Analysis and Interpretation of Water/Oil Ratio in Waterfloods

Abstract

SummaryAn important problem in water control is the identification of the dominant reservoir or production mechanisms. Recently, Chan (Chan, K.S.: "Water Control Diagnostic Plots," paper SPE 30775 presented at the 1995 SPE Annual Technical Conference and Exhibition, Dallas, 22–25 October) postulated that a log-log plot of the water/oil ratio (WOR) produced vs. production time may be used to diagnose these factors. In this paper we provide analytical and numerical results for a variety of waterflood conditions to explore this possibility.We show analytically that the late-time slope of the log-log plot can be related to the well pattern and the relative permeability characteristics, specifically the power-law exponent in the kro − Sw relationship or the reservoir heterogeneity. Analytical results are provided for the behavior immediately following water breakthrough. In certain simple cases (mobility ratio equal to 1, layered systems), analytical type curves can be derived. In the general case, we use numerical simulation to provide numerical type curves.The results are summarized in terms of the various power-law scalings in different time regimes and by a catalog of numerical type curves. They confirm the potential of WOR-time plots as diagnostic tools for reservoir analysis and characterization.