A drill-bit supplier provided mills and bits for drilling out fracturing plugs for a new project in the Vaca Muerta formation in Argentina; however, it was difficult to locate information on similar experiences elsewhere. This paper presents the experience gained during execution of a completions project that included fracturing plug drillouts. Several technologies were used, and their performances are reviewed, including mills, roller-cone bits, and polycrystalline diamond compact (PDC) bits. Drillout times, size and shape of debris, hole cleaning, and tool dull grades are analyzed. All operations were performed with coiled tubing (CT) equipment. Other parameters considered in the analysis include drilling parameters, number of runs to complete a well, plugs per run drilled, and tolerances with respect to casing drift. Some problems that occurred during project execution are discussed, such as motor stall and casing deformation. The operations were performed in a combination of horizontal and vertical wells. More than 500 fracturing plugs were drilled out in more than 60 wells, gaining sufficient experience to derive significant conclusions. To help reduce drilling time, improve economics, minimize risks, and reduce CT system fatigue, the five to six-blade PDC bit was verified as the best option in this context. This drill type has an acceptable rate of penetration (ROP), does not risk losing moving parts, and minimizes motor stall. When tolerance with respect to casing drift is correct, the five to six-blade PDC bit also minimizes debris size, which helps reduce stuck-in-hole risks and improves subsequent well production. Several statistics, images, and resolved issues are presented to advise future CT and well intervention projects. Conclusions regarding various plug types, materials, and drillout procedures are also explained to aid similar projects.
Advanced horizontal drilling, multi-stage hydraulic fracturing techniques and other innovative technologies have helped make the Vaca Muerta shale oil and gas resource economically viable. Well Operators developing this resource are continuously revising drilling programs and well designs to better exploit this valuable resource. One option in this development is to increase the length of the horizontal section of each well to add hydraulic fracture stages. This option can potentially increase production significantly with minimal incremental drilling and completion costs. In response to Operator requests, Service Companies are now seeking improved technologies and equipment to enable them to provide more effective service in extended horizontal well environments. Utilizing refined, custom-engineered Coiled Tubing (CT) string designs to perform certain intervention techniques and procedures appear to be an economic and efficient solution in this shale development phase. Anticipated high-angles in deviated well sections, along with the extended horizontal length of the planned wells formed an expectation that conventional CT designs would not be able to service new well designs. The frictional wall contact force between the coiled tubing and the wellbore, which promotes helical buckling, was greater than the axial compression force limit of the typical coiled tubing designs being used in the area; therefore, a customized taper design was necessary for the expected extended lateral, high pressure wells. An iterative collaboration between the well Operator, CT Service, and CT Manufacturing Companies took place to purpose-build a CT string design with extended reach capabilities while considering logistics and CT equipment available in the area. An extensive CT string design evaluation, which analyzed tubing forces, downhole buckling, and lock-up behavior in different planned wells, was performed to determine the optimum combination of tubing grade, taper design, wall thickness and section lengths to ensure the likelihood of reaching target depths with adequate weight-on-bit (WOB) for milling operations. Bottom Hole Assemblies (BHA), fluids and cleanout efficiencies were also analyzed in this study. The use of a proprietary technology from the CT manufacturer facilitated the required wall thickness transitions to strategically place specific thicknesses along the length of the string to enhance force transmission to the end of the tubing, increase strength and stiffness where needed, and reduce fatigue accumulation, and weight. Field results demonstrated that the use of custom-engineered CT design, extended reach tools and fluid additives, aligned with strict operational practices, has had a great impact on the economics and efficiency of post fracture plug mill-out operations in the Vaca Muerta region. This study documents the improved CT extended reach applications reliability to strategically support this unconventional shale development. Outlined in this study is the evolution of a unique, engineered coiled tubing design, considerations and operation details which helped set and push the limits of extended reach CT interventions, utilizing available CT equipment and technology in the Vaca Muerta shale.
