Seepage’s Electrical Characteristics Research On Low Permeability Sandstone Reservoir

Electric logging is primarily method to study the distribution and the properties of the reservoir’s oil and water.However, geological character and rock physical properties are complex and more special in Low permeability reservoirs. So,it is usually oil-gas-water layers can’t be clearly displayed on logging curves.Meanwhile, The pore configuration of reservoir and Seepage law are complex,so that, there are more difficult in laboratory experiments. Therefore,on basis of the understanding characteristics of reservoir,this paper has studied the relationship between the seepage law and rock electricity’ properties, through a large number of laboratory experiments about electricity and oil-water percolation. By studying in this paper, the following key understandings and results are obtained:(1) The study area reservoir’s main rock types are feldspathic sandstone and quartz sandstone. Chang2reservoir of FJ has lower clastic sandstone and mainly fine-medium feldspathic sandstone.Chlorite and kaolinite are mainly chink and type of rock cementation is porous cement-based.Fine-the grain of debris feldspar sandstone is primary rock type in Chang6reservoir of JZG. Chlorite and water mica are mainly chink and type of rock cementation is mainly pore and pore-thin film. The Chang2reservoir of FJ permeability distribution is from0.416～28.9×10-3μm2, with an average5.67×10-3μm2and average porosity15.9%. Chang6reservoir of JZG permeability distribution is from0.0124～1.556×10-3μm2, with an average0.304×10-3μm2and average porosity9.34%.So the study area reservoir is a low porosity and low permeability reservoir.(2) Through the experiment equipment improvement, the problem about irregular core edge is solved, modifying the pore volumes and water saturation,and determining measurement time of rock sample’s resistance that the fluid distribution achieves stability(general for30minutes).(3)In the process of single-phase oil seepage for Chang2reservoir of FJ, displacement pressure and resistivity have different curve shapes.When is Ka>1.0×10-3μm2, the curve shape is linear. When is Ka<0.5×10-3μm, the curve shape is quadratic polynomials. In the process of single-phase Water seepage, displacement pressure and resistivity have satisfied with power law relationship.(4) In the process of single-phase fluid seepage for Chang2reservoir of FJ, Overburden pressure’s change has influence on rock electrical. In a general way, along with the overburden pressure increasing, the rock resistivity is increasing. Especially,this chage has obvious influence on the process of single-phase oil seepage.(5) With water saturation increasing, the resistivity curve becomes irregular "Z"shape during staticaldisplacing oil by water. When water saturation is below70%, drop in the rock resistivity is small, along with the increase of water saturation. When water saturation is between70%and75%, the rock resistivity appears sudden decline and has a transition point.(6) In the dynamic process of water-oil two phase flow, after the core of the water saturation achieving a characteristic value Swp(Chang6reservoir of JZG is about65%,(Chang2reservoir of FJ is about61%), improving trend of resistivity index is moderating, and water saturation and resistivity index’s curve appear a turning point,which is closer the position of the point that Ko is Equal to Kr in relative permeability curve.(7) Through the statistic regression of method,it is determined that the relationship between Seepage rule and rock electrical has satisfied non-linear.