MOHAGHEGH, SHAHAB, KHASHAYAR AMINIAN and W. WALLACE, West Virginia University, Morgantown, WV

ABSTRACT: The Application of Modified Electron Microscopy for Detection of Clays in Reservoir Rock

The conventional methods of detecting and measuring clays in the reservoir rock matrix provide information on the bulk mineralogy. However, the clay minerals that are present on the pore surface are mainly responsible for formation damage due to clay swelling and migration. This paper introduces a new approach that can help petroleum geologist and petroleum engineers to detect and measure the clays minerals on the pore surface using Modified Scanning Electron Microscopy (MSEM). This method was originally developed by Wallace et al to study the effect of coal dust on miners and allows the researchers to concentrate on the surface of the grains rather the whole grain.

To evaluate and verify the proposed approach, Granny Creek Oil Field in West Virginia was selected for study. This field which has produced from Big Injun Formation since early 1900s, is being waterflooded. Majority of the injection wells in Granny Creek Field require pressures that are significantly higher than those evaluated according to engineering calculations utilizing core and well log analysis results. The optical microscopy studies on thin sections do not indicate the presence of clays minerals in significant amounts. However, the investigations utilizing MSEM indicate the clay minerals are present in sufficient amount on the surface of the, pore to cause formation damage that explains the high injection pressures. The pressure fall-off tests on several wells have verified th s conclusions.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.