Casing Wear Prediction and Management in Deepwater Wells

Abstract

Deepwater Gulf of Mexico wells are generally deep and they may incorporate casing designs that provide only a single-casing barrier between the wellbore and the formation. These aspects present unique issues and risks in regard to casing wear. The extreme depths (>30,000 ft) of many wells in the Gulf of Mexico create the potential for high side loads imparted by the drillstring to the casing, even with low doglegs (1.0°/100 ft or less) in the upper part of the well. This, combined with potentially high rotating hours, particularly on exploration wells with sidetracks, creates the potential for casing wear that exceeds allowable limits. In order to proactively manage and mitigate casing wear during drilling operations, Chevron has developed a Casing Wear Monitoring standard operating practice (SOP). Deployment and application of this SOP has proven effective. Application of this SOP indicates that casing wear can be predicted, managed, and/or mitigated with proper planning and execution. This paper illustrates a casing wear event on a Chevron well and provides an overview of the Chevron Deepwater Casing Wear Monitoring SOP. Additionally, the paper highlights some casing wear processes, well control issues, and environmental risks that are unique to deepwater wells. Application of the casing wear prediction and monitoring procedures outlined in this paper help to ensure that the integrity of the casing is maintained during drilling operations, thereby reducing the risk of a health, safety and environment event or loss of the well due to excessive casing wear.

The Mechanism of Wellbore Weakening in Worn Casing-Cement-Formation System

“…The casing wear was tested in single, sharp, and blunt groove forms. Another study emphasized the alleviation and prevention of casing wear by using optimized well operations, such as dogleg severity control and sealant application in the worn sections [11].…”

Analysis of Casing Strength after Casing Wear in Ultra-Deep Rock Salt Formation

“…For ultra-deep well, the lateral load will be high due to the high lateral load produced by the drill string on the casing, even with low dog legs (approximate 1.0°/100 ft) in the upper part of the well. This lateral load will wear casings and even exceeds allowable limit strength, which combined with potentially high rotating hours, particularly on exploration wells with sidetracks [7] . The thickness of the casing turn to be thin and non-uniform after wear, and all kinds of strength and corrosion resistance will decrease while the worn casing can't be replaced.…”