Abstract: Geological Description and Flow Characterization of a North Sea Chalk Containing Stylolites and a Gouge-Filled Fracture
D. P. Tobola, H. E. Farrell, B. A. Baldwin
A geological description and fluid displacement experiment have been conducted on a core sample exhibiting both stylolites and a gouge-filled fracture in order to investigate their characteristics and affect on fluid flow. Magnetic Resonance Imaging (MRI) was utilized during the displacement experiment to monitor the fluid movement within the core sample.
SEM analysis performed on the sample indicated that both the grain and pore size within the gouge-filled fracture had been reduced with respect to the adjacent chalk matrix. This reduction resulted from the mechanical breakdown of the coccolith fragments that made up the bulk of the chalk matrix into their constituent, submicron size platelets, as opposed to the crushing of individual calcite crystals. The reduction in pore size contributed to an increased degree of capillarity within the gouge-filled fracture as was evidenced during the displacement experiment.
During the gas-displacement experiment, the core sample, containing decane and residual water, was progressively desaturated by the injection of nitrogen. MRI analyses were performed at each level of desaturation. The gouge-filled fracture was observed to exhibit a displacement pressure that was greater than that of the adjacent bulk matrix. MRI analyses also indicated that the effect of stylolites on fluid flow was negligible. The final distribution of the residual fluids upon desaturation indicated that the stylolites and the gouge-filled fracture did not act as an impediment to fluid movement.
AAPG Search and Discovery Article #90957©1995 AAPG Mid-Continent Section Meeting, Tulsa, Oklahoma