Excessive solids production and liner issues are familiar complications in maturing SAGD operations, potentially causing well integrity concerns. There are several factors that can occur, in isolation or in combination, to cause excessive solids production and/or liner failures in SAGD wells. Reservoir characteristics, well construction and known downhole conditions contribute to production results and potential liner degradation over time. The production strategy typically considers fluid mechanics, metallurgy, and thermal cycling to limit steam breakthrough, channeling, and/or low sub-cool events. Even with the best construction and production practices, the gradual accumulation of solids in a production well can limit optimal productivity. SAGD Operators may choose a downhole intervention to mitigate the potential of a future failure or require an intervention to prepare for liner remediation. The paper begins by outlining common cleanout methods used in SAGD wells. Then, it discusses a SAGD downhole intervention in three stages: (1) a jetting venturi cleanout, (2) a gauge mill run, and (3) installation of a remedial liner system. The jetting venturi cleanout is comprised of concentric coiled tubing coupled with an engineered jet pump. It is designed to artificially lift wellbore materials, cleaning the SAGD wellbore while recording the volume of solids returned from a specific location. The gauge mill run confirms an acceptable diameter for smooth liner installation. These first two stages ensure seamless installation of the remedial liner system to mitigate detrimental mechanisms that limit production or impact well integrity. Two case studies, in two heavy oil formations from two Operators, support the effectiveness of the SAGD liner intervention. The case summaries and results demonstrate the success of the SAGD liner intervention, corroborate its consistent and repeatable use and show its compatibility with remedial techniques in SAGD operations. The paper establishes the importance of effectively cleaning and clearing a SAGD wellbore in preparation for liner remediation and to provide insight into future well integrity operations.
This paper investigates the fatigue behavior of Concentric Coiled Tubing (CCT) and specifically the influence of internal and annular pressures on fatigue life and diametral growth rate. This behavior is assessed relative to that of conventional Coiled Tubing (CT) using samples of identical material, with software modelling predictions providing an additional basis for comparison. Samples of 1.25" CT were situated concentrically within samples of 2.375" CT, and both were repeatedly bent and straightened on a standard CT fatigue testing system, with separate pressures in the inner volume and the annular volume between the CT samples. Current SPE literature does not include prior art for any type of concentric coiled tubing fatigue testing or analysis. The testing apparatus used in this study is the industry standard for the assessment of conventional coiled tubing, however this paper presents the world-first experimental study of concentric coiled tubing fatigue. Since the testing focused on the failure of the smaller diameter samples, baseline fatigue tests were only conducted on the smaller, inner coiled tubing samples. These results are cross referenced to current fatigue models. Concentric samples were tested on the same machine and setup parameters, using special fixturing that allowed the internal sample to move axially on one end, with its pressure contained. A matrix of pressure differentials was examined, with various levels of inner and annular pressures. The exterior pressure was atmospheric for all tests. The orientation of the longitudinal Electric Resistance Welding (ERW) seams in both samples was examined in this study. The current approach to monitor CCT fatigue integrity is to use a conventional CT fatigue model, based on the differential pressures caused by the inner CT pressure, annular CCT pressure, and well pressure. While pressure may be monitored accurately, uncertainties exist with regards to the influence of radial stress in the tube wall and factors such as mechanical abrasion between the inner and outer coiled tubing strings, especially due to the presence of internal longitudinal ERW seams. Current models assume perfect concentricity; however, eccentricity varies throughout the string in real-world applications. Results from this study include an empirical derating factor, post mortem failure analysis (including assessment of the influence of ERW seam abrasion), diametral growth analysis, and recommendations for future testing.
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