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Specialized Cement Design and Placement Procedures Prove Successful for Mitigating Casing Vent Flows-Case Histories. (76333) This paper documents recent field cases in which attempts were made to mitigate casing vent flows (CVF's) on producing and abandoned wells by incorporating permeability-blocking gels with specialized cement blends. CVF's are defined in this paper as sustained gas pressure on the annuli of producing and surface casings. The amount of gas flow rate can vary from a few bubbles to cubic meters per day. However, when the annuli are shut-in, the gas pressure can build to a significant amount. The procedures detailed in this paper are the result of lab studies and postjob reviews of failed remedial attempts. Specific attention is given to why squeeze-cementing procedures can fail to provide long-term seals against source-gas production from casing vents. In most cases, rework of the abandonment procedures cost the operators over $200,000 CAD. The studies showed four possible causes of recurring CVF's: * Development of thaumasite in the
setting cement Cement-source quality and bulk handling methods were also investigated, but showed no evidence of probable cause. This paper explains the findings from laboratory studies and job reviews that lead to improved procedures. These improved solutions were conducted on 23 wells in the later part of 2001.
Neural Network Analysis Identifies Production Enhancement Opportunities in the Kaybob Field. (71040) Evaluating and optimizing well completion procedures can be difficult because of the complexity of reservoir and completion dynamics. Although a vast amount of data is available within the industry, we need to analyze this data to enhance our ability to improve well economics. In this paper, we discuss the use of an artificial neural network (ANN) as a tool to evaluate and optimize stimulation methods and to develop a prediction model for three specific producing formations in the Kaybob field of northwestern Alberta, Canada. The area is gas prone, with multiple producing horizons. Significant amounts of gas have been produced from the Bluesky, Cadomin, and Gething formations. Permeability is typically low, and hydraulic fracturing is required for economic production. Fracture treatment designs have varied considerably, with no apparent consensus as to the optimum fracturing fluid, proppant type, or treatment volume.
Selection of Foam Flushes and Foamed Cement Proves Effective for Remedial Operations of Low-Pressured Formations-Case Histories. (80939) Remedial cementing operations and zone abandonment are difficult to accomplish when low-pressure formations possess high feed rates at low, or even vacuum, surface pressures. Such is the case with several heavy-oil wells recently abandoned in Western Canada. These wells and their respective formations average an economic life of approximately ten years, during which a large amount of formation sand is produced. Traditionally, whenever exposed to hydrostatic pressure, these zones exhibit a vacuum at very large feedrates. Scorecard results of conventional cement squeezes required an average of 2.6 attempts to obtain a positive squeeze pressure. Many conventional cementing abandonment attempts were unsuccessful, resulting in the placement of a casing patch across the open perforations. The mechanical seal was effective in sealing the wellbore, which allowed exploitation of deeper zones. However, this seal reduced the casing internal diameter and can limit further production operations. Also, this mechanical seal may not serve as a final abandonment under certain government regulations. The solution to this challenge was developed by tailoring a treatment pumping schedule that incorporates the use of foamed nonreactive, reactive spacers and foamed cement blends. This new treatment design was used on several wells in early 2002. On most of the wells, positive squeeze pressure was obtained on the first attempt and saved approximately CAD $15,000 per well. The improved process is now being planned for two adjacent fields. This paper details the well challenges and results found by a Canadian operator to successfully abandon low-pressure, heavy-oil producing zones. The solution developed for the case history wells is also presented.
Gas Migration Database Helps Improve Vent Flow Risk Assessment 03-001 Traditionally, gas migration analysis studies have focused on the mechanics of good primary cementing practices. These practices include items such as mud displacement, annular velocities, slurry properties, and casing movements. A database exists in Alberta, Canada, that registers gas migration based on preset guidelines. This database currently has over 5,000 recorded vent flows, some serious, but most recorded as non-serious. This paper describes the mapping of gas vent flows and subsequent findings of the mapping process. The mapping process was capable of locating pockets of vent flows. With this finding, the authors were able to evaluate new drills based on a localized risk analysis, which allows efforts to be focused on high- and medium-risk areas and standard practices to be implemented on low-risk wells. Costs are reduced and compliance to controlling vent flow is ensured.
Non-Portland Annular Sealant for Acid-Gas Injection 97-136 This paper reports the results of field use, during primary cementation of disposal –injection wells, of an annular sealant that resists acid corrosion caused by acids introduced through gas injection. The sealing system consists of latex, a crosslinking agent, crosslinking activators, a crosslinking accelerator, and reinforcing agents. This combination yields a cementing system that is resilient, corrosion-resistant, ductile and drillable with conventional tooth bits. In acid-gas disposal operations, conventional Portland cement compositions placed across injection zones are prone to chemical attack and to the formation of unstable cement hydrates. During acid stimulation or acid cleanup treatment, subsequent exposure to acid dissolves the free lime associated with cement hydration, destroying zonal isolation. If sour gas is present, it can attack the free lime. And also react thermodynamically with calcium silicate hydrates to the cement to form calcium sulfide, which can crack and decay the cement sheath. In laboratory testing and field use to date, the cement composite described in this paper has shown total resistance to acid corrosion attack.
Framework for Optimizing Components in an Oil well Cement Slurry Design Fifteenth annual Canadian conference on markets for industrial minerals (2003) www.blendon.com Oilfield cementing has been utilized in the industry since the turn of the century. Originally, wells were shallow and criteria for well integrity were somewhat limited. Since that time wells have stretched the envelope in depth, temperature, and pressure. Environmental regulations have also become more stringent; thus, the importance of hydraulic isolation between permeable zones and between these zones and surface has become more and more important. Initially, oilfield cements were comprised predominately of construction cement and very limited additives. As time progressed, additives were incorporated to control pumping time or placement time and little effort was placed on optimizing actual components within the cement chemistry. This paper presents issues and concerns created by adding just one new component to the fundamental chemistry of an oilfield cement.
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