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.

Casing connections in thermal wells, such as SAGD and CSS wells, experience extreme loads due to exposure to high temperatures up to 200°C-350°C, stresses exceeding the elastic limit, and cyclic plastic deformation. To-date, no standard procedure has been adopted by the industry to qualify casing connections for such conditions. In particular, the existing evaluation standard ISO13679/API5C5 excludes temperatures above 180°C and tubular loads beyond pipe body yield. Proprietary procedures have been used to qualify connections for individual thermal operations, but none of those has been accepted as an industry standard.This paper introduces a new protocol for evaluating casing connections for thermal well applications: Thermal Well Casing Connection Evaluation Protocol (TWCCEP), founded on long-standing work in the thermal-well arena. TWCCEP has been developed through a multi-client project, sponsored by operators and connection manufacturers involved in thermalwell operations in Canada: EnCana, Husky Energy, Evraz (formerly Ipsco), Nexen, Pengrowth, Petro-Canada, Shell, TenarisHydril, and Total. Recently, International Organization for Standardization (ISO) Technical Committee 67 Sub Committee 5 registered a new work item to consider adopting TWCCEP as an international standard.This paper refers to the TWCCEP version available at the time of submitting the paper manuscript. TWCCEP employs both analytical and experimental procedures to assess performance of a candidate connection under conditions typical of service in thermally-stimulated wells. The objective of the analytical component is to assess sensitivities of the candidate connection to selected design variables, and identify worst-case combinations of those variables for subsequent configuration of specimens for physical testing. The purpose of the physical testing is to verify performance of the connection specimens under assembly-and-loading conditions simulating the thermal-well service.In addition to the protocol overview, this paper illustrates how engineering analysis, numerical simulation, and reducedscale physical testing were used in the protocol development to examine impacts of various design and loading variables on connection strength and sealability, and how those results were utilized to formulate the analysis-and-test matrix prescribed in the TWCCEP evaluation procedure.Adoption and consistent use of TWCCEP is expected to increase operational reliability and decrease failure potential of casing strings in thermal wells. Learnings from the protocol development will also help define requirements for connection re-qualification in cases when one or more of the design variables change (i.e. in product line qualification). Thermal well service conditionsLoading conditions in extreme-temperature wells, such as Steam Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS), are severe. Maximum operating temperatures in those wells currently reach into the interval between 200°C and 350°C. Large temperature variations occur due to produ...

fax 01-972-952-9435. AbstractEngineering studies demonstrate the significance of post-yield mechanical characteristics of Oil Country Tubular Goods (OCTG) for governing the service limits of casing and liner products in Steam Assisted Gravity Drainage (SAGD) operations. New test methodologies have been developed to characterize these post-yield properties in a thermal environment at field-representative strain rates and static strain conditions. This provides a basis for quality assurance programs to verify that materials used in well construction meet the requirements for post-yield service in thermal operations. This paper provides an overview of a quality program implemented for a major SAGD development in Western Canada. The program was designed to provide a statistically significant description of the thermo-mechanical properties of the tubulars used in the well construction. The overview includes a discussion of the material characterisation basis, the statistical design basis, a summary of material test results, and conclusions for ongoing testing in forthcoming phases of the project.

Use of slotted liner as a sand control device is widespread in SAGD operations in Western Canada. Operating temperatures in such thermal EOR wells can be extreme, sometimes exceeding 270°C (518°F), and the associated compressive axial mechanical strain imposed by constrained thermal expansion can load the pipe material beyond its proportional limit. Selection of an appropriate slotted liner configuration is critical to ensure that structural stability (and hence sand control) is reliably maintained during operation. Mechanical properties of the tubular material at elevated temperature strongly influence the compressive stability of the liner structure, but lower-temperature properties also affect the ease of pipe slotting on a production scale, which is typically achieved by plunging thin saw blades through the pipe wall. Common slotting issues include breakage or unacceptably high blade wear rates. This paper describes the developmental basis for a new tubular material formulation that is specifically optimized for thermal structural stability in SAGD applications without compromising slotting performance. Elevated-temperature mechanical properties are designed to prevent compressive buckling failures and to minimize strain localization potential. Results of analytical and experimental work (including stability analysis of the liner structure, thermo-mechanical material testing, and bench-scale slotting trials) are described. Introduction Ongoing rapid development of bitumen reserves in Western Canada has led to an increased focus on developing robust tubular design bases for extreme service conditions in in-situ recovery schemes such as SAGD. Specifically, cemented or frictionally-constrained tubulars are subjected to thermally-induced, deformation-controlled loading that leads to a unique set of design challenges and more stringent requirements for post-yield material response than those employed in traditional elastic design. Slotted liner is used as a sand control device in a majority of SAGD wells. Slotted liners used in thermal applications must provide a stable structure under extreme thermally-induced compressive loading in order to maintain wellbore access and to prevent excessive sand from entering the wellbore. While the deformation resistance of slotted liners depends on geometric attributes such as pipe wall thickness, slotting configuration, and slot geometry, material properties have a considerable impact on structural stability and localization resistance.

Although thermal heavy oil recovery methods are extensively used, no unified and standardized basis exists for selecting materials and configuring intermediate (production) casing/connection systems for these extreme-service applications. Thermal intermediate casing systems must accommodate a wide variety of mechanical and environmental loads sustained during well construction, thermal service at temperatures exceeding 200°C, and well abandonment. Numerous operator- and field-specific designs have been used with good success and only a few isolated challenges, but industry's use of its operating experience to calibrate tubular design bases for future wells has been limited. This paper identifies the benefits and components of a unified casing system design basis for thermal wells, aimed to be technically comprehensive, inclusive of the available elements of industry's collective knowledge and experience, and adaptable to technological advancements. The technical element of the unified basis broadly relates to the engineering foundation used to make three primary design selections: material, pipe body, and connections. For each design selection, the paper provides an overview of the associated technological challenges and the current state of the industry in addressing those challenges, including the commonly-adopted design approaches. Key performance considerations include integrity during well construction, connection thermal service structural integrity, pipe thermal service integrity and deformation tolerance, connection sealability, and casing system environmental cracking resistance. Where applicable, the paper identifies interdependencies that exist between design selections (for instance, the impact of pipe material selection on the thermally-induced axial load that must be borne by the tubular and connection), and discusses mechanisms for accounting for those added complexities in the design. Ultimately, the intent of this paper is to provide a framework for referencing existing technical knowledge and for considering further development and field benchmarking work that will reduce the technological uncertainty and increase simplicity in thermal casing system designs. Industry will benefit from a unified engineering approach that offers operators sufficient flexibility to accommodate application requirements and prior experience.