f Validating Water Saturation Calculations from Log Data with Capillary Pressure Measurements using 3D Geocellular Models

Accuracy in reserves calculation is one of the most important requirements at any stage of the life of a hydrocarbon field. Moreover, one of the most important elements in reserves calculation (as well as one of the most uncertain) is the calculation of water saturation and its extrapolation away from the wells. Traditionally, workflows for water saturation interpretation for 3D geological models are based uniquely in water saturation measurements from log data using the Archie Equation. These techniques although proven in several fields around the world, are heavily affected by the mineralogical content of the rock, porosity, permeability cementation, saturation exponents, etc. Two examples are shown in this paper. The first one presents exactly this problem due to the presence of metamorphic fragments in the reservoir rock. The log response to these fragments affects the water saturation radically, by showing very high saturations where DST tests shown high gas production. The second example shows how this technique could be effective even if the data is scarce. The methodology described in this paper uses capillary pressure data in conjunction with log data to reconcile the water saturation values both at the well locations and between them. However, when comparing water saturation from these two different methods, a direct comparison is very cumbersome and could be misleading. The use of Leverett J(S) correlated functions (Leverett, 1941) are use to overcome this problem. The method is based in cloud transform fitting instead of the traditional curve fitting described by Gomez-Zuluaga (2003) and honors the data points without introducing any statistical deviation. This paper describes the process followed by Chevron Petroleum Company to evaluate and populate water saturation away from the wells in a 3D geological model. The methodology has proven to deliver trustful results and can be applied to any field with log data and basic capillary pressure measurements.