The production of oil from horizontal wells in thin rims sandwiched between gas and water is notorious for coning problems. There is a strong tendency for early gas or water breakthrough at the heel, especially if the pressure drop over the length of the well is in the same range as the drawdown. We present two conceptual solutions to counteract the negative effect of well bore pressure drop through the application of downhole measurement and control. One solution concerns inflow switching in a segmented well bore and allows for coning control after breakthrough has occurred. The other solution aims at preventing breakthrough as long as possible. This is achieved by flattening the drawdown profile along the well through controlling inflow at one or more points in an extended stinger. The feasibility of the solutions was demonstrated through numerical simulations over a range of reservoir and well bore parameters. Implementation would require further development of downhole water and gas detection capabilities. Introduction Thin oil rims are relatively thin oil columns, in the order of a few to tens of meters thick, sandwiched between water and gas layers. They often occur in reservoirs with lightly compacted sands having high porosities and high permeabilities of up to several Darcy, and they commonly contain light oils. These properties culminate in favorable reservoir flow conditions, reflected in a low drawdown required for production. However, these properties can also cause production problems, in particular water or gas coning leading to early water or gas breakthrough. Horizontal wells are an attractive solution to reduce the potential for coning because they require lower drawdown than vertical wells for the same production rates. However, a possible problem of horizontal wells is the pressure drop over the well bore caused by friction forces between the fluid and the well bore (Fig. 1). As a result the drawdown at the heel of the well becomes higher than the drawdown at the toe, which increases the tendency for water and gas coning at the heel and thus partially cancels the beneficial effect of the horizontal well. The reduced draw down near the toe of the well also lowers the effectiveness of increasing the well length. Pressure drop over horizontal oil wells has been modeled to various degrees of sophistication1–3. These studies show that, roughly speaking, well bore pressure drop over a horizontal well becomes a problem when it is in the same order of magnitude as the drawdown at the heel. The ratio between pressure drop and drawdown increases for reducing well diameter, increasing well length, and, importantly for many oil rims, increasing reservoir permeability and reducing oil viscosity. Stinger completions Passive stinger completion One of the solutions to the non-uniform drawdown problem is the use of an ‘extended stinger’ to shift the tubing inflow point from the heel of the well to somewhere near the middle4,5. This effectively replaces the horizontal well by two shorter ones (Fig. 2). However, such a ‘passive’ stinger has a number of practical disadvantages:Its dimensions are based on a fixed inflow profile along the well. However, the inflow profile may change over the life of the well due to reservoir pressure transients and due to the breakthrough of gas or water.It requires that the inflow profile along the well bore is known at the design stage. This is usually quite unrealistic because of unpredictable reservoir heterogeneities, in particular near-well bore permeability fluctuations. Passive stinger completion One of the solutions to the non-uniform drawdown problem is the use of an ‘extended stinger’ to shift the tubing inflow point from the heel of the well to somewhere near the middle4,5. This effectively replaces the horizontal well by two shorter ones (Fig. 2). However, such a ‘passive’ stinger has a number of practical disadvantages:Its dimensions are based on a fixed inflow profile along the well. However, the inflow profile may change over the life of the well due to reservoir pressure transients and due to the breakthrough of gas or water.It requires that the inflow profile along the well bore is known at the design stage. This is usually quite unrealistic because of unpredictable reservoir heterogeneities, in particular near-well bore permeability fluctuations.

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