An Accurate Method For Water Saturation Evaluation Based On Advanced Theory Of Electrical Conductivity Of The Terrigenous Rock

In practical well log interpretation of terrigenous sections, Waxman-Smits and dual-water models are used to evaluate water saturation (Sw) of the rock. These approaches need a whole range of corrections in the model parameters, first of all the structural coefficient m. Different researchers use different approximations of m as a function of Qv. The authors of this paper, on the basis of detailed studying sandstone and shale conductivity experiments published in the world, as well as their own data, found out new, never established earlier regularities in forming the relationship C = f(Cw). Taking these data into consideration, a new model of terrigenous rock conductivity was developed and presented at the 15th European SPWLA Symposium in 1993. This paper provides new data for theoretical validation of the electrical conductivity model. It is compared with the Waxman-Smits and dual-water models. The study showed that the new model more accurately describes the electrical conductivity of electrolyte, Cel, in the pore space. That gives an opportunity to assume m = const ~1.7 in the model. It was also established that the Waxman-Smits and dual-water models gave the very Sw values obtained with the new model if their m values were properly adjusted. However, when processing specific reservoirs, the latter procedure appears to be a source of uncertainty and excessive errors in Sw evaluation. Applying the new model forms a basis for developing a reliable method for the evaluation of water saturation of the terrigenous rock.