Modeling Horizontal Completion Deformations in a Deepwater Unconsolidated Sand Reservoir

Abstract

We present the development and results of geomechanical models and analyses used to assess the risks of compaction-induced deformation and potential failure of horizontal gravel-pack completions in a field located in deepwater, but at shallow depth below the sea floor. The target reservoir consisted of high-porosity, under-consolidated stacked turbidite sandstones, which are comparable to some of the more well-known, problematic compactive reservoir sands. The formations indicated a high level of risk of depletion-induced compaction, which could produce large deformations and potential failure of completion equipment in horizontal wells. Coupled poroelastoplastic geomechanical finite element models were constructed to assess the risks of completion equipment damage due to depletion-induced reservoir compaction. Both open-hole and cased-hole gravel packed completion configurations were analyzed. Details of the pre-packed screen assembly components were included in the models, such as the ribs between the base pipe and inner screen, and deformable epoxied sand between inner and outer screens. Model results presented in this paper include deformations of the completion equipment and stresses in the screen components, as a function of reservoir depletion pressure. The results of the geomechanical modeling indicated that the overall compaction loading should not cause significant deformation of the specified completion equipment. Background The objective of the work presented in this paper was to quantify deformation of completion equipment as a function of reservoir depletion for shallow unconsolidated turbidite formations in deepwater Gulf of Mexico (GOM). Exploration, drilling and production in such fields can be extremely expensive and challenging The demanding technical and economic challenges of such large projects drive the motivation for increasing production and ultimate depletion pressure. In problematic rock reservoirs, such as that documented herein, economic demands have pushed upward the level of technical sophistication necessary to determine and define the operating limits. Advanced nonlinear geomechanical and mechanical modeling have become an integral part of efforts to extend the operating limits of completion equipment, as documented recently by Grueschow et al. (2008) and Hilbert and Bergström (2008). The field under study in this work is located in deepwater, but the target stacked turbidite sand formations are only 1,640 ft to 2,500 ft (500 m to 750 m) below the sea floor. The sands exhibit high porosity and moderate permeability for the region. This type of reservoir is similar to that studied by Schutjens et al. (2008) and is comparable to sands from some of the more well-known, problematic compactive reservoirs. There is a considerable literature addressing the physics and analysis of compaction and subsidence due to hydrocarbon production (Hilbert 2003 and references therein; Schutjens et al. 2008; Schutjens et al. 2004; Hettema et al. 2000; Khalmanova et al. 2008). If reservoir depletion is sufficiently large, compaction-induced deformation, activation of fault slip, and stiffness contrasts between sands and shales can result in significant casing damage and potential completion equipment failure (Segall 1989; Cernocky and Scholibo 1995; Fredrick et al. 1998; Hilbert et al. 1999; Li et al. 2003; Lee et al. 2008).