Downhole Fluid Analysis and Fluid Comparison Algorithm as an Aid to Reservoir Characterization

Abstract

Abstract In recent years, formation sampling and testing tools have provided a variety of new downhole optical measurements for downhole fluid analysis (DFA). DFA involves in-situ measurement of optical absorption spectra used to compute properties such as hydrocarbon composition and gas oil ratio (GOR). Abrupt changes in these fluid properties with depth may be a marker for reservoir compartmentalization. However, hydrocarbon differences can be reliably identified only when the significance of uncertainties due to measurement and oil base mud filtrate has been taken into account. Recently, an algorithm called the fluid comparison algorithm (FCA) has been developed to address this issue. FCA propagates uncertainties in optical measurement and contamination into uncertainties in fluid properties, such as color, composition, and GOR. The output of FCA is the probability that two fluids are statistically different. Real-time application of FCA can optimize capture of downhole fluid samples and generation of a continuous downhole fluid log representing the fluid complexity in the reservoir. In addition, by identifying abrupt changes in fluid properties with depth, FCA may in some circumstances be an assay for reservoir compartmentalization. In this paper, we briefly review the theory of FCA. The strengths and limitations of the technique to improve understanding of reservoir architecture and fluid complexities are presented through two case-studies.