Cased-Hole Gravel Pack
Openhole Stand-Alone Screen Blank pipe Screens Perforations Gravel Gravel Screens
Production casing
Filtercake
Openhole Gravel Pack
Production casing
Open hole
> Cased-hole and openhole gravel packs. Cased-hole gravel packing requires perforating of the completion interval and is often used in vertical, or near- vertical, wells producing from laminated reservoirs (left). Openhole stand-alone screens are used to control sand production in clean reservoirs that have relatively short production lives (center). Openhole gravel packs are common in horizontal wells, require no perforations, and are a viable option in highly productive, risky deepwater completions (right).
space between a carefully selected centralized screen and perforated casing, or the formation in the case of an openhole gravel pack (above). Cased-hole gravel-pack design should include perforating optimization. The selection of the most suitable perforating-gun system and perfo- rating method can also improve gravel-pack effectiveness by minimizing perforation damage.20 In moderately competent reservoirs, the PURE Perforating for Ultimate Reservoir Exploitation system produces the optimum amount of under- balance for a given reservoir pressure, generating improved perforation cleanup.21 Openhole gravel packs require removal of
fi ltercake from the completion in addition to the standard design considerations. Careful selection of proper drilling and completion fluids helps ensure adequate fi ltercake development and its subsequent removal. It is imperative to remove as much filtercake as possible to maximize gravel-pack permeability. This is best accom- plished by using a fully integrated process such as the MudSOLV fi ltercake removal service and antiswab tools to maintain hydrostatic pressure on the wellbore during the gravel-packing opera- tion. The MudSOLV service includes full consideration of the completion, selection of the chemistry with the lowest risk, the use of perfor- mance metrics, economic analysis and laboratory verifi cation testing.22 In low-permeability reservoirs, reservoirs pro-
ducing high-viscosity fl uids, or layered reservoirs with low net-to-gross pay intervals, the technique of frac packing has been widely successful.23
In Borehole Stresses Near-Vertical Well
Maximum stress
High stress on perforations
Minimum stress
Damage occurs at stress
concentrations
Maximum stress
> Stress concentration around a borehole. Perforated completion designs for sand control should consider the stresses around the borehole to help prevent perforation-tunnel failure (left). Unlike perforating for hydraulic fracturing, perforations should avoid the highly stressed regions typically aligned with the maximum horizontal stress in vertical wells, which is the vertical direction in horizontal wells (right). Perforating in the minimum horizontal stress direction should also be avoided to minimize perforation-tunnel failure. Oriented perforating allows the perforations to be aligned based on perforation stability models to optimize a completion.
soft rocks, this method produces a short, wide hydraulic fracture and relies on achieving a tip screenout (TSO) fracture. Unlike conventional hydraulic fracturing, TSO designs limit fracture length by dehydrating the proppant pack within the fracture early in the treatment. This helps prop the fracture near the tip, creating a short but conductive fl ow path to the wellbore. This technique increases the effective com-
pletion radius and the area open to flow, and reduces sand production associated with high
fl uid velocities and unstable perforations. In the past, separate operations included wellbore cleanout, sand-exclusion screen installation and gravel packing, all conducted after fracturing. However, advances in downhole hardware associ- ated with the STIMPAC fracturing and gravel-packing service now allow the fracturing operation to be completed with the screen already in place, and then followed by gravel packing.
Wellbore damage
Minimum stress
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Oilfi eld Review
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