Sintered bauxite is the primary proppant used during deepwater Gulf of Mexico (GOM) operations because of its high strength and conductivity. However, the use of bauxite proppant presents operational issues for coiled tubing (CT) resulting from its high specific gravity (approximately 3.6). This paper describes the planning and execution of a heavy post-fracturing proppant cleanout operation using CT in the operator's Tahiti field in the US GOM.
During completion operations on a subsea well, access to the well was provided by a dynamically positioned drillship. After installing the lower completion in the well using drillpipe, a proppant-laden stimulation treatment was pumped. During this process, an early screenout was encountered, and approximately 171,300-lbm proppant remained in the drillpipe that was unable to be reversed out. A CT unit was rigged up in a tension-lift frame that suspended the drillpipe string, allowing for a motion-compensated window to rig up the CT injector head and pressure- control equipment. A 1.75-in. outer diameter (OD) CT string was used to clean out the wellbore to 24,215 ft by circulating brine down the CT string and up and out of the drillpipe through a flow cross.
Preexisting contingency planning proved invaluable for efficient cleanout operations by providing the physical assets necessary to perform a successful operation as well as a framework for the engineering and procedures required. The drillstring was effectively cleaned of proppant to 24,215 ft. Once the well was deemed clean, kill-weight fluid was circulated into the well to allow for further well intervention operations and the eventual return to completion operations.
This case study illustrates the importance of contingency planning to help minimize overall operation costs. The large-scale and challenging well conditions of this unique project led to valuable lessons learned that can be used to optimize performance during future cleanout and drillship operations.
An intervention program in a well may require the use of both electric line and slick line to convey a variety of services. This calls for the swapping between conveyance systems, often multiple times in a single intervention program. A viable solution is a new system for carrying out interventions in oil wells which is designed to convey electrical, electro-mechanical and mechanical services. The paper aims to describe this new conveyance system and discuss field experience to date.
Carbon composite material technology confers the benefit of higher strength at reduced weight when compared to conventional cable materials and the slick surface eliminates the need for grease injection pressure control systems. The ability to perform both precision logging and heavy duty mechanical services within the same rig-up allows complex well programs to be executed with only one unit and a multi-skilled crew.
The first field trial for the new conveyance system was conducted offshore in the North Sea, and proved the carbon composite rod capable of performing both mechanical intervention (16 runs) and electric line (12 runs) services. The strength of the rod material enables the running of long and heavy bottom hole assemblies. Run in conjunction with electrical or mechanical release devices, the carbon composite rod is able to deploy strings beyond the capability of conventional wirelines.
The physical strength and rigidity of the rod, coupled with its light weight, allow efficient planning of intervention programs where mechanical and electric services are combined in a single rig-up. Since the first trial, advances in technique have brought 10km (32,000 ft.) rods to the field enabling intervention access to, and perhaps more importantly retrieval from, extended reach wells. Equally of interest is the ability of the rod to access short lateral sections without resorting to tractor technology, allowing faster and more economical intervention.
As a result of many industry efforts, the premature fatigue failure of undamaged coiled tubing (CT) strings is almost negligible. However, despite the current understanding and control of low-cycle fatigue, CT string failures remain present in the industry. Several prior technical publications reviewed the causes and trends of CT string failures that occurred within the period of 1994 to 2005. This paper will review CT failures mechanisms and trends as observed over the last twelve years and compare them to the prior ten years period. It will also review the new failure mechanisms that have appeared with more challenging operational conditions and the associated actions taken to reduce their influence.
Within one major service company, all failures that occur are analyzed for the root cause(s) of failure. This results in the identification of corrective actions to avoid their recurrence. Statistical data is kept to observe trends on failure causes.
Several technical publications show that approximately 80% – 90% of CT string failures within the period of 1994 to 2005 were associated with corrosion, mechanical damage, human error, and string manufacturing problems. Actions taken in the last two decades by the CT services companies, and constant improvement implemented by CT manufacturers have reduced the influence of some of these causes. However, work in ever-more challenging well conditions (such as higher pressures, temperatures, and depths), the need to use larger-diameter and higher-strength CT, and the use of recycled fluids for the interventions, have created new issues and introduced new CT failure mechanisms. The new mechanisms within the industry include: microbiologically influenced corrosion (MIC), premature fatigue failures on bias welds of high-strength grades, and mechanical damage associated with pipe slippages.
