Risk assessment of corroded casing based on analytic hierarchy process and fuzzy comprehensive evaluation
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ORIGINAL PAPER
Risk assessment of corroded casing based on analytic hierarchy process and fuzzy comprehensive evaluation Sheng‑Shan Chen1 · Han‑Xiang Wang1 · Hao Jiang1 · Ya‑Nan Liu1 · Yan‑Xin Liu1 · Xiao‑Xiao Lv1 Received: 18 March 2020 © The Author(s) 2020
Abstract Casing corrosion during C O2 injection or storage results in significant economic loss and increased production risks. Therefore, in this paper, a corroded casing risk assessment model based on analytic hierarchy process and fuzzy comprehensive evaluation is established to identify potential risks in time. First, the corrosion rate and residual strength characteristics are analyzed through corrosion tests and numerical simulations, respectively, to determine the risk factors that may lead to an accident. Then, an index system for corroded casing risk evaluation is established based on six important factors: temperature, CO2 partial pressure, flow velocity, corrosion radius, corrosion depth and wellhead pressure. Subsequently, the index weights are calculated via the analytic hierarchy process. Finally, the risk level of corroded casing is obtained via the fuzzy comprehensive evaluation. The corroded casing risk assessment model has been verified by a case well, which shows that the model is valuable and feasible. It provides an effective decision-making method for the risk evaluation of corroded casing in CO2 injection well, which is conductive to improve the wellbore operation efficiency. Keywords Corrosion rate · Residual strength · Analytic hierarchy process · Fuzzy comprehensive evaluation
1 Introduction Injecting CO2 into the depleted oil reservoirs for storage or to enhance oil and gas production is considered as one of the effective measures to reduce the content of CO2 in the atmosphere (Ajayi et al. 2019; Kalra et al. 2018; Khather et al. 2019). However, as an acid gas, CO2 is highly corrosive in water-containing environment (Zhu and Liu 2018). After operating under highly corrosive conditions for a certain period, the casing of CO2 injection wells in Shengli Oilfield exhibited serious corrosion behavior, posing a threat to well safety and severely limiting the promotion of CO2-enhanced oil recovery technology. In addition, some C O2 injection wells are modified from legacy oil wells that have been in service for a long time (Laumb et al. 2016), so casing corrosion problems are inevitable. Laumb et al. (2016) presented Edited by Xiu-Qiu Peng * Han‑Xiang Wang [email protected] 1
College of Mechanical and Electronic Engineering, China University of Petroleum (East China), Qingdao 266580, China
two cases of Weyburn Oilfield and proposed that the casing corrosion ranges from small pits to complete penetration in a CO2-rich environment. In one of the case wells, the entire lower section of casing was completely corroded during the 6-year time period when CO2 was injected. Therefore, it is important to study the corroded casing risk assessment of the CO2 injection wells to ensure the safe operation of these wells. In academia
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