Quantitative characterization of clastic particle size of tight sandstone and its indicative significance for productivity

[Objective]Particle size analysis is important for the evaluation of clastic oil and gas reservoirs because it can identify the stratigraphic depositional environment and evaluate the permeability of reservoirs. [Methods]Taking the dense sandstone reservoir of Shaximiao Formation in Tianfu Gas Field in Sichuan Basin as the research object, firstly, we analyzed the influence of the particle size and shape of the clastic rock on the permeability of the reservoir, and then, based on this, we combined the median value of the particle size, the C value of the particle size, and the sorting coefficient, and put forward a comprehensive characterization of the indicator parameter of the particle size PI, and then we carried out a principal component analysis on the natural gamma, the photoelectric absorption cross section index, and the neutron, which are more sensitive to the particle size. The exponential relationship model between the particle size indicator parameter PI and the principal component parameter is established. Finally, the correlation between the particle size indicator parameter PI and reservoir production capacity is analyzed by combining the test and logging data. [Results]The statistics of 8 test gas sections of 7 wells in Shaximiao Formation of Tianfu Gas Field were collected, and the values of particle size indicator parameter PI of 7 wells were calculated by the above method, and the response relationship between the unimpeded flow rate of the test sections and the particle size indicator parameter PI was analyzed, and the results show that: the cumulative values of unimpeded flow rate of the test sections in Shaximiao Formation of Tianfu Gas Field and the particle size indicator parameter PI, X, showed an exponential relationship, and their correlation coefficients reach to 0.85. [Conclusion]The study shows that for reservoirs with lithology mainly dominated by medium-fine-grained sandstone, with large variation of grain size, and with storage space dominated by residual intergranular pores, the grain size indication parameter PI can to some extent indicate the production capacity of this type of reservoir.