A Mixture Electrical Conduction Model For Shaly Sands And Its Application

Shaly-sand reservoirs, as dominating oil/gas reservoirs in the world, are always in the regard of the log analysts. Recently more and more complex shaly-sand reservoirs have been explored for the increased demand of oil and gas in the world, such as low-resistivity oil/gas reservoirs, high-resistivity water reservoirs etc. The complex porosity shape in these reservoirs results in the difficulty of interpretation of their electrical conduction with conventional model. The complex shape of porosity in Shaly sands make their electrical conduction complicated, and microporosity in the porosity is the main cause. According to the standpoint, some electrical conduction models had been presented. However, some of these models cann't be brought into practice, others are diffcult to be applied owing to too much new parameter. Thus, none of these models can be applied in the interpretation of shaly-sand reservoirs. In order to solve the problems above, a series of researches covering both theories and pratices have been offered in this paper. From three aspects of theories, experiments and practices, microporosity has been deeply reviewed to clarify the limit among free porosity, microporosity and clay porosity. And the limit of 0.2μm has been found. In the electrical conduction of the whole rocks, the relations of the three porosities and the effect of oil and gas on the three porosities have been analysed in detail in order to improve the understanding of the complicated electrical conduction in the rocks. The analysis indicate that the relations of in parallel,in series and scaling addition, adopted in those models before, cann't exactly represent the complex relations of the three porosities in the electrical conduction of the rocks. When oil and gas migrate into rocks, the electrical conduction of the three porosities will be affected., but the extents are different. Direct effects are fuctioned on free porosity, and indirect effect on...