Comparison of otherness on hydrocarbon accumulation conditions and characteristics between deep and middle-shallow in petroliferous basins

Abstract

Deep strata is defined as the stratigraphic field with buried depth greater than 4500 m in hydrocarbon basins. All around the world, a total of 1477 hydrocarbon reservoirs have been discovered in deep and ultra-deep strata (with buried depth greater than 6000 m), of which hydrocarbon reserves account for 40% and 49% of the total respectively. At present, annual hydrocarbon reserves discovered in deep Tarim Basin, China account for more than 90% of the total discovery. With the increasing demand for oil and gas resources in the world, the deep hydrocarbon exploration is sped up, thus leading to more challenges. Therefore, the research on the differences in hydrocarbon accumulation conditions, geological and distribution characteristics of hydrocarbon reservoirs between deep and mid-shallow reservoirs has important practical significance to reveal and clarify the deep hydrocarbon accumulation mechanism and distribution laws. Research results have indicated that six great differences exist in deep hydrocarbon accumulation conditions involving source rocks, reservoir, cap rocks, migration, trap and preservation from mid-shallow strata. Thus, the criteria and methods established based on researches on the geological conditions of mid-shallow hydrocarbon cannot be used to judge and evaluate the geological conditions of deep hydrocarbon and its exploration prospect. Moreover, great differences also exist in trap type, reservoir characteristics, fluid phase state, temperature and pressure environment and other aspects between deep and mid-shallow hydrocarbon reservoirs. As a result, the mid-shallow hydrocarbon accumulation mode and exploration experience could not be applied to guide the prediction and exploration of deep hydrocarbon reservoirs. In addition, deep hydrocarbon reservoirs have their own characteristics of distribution and development in different types of basins, different ages of formation and different burial depth conditions. Thus, the existing understanding of mid-shallow reservoirs cannot be completely applied to determine exploration direction and drilling target, and it is required to make a decision based on the actual geological conditions.