Capillary Shockwave Front Blind Imaging of Reservoir Limits: A Case Study

Abstract

Abstract Reservoir boundary information is gleaned from a steady-flowrate-drawdown test and/or a subsequent buildup following the steady flow period. Singularities are observed to be present in virtually all transient pressure data that can provide direct information about the limits around a well. Multiple limits can be detected discretely and described by distance from the well and angular shape at the point of contact. The input information required is pressure data acquired while flowing on a fixed choke, petrophysical properties from cores and electric logs, and fluid production rates and compositions during the flow period.(2) Reservoir limits can be assembled into an energy equivalent image based upon cone of influence energy growth behind a bounding initiating capillary pressure shockwave front. The resulting image can then be compared with a seismic data based map or a geologic map. Volume integrals for gas inplace can provide an early physical measurement for reserve accounting purposes.(4,5,6,8) A variety of boundary contact shapes were assembled into a "blind" energy map that was later confirmed by seismic imaging. A direct overlay comparison of the "blind" energy image and a 3D seismic map is presented. The limit information will be compared with the seismic image to confirm it point by point. This new transient pressure analysis method is based upon a real capillary network growing from the well bore. Flow into the well bore is restricted to radial flow and confined to the real capillary flow paths by initial capillary pressure.(2) The cone of influence is bounded by an associated capillary shockwave front that restricts its growth. The bounding initiating capillary pressure shockwave front is the physical phenomenon that exists at the radius of investigation(1,7,10) The capillary networks give rise to secondary pressure singularities when a boundary is encountered. The method extends traditional analysis to the realm of wave mechanics(8,9,11) and allows direct data processing. The solution is based upon an energy model that solves for boundary geometry directly from flow and buildup data without the process of traditional iterative history matching. The boundary contacts can then be assembled into an image of the reservoir based upon relative disposition of individual limit contact.