Отправлено: 29.10.13 04:31. Заголовок: Title Environmental and Transport Effects on Core Measurements of Water Saturation, Salinity, and We

Title Environmental and Transport Effects on Core Measurements of Water Saturation, Salinity, and Wettability
Authors
S. Misra, C. Torres-Verdin, SPE, and K. Sepehrnoori, SPE, The University of Texas at Austin

SPE Annual Technical Conference and Exhibition, 30 September–2 October 2013, New Orleans, Louisiana, USA
ISBN 978-1-61399-240-1
Copyright
2013, Society of Petroleum Engineers

Abstract
Unaltered portions of whole core provide the most reliable measurement of rock properties for hydrocarbons-in-place, reserves, and reservoir-development calculations. However, core cutting and core surfacing operations can significantly alter the water saturation, salinity, hydrocarbon composition, and wettability of the whole core, among other rock core properties.

It is necessary to correct laboratory measurements of rock core properties to their in-situ values, and to identify the unaltered volume of whole core that is representative of in-situ reservoir properties.

To that end, we have developed a numerical simulator based on an equation-of-state compositional method that models three-dimensional time lapse variations of multiphase fluid saturation, water salinity, phase composition, and wettability of a whole core during core cutting and subsequent core surfacing operations in a vertical wellbore.

The UT Coring Simulator (UT-CS) quantifies mudcake growth, mud-filtrate invasion, miscibility of invading filtrate with connate fluid, wettability alteration due to surfactants in invading mud filtrate, phase transition and fluid expulsion during core surfacing. UT-CS delineates four distinct fluid flow mechanisms that occur within whole core during coring, namely, compressibility-driven concurrent flow, capillary pressure-driven countercurrent imbibition, axial flow, and surfacing-induced fluid phase expulsion. During core cutting, we observed that at the center of a whole core water-base coring mud could cause relative changes in fluid saturations, up to +/-100%, and in salinity, up to +/-15%.

More importantly, measurable changes in in-situ core properties can also occur during oil-base mud (OBM) coring owing to countercurrent imbibition flow. We show that mudcake quality is critical towards preserving core properties during core cutting.
On the other hand, during core surfacing (when mudcake is nonexistent), alteration of core properties is minimized by reducing the speed of core surfacing after reaching the depth at which there is an abnormally large increase in the gas volume fraction in the whole core.