Study on distribution law of irreducible water and gas saturation of tight sandstone gas reservoir

Initial oil or gas saturation is one of the most important parameters to calculate and evaluate the reserves. A set of various centrifugal forces were used in the centrifugal experiment in order to find the suitable force corresponding to the tight gas reservoir. The experiment indicated that 2.07 MPa was suitable and the classical centrifugal forces such as 0.69 MPa and 1.38 MPa were less appropriate to the tight gas reservoir. Combined with the Laplace equation, results indicated that the lower limit of the effective flow throat radius of the tight gas reservoir was close to 0.07 μm. This value laid the foundation for the reservoir evaluation. Low field nuclear magnetic resonance (NMR) experimental results also implied that the irreducible water located in micro-pore space and traped in some large pores, which was related to the small throat radius but large pore-to throat ratio. Compared with the results of sealed cores, the centrifugal experimental results such as irreducible distribution feature and gas saturation are consistent with the results obtained from the initial gas reservoir. In summary, the irreducible water saturation of the tight gas reservoir is high and its initial gas saturation is as low as 26.76%.