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Criteria and risk of integrity loss for wells with sustained casing pressure

Yao T., Wojtanowicz A.

AGH Drilling, Oil, Gas

2017

Vol. 34, no. 2

639--654

Sustained casing pressure (SCP) represents a major issue because of its large scale occurrence and risks to health, safety, and the environment. Present regulatory assessment of sustained casing pressure is mostly qualitative with implicit risk formulation. It currently holds that wells with casing head pressure that can be bled-down to zero and is followed by slow 24-hour pressure buildup are below acceptable level of risk. This study introduces new quantitative metrics of well integrity loss risk - the instant cement sheath leak rate of 15 scf/min (barrier integrity), and the total annual environmental gas discharge of 6 tons of volatile organic compounds (VOC) per year. Field data from 19 wells reportedly affected by sustained casing pressure (SCP) are examined with a SCP testing software to assess whether or not wells with pressure that is able to bleed to zero would meet the proposed criteria. Using modeling and software tools developed by Xu and Wojtanowicz (2001) and Kinik and Wojtanowicz (2011), it is determined that three of the 19 wells (15.8) examined would fail the instant leak rate criterion. On the total discharge criterion, assuming the wells' annuli above the cement top filled out with seawater, it was also found, again, that 15.8 percent of the wells would fail the total environmental discharge criterion. Moreover, for the worst-case scenario of absolute open gas flow (empty annulus above the cement top), five of 19 wells (26.3) would fail the criterion. It is shown that - statistically, the bleed-down of casing pressure to zero gives a 90-percent confidence of the well passing the proposed criteria. Furthermore, no clear correlation was observed between pressure build-up and the barrier integrity or the environmental gas discharge criteria, thus questioning the 24-hour pressure buildup relevance as a risk indicator.

Experimental and numerical investigation of expandable tubular structural integrity for well applications

Pervez T.

Journal of Achievements in Materials and Manufacturing Engineering

2010

Vol. 41, nr 1-2

147-154

Purpose: The ever-increasing energy demand has forced researchers to search for new and cheaper solutions for oil and gas production. The recent development of solid expandable tubulars (SETs) has resulted in design of slim oil and gas wells. The large plastic deformation experienced by the tubular under down-hole environment may result in premature and unexpected failures. The objective of this research is to investigate the structural integrity of SET for well applications to avoid such failures. Design/methodology/approach: In order to achieve the objectives, simulation work was carried out using finite element method and experimental tests were conducted on full size tubular for validation of numerical results. Findings: The required drawing force for expansion under different expansion ratios, surplus deformation, variations in tubular thickness and length were estimated numerically and experimentally. The differences in values using two approaches vary from 5% to 12%. Tubular wall thickness decreases as the mandrel angle, expansion ratio, and friction coefficient increase. Research limitations/implications: The issue of maximum expansion a tubular can be subjected to needs to be further investigated. Furthermore, the pre and post-expansion material properties need immediate attention of researchers to fulfil the dream of low-cost expandable solution. Practical implications: In recent years, solid expandable tubular technology has already made significant inroads in replacing conventional telescopic oil wells. It allows design and realization of slim wells, accessing difficult and ultra-deep reservoirs, well remediation, zonal isolation, drilling of directional and horizontal wells, etc. Originality/value: SET is an emerging technology for oil and gas industry. The current findings are very valuable for researchers and well engineers to design slim wells and enhance the productivity of older wells.