Innovative Sand-Control Screen Assembly Enables Successful Multi-Lobe Frac Packs in Adverse Recompletion Conditions
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Concentric Annular Packing System Successfully Frac Packs Longest, Highly Deviated Intervals at Highest Record Treatment Rate Attempted Worldwide: Angola Case History
Total E&P Angola operates the deep offshore ROSA field on Block 17. On the fifth development well in the field. Two zones in the Oligocene sandy layers are transversed at a well deviation of 48° and required the implementation of the stacked frac-pack technique. The perforated length of zones was approximately 118 ft and 213 ft. Multiple fracture initiation and early screen out were expected, requiring consideration for an enhanced frac-packing method. In order to facilitate placement reliability, a concentric annular packing system was chosen to limit slurry bridging during placement in combination with an aggressive pumping design (25 bbl/min for the lower zone and 32 bbl/min for the upper zone). This paper will discuss the system used for successful frac packing and how it provided alternate paths for the slurry flow when a bridging occurred while keeping the same high flow rate. Data collected on the two zones during treatment have shown that early annular bridging had occurred during slurry placement, but the system had successfully created a high-velocity flow path with minimal pressure drop to bypass the bridge. Once the bridge was bypassed, the full flow area was again used, minimizing turbulence and potential for damaging screens. The paper will describe:The target zonesThe concentric annular packing system designIntegration of the concentric system in the dual stacked frac packs architectureHole pattern design and velocity calculations in shroud orificesThe service tool design for stack frac-packsPumping treatment analysisObservations gathered during the jobHow technique and job-treatment design versus use of a regular frac-pack system or other alternate-path systems was justified. Although alternate path technique has been used in frac-packing more than 30 times globally, the stack frac-pack performed on this case history well (WELL-5) holds the record for being the longest treated length, steepest deviation, and highest pumping rate ever attempted thanks to the concentric annular packing system originally designed for the horizontal gravel pack completions. High completion efficiency was achieved. Productivity data are provided (skin, PLT, etc). Introduction The Rosa field was discovered in January 1998 and was appraised with two additional wells at the beginning of 1999 and at the end of 2000. The field is located in Block 17, offshore Angola, 210 km northwest of Luanda, in an average water depth of 1,400 m (Fig. 1). Rosa field is one of several fields in this prolific block. Under a production sharing agreement with Sociedade Nacional de CombustÍveis de Angola (SONANGOL), the Angolan state oil company, partners in the field include Total E&P Angola (40%, operator), Esso Exploration Angola (Block 17) Ltd (20%), BP Exploration (Angola) Ltd (16.7%), Statoil Angola Block 17 A.S (13.3%), and Norsk Hydro Dezassete A.S. (10%).
Concentric Annular Packing System Successfully Frac Packs Longest, Highly Deviated Intervals at Highest Record Treatment Rate Attempted Worldwide: Angola Case History
Total E&P Angola operates the deep offshore ROSA field on Block 17. On the fifth development well in the field. Two zones in the Oligocene sandy layers are transversed at a well deviation of 48° and required the implementation of the stacked frac-pack technique. The perforated length of zones was approximately 118 ft and 213 ft. Multiple fracture initiation and early screen out were expected, requiring consideration for an enhanced frac-packing method. In order to facilitate placement reliability, a concentric annular packing system was chosen to limit slurry bridging during placement in combination with an aggressive pumping design (25 bbl/min for the lower zone and 32 bbl/min for the upper zone). This paper will discuss the system used for successful frac packing and how it provided alternate paths for the slurry flow when a bridging occurred while keeping the same high flow rate. Data collected on the two zones during treatment have shown that early annular bridging had occurred during slurry placement, but the system had successfully created a high-velocity flow path with minimal pressure drop to bypass the bridge. Once the bridge was bypassed, the full flow area was again used, minimizing turbulence and potential for damaging screens. The paper will describe:The target zonesThe concentric annular packing system designIntegration of the concentric system in the dual stacked frac packs architectureHole pattern design and velocity calculations in shroud orificesThe service tool design for stack frac-packsPumping treatment analysisObservations gathered during the jobHow technique and job-treatment design versus use of a regular frac-pack system or other alternate-path systems was justified. Although alternate path technique has been used in frac-packing more than 30 times globally, the stack frac-pack performed on this case history well (WELL-5) holds the record for being the longest treated length, steepest deviation, and highest pumping rate ever attempted thanks to the concentric annular packing system originally designed for the horizontal gravel pack completions. High completion efficiency was achieved. Productivity data are provided (skin, PLT, etc). Introduction The Rosa field was discovered in January 1998 and was appraised with two additional wells at the beginning of 1999 and at the end of 2000. The field is located in Block 17, offshore Angola, 210 km northwest of Luanda, in an average water depth of 1,400 m (Fig. 1). Rosa field is one of several fields in this prolific block. Under a production sharing agreement with Sociedade Nacional de CombustÍveis de Angola (SONANGOL), the Angolan state oil company, partners in the field include Total E&P Angola (40%, operator), Esso Exploration Angola (Block 17) Ltd (20%), BP Exploration (Angola) Ltd (16.7%), Statoil Angola Block 17 A.S (13.3%), and Norsk Hydro Dezassete A.S. (10%).
