Thermal-Deformation-Resistant Slotted-Liner Design for Horizontal Wells
- M.W. Slack (Noetic Engineering Inc.) | W.D. Roggensack (Noetic Engineering Inc.) | G. Wilson (Marathon Canada Limited) | R.O. Lemieux (SynecTec Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE/CIM International Conference on Horizontal Well Technology, 6-8 November, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2000. SPE/PS-CIM International Conference on Horizontal Well Technology
- 1.2.2 Geomechanics, 3 Production and Well Operations, 4.1.2 Separation and Treating, 1.2 Wellbore Design, 5.2 Reservoir Fluid Dynamics, 5.3.9 Steam Assisted Gravity Drainage, 4.3.4 Scale, 3.2.5 Produced Sand / Solids Management and Control, 1.14 Casing and Cementing, 5.4.6 Thermal Methods, 5.8.5 Oil Sand, Oil Shale, Bitumen, 1.6 Drilling Operations, 1.10 Drilling Equipment, 1.14.1 Casing Design, 2.4.3 Sand/Solids Control, 4.1.5 Processing Equipment
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Liners for wells produced using the SAGD process (steam assisted gravity drainage) must balance sand control requirements and inflow characteristics against the structural demands of thermally induced loads. These challenging design issues require a switch from conventional load-based casing design principals to a deformation-controlled design basis. This paper first develops this design basis, describing the problem in terms of the controlling variables, then applies the results to the liner design for a specific reservoir in a reliability based context. The developed design implements innovative and recently commercially available deformation control devices to manage competing thermal and geo-mechanical loads in the intermediate casing and horizontal liner. For the candidate well, a purpose-specific slotting configuration was also defined to control inflow distribution and reduce risk of undesirable slot deformations under thermal loads. (SPE Paper 65517 describes the inflow design basis.) The resulting liner design maintains structural integrity and provides slot geometry protection to ensure effective sand control supporting the extended production life obtained through managed slot distribution.
Slotted liners in SAGD horizontal wells producing from unconsolidated sandstone reservoirs are generally designed to prevent sand inflow, maximize inflow area and resist modest collapse loads. However, both analysis and field experience demonstrate that these simple objectives often fail to address many factors controlling both inflow optimization and structural integrity. Horizontal wells often fail to achieve their production potential, water out, or both. Sand control frequently breaks down and work-overs show evidence of deformations resulting in access impairments or complete closure.
Over several years operating the horizontal wells in their Paradise Hills SAGD Pilot Project, Marathon Canada Ltd. has encountered several of these effects. The wells are producing from the South Bolney field and are located in Canada, near the town of Lloydminster on the Alberta Saskatchewan border. The producing horizon is a typical unconsolidated heavy oil sandstone reservoir about 20m thick at an average depth near 450m below surface and is completed with 178mm (7 inch) slotted liners.
During the history of the Bolney field, these wells have experienced minor to severe sand production control problems stemming from both screen geometry and damage mechanisms. Initially, a larger slot size (1.5mm (0.060") keystone) was implemented to encourage inflow. However, when unacceptably high sand production occurred during production, the slot size was reduced in stages on subsequent drilling programs to 0.635mm, 0.457mm (0.025", 0.018") and finally to 0.305mm (0.012") keystone slot width. With each slot width reduction came some relief from sand control problems but issues with sand production still existed. As a remedial measure, it was decided to install a 0.127mm (0.005") wire-wrapped screen within the slotted liner in several wells. Initially the modified wellbore design showed very good results during startup but ‘production slugs' of sand were eventually experienced when steam communication was established with the horizontal producer. A wire-wrapped liner was pulled confirming at least one eroded hole in the screen.
With a liner breach confirmed, Marathon began reviewing flow design and modeling criteria, as well as startup and production practice, for the initial and continuing phases of production for its contemplated new producers. The review encompassed flow modeling and geomechanical evaluation to define the slot distribution and structural design basis, and led to a complete redesign of the wellbore liner completion for the test well being monitored.
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