Development of an Optimized Tubular Material for Thermal Slotted Liner Completions
Authors: Dall'acqua D. , Turconi G. Lopez , Monterrubio I. , Allen M.D. 
Published: March 2010

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 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 development 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 thermallyinduced, 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.

Materials typically employed in slotted liner installations include API grades such as K-55 and L-80. However, the API mechanical property requirements for such materials are defined at room temperature, and the variability permitted by the API specification is large. Efforts to develop engineering design bases for liners in specific fields must consider the operating conditions of the application, and generally result in a more specific requirement for post-yield material properties than is offered by API. Hence, an API grade designation is not considered to be a sufficient description of material requirements for such tubulars.

The manufacturing process for slotted liner involves plunging a series of thin sawblades through the wall of the tubular. Typical slot quantities are in the hundreds per metre of pipe length, and with individual well lengths of 600 m to 1000 m, an efficient slotting process is desirable.