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

Abstract

Maintaining casing integrity, in terms of downhole zonal isolations and well stability, is extremely important in oil/gas wells. Casing wear occurs not only in directional drilling, but also in vertical drilling with a slight deviation angle. In most hydrocarbon wells, deteriorated casing was reported from the onset of casing wear by the presence of friction force during the rotation of drillpipe. The friction force against the casing wall causes the reduction of casing strength. Furthermore, the rotation of drillpipe combined with corrosive drilling fluids could dramatically degrade the casing strength. We used a finite element analysis to focus on the stress evolution in worn casings. Comparison study between worn casing and perfect casing was conducted. Our study showed that the thermal load significantly increases the stress concentration of the worn casing in the wellbore. Finite element solutions indicated that the radial stress of the worn casing is not affected as much as the hoop stress. Along with the increased burst pressure or the elevated temperature, the unworn portion of the casing also suffers from severe compression stress. This work is important to broadening the understanding of well engineers through addressing the true stress profile of worn casing in cemented wellbore.

Calculation of Average Reservoir Pore Pressure Based on Surface Displacement Using Image-To-Image Convolutional Neural Network Model

“…Therefore, monitoring and prediction of the formation pore pressure are important to ensure daily oilfield production (Tang et al, 2018;Xu X. Q. et al, 2019;Tang et al, 2021). However, the average pore pressure during formation cannot be directly obtained (Shen et al, 2014;Li et al, 2017;Ameh 2019). Additionally, the formation-pressure gradient near water injection and oil production wells is excessively large to be used as the basic parameter for calculating the average formation pressure (Wang and Sheng, 2018;Zhang et al, 2020).…”

Relevant Information on Oil and Gas Casing Design

“…Tensile, compressive, bending, tensional stress jointly affect on the tube, which makes the casing itself, need the higher quality requirements [1]. Casing wear in the oil and gas industry is recorded on a world basis [4]. Rotation of drill-pipe during the drilling process creates significant contact forces that result in the reduction of casing wall thickness [4].…”

“…Casing wear in the oil and gas industry is recorded on a world basis [4]. Rotation of drill-pipe during the drilling process creates significant contact forces that result in the reduction of casing wall thickness [4]. Thickness reduction of the casing wall weakens the burst and collapse strength of casing.…”

Casing structural integrity and failure modes in a range of well types - A review

“…The research by Gao et al (2010) and Shen and Beck (2014) observed that the casing wear is often encountered as a result of contact between rotating drillstring and the stationary casing during extended reach drilling. Under this circumstance, a major wear of the casing can cause delays, costly repairs and huge economic loss.…”