Gravel-packing of open-hole highly-deviated or horizontal wells is increasingly becoming a common practice, especially in deep water and sub-sea completion environments where production rates may reach up to 50,000 BOPD or 250 MMSCFD. In these wells, reliability of the sand face completion, in addition to other factors, is of utmost importance due to the prohibitively high cost of intervention or side-tracking and the very high hydrocarbon recoveries required per well. To date the norm in gravel-packing such wells is water-packing or shunt-packing with water-based fluids. With both techniques, filter-cake removal treatments are conventionally done through coiled tubing after gravel packing, pulling out of the hole with the service tool and running in with the production/injection tubing. Furthermore, because conventional gravel-pack carrier fluids are water-based (brine or viscous fluids), water-based drilling fluids are traditionally used to drill the reservoir section to ensure compatibility and improve wellbore cleanup, even if the upper hole is drilled with a synthetic/oil-based drilling fluid. In this paper, we discuss several novel techniques that can substantially improve return on investment in gravel packing of open-hole horizontal completions, through reduced cost and process time, improved fluid management practices, increased productivity and/or reduced risk of future interventions, so mitigating against the risk of sand face completion failure or under-performance. The proposed techniques include:Simultaneous gravel-packing and filter-cake removal with water-based carrier fluids when the reservoir is drilled with a water-based drilling fluid: laboratory data relevant to gravel-packing are given and field case histories are discussed in detail.Simultaneous gravel-packing and cake cleanup with either water or a synthetic/oil-based carrier fluid when the reservoir is drilled with a synthetic/oil-based drilling fluid: laboratory data on cake removal while gravel packing are presented for both water-based and oil-based carrier fluids along with data on kinetics of cake removal.a new service tool that utilizes wash-pipe as continuous tubing and thus allows spotting of breaker treatments immediately after gravel packing: detailed description of the tool and its operation is given.Gravel-packing of highly-deviated or horizontal wells above fracturing pressure. Benefits offered by each of the proposed techniques are discussed in detail along with their current limitations. Introduction A great majority of the highly-deviated and horizontal wells are being completed as open holes, primarily because of their much higher damage tolerance, higher well productivities at high mobilities (kh/µ) and lower cost compared to cased holes. Although most of these wells in areas requiring sand control have been completed with standalone screens, a rapidly increasing fraction of them are now being gravel packed, particularly in deep water, high production rate and/or sub-sea completion environments (currently ca. 40%, and projected to be ca. 60% by 2003/2004). The major drivers for this current trend are the prohibitively high cost of intervention and much higher reliability associated with gravel packs.1,2
This paper describes a Gulf of Mexico case history that successfully demonstrates a horizontal well can be drilled with synthetic oil based mud (SOBM), and gravel packed with aqueous fluids while still offering excellent well productivity and sand control integrity. The result significantly expands the application of open hole gravel packs to encompass a range of reservoir types and well trajectories thought to date to be unachievable. Key aspects of delivering this technology are discussed in this paper: what major technical risks were identified, how these were managed through an intensive laboratory testing program, engineering, global resourcing, and teamwork put into this project. In particular the following key achievements will be discussed in detail: the successful horizontal balanced displacement from SOBM to kill weight brine, back production of barite laden SOBM filter cake through the gravel pack with minimal productivity impairment, and some important data acquisition results designed to increase our insight into this well type. P. 121
Chirag field was the first of three fields put into production in the Azeri -Chirag -Guneshli (ACG) megastructure, located in the Azeri sector of the Caspian Sea and operated by BP on behalf of Azerbaijan International Operating Company (AIOC). Production commenced in late 1997 after completion of the Chirag A01T1 well. A number of different sandface completion types have been installed in Chirag injectors and producers during the Chirag Early Oil Project (EOP), and significant data have been collected to evaluate the performance of each completion type. Completion types include cased and perforated, open hole gravel packs (OHGP) using wire-wrapped, pre-packed and alternate path (shunttube) screen technology, stand-alone porous metal fiber premium screens, and expandable screens. To date, 29 completions have been installed in 19 of 24 available well slots in primary and sidetrack wells.Many of the producing wells are equipped with permanent downhole pressure-temperature gauges, the flowlines are equipped with acoustic sand detection devices, and an active separator production test and surveillance program has resulted in a quality data set to evaluate completion performance under initial "dry oil" (water free) conditions, and upon the onset of produced water. This quality data set has greatly assisted the completions performance analysis, which has helped shape completion decisions and technology requirements for full field development.The paper will review the completion evolution in Chirag field, the relative performance of completion types over a broad range of indicators, and will include a discussion about measures taken to improve open-hole gravel pack performance from a reservoir damage perspective, with a focus on producers.