ,sand-mud, mud-sand, and they were in orderline on the plane. The stratification of the vertical structure can be shown in lithology, well-logging response, fluid seepage, mineral composition, element characteristics and so on. The structure is divided into three-layer or two-layer, and the different structures were controlled by lithofacies, paleoclimate and paleotopography, which made a different effect on the hydrocarbon migration and accumulation in vertical or lateral direction. Physical modeling experiments showed that the type of "S" paleotopography controlled the distribution of strata reservoirs, and the porosity and permeability of transforming layer in uncomformity and the gradient of the paleotopography could control the migration ability of hydrocarbon and the position of the reservoirs. The dual migration passages consisting of the half-weathered rock and the upper basal conglomerate were highly effective movement passways for hydrocarbon, and the loss of weathered clay could form clear scuttle-like vertical migration pattern. The reservoirs were controlled by the "T-S" transforming system, which was comprised of the rupture, uncomformity and glutinite. The forming of the strata reservoir was determined by uncomformity style, the matching of the traps forming phase and the main hydrocarbon migration phase or the paleotopography. The "double channel" uncomformity between Mesozoic and Palaeozoic which was both composed of sand could be still gas migration passage, because the sands were little affected by the compaction and diagenism.