Post-Yield Thermal Design Basis for Slotted Liner

Abstract

Slotted liners used for primary heavy oil recovery support relatively minor operational loads at the depths and pressures common in Western Canada. In such applications, installation loading is the primary concern, and load limits can be defined using an elastic design basis to support running operations. In thermal operations, the installation limits need to be more stringent, because of the impact of residual stresses and deformation on the operating response. Furthermore, the high axial loads induced by confined thermal expansion can place the liner into large-scale yield, where localization resistance is virtually eliminated and a variety of deformation failure mechanisms can become manifest. A prudent design takes the deformation mechanisms into consideration, balancing the mechanical requirements for supporting thermally-induced loads against the inflow requirements to generate the final design. Commercial Steam Assisted Gravity Drainage (SAGD) projects currently under development in Northern Alberta typically use slotted liner for both injectors and producers. Reservoir sand grain size distributions and inflow requirements require slot densities as high as possible without compromising the structural integrity of the wells. Therefore, a design assessment was required to determine the relationship between slot geometry and density, thermal and production loading, and post-yield material properties. A variety of possible failure mechanisms were considered, and failure limits in terms of these controlling parameters were evaluated. The outcome was an allowable slot density, slot geometry and post-yield material description required for the liner to operate reliably, and corresponding quality assurance programs to ensure the slots and material satisfy the requirements for reliable operation. Introduction The vast majority of steam assisted gravity drainage (SAGD) wells in Western Canada use slotted liner for sand control. A standard basis for the design of these liners has not been formulated. Frictional restraint from unconsolidated reservoir sand can cause large-scale yielding of liner material, and the liner geometry and material properties must be selected to ensure sand control, wellbore access, and flow performance are not compromised during operation. Application Description A rigorous design basis for slotted liner was required for Nexen Inc. installations at Long Lake (Phase 1) in the Fort McMurray region of Northern Alberta. Recovery is achieved through the steam-assisted gravity drainage (SAGD) process in unconsolidated sand. Nexen's Phase 1 installation has an expected total bitumen production of 11,000 m3/day. Sand control in injector and producer wells is obtained exclusively through the use of slotted liners. Tubular Design Tubular design challenges in SAGD applications are primarily associated with overload due to restrained thermal expansion. Planned steam injection temperature at the wellhead at the Long Lake project is over 270°C, and expected liner operating temperatures are on the order of 240°C. For liner, frictional restraint is provided by unconsolidated reservoir sand, where the borehole is expected to collapse and re-establish radial stress against the liner wall (Figure 1). A detailed discussion of these geomechanics and predicted drag and axial load profiles is presented by Slack et al. in SPE 65523.

Protocols for Slotted Liner Design for Optimum SAGD Operation

“…This program was, in part, motivated by the relatively poor historic performance of many straight and keystone cut type slotted liners where either high liner generated differential pressures (sometimes exceeding 1000 kPa) or significant physical production of sand was occurring. The motivation of this study was to investigate the mechanisms of why slotted liners tend to plug, and to provide potential solutions and optimum completion geometries for practical field application in active and future SAGD projects (6)(7)(8)(9)(10) .…”

Development of an Optimized Tubular Material for Thermal Slotted Liner Completions

“…The majority of SAGD liners are subjected to temperatures high enough to cause global material yielding if the pipe is constrained from expanding during operation (1,2) . Design situations involving global material plasticity are invariably more complex than those in which the material remains in its elastic (linear) range.…”

“…A previous study identified pipe weight, slotting configuration, slot geometry, material properties, and secondary loads as contributors to the stability of slotted liner when subjected to thermally-induced compression (2) . Most importantly, selection of an appropriate liner material can increase the inherent stability of a given geometrical configuration under a particular set of operating conditions.…”

Post-Yield Material Characterization for Thermal Well Design

“…Recent efforts to characterize limit states for structures and components in wells 19,20 and pipelines 21 demonstrate the need for more rigorous strength information than current testing standards can provide. These are examples of a broader recognition of issues related to post-yield material properties that need to be addressed.…”