This paper will compare the failure trends reported for the period before 2005 with the trends observed for this service company within the period of 12 years after 2005 (i.e., from 2006 to 2017). The changes in the failures trends are analyzed, and examples of the newer CT failure mechanisms and the mitigating actions taken are presented.
While the oil and gas market continues to fluctuate, operators are forced to reduce drilling costs and increase efficiency to remain profitable; therefore, the focus on well reentry, sidetracks, and multilaterals from existing wellbores is growing in popularity, particularly within Australasia. Coiled tubing drilling (CTD) technology has been explored in New Zealand; however, successfully executed operations have so far been limited. After evaluating economic benefits and finding a suitable candidate trial well, a Canadian-based operator attempted a CTD operation in New Zealand that was technically successful.
This case history outlines the two-phase project and discusses well intervention to isolate existing perforations and the sidetrack from the primary motherbore to drill to the base of the new reservoir. The objectives were to convert the suspended well from an oil producer to a water injector, enhance oil recovery within the field, and prolong oil production by reviving an underused asset. This paper discusses the engineering and technology used as well as regulatory obstacles and challenges encountered that were overcome to reach the operator’s objective.
A 2 7/8-in. coiled tubing (CT) string was used for both phases of the operation, spanning intervention and drilling to perform all scheduled operations as efficiently as possible. The resulting completion, post-sidetrack, was to incorporate the CT workstring with approximately 100 m of a perforated 2 7/8-in. jointed pipe to maintain openhole stability across the injection zone.
As well production declines in mature fields and becomes unprofitable, operators must shut the wells in and permanently plug and abandon (P&A) them. It is presently estimated that thousands of such wells will require permanent P&A.
Historically, the P&A of wells in the North Sea were performed using either drilling or workover rigs. In many cases, wells drilled from fixed platforms in the North Sea no longer have operational drilling rigs requiring recommissioning of existing facilities or mobilization of workover rigs.
Regulatory authorities in the North Sea have defined standards for creating permanent reservoir barriers for the P&A of wells, which includes requiring a "rock-to-rock" barrier.
This paper discusses an alternative approach to P&A using coiled tubing (CT) processes and techniques to create these permanent reservoir barriers. One process rigged CT up from the drill floor and pipe deck in a conventional fashion. During the intervention, standard milling and tubular cleanout techniques were used to gain access to the reservoir, and then a novel perforating, washing, and cementing (PWC) technique created the reservoir barrier. Finally, an additional tubing punch run was made, and the barrier was tested. In a single, multiwell campaign, 13 wells in the field had successful permanent reservoir barriers created using CT.
This paper illustrates the successful creation of permanent reservoir barriers using CT. Additionally, the paper highlights that using CT can provide economic benefits for creating the barrier compared to more conventional drilling or workover rigs.
"Run in hole", "stop CT", "pickup", "drop pumps"… All common commands heard in the control cab during a coiled tubing plug drillout (CTDO). What drives the decision making process and what information has been processed to arrive at such a conclusion? During a coiled tubing (CT) operation, many parameters are being acquired including pump rate, pressures, weights and speeds, and the success of the operation relies on how the supervisory personnel interpret this data and advise on next steps. At the end of the job, if lucky, this crucial data is archived in the catacombs of the well file on some network server. What if instead, this information was analyzed to detail the operation, develop performance metrics to help understand why the results were what they were, and ultimately provide guidance for future operations? This paper discusses an algorithm developed to support analysis and a philosophy of job review that has been utilized to robustly process a rich, continuous and widely available CTDO data set.
