cold heavy oil production with sand

Cold heavy oil production with sand (CHOPS) is a non-thermal primary recovery technique applied to shallow unconsolidated heavy oil reservoirs in which reservoir sand is intentionally co-produced alongside heavy crude rather than excluded by gravel packs or screens, because the deliberate sand influx creates a branching network of high-permeability wormhole channels extending 50 to 100 m radially from the wellbore that dramatically expands the drainage area and, in combination with a dissolved-gas foamy oil drive that keeps exsolved gas dispersed as stable microbubbles within the viscous crude, enables production rates of 50 to 200 m3/d per well compared to 5 to 10 m3/d from conventionally completed wells in the same formation; CHOPS achieves incremental recovery factors of 10 to 20 percent of original oil in place versus only 3 to 5 percent for sand-excluding completions in the same Mannville Group reservoirs. In the Western Canada Sedimentary Basin, CHOPS is the dominant primary recovery method in the shallow Cretaceous Mannville Group heavy oil fairway that extends from Lloydminster on the Alberta-Saskatchewan border northwest through Cold Lake and east through the Edam, Waseca, McLaren, Sparky, and General Petroleum members at depths of 300 to 800 m: Canadian Natural Resources, Husky Energy (now Cenovus), Baytex Energy, Pengrowth, and numerous smaller operators run CHOPS completions in wells drilled to the Lloydminster, Sparky, and Cummings heavy oil pools with oil gravities of 8 to 14 API and reservoir viscosities of 3,000 to 100,000 mPa.s at reservoir conditions, where the combination of unconsolidated sand with low cohesive strength, sufficient dissolved solution gas (gas-oil ratio 5 to 20 m3/m3), and shallow overburden that allows wormhole networks to propagate radially without collapsing under geostatic stress creates the specific mechanical and thermodynamic conditions necessary for CHOPS to function as intended; production from active CHOPS wells is managed using progressive cavity pumps (PCPs) with elastomeric stators tolerating up to 30 percent solids by volume, and surface sand management trains including hydrocyclone desanding vessels, sand dewatering screens, and either lined surface disposal pads or slurry reinjection wells handling 0.5 to 5 tonnes of produced sand per well per day under AER Directive 058 in Alberta.