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMany of the recently discovered reservoirs in deepwater/subsea environments are prime candidates for horizontal open-hole gravel packs. Presence of multiple reactive shale breaks and penetration of different sand bodies along these holes introduce a formidable challenge for selection of proper carrier fluids, considering that most of these wells require oilbased (OB) drilling fluids.Various procedures were practiced for gravel-packing wells drilled with OB fluids, most utilizing water-based (WB) carrier fluids. Primary concern in using WB carrier fluids is the destabilization of the shales.If the displacements to WB fluids are performed prior to running in hole with the sandface completion assembly, inability to run the screen assembly to target zone is the risk. Consequently, operators were forced to use a two-step process, whereby a predrilled liner is run in hole in OB fluid environment, followed by displacements to WB fluids and gravel-packing with WB fluids. This approach introduces additional rig time and increases completion costs.If the displacements to WB fluids are performed after running in hole with completion assembly, primary challenge is the prevention of screen plugging. This necessitates a comparison of the benefits and risks of displacements to solids-free oil-based fluids and conditioning of the OB drilling fluid, considering logistics.An additional consideration in gravel packing with WB fluids in reactive-shale environments is the risk of intermixing of gravel with shales, thus reduced gravel-pack permeability. Various approaches may be taken to minimize this risk. The type of carrier fluid must also be kept in mind from a formation and gravel pack damage standpoints, should losses be experienced during gravel packing.Another approach in reactive shale environments is to use an oil-based carrier fluid and avoid exposure of the open hole to WB fluids both prior to and during gravel packing. This approach, practiced in two applications, also has its limitations.In this paper, a critical review of gravel-packing practices in oil-based drilling environments is provided, along with some of the recent developments and recommendations for future applications based on lessons learned from earlier practices.
Open hole gravel packing for sand control can offer productivity and cost reduction advantages over cased-hole completions, particularly in thick, high permeability sands. The filter cake formed by the reservoir drilling fluid can be trapped by the gravel, resulting in high drawdown requirements, non-uniform inflow profiles and/or low productivity. Effective clean-up and flow-back of this filter cake is necessary to fully realize productivity advantages of open-hole completions. A comprehensive series of over 20 laboratory experiments were carried out to better understand filter cake flow-back in sand control completions. Variables investigated included mud weight and type, gravel size, additives like enzymes and acids, gravel size, and screen type. Results from 12 of these experiments are summarized in this paper. Key findings include:Tested synthetic oil base muds resulted in filter cakes which were much easier to remove than those formed from tested water-based muds.40/60 mesh gravel can severely inhibit filter cake removal compared to larger gravel sizes, which still maintain sand control.An expandable screen pressed into the filter cake does not inhibit filter cake flow-back as long as solids are sized correctly, i.e. the drill-in mud is properly conditioned at the rig site. Experiments were conducted in a standard cell where filter cakes were dynamically deposited and allowed to flow back through gravel and/or screens at scaled flow rates - many with gas. Following each experiment, the entire cell was saturated with epoxy and thin sections were cut across the filter cake and gravel. These visual images dramatically complement return permeability and "lift-off" pressure measurements and help illustrate the mechanics affecting return permeability performance. Introduction Many new prolific reservoirs are being found and developed in high permeability sands. Completion of wells in these sands often requires some type of sand control to maintain sand-free, high-rate production. An increasing number of these wells requiring sand control are completed using open-hole techniques. Completing the well as an open hole offers several advantages over other completion techniques including:Provide a simple lower cost and risk way of completing long intervals without complicated stacked multiple frac-packs and gravel packs;Provide an efficient completion in high mobility formations where the stimulation benefits of fracs are lost;Allow completion of long horizontal or high-angle wells. Several studies have demonstrated the impact and dominance of perforation tunnels on the inflow performance of high rate wells.1–4Turbulence and limited in-flow area can hurt in-flow potential. Stimulation benefits of fracturing can be lost in high mobility (kh/viscosity) reservoirs as flow is choked by perforations. Area open to flow is significantly greater in an open hole relative to cased and perforated completions. Until recently, many of these open-hole completions would have been accomplished with only screens in the open hole.5,6Several wells completed in this fashion have suffered premature failures due to screen plugging leading to productivity loss. In some cases this plugging led to such small inflow areas that screens were eroded and no longer able to hold back formation sand. Stand-alone screens are still a viable option for high permeability, well-sorted sands; but many heterogeneous formations require that the annulus between the screen and formation be stabilized by gravel or an expandable screen.
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