A deviated well is any well where the bottomhole location is drilled at a horizontal offset from the surface location (wellhead). Cold Lake CSS wells are almost always deviated, since the bottomhole targets are drilled from a centrally located surface location.
Through ongoing development at Cold Lake, the length, bottomhole angle (well deviation) and pumping capacity of deviated wells have increased. Conditions now require some wells to exceed 1000 m in length, with a 750 m horizontal offset from the wellhead to bottomhole target and an 80 degree angle at the target. Recent additions to Cold Lake CSS well designs include using short horizontal wells on some pads. Short horizontal wells typically access the equivalent of two or three deviated CSS-well bottomhole locations. About 20 m to 30 m of conductor pipe is commonly present on each well before the well is directionally drilled to target depth and logged, if required. Production casing (typically 177.8 mm L-80 with metal-to-metal seal connections) is then installed from target depth to surface. Wells are cemented back to surface with thermal cement. Cement tops are maintained at surface to reduce the potential for external corrosion.
Surface casing is usually only installed on the first well drilled to confirm that the Clearwater Formation pressure is low enough to enable the remaining wells on the pad to be drilled without surface casing. Surface casing is set into competent shale below the glacial till and cemented in place with thermal cement. Alternatively, previous evaluation wells on or near specific pads are used to confirm that Clearwater Formation pressure and wellbore drilling conditions are suitable to drill selected pads without installing surface casing on the first well.
Directional Control
Wells are drilled using a downhole motor with a bent housing. To achieve directional control, a measurement-while drilling tool is used. Typical survey intervals are at:
• no more than 30 m in the vertical hole section • every connection in the build hole sections • 30 m in the hold hole and tangent sections
Hole Section Interval Planned Constraints
Vertical Section surface to kickoff point – typically 25 m true vertical depth
none Build Section 1 within the glacial till to
typically 130 m maximum dogleg of 3 degrees per 30 m Build Section 2 below the glacial till, as
required maximum dogleg of 10 degrees per 30 m
Hold Section after build section 2 maximum dogleg of 10
degrees per 30 m Tangent Section from end of hold section to
final total depth
maximum dogleg of 3 degrees per 30 m
Factors Affecting Drilling
Formation factors that affect the quality of the drilled hole include:
• gravel and boulders in the glacial till, which cause rough drilling for the first 60 to 80 m
• bridges in the glacial till, which make it possible to start a new hole while attempting to work the drill string through bridges in the original hole. To reduce the difficulty of re-entry, planned wellbore doglegs are kept less than three degrees per 30 m in the glacial till whenever possible.
Casing Installation
On all wells, 20 to 30 m of conductor pipe is preset to provide a stable wellbore for drilling operations. For wells requiring surface casing, the casing is typically set into a competent shale below the glacial tills, or at about 150 m. Production casing is installed after the well is drilled to target depth.
Each CSS well is cased and cemented with thermal cement from total drilled depth to surface. In the production casing, metal-to-metal seal connections is used to provide connection integrity. The casing is sealed at the surface by a thermal wellhead for steam injection and production operations.
Short Horizontals
At specific locations, short horizontal wells are used to access two or three bottomhole locations from a single wellbore. A horizontal extension is drilled after installing a standard CSS well to an initial bottomhole location. The standard well is drilled and cased to an inclination of 85 to 90 degrees at the initial bottomhole target.
Casing Grade
API 5CT L-80 Type 1 or equivalent proprietary grad steel is used in production or intermediate casing strings.
Casing Centralizers
Casing centralizers are installed on the outside of the casing to centre the casing in the borehole. Casing centralization is important for achieving good mud displacement while cementing, particularly from the narrow side of an eccentric annulus. Currently, centralizers are installed on every joint of casing from the surface down to the top of the Clearwater Formation. Two centralizers are installed on every joint across the Clearwater Formation.
Horizontal liners are typically set in an open hole, without cementing. Horizontal liners access the reservoir through perforations and wire wrapped screens.
Depending on the required well capacity, casing and production-liner designs use either: • a 219 mm production casing and a 140 mm production liner
• a 244 mm production casing and a 178 mm production liner
Production casing size depends on wellbore configuration. Depending on the production and injection requirements, the production casing size varies from 140 to 244 mm in diameter.
Production liner is a type of casing used in a lower part of a well.
Where short horizontal wells are used, standard wellbore configuration requires a 114.3 mm diameter production liner to be run from the base of the 177.8 mm diameter intermediate casing to total drilled depth and set in the horizontal section. The liner, normally:
• is set in the open hole without cementing
• is equipped with perforations and wire-wrapped screens
Metal-to-metal seal casing connections are used to provide improved connection integrity throughout CSS operations.
Imperial oil CSS developments typically use pads with 24 to 28 wells. Single bottomhole locations will cover 3.2 ha.