An Extended JBN Method to Determine the Flow Function and Relative Permeabilities from Composite Core Flooding Experiments – Preliminary Results

Abstract

Abstract Core flooding is a standard experiment where for example water is injected to displace oil, and the production, pressure drop, efficiency and ultimate recovery of the process are parameters of interest. Transient pressure drop, and production data can be used to calculate relative permeability functions characterizing the porous media. An analytical technique for this calculation is the JBN method, which assumes immiscible, incompressible fluids, a homogeneous system and negligible capillary and gravity forces. These conditions may be met for oil-water systems flooded at high rate or in long horizontal cores. However, in many cases, composite cores are used experimentally, i.e. several short cores with different properties (lengths, porosities and permeabilities) are put together to form one long core during flooding. The JBN method then calculates incorrect relative permeabilities. This work derives theory for an extended JBN method to interpret unsteady state flooding experiments of composite cores accounting for the spatial variation in core properties. The method calculates outlet saturation, fractional flow function and relative permeabilities based on production and pressure drop data, for a composite core with known porosity and permeability distribution. The saturation profile in the composite core can be calculated by taking the Buckley Leverett profile of a uniform core and converting the spatial axis. Assuming negligible capillarity and compressibility, the saturation profiles in composite cores depend on the porosity distribution, not the permeabilities. However, a saturation arrives at the outlet after the same number of pore volumes injected, regardless of porosity distribution. Thus, the resulting breakthrough, producing flow fraction, average saturation and outlet saturation reported in terms of pore volumes injected are the same and only depend on the fractional flow function. The fractional flow function can be estimated accurately between the front saturation and the highest obtained outlet saturation from composite core flooding experiments. The method is validated on synthetical data using CO2-water primary drainage literature curves where the relative permeability curves.