• Wormhole network growth mechanics, propagation rates, and monitoring in WCSB Lloydminster CHOPS operations: Wormhole initiation occurs when wellbore drawdown pressure exceeds the tensile and cohesive strength of the unconsolidated Mannville sand face (typically 50 to 200 kPa cohesion in the Lloydminster Sparky), causing progressive sand arch failure rather than the stable arch formation that conventional sand-exclusion completions rely upon; once initiated, individual wormhole branches advance at 0.5 to 2 m per day radially from the perforations through a combination of fluid drag (heavy oil and dissolved gas carrying loosened grains forward), elevated pore pressure gradient at the wormhole tip, and localized shear failure of the loosely cemented grain contacts ahead of the advancing channel. After 2 to 5 years of production in the WCSB Lloydminster Sparky and McLaren members, the wormhole network reaches a quasi-stable configuration with 300 to 2,000 tonnes of cumulative produced sand per well removed from the formation; distributed fiber optic temperature sensing (DTS) on monitoring wells in CNRL and Husky Cold Lake CHOPS pilots has confirmed wormhole network extents of 30 to 80 m radius by detecting the pressure and temperature anomalies as the wormhole front passes the monitoring well, validating the geomechanical models used to predict drainage area and design infill well spacing in WCSB CHOPS programs.
• Foamy oil drive mechanism, bubble point behavior, and its contribution to WCSB CHOPS recovery efficiency: Foamy oil drive is the dissolved gas energy mechanism unique to WCSB heavy oil that distinguishes CHOPS recovery factors from those achievable by primary production in conventional light oil reservoirs: as wellbore pressure drops below the bubble point during production (typically 1 to 4 MPa in Lloydminster Sparky pools), dissolved solution gas exsolves from the heavy crude but, rather than coalescing into a continuous free gas phase that would reduce oil relative permeability as in a light oil reservoir, the exsolved gas forms stable dispersed microbubbles of 1 to 50 micron diameter that remain suspended in the viscous heavy oil matrix due to the high viscosity that prevents bubble migration and coalescence. The foamy oil mixture behaves as a compressible pseudo-single-phase fluid with effective density lower than the degassed oil and apparent viscosity 20 to 50 percent lower than the degassed oil viscosity at the same temperature, providing an expansion drive energy that accounts for 20 to 40 percent of total CHOPS production in Lloydminster pools; reservoir simulation of WCSB Lloydminster CHOPS wells using the STARS or CMG simulator with foamy oil relative permeability tables calibrated to laboratory pressure-depletion experiments on Lloydminster Sparky core samples is the standard workflow for history-matching CHOPS production and forecasting the timing of foamy oil drive exhaustion, which signals the transition from primary CHOPS to thermal follow-up.
• PCP selection, sand tolerance, and surface sand management systems in WCSB CHOPS operations: Progressive cavity pump selection for WCSB CHOPS wells balances sand abrasion tolerance (requiring a sufficiently large rotor-stator fit clearance and abrasion-resistant elastomer compound) against volumetric efficiency (which decreases as fit clearance increases) and drawdown rate (which must be controlled to sustain wormhole growth without collapsing the wormhole network or loading the PCP with a sand slug that overrides pump capacity); WCSB Lloydminster and Cold Lake CHOPS operators standardize on Netzsch, Roper, or Kudu PCPs in 200 to 800 m3/d capacity with Nitrile (NBR) or Hydrogenated Nitrile (HNBR) stator elastomers rated to 80 degrees Celsius in Lloydminster's 12 to 25 degree Celsius reservoir temperature environment, with sand cuts managed to below 15 to 20 percent by volume at the pump intake by controlling drawdown speed (typically 2 to 5 m/min pump tubing descent for initial CHOPS startup) to allow gradual rather than catastrophic sand arch failure. Surface sand management trains at WCSB CHOPS batteries process produced fluid through primary desanding hydrocyclones (Mozley or Vortoil designs removing 90 to 95 percent of sand above 50 micron diameter), gravity settling tanks, and secondary fine-sand desanding screens, with produced sand dewatered on vibrating screens to below 15 percent moisture before disposal or slurry reinjection at 5 to 8 MPa into a dedicated Class IIa disposal well licensed by the AER under Directive 051.
• CHOPS reservoir screening criteria and WCSB pool suitability assessment for the Mannville heavy oil fairway: Not all WCSB Mannville Group heavy oil pools are suitable for CHOPS; the key screening criteria are sand cohesive strength (must be low enough to allow wormhole initiation at economic drawdown pressures, typically below 200 kPa cohesion measured by triaxial testing on preserved core), oil viscosity (must be in the 1,000 to 100,000 mPa.s range at reservoir temperature for foamy oil behavior; above 100,000 mPa.s in Athabasca cold crude, the oil is too viscous for foamy oil microbubble suspension and CHOPS recovery is negligible), solution GOR (must be sufficient to provide foamy oil drive, typically above 5 m3/m3 at initial reservoir pressure), and overburden effective stress (must be low enough at 300 to 800 m depth to allow wormhole propagation without irreversible collapse from geostatic load). WCSB Lloydminster Sparky, McLaren, Waseca, and Cummings members at 350 to 700 m depth with 12 to 22 API oil gravity and 5 to 15 m3/m3 GOR are the core CHOPS play in Alberta; the Pelican Lake pool in northeast Alberta (8 to 14 API) has been targeted with CHOPS but with lower recovery factors due to limited solution gas, and polymer flooding has largely replaced CHOPS at Pelican Lake as the preferred primary follow-up, while the Athabasca oil sands at 1 to 15 m depth have insufficient reservoir depth and pressure for CHOPS wormhole propagation and rely on SAGD instead.
• Post-CHOPS thermal and polymer follow-up recovery options in WCSB Lloydminster and Cold Lake heavy oil pools: When CHOPS primary production declines after 2 to 5 years as wormhole network growth stabilizes and foamy oil drive depletes, the enhanced wormhole permeability network creates an ideal conduit for follow-up thermal or polymer recovery that would be less efficient in a virgin undisturbed Mannville sand: cyclic steam stimulation (CSS) injected into the wormhole network distributes heat more rapidly than in an undisturbed formation because the existing high-permeability channels accept steam injection at 1 to 3 MPa above hydrostatic without fracturing, thermally thinning the residual 60 to 80 percent of OOIP that primary CHOPS could not recover; Husky Energy's Tucker Lake SAGD development in northeast Alberta and CNRL's Lloydminster area thermal pilots have demonstrated that post-CHOPS CSS and SAGD in Mannville pools recover an additional 15 to 30 percent OOIP at capital costs 20 to 40 percent lower than applying thermal methods to undisturbed formations, because wormhole networks provide immediate steam injectivity without a lengthy matrix permeabilization period. Polymer flooding at 0.5 to 1.0 percent HPAM or xanthan polymer concentration in Pelican Lake and selected Lloydminster pools has demonstrated incremental recovery of 10 to 20 percent OOIP above primary CHOPS by improving displacement efficiency of the viscous flood front, and is increasingly selected over thermal follow-up for shallower (below 300 m depth) Mannville pools where steam injectivity is insufficient to maintain steam quality above 60 percent due to heat losses through thin overburden.