World energy demand has led unconventional reservoirs to become a focal point for operators worldwide. In some regions, including North America, unconventional resources have been developed successfully, accumulating important experience and lessons learned in the process, allowing these resources to become important contributors to countries’ energy production. In an attempt to reproduce this effect in other regions, operators are also looking into important unconventional reservoirs outside North America. Currently the world’s third-largest shale oil and gas resources holder, Argentina has become a key focus for many operators initiating exploration and development operations. This brings many challenges to operators trying to take over this market as quickly, efficiently, and safely as possible. When developing unconventional reservoirs in the magnitude expected, one of the most important challenges for service companies and operators in Argentina is effectively grasping the global expertise, best practices, and lessons learned from these types of operations and adapt them to the local environment. This should reduce the learning curve experienced while starting a new development. A key component of these challenges includes all coiled tubing (CT) interventions involved in well completion; expertise in CT intervention is critical because of the risks concerning these operations, which include wellbore calibration, perforating, fracture plug drillouts (FPDOs), and sand cleanouts. Overcoming this challenge can translate into valuable time and cost reductions and allow operators to reach the efficiency that took years to attain in other parts of the world in much less time. Lessons learned and best practices incorporated from global experience, in addition to the local ideas, contributed to the implementation of CT interventions for the shale startup and beginning of the development phase in Argentina. Statistics and results from jobs performed in these reservoirs in its first year since startup reflect the changes and adaptations undertaken to successfully develop the shale resources in Argentina and to inform future plans for this rapidly evolving market.
Horizontal shale wells’ drilling has been challenging the technical limits since its beginning, and the same challenge was faced in completion phase with the Plug&Perf method. Vaca Muerta shale play in Argentina is not an exception of this. Lateral lengths in Vaca Muerta achieved 800-1000 m in the beginning of its shale operations with horizontal wells, and now they are designed to achieve more than 2500 m, even 3200 m, similar to the major laterals in the main shale plays of USA and Canada. In Plug&Perf completion method, new materials for fracture plugs and advanced designs of perforating guns were also influenced by the technological advances of the industry. Coiled Tubing (CT) was not an exception of this trend. CT strings for milling out plugs have been demanded to achieve longer laterals without loosing efficiency, with the required Weight on Bit (WOB). Two main aspects must be taken into account for CT string design: Lateral reach with enough WOB depends mainly on geometrical aspects (external diameter and combination of different wall thicknesses) in order to minimize the occurance of buckling by decreasing the friction caused by the contact of the string with casing wall.Extended fatigue life In this way, a new technology in CT manufacture was developed and patented, and introduced by the first time in the market in 2005 (R. Rolovic. M. Valdez et al, 2017). This technology employs materials with a new chemistry, and involves a heat treatment for achieving a complete microstructure transformation and homogeneous properties all along the string. Hence, bias weld, heat affected zone and longitudinal seam weld. Field performance of this new technology in CT has gone beyond the experience achieved with conventional CT. Furthermore, testing of several strings after being removed from the field have shown a superior residual fatigue life than conventional strings, confirming the stated conclusions and pevious observations.
An operator company in Bolivia needed a solution to a corrosion and pressure integrity problem caused by the presence of CO2 gas in the production fluids, resulting in deep tubing corrosion over certain sections of completion components with measured penetrations up to 96% of tubing's wall thickness. Based on the corrosion's profiles, the intervention objective was to install a 16% chrome corrosion-resistant velocity string inside the production string to produce the well avoiding the exposure of those highly corroded components from the tubing. The repair intervention concept was to set a hydraulic packer over the lower completion below the most compromised section of the production string and connect the isolation packer with 2" OD 16%Cr coiled tubing pipe up to the surface, hanging the string on the wellhead. The velocity string installation should be performed in a single run with the well in live condition, avoiding the need to kill the well during the intervention. The well's lower completion was composed of TPC-fired guns, a combination of 2-7/8" 6.4# and 3-1/2" 9.2# N80 tubing, and a 7" 23-29# packer. The upper completion was basically an arrangement of 3-1/2" 9.2# N80 tubing with a retrievable SSSV set at 107 m, a sliding sleeve device, and a seal unit sub to connect the upper to the lower completion.
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