DIFFERENTIAL ACCUMULATION OF HYDROCARBON IN THE GUANTAO FORMATION OF MIAOXINAN UPLIFT

The differential hydrocarbon accumulation including the differentiation of hydrocarbon enrichment degree in different types of sandbodies on the Miaoxinan Uplift is studied in this paper in a viewpoint of hydrocarbon migration and accumulation. A conceptual model is established as a result for differential accumulation of hydrocarbon. It is found that hydrocarbon movement follows a relaying migration model when it passes through a multiple "ridges-faults system" of a faulted terrace zone as that prevailed on the Miaoxinan Uplift. After moving up to a higher terrace of sandstone ridges of the Lower Guantao Formation, hydrocarbon will move laterally. It will further move along the faults connecting "ridges" to a shallow terrace once it is filled. The distribution and strength of structural compression, driving force to the migration and preservation of oil and gas, control the types of sandy accumulations and the degree of hydrocarbon saturation. High stress area was prone to hydrocarbon preservation. Thicker sandbodies are prioritized. Low stress area is favored to oil and gas migration rather than accumulation, hence thinner sand bodies dominate hydrocarbon accumulations. Fault blocks in the lower position of the low stress area as well as the blocks in higher position of high stress area are the places for optimal migration and preservation of hydrocarbon. Therefore, the regions at higher tectonic position on the transporting ridge with large cumulative dislocation and effective connection to faults will have greater hydrocarbon abundance. Based on the understanding mentioned above, the exploration of hydrocarbon resources on the Miaoxinan Uplift is quite successful.