Abstract Cold production is a recovery process used in unconsolidated heavy oil reservoirs in Alberta and Saskatchewan, Canada. In this process, sand and oil are produced together under primary conditions. Oil production rates can typically increase by one order of magnitude when sand is produced. The production of sand into a perforation was modeled using a horizontal sand pack flooded with live oil. Previous sand production experiments were performed using dead oil. The pack was scanned with an X-ray computed tomography (CT) scanner. A wormhole (high porosity channel) developed within the sand pack starting at the production end as soon as the back pressure was decreased suddenly from 780 psi (5.38 MPa) to 500 psi (3.40 MPa). The wormhole was stable to collapse when the production pressure was decreased from 780 psi (5.38 MPa) to 500 psi (3.4 MPa) and maintained at that pressure for 3 hours. The wormhole developed within the high porosity region (lowest cohesive strength) of the sand pack indicating that worn-holes in the field will likely develop in the weakest sands which are normally the sands with little cementation and therefore more oil. Under this rapid depressurization, gas did not come out of solution while the back pressure was maintained at 500 psi (3.4 MPa). The wormhole collapsed when the production pressure was decreased to atmospheric pressure. This indicates that a sudden decrease in the bottom hole pressure in a well may lead to wormhole collapse. Introduction Cold production has been used with commercial success to recover heavy oil in the Lloydminster area of Alberta, Canada. High production rates have been reported for heavy oil fields under primary recovery 1to11 when large quantities of sand are produced with the oil. Several authors have attributed this high oil production rates to the formation of high permeability cavities 1,2,12,13 , channels (wormholes) 5to10 or both 11,12,13,16,17 . Solution gas drive is generally considered to be the main drive mechanism 1,2,3 . In many cases, solution gas drive by itself is not sufficient to explain the enhanced oil recovery. Significant increases in oil production occurred only when large quantities of sand were produced. Experiments in sand packs with live oil (without sand production) have shown that the permeability of the sand pack is not increased when gas bubbles are generated 3 . Tracer experiments between injection and production wells have been performed in the field by several operators 5to11 to measure the travel time between wells after considerable sand production has taken place. In general, this time was at least one order of magnitude shorter than that normally predicted for unaltered formations. These anomalously short times were explained by the formation of either fractures or wormholes. Theoretical models of cold production, which assume that a radial zones of dilated sand develops from a wellbore when sand is produced into a well, have been developed 14,15,16 . The assumption of a large dilated zone around a wellbore differs from our observation of a high permeability channel (wormhole). Materials The Clearwater sand used in the experiment was obtained from the collection tanks at Suncor's former Burnt Lake pilot project 4 .
Abstract Cold Production is a recovery process used in un-cemented Heavy oil reservoirsin which sand and oil are produced together under primary conditions. Sandproduction is known to be necessary in order to better access heavy oilreservoirs. The production of sand into a casing perforation was modeledexperimentally using a horizontal sand pack. Heavy oil flowed through the sandand out the orifice at one end of the pack. The pack was scanned using an X-Ray CT scanner. A high porosity (53%) channel (wormhole) was observed to develop inthe sand pack above a critical pressure gradient. The sand CUI was 44% (byvolume) as the wormhole was developing. When the wormhole broke through theinlet, the sand cut decreased sharply. CT images taken at this time showed thatonly the loose sand within the wormhole started In be scoured away from the topdown. The experimental observations suggest that the high sand cuts (20% to40%) from wells at the start of cold production are due ID the growth ofwormholes while the sudden decrease in sand cuts (ID 1% – 3%) indicates thatthe wormholes stopped growing. The residual sand cuts observed in the field arelikely due to the scouring of the sand within the wormholes. INTRODUCTION Several heavy oil producers 1,2,3,4,5 have recognized that producingsand with oil significantly enhances primary recovery. The widespread use ofprogressive cavity pumps has been a key factor in making the Cold Productionprocess economical by reducing the damage to wells caused by the pumping ofsand. Elkins et al. 1 were among the first to suggest that highpermeability channels, which they called wormholes, develop in oil formationswhen sand is also produced. The