Jinjie Wang

Summary: A new classification of gas-hydrate deposits is proposed that takes into account their location (marine vs. permafrost), porosity type (matrix vs. fracture), and gas origin (biogenic, thermogenic, or mixed). Furthermore, by incorporating currently used Classes 1 through 4, which describe the nature of adjacent strata, a total of 16 classes of hydrate deposits have been identified. This new classification provides detailed information on the properties of the hydrate-bearing layer and adjacent strata that can be used for both scientific research and ranking of field-development potential. Using this new classification system, a qualitative ranking of field-development potential for different classes of hydrate deposits according to likely productivity, capital, and operating costs can be conducted. Finally, we demonstrate the usefulness of this new classification by applying it to 11 well-known gas-hydrate deposits worldwide.

The Chang 7 reservoir in Changqing oilfield is rich in tight oil. However, due to the low formation permeability, it is very difficult to obtain economical oil production without stimulation treatments. Volume fracturing seems to be a more efficient tight oil recovery enhancement (EOR) method in Chang 7 pilot tests compared with conventional hydraulic fracturing. In this study, Chang 7 tight oil reservoir was first characterized by its geological property, hydrocarbon source rock distribution, and formation physiochemical property. Tight core flooding tests were then conducted to experimentally investigate the EOR ability of the volume fracturing technique. The field-scale practice was also demonstrated and analyzed. The results show that Chang 7 reservoir is favorable for the generation of a large amount of tight oil. Fractures created in tight cores can significantly improve the fluid flow conductivity and enhance the imbibition of displacing water, resulting in a greater tight oil recovery increment. Volume fracturing is an effective way to generate a larger number of fractures. Field application indicates that volume fracturing treatment can form a much greater reservoir stimulation volume. Daily oil production in the volume-fracturing-treated wells can be more than twice as high as that in the conventional-fracturing-treated wells.