Ccme Breakthrough Time for Horizontal Wells

Summary. RecoveW from an oil zone underlying a gas cap, overlying an aquifer, or sandwiched between gas and water can be improved by repressing the coning problem through horizontal-well drainage. Literature methods to predict coning behavior are limited to steady-state flow conditions and determimtion of the critical rate. The results in this paper are based on new semianalytical solutions for time development of a gas or water cone and of simultaneous gas and water cones in an a.nisotropic iniinite reservoir with a horizon-tal well placed in the oil column. The solutions are derived by a moving-boundary method with gravity equilibrium assumed in the cones. For the gas-cone case, the semiamlytical results ~e presented as a single dimensionless cnrve (time m breakthrough vs. rate) and as a simple analytical expression for dimensionless rates> ‘h. For the simultaneous gas- and water-cone case, the results %e given. in two dimensionless sets of curves: one for the optimum vertical well placement and one for the corresponding time to breakthrough, both as f.mctions of rate with the densi ~ contrast as a parameter. The validity of the results has been extensively tested by a general rmmerical simulation model, Sample calculations with reservoir data from the Troll field and comp%ison with test data from the Helder field demonstrate how the theory can be used to estimate the time m cone breakthrough and its sensitivity to the uncertainties in reservoir parameters