Study On The Effective Medium Pore Combination Resistivity Model For Low Porosity And Permeability Shaly Sand Reservoir In The East China Sea

Along with the development of exploration activity in sea areas, some low porous and permeable oil and gas reservoirs or structures have been found. However, the exploration technology of low porosity and low permeablility reservoirs is not very mature now. Therefore, providing a better method of log interpretation for offshore low porous and permeable reservoirs becomes the most important issue to be resolved.In this paper, based on experimental data of high-temperature and high-pressure rock resistivity, the conductivity law of low porosity and permeability reservoirs in the East China Sea is analyzed, and m and n of the reservoirs are found out. Since low porosity and low permeability reservoirs in the area have complex pore structure and high capillary bound water, an effective medium pore combination resistivity model is proposed for low porosity and low permeability shaly sand reservoirs based on conductivity difference equation and three-water conductance theory. By analyzing effects of some factors on the proposed model, we find that the curvatures of the curves between resistivity index and water saturation are greatly affected by the content of the dispersed clay. Also resistivity index decrease as fraction of dispersed clay, saturation of capillary bound water, movable water exponent. Resistivity index increases as matrix cementation exponent , dispersed clay cementation exponent, saturation exponent, clay bound water cementation exponent increases. Fitness of measurement data of rock resistivity with the resistivity model shows that the model can describe the conductive laws of low porosity and permeability reservoirs in the area. The methods to calculate shale content, porosity, permeability, capillary bound water saturation are established, and the methods are given to calculate the values of movable water cementation exponent, capillary bound water cementation exponent, matrix cementation exponent and saturation exponent with experimental data of size and mercury injection etc.. The log data of low porosity and permeability shaly sand reservoirs in the East China Sea are processed with the established interpretation methods, and the result agrees with testing for oil very well. It shows that the model can be used to interpret low porosity and permeability shaly sand reservoirs with the East China Sea.