Reservoir Zonation - A Novel Approach: Use of Core Derived K-?-Swirr Relationship to Define Reservoir Rock Types (RRTs)

摘要

Rock typing is an essential reservoir characterization tool to reflect the spatial variation in initial fluid distribution and flow behavior characteristics. Rock typing techniques are generally based on porositypermeability relationships to establish the types of rocks present in the reservoir. These techniques lack in effective segregation of reservoir into definite number of zones/rock-types with clear boundaries. This results in a non-unique rock-typing scheme with arbitrary number of RRTs depending on data manipulation. Moreover, these RRTs do not correspond to separate J-function curves due to negligence to water saturation term. To overcome these problems, a new approach for reservoir zonation is developed which has been tested in a few off-shore sandstone reservoirs. This paper illustrates a robust method of rock typing using a new theoretical development and mathematical formulation. The method integrates irreducible water saturation term with modified Carmen- Kozney equation using a proposed pore-throat dependent water saturation function [S_(wirr) = exp (-ar~t)]. The generalized porosity-permeability-saturation equation [K = A?~3(lnS_(wirr))~B] thus derived is fitted on the Routine Core Analysis (RCAL) data for division of reservoir section into different layers having unique coefficient-exponent set (A, B) representing RRTs. Application of this method resulted in an effective RRT scheme as evident from the unique coefficientexponent sets as well as separate J-function curves. The unique porosity-permeability-saturation relationship existing for each RRT has been thus obtained from the RCAL data. This relationship can be used as an efficient tool for reservoir zonation. Reservoir zonation algorithm, analysis results and validation procedures are discussed using field examples. Reservoir characterization is the key to improve reservoir performance prediction and recovery optimization. This paper presents a novel approach to effectively segregate the reservoir into definite number of RRTs using only RCAL data. This work also presents a theoretically derived K-?-Swirr relationship based on pore scale attributes. Irreducible water saturation, being an eminent parameter describing the internal architecture of the rock, is included in formulation and derivation of a theoretical framework to address classification of RRTs.