Near-Surface External-Casing Corrosion in Alaska: Cause and Mitigation
- Jerald C. Dethlefs (ConocoPhillips Co) | Curtis G. Blount (ConocoPhillips Co) | John C. Bollinger (Farwest Corrosion Control)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 2008
- Document Type
- Journal Paper
- 339 - 346
- 2008. Society of Petroleum Engineers
- 2.7.1 Completion Fluids, 5.2.1 Phase Behavior and PVT Measurements, 4.3.1 Hydrates, 4.1.5 Processing Equipment, 1.14 Casing and Cementing, 1.14.1 Casing Design, 1.6 Drilling Operations, 4.2 Pipelines, Flowlines and Risers, 4.2.3 Materials and Corrosion, 4.1.2 Separation and Treating, 3 Production and Well Operations
- 1 in the last 30 days
- 815 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 12.00|
|SPE Non-Member Price:||USD 35.00|
Recently, a number of external-casing failures on a group of relatively new wells in the Kuparuk field of Alaska prompted an investigation into the cause. The investigation determined that external surface-casing-corrosion failures had occurred near the top of the casing cement within the conductor.
The surface-casing corrosion was found to be caused by repetitive events of surface water entering into the top of the annulus between the surface casing and the conductor above the primary cement top. Testing of water and cement samples taken from the field indicates that the addition of oxygenated water and chemical salts that leach from the cement creates a low-resistance electrolyte resulting in an extremely corrosive environment. The yearly replenishment of oxygenated water in this environment sets up an electrochemical cell that corrodes the surface casing. Elevated casing temperatures (˜125°F) accelerate the corrosion rates and increase the temperature gradient between the casing and the conductor, creating a thermogalvanic-corrosion cell.
Although damaged surface casing has been repaired mechanically on numerous wells by excavation and installation of welded sleeve patches, accessing the damaged surface casing can be difficult. Inhibiting the corrosion mechanism is considered a more tenable solution.
This paper will
- Provide an outline of the extent of shallow external-casing corrosion seen in the field.
- Detail the mechanisms for the external corrosion.
- Detail the mechanical-repair procedures used to return the wells to service.
- Discuss possible mitigation methods to inhibit corrosion on existing wells.
- Discuss the treatment chosen to stop the corrosion.
- Provide details of treatments used to inhibit further shallow-casing corrosion.
The Kuparuk field is located on the North Slope of Alaska, USA, approximately 30 miles west of Prudhoe Bay (Fig. 1). The Greater Kuparuk Area (GKA) includes Kuparuk and a number of smaller oil pools in the operating unit. The wells are divided almost equally between producers and injectors.
The majority of GKA wells are configured with a conductor casing (CC), surface casing (SC), production casing (PC), and tubing string. A smaller number of wells have a single-casing design. Within specified limits, annular pressure is allowed on most wells, and each casing string is expected to handle the pressure within its allowable range (CO 494, Proposed Rules 2003).
The SC functions as an element of a secondary or tertiary layer of protection between the reservoir and atmosphere. For single-casing wells without a packer, the SC is the primary layer of protection. Therefore, degradation of the SC caused by corrosion processes is a threat to the integrity of a given well. SC corrosion can result, and has resulted, in wells being removed from service because of the loss of the layer of protection. Prevention of SC-corrosion problems is considered very important to maintain the mechanical integrity of the field, ensuring personnel safety and environmental protection and maximizing the service life from the wells.
|File Size||1 MB||Number of Pages||8|
CO 494, Proposed Rules Regulating Sustained Casing Pressures inDevelopment Wells in All Pools Within the Kuparuk River Field. 2003.Anchorage: Alaska Oil and Gas Conservation Commission (4 September).
Farooqui, M.A.S.Z. and Bitar, G.E. 1998. Corrosion Problems in Below-GradeWellhead Equipment and Surface Casings. SPEPF 13 (3):208-212. SPE 50967-PA. doi: 10.2118/50967-PA.