The influence of early oil and gas charging on diagenesis

Abstract:

With the increase of depth, the growing influence of compaction and diagenetic cementation should make reservoir physical properties worse and worse, but we found that the reservoir property deviated from the normal compaction curve through researching the development of high porosity and its control factors in deep sandstone reservoirs all over the world. Some data from different basins at home and abroad showed the bigger solubility of carbonate type (such as calcite) and aluminum silicate type (such as feldspar) and good development of secondary pore in oil-bearing sandstone than that in the no oil-bearing sandstone. And, calcite cementation, dolomite cementation, quartz cementation in the oil reservoir are more than that of the no oil-bearing reservoir. The effect of oil and gas charging on the diagenetic evolution is complicated. The degree of mineral cementation is also relevant to the saturation of oil and gas, influence of low oil saturation on diagenetic environment was not distinct. By studying different basin, different geology, we found that the oil and gas filling impacts on deep sandstone properties by influencing the diagenetic compaction, cementation and dissolution of deep reservoir: (1) the overpressure of oil and gas charging can buffer compaction of overlying strata; (2) the early oil and gas filling inhibit or slow down the cementation process, especially to illite and quartz, (3) the organic acid dissolution in oil and gas can improve the physical properties of deep reservoir. These three aspects are essentially improved reservoir for deep hydrocarbon accumulation, having very realistic significance for the deep oil and gas exploration.