Tip Screenout Fracturing of Gas Wells
- Yong Fan (U. of Tulsa at NIPER) | F.M. Llave (BDM-Oklahoma, Inc. at NIPER)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- December 1996
- Document Type
- Journal Paper
- 463 - 472
- 1996. Society of Petroleum Engineers
- 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 3 Production and Well Operations, 1.8 Formation Damage, 5.2 Reservoir Fluid Dynamics, 2.2.2 Perforating, 5.6.4 Drillstem/Well Testing, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.6 Drilling Operations, 4.1.2 Separation and Treating, 2.4.5 Gravel pack design & evaluation, 2.4.6 Frac and Pack, 2 Well Completion, 3.2.5 Produced Sand / Solids Management and Control, 5.4.2 Gas Injection Methods, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4.3 Sand/Solids Control
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Tip screenout fracturing, also known as frac&pack, has gained increasing prominence for well completion of unconsolidated and medium-high permeability formations. Oil wells with permeabilities up to 1,000 md have been treated using this technology. It is easy to postulate that gas wells with permeabilities of 50 md or higher can also be effectively frac&packed. This paper presents a rigorous model that describes the transient flow of polymer solution through a filter cake and the reservoir as a means to account for leakoff behavior during tip screenout fracturing of gas wells. The leakoff rate into the formation is determined by the pressure profile established during the treatment as a function of the properties of the fracturing fluid and the reservoir formation. Consequently, no constant bulk property such as the leakoff coefficient is used in the fracturing model. This paper shows how to terminate the fracture growth at the appropriate time, and how to design frac&pack treatments resulting in fracture widths several times larger than those from traditional fracturing.
Sand production associated with relatively permeable, unconsolidated or loosely consolidated formations is a recurrent problem. Gravel packing is a technique that is traditionally used to control the sand flow. However, when gravel packing is implemented, field experience and well testing often indicate the occurrence of large positive skin factors. This skin effect is possibly due to insufficient gravel placement in all perforations, or hydraulic discontinuity between perforation and the formation. Sand control is therefore achieved at the cost of grossly reducing well production. This drawback has been largely mitigated in recent years with the emergence of what has been called tip screenout fracturing or frac&pack.
Frac&pack is a well completion technique that combines the advantages of hydraulic fracturing and gravel packing. The treatments consist of two distinct injection stages, performed in one step. The first stage involves creating a hydraulic fracture and terminating its growth by tip screenout. The second stage involves continuous injection of high concentration slurry after the screenout resulting in fracture inflation and packing. The created fracture bypasses the wellbore damage incurred by drilling and well completion, transforms the radial flow to linear, accelerates oil and gas recovery and increases ultimate recovery. The large amount of proppant packed in the fracture props a large fracture width to ensure sufficient fracture conductivity. The proppant pack also functions as a filter to control sand flow. This stimulation technique greatly extends the traditional permeability ranges of fracture candidates. Oil wells with permeabilities up to 1,000 md have been treated. Gas wells with moderate permeabilities have also been effectively frac&packed.
The first treatment using tip-screenout design was conducted in the middle 1980's. Frac&pack has gained increasing prominence for well completions of soft and medium-high permeability formations. For the past several years, many treatment jobs have been successfully done in the Gulf of Mexico Prudhoe Bay, North Sea and others. Frac&pack technology has been implemented as a simultaneous solution of sand control and production problems. However, despite widespread claims of success, frac&pack treatments have been far from achieving optimum production increase. Some operators experienced treatments that did not respond as designed, because of failure to achieve the tip screenout due to inappropriate pad volume used, or premature termination due to uncontrolled pressure increases.
The critical elements in the design, execution and interpretation of frac&pack treatments are dramatically different from those of conventional fracturing treatments.
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