Well-Completion Effects on the Performance of Horizontal and Multilateral Wells

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 96530, "An Evaluation of Well-Completion Impacts on the Performance of Horizontal and Multilateral Wells," by L.-B. Ouyang, SPE, and B. Huang, SPE, Chevron Energy Technology Co., prepared for the 2005 SPE Annual Technical Conference and Exhibition, Dallas, 9–12 October. Well completion is critical in well design and the performance of the well for its entire life. The major objective for this study was to provide guidance in the design of completion configuration with a series of simulations with different completions in different flow and reservoir environments. Completion options including open hole, slotted liner, inflow-control devices, intelligent-well completions (i.e., downhole instrumentation and control system), perforated/cemented liner, wire-wrapped screen, external casing packers, gravel pack, and frac pack were reviewed. Introduction With many advanced well-completion options deployed in new wells, especially in deep- and ultradeepwater environments, well-completion details often are not taken into account in reservoir simulators. Reservoir simulators should be connected with wellbore hydraulics and tubing-performance prediction software regarding the ability to model complex well hydraulics, including an appreciation of the influence on deliverability of reservoir effects and completion design. This study evaluated the performance under different completion designs for two proposed gas wells and one existing oil well. Several potential factors that could affect well production were evaluated including pressure drawdown, wellbore damage, non-Darcy effect, zonal isolation, wellbore-pressure drop, fluid flow in the annulus, and well position. Simulation Tool A commercially available completion-modeling and well-planning simulation tool was used that models production fluids flowing from the reservoir through well completions into a wellbore. It is used for well-placement and -completion screening and/or design studies of local variations in reservoir properties. It allows scaleup and honors complex reservoir-description information from an Earth model to compute multiphase flow from the reservoir through the well completion, into the wellbore, and up to the wellhead. Through alternative well placement, the well behavior can be estimated for the given reservoir description and well-completion design. The steady-state oil-, water-, and gas-production rates as well as the production profile along the length of the horizontal wellbore can be calculated. Completion Option Different completion designs were proposed for the two gas wells, including openhole gravel pack (OHGP), cased-hole gravel pack (CHGP), standalone screen (SAS), cased-hole frac pack (CHFP), and expandable sand screen (ESS). For a CHGP or CHFP completion, an isolation string could be required. The detailed completion parameters for all the completion options are given in Table 1 in the full-length paper. Skin factor is a measure of the amount of additional pressure draw-down encountered because of mechanical or turbulent effects. The higher the skin factor, the larger the extra pressure drawdown, resulting in reduced well production. Mechanical skin is a factor closely related to well completion and independent of flow rate. The skin caused by turbulent effects (normally called non-Darcy effect, or non-Darcy skin) depends primarily on flow rate. Typically, non-Darcy skin is trivial and can be ignored for liquid wells or low-rate gas wells. However, the non-Darcy skin for high-rate gas wells could be as significant as the mechanical skin.