Acid systems are widely recognized by the oil and gas industry as an attractive class of fluids for the efficient stimulation of carbonate reservoirs. One of the major challenges in carbonate acidizing treatments is adjusting the convective transport of acid deep into the reservoir while achieving a minimum rock face dissolution. Conventional emulsified acids are hindered by several limitations; low stability at high temperatures, a high viscosity that limits pumping rate due to frictional losses, the potential of formation damage, and the difficulty to achieve homogenous field-scale mixing. This paper highlights the successful application of an engineered low-viscosity retarded acid system without the need for gelation by a polymer or surfactant or emulsification by diesel. An acid stimulation job using a new innovative retarded acid system has been performed in a West Kuwait field well. The proposed acid system combines the use of a strong mineral acid (i.e. hydrochloric acid "HCl") with a non-damaging retarding agent that allows deeper penetration of the live HCl acid into the formation, resulting in a more effective stimulation treatment. The retardation behavior testing includes dissolution experiments, compatibility testing, coreflood study, and corrosion rate testing (conducted at 200°F). The on-job implementation included the use of a packer to pinpoint fluid pumping (pre-flush) at the point of interest, followed by the customized novel retarded acid system for improving conductivity at perforations and effective reservoir stimulation. This acid system is characterized by having a low-viscosity and high thermal stability system that can be mixed on the fly. This approach addresses the main challenges of emulsified acid systems and offers a cost-effective solution to cover a wide range of applications in matrix acid stimulation and high-temperature conditions that require a chemically retarded acid system. The application of this novel acid retarded system is a fit-for-purpose solution to optimize the return on investment by maximizing the well production and extending the lifetime of the treatment effect. This new system also offers excellent scale inhibition and iron control properties which eliminates the need for any acid remedial work, making it an economical approach over other conventional acid systems. The paper presents results obtained after stimulating the carbonate reservoir and describes the lessons learned from the job planning and execution phases, which can be considered as a best practice for application in similar challenges in other fields. Proper candidate selection, best available placement technique, and lab-tested formulation of novel retarded acid system resulted in achieving 1700 BOPD of oil production (27% higher than expected).
Objectives/Scope The latest developments in well construction demand equipment that defies the current industry limits to access the full length of the pay zones in 40,000+ ft wells. With the growing trend of drilling horizontal wells in the mega reach category and beyond, there is a need for a new level of engineering design of Coiled Tubing (CT) strings and downhole technology with a specific approach to reach these new and expanding requirements. Methods, Procedures, Process Extended reach conveyance of CT is a challenge that service companies and operators have progressively addressed as wells are drilled deeper into the mega reach area. Advanced CT string designs and materials, as well as systematic variations of parameters affecting friction coefficients between CT and wellbore completions, provide benefits to operators in extending the reach of the horizontal sections. Special downhole tools and engineering testing are required to plan the best outcome from the available downhole force technology to increase wellbore coverage while maintaining well underbalance, reducing operational footprint, and safely deploying the heaviest 40,000 ft 2-3/8 in CT pipe offshore. Results, Observations, Conclusions This paper describes the systematic process used to address the mega reach challenges, as CT is required to reach Total Depth (TD) in wells longer than 40,000 ft in one offshore oil field in Abu Dhabi. It summarizes the considerations taken to design the right string for the project and describes the multiple technologies used to extend the reach of the CT in the horizontal sections while remaining underbalanced. Additionally, this paper discusses the implementation of a surfactant-based Friction Reducer (FR) system to extend the CT reach and the friction matching analysis performed while calculating the extended lock-up depth. In addition, the special transportation solutions to deploy the CT reel to the wellhead are discussed, along with the track stack required to make these operations possible. Novel/Additive Information Detailed data collected throughout the campaign enabled the operating company and the service company to benchmark the results of the operations, drawing better conclusions well after well and enabling a positive loop of improvement leading to economic gains as the campaign was executed. Technical challenges, downhole tools, and fluid solutions to reach TD Transportation solutions for mega reach CT string deployment