In recent years, the use of fracpack treatments has gained attention and is becoming increasingly popular because of their dualbenefits of stimulation and sand control. A fracpack is a hydraulic fracturing treatment using a very high proppant concentration that attempts to "pack-off" the mouth of the fracture. Fracpacking is widely used in high-permeability, poorly consolidated to unconsolidated sandstone formations. Accurate estimation of fracture width is important for both fracpacking and hydraulic fracturing to help ensure a successful treatment. With the development of low-leakoff fluid systems, it has become possible to force the fluid through the proppant pack and out through the tip of the fracture without losing all the fluid through the fracture faces in a high-permeability, soft formation. In such scenarios, the effec of fluid leakoff on the fracture width profile for the case of arbitrary pressure distribution developed as a result of flow of non-Newtonian fluid through the proppant pack has been discussed in the literature. In this paper, the work has been further extended to include the effect of fluid leakoff through fracture faces for radial fractures. The fracture face leakoff phenomenon is modeled using a generalized Carter equation, with different leakoff rates being incorporated in the form of fracture face leakoff coefficient values. The effect of fracture face leakoff on the final width profile, net pressure, fracture volume, and pack radius was investigated. It was observed that the width profile is significantly affected when fluid leakoff through the entire fracture face is considered. Controlling fluid leakoff through the fracture faces can result in much wider fractures because of large net pressure developed inside the fracture from fluid squeezing through the proppant pack.
Operators have found that by integrating drilling and completion techniques, they can develop a highly reliable openhole horizontal gravel-pack completion that can control sand production and produce hydrocarbons at a high-rate. Because of the success of this methodology, it has become a mainstay completion technique in the deepwater developments in Brazil and has shown the same potential for upcoming deepwater developments in West Africa. This paper will discuss the evolution of the integrated concepts, the "lessons learned" that are being used to increase the scope of application, and how new techniques are enhancing reliability for these completions. Specifics include advances that eliminate openhole tortuosity in openhole drilling techniques, new downhole tools that can reduce risk as well as completion cycle time, and improvements in gravel pack fluids. These advances are continuing to push the technological envelope. The new technological benefits are:Reduced completion cycle time, thereby reducing completion costReduced formation damageImproved completion reliability throughout the potential life of the well. Introduction Openhole horizontal gravel packing (OHHGP) has gained acceptance as a mainstay completion technique. Projected reliability and the potential to achieve significantly higher sustainable production rates have been the major drivers for pursuing this type of completion. Interval lengths in excess of 2500 feet are now fairly common, with the current record being 6,938 feet in a well completed in the North Sea by the Texaco North Sea UK Company. In the early 1990's, the advent of enhanced drilling and fluids technology led to advances in extended reach and horizontal drilling.1,2 Screen only completions became the favored choice for completing in long openhole soft-rock formations in wells having capability to deliver high production rates.3,4,5 This technique is being successfully used in some areas including West Africa and the North Sea. But, as development moved into dirtier, more laminated reservoir sands and because of the huge variation in formation types, this completion method started experiencing high failure rates.6 The next move in development went from shelf to deepwater. This expansion into the higher cost operating environment inherent to deepwater further increased the need to improve completion reliability without impacting the desirable high-flow-rate capability. These drivers led to the development of the horizontal openhole gravel-packing technique and the state-of-the-art tools being used today.7,8 The ongoing improvements in drilling and drill-in fluids, filter cake technology, downhole tools and screens are enabling the application envelope for openhole horizontal gravel packing to continue to expand. As with any new technology, there are still limitations. For example, a primary limitation is that the reservoir completed must have a sufficient spread between pore pressure and fracture gradient to allow gravel pack placement. Devices to lower equivalent circulating density (ECD) so that successful packing of longer intervals with tighter pressure spreads can be performed are now available. Invert gravel-pack fluids that eliminate the need to switch from an oil or synthetic oil-based system to a brine-based, solids-free, gravel-pack fluid are now being marketed. Further improvement in brine-based gravel-pack fluids has led to the development of an in-situ acid-generating fluid that should eliminate the need for a post acid treatment in injection wells and producers. Drilling technology has been also been advancing, and bottomhole assemblies (BHAs) that can drill straighter holes that eliminate spiraling normally associated with conventional drilling assemblies have been introduced. These BHAs not only aid in hole cleaning but also in running the screen assembly to depth and achieving successful sand placement.
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