WCSB Lloydminster Sparky CHOPS Well Achieving Wormhole-Driven Recovery

A Lloydminster area CHOPS operator completed a Sparky Formation well at 485 m depth using a large-bore perforated liner with no sand exclusion and a 300 m3/d PCP. Initial production at first drawdown was 8 m3/d (50 bbl/d), typical of the pre-wormhole period when the sand face had not yet begun sustained failure. Over 90 days of controlled drawdown at a PCP intake pressure held at 350 kPa above the Sparky bubble point, sand production accumulated to 180 tonnes (averaged 2 tonnes per day) and production climbed to 115 m3/d (723 bbl/d) as the wormhole network extended to an estimated 45 m radius. By month 18, sand production had declined to 0.3 tonnes per day (wormhole stabilization) and oil rate was 95 m3/d (598 bbl/d) on established foamy oil drive. Cumulative 18-month production of 54,000 m3 (339,000 bbl) against a well capital cost of $850,000 and operating cost of $12/m3 confirmed payback in 4 months at $60/bbl WTI, validating the CHOPS completion design against the operator's offset Sparky wells completed with gravel packs that averaged 12 m3/d (75 bbl/d) peak production in the same pool.

Related Terms

Foamy oil is the dispersed-microbubble dissolved gas phase providing expansion drive energy in WCSB CHOPS; microbubble suspension in viscous Lloydminster crude reduces apparent oil viscosity 20-50% and accounts for 20-40% of primary production energy. Progressive cavity pump (PCP) is the standard artificial lift for WCSB CHOPS wells; rotor-stator geometry and elastomer compound balance sand abrasion tolerance against volumetric efficiency at Lloydminster reservoir temperatures of 12-25 degrees Celsius. Wormhole is the high-permeability channel created by CHOPS sand removal from unconsolidated Mannville formation; individual branches advance at 0.5-2 m per day, creating a dendritic drainage network extending 50-100 m radially. Cyclic steam stimulation (CSS) is the primary thermal follow-up to WCSB CHOPS; steam injection into established wormhole networks recovers an additional 15-30% OOIP at lower capital than virgin thermal in the same Lloydminster pools. Cold production is the broader nonthermal primary recovery category including CHOPS, horizontal well primary, and waterflood in WCSB shallow heavy oil; CHOPS dominates for unconsolidated Mannville sands with sufficient dissolved gas.