Abstract:

In order to accurately calculate the cation exchange capacity Q_v of shaly sand reservoirs, a Q_v calculating method using NMR logging data was presented, a correlation model between Q_v and synthesized index was established by analyzing 56 core samples with porosity, permeability and CEC, considering the problem that it was difficult to accurately calculate synthesized index, the novel method was presented to calculate Swanson parameter from NMR T₂ geometric mean value and to obtain the synthesize index from Swanson parameter. At the same time the data of four wells at the southern margin of Junggar Basin were processed using Q_v calculated by three different methods of NMR logging, natural gamma ray logging and spontaneous potential logging, and comparative analysis was carried out. It is showed that Q_v can be simply and efficiently calculated by these three methods in thick layers of shaly sand, compared with the core analysis results, the relative error based on NMR logging, natural gamma ray logging and spontaneous potential logging respectively is 13%, 19% and 22%; in thin alternating layers of shale and sandstone, Q_v calculated using NMR logging is more reliable than that calculated by the other two methods, and better reflects the true situation of formations.

Key words: cation exchange capacity Q_v, NMR(nuclear magnetic resonance), natural gamma rays, spontaneous potential logging