Inflow Control Devices (IDCs) were initially developed to avoid water coning problems in long horizontal wells. They have been used with success the past 15 years. There are, however, issues that needs to be resolved.
A pressure drop model of the ICD is presented herein. The physical model of the ICD consists of pressure drop equations from the reservoir, through the screen, through the flow conduit, through the ICD nozzle and into the production tubing, and, pressure drop through the lower completion system. Evaluation of the model shows that for current commercial tools, turbulent flow through the ICD dominates the pressure drop, leading to a density controlled flow. This is fortunate as density varies much less than viscosity over the production life of a field.
Due to the inherent non-linear nature of a production system, the pressure drop versus flow rate will vary with degree of depletion. An ICD may be optimal initially, but not when the reservoir pressure is depleted. This paper also presents a new designer IDC concept which maintains constant flow regardless of the degree of field depletion. It is based on a hydraulic feedback principle, and ensures controlled flow throughout the life of the oil field.
The Inflow Control Problem
Figure 1 shows a typical coning problem in a long well in a thin reservoir. Because the production tubing is very long, there is a considerable pressure drop in the tubing itself. The oil at the far end (the toe) has to overcome this pressure drop. The oil at the heel does not see this pressure drop. The consequence is that the flow rate is higher at the heel than at the toe. The area close to the heel will produce more liquid hydrocarbons, resulting in coning of the water-oil-contact or the gas-oil-contact. When water or gas production starts, the process will accelerate. Over time as the water production increases, it leads to reduction in oil production and more produced water disposal problems. Most of the oil near the toe will not be produced, and new wells are required to drain this. The recovery aspect is of utmost importance for these types of wells.
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