Horizontal Open Hole Gravel Pack Placement Requirements in Selective Completion Projects

Abstract

Horizontal Open Hole Gravel Pack (HOHGP) is the conventional sand control technique for offshore non consolidated reservoirs in Brazil. Gravel pack placement requirements include the design of pumping pressures inside the operational window formed by the minimum pump rate to avoid premature rat hole screen-out and maximum pump rate to avoid formation fracture. Some special projects require additional equipment to provide selective completion - External casing packers (ECP) installed at different positions along the production screen aim the isolation of certain reservoir zones. In these cases, gravel pack placement present an additional constraint - operational pump rates should be high enough to avoid alpha wave sedimentation around the packers to assure sealing after the packer inflation process. Traditionally, design criteria consider a minimum critical velocity to avoid sand deposition. The specification of minimum flow for cleaning the ECP, and prevent the deposition of sand in the annular space can be obtained from different criteria. Two methods are proposed to analyze the problem: a constant velocity and a constant shear stress approach. The major contribution includes computational fluid dynamic simulation (CFD) of the 3D flow around the packer, using a finite volume method. The methodology based on the estimation of the local shear stresses at the interfaces, suggests less conservative numbers which allows effective gravel pack placement in selective completion projects for narrow operational windows. Introduction The unique conditions found in the Brazilian deepwater fields pushed the industry to develop dedicated technology to guarantee technical feasibility and economicity of such projects. Non consolidated reservoirs require sand control and Campos Basin history have been constructed with gravel packing techniques (Marques et al, 2007) and different technological implementations allowed overcoming hydraulic issues in narrow operational window scenarios. Meanwhile optimization of reservoir management practices pushed the development of smart completion technology (Pinto et al, 2001 and 2006), allowing continuous adjustment in multizone wells by remote control of downhole valves, minimizing intervention costs (Robinson, 2003). Besides, improved recovery techniques for viscous oil (Trindade and Branco 2005) and selective completion by isolation of shale interlayers inside horizontal gravel packed wells (Machado et al, 2001) constituted expressive challenges. Selective completion in long horizontal sections was achieved through the use of two equipments which already existed in the oil industry but never had been used together by that time: expandable casing packers (ECP) and diverter valves (DV). To manage production or injection along long horizontal intervals, the reservoir section has to be segmented in a way that each segment can be controlled individually. Selective completion gains in importance in front of reservoir heterogeneities and of lateral permeability contrasts. One additional way to achieve this segmentation would be to split the wells using open hole packers. Concurrently, open hole packers and swellable elastomer technologies are being pursued to achieve segmentation without cemented liners and perforation, which is inherently time consuming, expensive and perhaps sub optimum (Ritchie et al, 2008). Until this moment 9 wells were gravel packed and completed successfully using external casing packers plus diverter valves. Other 8 wells used only ECPs.