The objective of this paper is to clearly outline the basic principles and techniques required to successfully perform well intervention in wells with low-pressure formations, thief zones, and/or depleted reservoirs—specifically, horizontal or highly deviated wells. The paper aims to review the considerations and provide an example of reliable execution in its most basic form, including simplified calculations designed to be used in conjunction with advanced modeling software available in the industry. Coiled-tubing intervention in lateral wells with fluid-loss potential is inherently high risk. The risk of poor solid suspension or loss of fluid circulation results from the inability to avoid fluid loss and causes costly job failures, lost workstrings or equipment, or reduced well production. For land-based operations in the United States, coiled tubing has been reliably and successfully deployed in depleted and low-reservoir-pressure wells that were unable to support a hydrocarbon or water column to surface. These jobs include sand cleanouts, re-fracture preparation cleanouts, and underbalance millouts in extended laterals.
Commingled nitrogen and water-based systems were used to reduce hydrostatic pressures exerted on the reservoir and, thereby, allowed for successful continued circulation. The fluid system was adapted to each well intervention to consider formation type, reservoir fluid composition, job requirements, BHA requirements and limitations, chemical compatibility, cutting suspension potential, and foam integrity. When combined with real-time monitoring of, and response to, well conditions, the occurrence of job failure was greatly reduced.
The Kuparuk River unit (KRU) on the North Slope of Alaska is a maturing asset providing a variety of well intervention opportunities necessary to maintain production. Because of the high well count, interventions need to be efficient, and the traditional slickline and electrical line model are being challenged. The primary concern is the multiple rig ups and rig downs to complete the scope of work, but there are also local concerns, such as maintaining a workable equipment schedule in a cold-weather region. Another unique feature of the KRU is that many of the wells have scale deposits.
Digital slickline (DSL) has been successfully used in the KRU and was highlighted in previous papers (
In 2017, more than 400 digital subscriber line (DSL) runs covering a wide variety of tasks were successfully completed, including removing and replacing gas-lift valves, fishing packers, string shots, perforating, setting packers, and patches. An interesting result of the KRU digital slickline interventions was that approximately 60% of the runs were slickline centric involving jars and 40% were considered e-line replacement services. This trend suggests that a successful product should be able to complete all typical slickline runs to maintain the efficiency advantage.
Oil and gas wells are drilled with horizontal and multilateral architecture to improve reservoir contact and maximize production. To evaluate the performance of these wells, coiled tubing (CT) and Wireline (WL) conveyance are routinely used. CT inherently have many technical issues such as lock-up. The WL cannot reach the target depth. To address these challenges, the oil industry introduced well tractors that are combined with CT and WL to offer a significant improvement in well accessibility for all types of open- hole horizontal wells by providing extra pulling force to pull CT and WL all the way to target depth. The objective of this article is to evaluate most of the well tractor technology used in logging and stimulation operations. Moreover, the development of a new slim tractor with improved gripping and pulling force with ability to pass through restrictions in electrical submersible pump (ESP) is presented. This study can help identify areas of improvement for tractor capabilities in future operations.
This paper is a case study of a successful, complex, high-pressure, and heavy-duty fishing job on a live sour gas well in Saudi Arabia. The multidisciplinary effort involved braided line, various sizes of slick line and coiled tubing (CT) intervention.
The paper examines details of the job planning and design as well as the job execution. The well control philosophy and compliance to some of the highest operational standards in the industry will be discussed along with the associated risk and mitigation strategy. This multifaceted job involved fishing a live perforating gun and plug assembly, which was stuck in the liner following a misfire while attempting to set the plug. The fishing job was further complicated due to the presence of a parted section of electric line on top of the original fish.
Recent developments in heavy-duty fishing operations were incorporated into the intervention process. Equally important is the integrated approach used for this complex fishing job with special safety procedures put in place for the use of multilevel scaffolding, multiple cranes, lifting plans, wire and live gun retrieval procedures, contingency plans and multipurpose pressure control equipment (PCE).
Lessons learned will also be presented in the paper. This successful heavy-duty fishing operation has helped push the boundaries of rigless well intervention, improved operational efficiency and opened up additional opportunities for this technology that previously required the deployment of a workover rig or snubbing unit.