Prediction of gas production in carbonates based on CT analysis and nuclear magnetic resonance (NMR) logging

Based on the analysis of 3-D CT data of full diameter carbonate cores and gas-test results of the coring formations, it is found there exists a quantitative relation between daily gas production per meter in effective intervals and CT70 porosity (according to the CT resolution of full diameter core, CT70 porosity is defined as the percentage of the volume of pores whose diameter is larger than 70 µm in the core), and a new method of gas production prediction in carbonates is put forward using CT70 porosity. Firstly, the exponential relationship between gas production and CT70 porosity is proved by effective medium approximate theory (EMA) in dual media and planar radial flow formula. Then the physical significance and varying pattern of each parameter in prediction formula are determined through theoretical analysis and calculation. The method of proportional transformation between CT and NMR data is put forward, therefore the application of gas production prediction based on NMR logging can be realized. The method has been used for the gas production prediction of 16 wells of the key exploration area in Sichuan Basin. The gas-test results prove the correctness and practicability of the method presented in this paper.