Barefoot Completion: Open-Hole Production, Horizontal Wells, and Reservoir Contact
A barefoot completion is a well production architecture in which the reservoir interval is intentionally left as open, uncased, uncemented, and unperforated borehole throughout the producing life of the well. In a barefoot completion, the casing or liner is landed above the top of the producing formation, and from that point to the bottom of the wellbore the formation face is in direct contact with the wellbore fluid, allowing reservoir fluids to flow directly into the borehole without passing through perforations, screens, or gravel packs. The barefoot completion is the simplest and lowest-capital-cost completion architecture available to an operator when the formation is mechanically competent enough to sustain borehole stability over the full production life, when zonal isolation between formation sub-units is not required, and when the formation's productivity can be realised without hydraulic fracturing through the wellbore tubular. It is widely used in dense carbonates, tight chalk, and some competent siltstones across the global oil and gas industry, including specific formations in the Western Canada Sedimentary Basin, and it remains a standard completion approach in the Devonian carbonate reef province of central Alberta.
The mechanics of a barefoot completion are straightforward: after drilling the producing interval to total depth, the drilling fluid is displaced with a completion fluid suitable for the formation and production conditions, the drilling BHA is retrieved, and the well is placed on production through the open borehole without running any additional downhole completion hardware across the pay zone. The producing interval provides the full cylindrical surface area of the borehole to the formation, which in a vertical well of 159 mm (6-1/4 inch) nominal diameter across 100 m of pay corresponds to approximately 50 square metres of flow face, compared to approximately 5 to 12 square metres of effective perforation area from a standard perf-gun design in the same interval. This raw flow area advantage translates to lower near-wellbore pressure drop and higher productivity index in moderate-permeability formations, which is one of the primary economic justifications for the barefoot approach over perforated completions in the same reservoir.
Key Takeaways
- Formation suitability and stability requirements: Barefoot completions require formations with unconfined compressive strength (UCS) sufficient to prevent spalling, sloughing, or plastic deformation of the borehole wall during drilling and throughout the production life. Minimum UCS guidelines for stable vertical barefoot wellbores start at approximately 20 to 30 MPa in normally stressed basins, rising to 40 MPa or higher in overpressured formations or high-horizontal-stress regimes where stress anisotropy creates borehole breakout risk at lower UCS. Dense carbonates in the Devonian reef trend of central Alberta (Leduc, Nisku, Cooking Lake formations) with UCS of 80 to 200 MPa are ideal barefoot candidates. Silicified tight siltstones such as the Bakken in southeastern Saskatchewan (80 to 120 MPa) have a documented history of stable barefoot horizontal wells. Weakly cemented sandstones, clay-rich shales, and evaporite sequences are fundamentally incompatible with barefoot completions regardless of reservoir quality.
- Horizontal barefoot completions and natural fracture utilisation: In horizontal wells, barefoot completions offer a significant advantage in naturally fractured reservoirs by intersecting the maximum number of open natural fractures along the horizontal section without the selectivity limitations of perforation placement. A 2,400 m barefoot horizontal lateral through a naturally fractured Devonian carbonate or a Bakken silicified siltstone intercepts all fractures that the bit encounters along the trajectory, providing direct connection to the natural fracture network without any dependence on the alignment of perforation charges relative to fracture orientation. This is particularly important in formations where fractures are the primary permeability pathway (as in the vug-and-fracture Leduc reef system and the micro-fractured Bakken siltstone) and where a perforated completion would require charge alignment within a few degrees of the fracture plane to achieve the same connection quality. The barefoot horizontal well achieves natural fracture connection by geometric inevitability rather than perforation placement precision.
- Productivity index comparison with perforated completions: Field data from central Alberta Devonian carbonate producers comparing barefoot and perforated completions in the same reef structures consistently shows barefoot productivity indices 20 to 60% higher than perforated completions in the same formation, attributable to the combination of larger flow area, zero perforation skin, and unrestricted access to the natural fracture network. In Leduc reef wells in the Pembina and Redwater fields where both completion types have been used on the same structure, barefoot wells typically produce 25 to 40% higher initial rates and achieve comparable or better EUR despite the absence of hydraulic fracturing, because the natural fracture network provides matrix drainage that a single perforation cluster in the same reef structure cannot match. The productivity index advantage diminishes in formations with low permeability where the natural fracture network is sparse, because the larger flow area of the barefoot completion provides less additional reservoir connection than would a hydraulically fractured perforated completion in the same tight matrix.
- Abandonment and regulatory compliance: The absence of casing across the producing interval in a barefoot completion creates a specific regulatory challenge at abandonment time. AER Directive 020 in Alberta requires that all producing formations be isolated at abandonment by cement barriers placed across every zone capable of sustained flow. In a barefoot well, this requires placing balanced cement plugs across the full open-hole producing interval, filling the entire borehole diameter from the bottom of the open hole to a point 25 m above the top of the highest producing zone. The abandonment cement volume for a 159 mm (6-1/4 inch) barefoot vertical well across 100 m of Leduc carbonate is approximately 2.9 cubic metres of neat Class G cement, compared to approximately 0.5 to 0.8 cubic metres of annular cement required to abandon the same interval completed as a cemented perforated 5-inch liner. The incremental abandonment cost for a barefoot well (approximately CAD 50,000 to CAD 90,000 per open-hole interval) represents a lifecycle liability that must be net present valued against the upfront completion cost saving when comparing barefoot and cased-hole completion economics.