wells were located in the Southeast Pauls Valley Fietd, Gavin County, Oklahoma. They inferred the presence of wormholesfrom tracer tests, caliper surveys of the well before and after sandproduction, permeability calculations and the large volume of sand produced. Vonde 2 reported a significant increase in oil production rates whenwells, initially completed with 16 mesh(0.40 mm) liner slots, were recompletedwith 250 mesh (6.35 mm) liner slots. The sand cuts also increased to 10% byvolume. The wells they investigated were located in the Cat-Canyon Field, California. Infectivity tests, performed by Amoco, Canada 6 , have shown that theconcentration of an aqueous solution of fluorescent dye did not change afterbeing produced from an adjacent well. In a separate laboratory experiment, these investigators observed that the dye was adsorbed completely after flowingthrough a sand pack. Since the concentration of the injected dye did not changesignificantly in the infectivity test they inferred that the dye did not flowthrough a porous medium. They concluded that the dye flowed through a channel. Undiluted slugs of dye travelled at speeds up to 7 meters/minute through whatthey believed were channel systems over 2 km in length that connected up to 12 wells 6 . The wells were located in the Elk Point/Lindbergh fields, Alberta, Canada. Communication between an injection well and a producing well 500 meters awaywas observed by Suncor' in their Burnt Lake field. Alberta, Canada.
Abstract Oil production in the province of Alberta will be increasingly dependent on Enhanced oil recovery (EOR) technology in the next decade. Successful implementation of an EOR process requires a thorough understanding of the reservoir flow behavior. The most difficult parameters to assess in EOR operations are the vertical and areal sweep efficiencies in the reservoir. Spatial and temporal distributions of the injected fluids between existing well locations are necessary quantify these parameters. Contemporary EOR monitoring schemes such as tracer or cased hole logging surveys can only provide flood information after inter-well communication is established. Knowledge of poor sweep conformance prior to breakthrough would allow time for corrective measures to be implemented. A three year joint research program has just been completed and results suggest that repeat seismic surveys can be selectively used to monitor the movement of injected EOR fluids between wells in the reservoir, and thus dramatically improve the opportunity for timely reservoir management. Some EOR processes impart a change in the acoustic velocity and density of the reservoir rock that can be measured using seismic methods. Laboratory tests have been performed on a wide variety of carbonate and clastic core samples to determine the acoustic effects caused by EOR processes. The laboratory results show that thermal, miscible or immiscible hydrocarbon solvent, and CO 2 floods can all cause significant change in the acoustic properties of the reservoir. Pore pressure variations and water injection can also cause an acoustic change under some circumstances. The magnitude of the acoustic velocity dependency on pore fluid saturation varies considerably in different rock-types. This suggests that laboratory testing should be performed to determine the amount of acoustic change like to occur in the reservoir before seismic monitoring a field is considered. Seismic modeling has been implemented to predict sismic monitor response based on the acoustic properties measured in the laboratory. Modeling results indicate that solvent, CO 2 , steam and fire flooding should all be detectable in a wide range of reservoir situations. Repeat seismic methodology should also be applicable to monitoring of gas production under aquifer or water drive. Gas production during the blow-down phase of a miscible flood is another excellent candidate for this type of monitoring. Research results indicate that miscible EOR monitoring should be technically successful. Economic justifications must also be met before this technology will become widely used. Geophysical EOR monitoring must be fully integrated with the standard tools of reservoir management in order to demonstrate the increased production efficiency that could offset the cost of the monitoring program. A reservoir management plan that incorporates the use of seismic monitoring information with standard engineering techniques will be presented and contrasted against current exploitation strategies. While the role of geophysical monitoring can be examined in the context of the EOR production, its ultimate value can only be assessed Through the course of actual field trials. Introduction As conventional oil recovery in the province of Alberta declines, there is an increasing need to implement Enhanced Oil Recovery (EOR) techniques in order to maximize production from our existing fields and oilsands deposits.