Improved near-well approximation for prediction of the gas/oil production ratio from oil-rim reservoirs

A model with short computational time has previously been developed to predict the rate-dependent gas/oil ratio (GOR) from a horizontal well. The oil flow towards the wellbore is based on a one-dimensional model by Konieczek. The model performs remarkably well for medium-time production optimization (weeks, months), while the predictions during the first days after a large change in the production can be poor. An improved one-dimensional model for the flow towards the wellbore is proposed, where the oil flow is treated as a superposition of three terms: 1) Radial flow towards the wellbore and towards a mirror well. 2) Flow to correct for modified boundary conditions due to the radial flows. 3) Flow due to height variations of the gas/oil contact (GOC). The new model takes care of the current short term and near-well deficiencies: Effect of 2D flow close to the wellbore, gas breakthrough due to viscous gas fingering, and horizontal/vertical anisotropy. Based on analysis and preliminary testing the new model should have equally good medium and long term capabilities and considerably improved short term and near-well behaviour, compared to the present implementation.