- Multi-stage and selective stimulation limitations: The barefoot completion's greatest technical limitation is its inability to support multi-stage hydraulic fracturing without additional wellbore hardware. Hydraulic fracturing of a barefoot horizontal well requires packers or bridge plugs to be set across the open hole to isolate stages, which in an uncased borehole requires inflatable packers or mechanical swellpacker elements that grip the bare formation face rather than casing collars. Open-hole packer systems are reliable in smooth, gauge boreholes but can fail to set properly or slip in washed-out or irregular borehole geometries, making multi-stage open-hole frac jobs operationally riskier than cemented-liner multi-stage fracs. Most WCSB tight formation development programmes (Montney, Duvernay, Cardium, Viking) that require multi-stage hydraulic fracturing use cemented liner completions rather than barefoot designs specifically because the cemented liner provides the reliable mechanical isolation surface required for reliable plug-and-perf or ball-sleeve completion architectures.
Open-Hole Completion Variants and Their Distinctions
The barefoot completion is the most elemental open-hole completion, offering no hardware between the formation and the wellbore fluid. Related open-hole completion architectures that are sometimes confused with barefoot but are distinct in design include the open-hole gravel pack, the open-hole liner (pre-perforated or slotted), and the swellpacker multi-stage open-hole completion. An open-hole gravel pack installs a gravel or sand-coated screen across the producing interval to prevent sand influx while maintaining high inflow efficiency; it is used in unconsolidated sand reservoirs where a true barefoot wellbore would immediately collapse. An open-hole slotted or perforated liner runs a metallic tube with pre-machined slots or perforations across the open hole and provides mechanical support to the borehole wall without requiring cement, offering a compromise between barefoot flow efficiency and the wall support of a cemented liner. Swellpacker multi-stage completions run packers across the open hole at defined depths; the elastomeric packer elements swell when contacted by oil or water in the formation fluid, creating mechanical isolation between zones that allows selective acid injection or limited hydraulic fracturing in individual zones without perforation guns.
These open-hole variants address specific formation conditions that make a true barefoot wellbore impractical while still avoiding the full cost of a cemented liner. For competent reservoirs that need no mechanical support, no sand exclusion, and no zone isolation, the barefoot completion remains the lowest-cost and highest-flow-efficiency option, and its continued use in central Alberta Devonian carbonates and the Bakken tight siltstones reflects its fitness for those specific geological environments even as more complex completion architectures have become dominant in the unconventional tight formation plays that define contemporary WCSB development activity.
Barefoot Completion in Horizontal Well Design for Naturally Fractured Carbonates
Horizontal barefoot completions in naturally fractured carbonates are designed to intersect the maximum number of high-conductivity fractures by orienting the wellbore trajectory perpendicular to the dominant fracture orientation, which in the WCSB Devonian reef trend is typically northeast-southwest based on borehole image logs and outcrop analogs. A 600 to 1,500 m horizontal barefoot lateral in a Nisku or Leduc reef intersects an average of 2 to 8 open fractures per 100 m of lateral length based on FMI log compilations from the Pembina, Redwater, and Wizard Lake fields, giving a total of 12 to 120 fracture intercepts across the full lateral. Each fracture intercept provides a direct conduit from the formation matrix to the wellbore, creating a high-productivity inflow point that a perforated vertical well would need an entire frac stage to simulate. The barefoot horizontal well thus achieves natural fracture access that a perforated and stimulated vertical well in the same formation would require 10 to 20 frac stages to approximate, at a fraction of the stimulation cost.
The risk of horizontal barefoot completions in naturally fractured systems is lost circulation during drilling through high-conductivity fractures, which can cause total mud losses that halt drilling, damage the formation face with solids from the wellbore fluid, and compromise the productivity of the fracture intercepts that the completion is designed to exploit. Managed pressure drilling (MPD) is used on some horizontal barefoot Nisku reef wells to maintain precise control of wellbore pressure at or slightly below formation pressure, eliminating the overbalance-induced invasion that seals fracture faces with mud filter cake and restores productivity that standard drilling with significant overbalance would sacrifice. MPD adds CAD 80,000 to CAD 200,000 per well in daily service costs and equipment mobilisation but is considered cost-effective on wells where the barefoot fracture productivity is the primary completion objective and where mud invasion damage from conventional drilling overbalance would reduce the productivity index by 30 to 50%.
Bakken Barefoot Horizontal Completions in the WCSB
The Bakken formation in southeastern Saskatchewan produces from a silicified tight siltstone with natural micro-fracture permeability of 0.01 to 0.1 mD in the better reservoir facies. Horizontal barefoot completions have been used in the Weyburn-Estevan area since the early 2000s, with laterals of 600 to 1,200 m drilled in the Bakken siltstone and left as open hole without casing, liner, or hydraulic fracturing. Production from these barefoot Bakken wells relies entirely on the natural fracture network and the micro-fracture permeability of the silicified siltstone, which is sufficient in the better reservoir facies to deliver 60 to 180 barrels per day of 40 API light oil at initial production from a 1,000 m barefoot horizontal lateral without any stimulation. The barefoot design is feasible in the Bakken because its UCS of 80 to 120 MPa in the silicified facies prevents borehole collapse, and because the tight siltstone matrix does not produce sand or fines that would plug the unscreened wellbore.