CLAY MICROPOROSITY IN RESERVOIR SANDSTONES - AN APPLICATION OF QUANTITATIVE ELECTRON-MICROSCOPY IN PETROPHYSICAL EVALUATION

Clay mineral microporosity in sandstones is measured using computer-as sisted image analysis of back-scattered electron micrographs of petrog raphic sections. Diagenetic kaolinite has a variety of textures with m icroporosity values ranging from 15 to 61%. Diagenetic chlorite has a generally uniform grain-coating texture and microporosity of about 50% . Fibrous illitic clays are difficult to characterize by the same meth od (an average value of 63% microporosity was recorded), but analysis of stereo-pair micrographs from scanning-electron microscopy analyses reveals that illite commonly has microporosity of approximately 90%. C lay microporosity data are used to calculate effective pore volumes an d volumes of clay-bound water for clay minerals in sandstones. Convert ing from weight percent clay to volume percent clay is important. Micr oporosity data are valuable input to V-shale evaluation where water sa turation is associated with day mineral type, texture, and volume.