A New Approach for Rock Typing Using Dimensional Analysis: A Case Study of Carbonate Reservoir

Abstract

In recent years, Petrophysicists have established that rock typing is an essential pre-requisite for estimating permeability in reservoir rocks. Any attempt that does not use rock typing for modeling permeability has been documented to be characterized by a large data scatter and associated with high uncertainty. In this paper, four common rock typing techniques are compared: Pittman, Lucia, Flow Zone Indicator (FZI), and Global Hydraulic Element (GHE). The performance of these rock typing approaches is assessed through intrinsic models for their ability to predict the permeability of a prominent carbonate field. The FZI and the Pittman approaches gave the best estimates of permeability with a coefficient of determination of approximately 0.98. By contrast, the Lucia approach gave the least precise estimates of permeability with a coefficient of determination of 0.81. The GHE approach gave a satisfactory estimation with a coefficient of determination of 0.90. A new technique for rock typing, based on dimensional analysis, is presented. Dimensional analysis leads to the derivation of two dimensionless groups: (λ) and (Ω). The λ group is a dimensionless Flow Zone Indicator (FZI) and the (Ω) group is the dimensionless photo-electric adsorption. The main advantage of the dimensional analysis technique is that it relies directly on open hole log measurements, such as the spontaneous potential, bulk density, interval transit time, and photoelectric absorption. A unique power-law relationship exists between the dimensionless FZI group (λ), and the dimensionless photo-electric adsorption group (Ω). For the studied carbonate field, a coefficient of determination of 0.98 was obtained when estimating reservoir permeability with the dimensional analysis rock typing. This paper will be of interest to subsurface modelers who need to estimate permeability. Using the dimensional analysis approach described and comparing this new method of estimation with established methods, it is proposed that rock typing by dimensional analysis for estimating permeability can be used as an alternative method.