Verifying that conventional coiled tubing (CT) has entered the correct lateral of a multilateral well can be a time-consuming and tedious challenge. While passing the kickoff point (KOP), surface pressure sensors may not clearly identify that a hydraulic knuckle joint has entered the lateral. To verify which lateral has been entered, the CT must be run-in-hole (RIH) to tag the unique total depth (TD) of the lateral. It can be difficult to prove that the correct lateral has been entered if the TDs for two laterals do not differ significantly. If the CT tags before or after the expected TD is reached, then the operator must pull out of hole (POOH) and repeat this process. This paper presents an improved method for detecting which lateral has been entered shortly after passing the KOP by using a real-time, fiber optic cable (RTFO) bottomhole assembly (BHA). The RTFO BHA is equipped with sensors for gamma radiation (GR), tool inclination, tool face, casing collar locator (CCL), internal and external pressure, and temperature. These readings enable the operator to use the CCL and gamma detector to correlate to the desired lateral’s pipe joints using an existing CCL/GR log. The tool face reading theoretically predicts which angle the knuckle joint should be indexed. The internal pressure sensor provides clear indication of pressure changes when a hydraulic knuckle joint has entered the lateral and the inclination sensor verifies that the inclination of the BHA matches the inclination of the desired lateral. This paper discusses two dual-lateral water injection wells; the TDs of the laterals in the first well were equal, with no trait that conventional CT would be able to distinguish. In addition, the inclination of each lateral was very close to the other, making the difference of pipe weight, read from the surface, not significantly different enough to verify which lateral had been entered. However, with the RTFO BHA, the correct lateral was easily entered and verified, significantly reducing time, risk, fluids, and CT pipe fatigue, while providing assurance that the stimulation fluid was accurately placed. This paper describes the first time that a flow-through gamma, inclination, tool face sensor module was deployed to accurately enter, identify, and stimulate a casedhole multilateral well without cycling the CT at the KOP, and without relying on tagging TD to confirm that the BHA is inside the desired lateral. The new process proved to be a better, more cost effective, and efficient way to stimulate multilateral wells. This solution can be used by operators to extend the life of their mature fields.
The procedural development implemented across an unconventional project in Middle East is explored, delving deeper into coiled-tubing (CT) design, from metallurgical properties and string specification to bottomhole assembly (BHA) and fluid selection, tailored to plug-and-perf operations involving the use of a specialized frac plug. Further discussed is the "learning curve" generated, highlighting improvements achieved across the "iron triangle" of operating time, cost, and quality, referring to case studies of interventions conducted across multiple horizontal wells. Unconventional CT interventions have always been challenged by an operator's quest to drill the longest possible lateral to maximize per-well estimated ultimate recovery (EUR) by maximizing the number of fractured clusters/stages. CT job designs across these projects usually rely on running the biggest outer diameter (OD) CT with the largest hydraulic downhole motors available to enable the deepest reach, highest weight on bit (WOB), torque, and circulation rate. However, this conservative approach causes operations to be overdesigned, ultimately resulting in excessive operational cost and nonproductive time. As observed from this experience, an engineered process enables an operator to select the correct resources to meet the operational objectives. A successful multiwell campaign of prefrac-drift, wellbore fluid displacement, cement sheath cleanout, followed by tubing-conveyed perforation (TCP) and post-frac 32–44 plug millout was performed across high-pressure/high-temperature (HP/HT), sour, unconventional wells in Middle East. After respective CT interventions, the wells were successfully fractured and flowed back. Based on lessons learned and various corrective action items implemented, service efficiency (single run) and job time (+50% reduction) were substantially improved. This enhancement was mainly attributed to the revised surface piping and instrumentation (P&I) rigup, CT material and dimension selection, BHA components, including custom-built mill/motor and extended-reach vibrating tool, gel and friction reducer fluid placement, reduced wiper trip frequency, etc. These optimized CT interventions created a more balanced approach to unconventional operations, wherein bigger is not always better. The CT procedure evolved, initially referencing best practices from analogue unconventional plays, while slowly progressing into a tailored fit-for-purpose operation. This approach enabled the operator to achieve operational objectives more efficiently.
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