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Abstract: An Experimental Investigation of Permeability and Porosity Alteration in Diatomite During Hot Fluid Injection

KOVSCEK, ANTHONY, Stanford University, Stanford, CA

Silica dissolution was studied to understand the evolution of permeability and porosity in siliceous diatomite during hot fluid injection such as water or steam flooding. Two competing mechanisms were identified. Silica solubility in water at elevated temperature causes rock dissolution thereby increasing permeability; however, the rock is significantly compressible leading to compaction of the solid matrix during injection and the loss of permeability and porosity. A laboratory flow apparatus was designed and built to examine these processes in diatomite core samples. At the core level, we measured the pressure drop as a function of time to determine the permeability variation and utilized an X-ray Computerized Tomography (CT) scanner to measure porosity. At the pore level, a scanning electron microscope (SEM) was used to observe changes in pore morphology. We found that porosity decreased initially due to compaction caused by the imposed pressure drop across the core. Later, porosity increased as silica dissolved. Dissolution of the rock matrix appeared to be relatively uniform in agreement with a scaling analysis. Wormholes in the rock matrix were not observed even after tens of pore volumes of fluid injection.


AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California