Analysis of Inflow-Control Devices

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 122824, ’Analysis of Inflow-Control Devices,’ by Bernt S. Aadnoy, SPE, University of Stavanger, and Geir Hareland, SPE, University of Calgary, prepared for the 2009 SPE Offshore Europe Oil & Gas Conference & Exhibition, Aberdeen, 8-11 September. Inflow-control devices (ICDs) were developed to avoid water-coning problems in long horizontal wells. The model for the ICD consists of pressure-drop equations from the reservoir, through the screen, the flow conduit, the ICD nozzle, and into the production tubing, along with pressure drop through the lower-completion system. Evaluating the model shows that turbulent flow through the ICD dominates the pressure drop, indicating density-controlled flow. The flow rate will vary with depletion. A new ICD concept can maintain constant flow regardless of the degree of field depletion. Introduction Long horizontal production tubing results in a considerable pressure drop over its length. Oil produced at the far end (the toe) must overcome this pressure drop. Oil produced at the near end (the heel) is not affected by this pressure drop. Therefore, assuming homogeneous reservoir characteristics, the flow rate is higher at the heel than at the toe. Because the area close to the heel will produce more liquid hydrocarbons, the result is coning of the water/oil contact (WOC) or the gas/oil contact (GOC), as shown in Fig. 1. When the WOC or GOC reaches the wellbore, the process will accelerate. Over time, as water production increases, oil production decreases and produced-water disposal can become a problem. Most of the oil near the toe will not be produced, and new wells will be required to drain it. The recovery aspect is of utmost importance for these types of wells. To control and equalize the horizontal-well drawdown, ICDs are installed along the production tubing. By applying flow restrictions, coning can be reduced or controlled. Ideally, the entire WOC or GOC should be parallel to the production tubing as shown in Fig. 2. If the waterfront enters the tubing over the entire length at the depleted stage, ultimate recovery has taken place. Hydraulic Model In a typical ICD tool, screens are wound over base pipes. Axial rods provide standoff of the screen from the base-pipe surface and provide a conduit for reservoir fluid to flow toward the ICD. The ICD is installed at one end of the base pipe. Reservoir oil flows through the screens into a pathway (conduit) along the base pipe. Going through the pathway shown in Fig. 3, the oil enters a chamber before going through orifices. After passing through the orifices, the oil flows through several large holes inside the casing. The orifices control the flow rate. The coupled flow model includes the pressure drop from the reservoir through the ICD and into the base pipe. The flow and pressure analysis detailed in the full-length paper is based on a typical ICD application in the North Sea. The flow path is coupled by a series of pressure losses and broken into the following components. Outside screen Conduit below the screen Chamber Orifices Holes through the casing

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