Horizontal Well Water Cut Estimation due to Water Coning in Heterogeneous Formations with Vertical Flow Barriers

Abstract

Water coning and cresting process complicates oil production from reservoirs with bottom water by severe water cut increase after water breakthrough and amplify the load on surface fluid processing equipment. Volume of easy to recover oil reserves declines gradually, thus creates the need in the instrument for economic evaluation of the profitability of such reserves, taking into account the possible geological risks. This instrument must account for formation heterogeneity and flow barrier distribution, wellbore trajectory and well spacing. It should be noted that oil production with drawdown below critical in most cases is not economically feasible, so water cut estimation after water breakthrough is an important factor. Water coning in horizontal well is a complex process indescribable by analytical models derived for homogeneous formations. Semi-numerical model of water cut estimation based on series of numerical calculations is presented. Model accounts for vertical flow barriers distribution and is compared with existing analytical and empirical solutions. To consider the impact of formation heterogeneity and flow barrier distribution the combination of geological and flow simulation software were used to produce a large series of simulation runs. Data analysis produced stable relationship of recovery factor to water cut for a simplified field block considering variations in facies distribution parameters and dip angle. Due to complexity and uncertainty of real field geological properties a statistical approach was used to achieve most accurate well production profile estimation. Water cut descriptive function was derived to allow model application in semi-analytical production profile estimation. After analysis of over 150,000 simulation runs with different reservoir parameters a reliable function of water cut to recovery factor for field block with horizontal well was achieved. This function takes into account flow barrier distribution through variogram stochastic distribution method, reservoir dip angle, oil column thickness, well construction and offset. Derived function allows exclude production rate and relative formation properties by usage of block recovery factor. Resulting model allows calculation of water breakthrough time and following water cut for horizontal well due to water coning process for various types of reservoirs. Large number of runs provides probabilistic estimation of well production profile (P10 P50 P90) for each reservoir properties combination.