Cold production in unconsolidated heavy oil reservoirs, where sand production is encouraged (CHOPS), has proven to be successful for vertical wells. However, the application of CHOPS to horizontal wells has been less profitable due mainly to excessive sand cleanout costs. Therefore, reducing sand cleanout costs by controlling sand production into horizontal wells while enhancing the surrounding permeability of the formation is an important factor in optimizing cold production from unconsolidated heavy oil reservoirs. This paper presents the results of an experimental investigation of the flow of oil and sand in the vicinity of a horizontal well under cold production. Specifically, the experiments physically simulated the flow of oil and sand into a slot in a horizontal well liner. The parameters studied include slot width and sand properties (morphology and grain size distribution). Experimental results suggest that sand production through horizontal well slots can be controlled, depending more on sand grain sorting than on grain morphology or average diameter. The sand cut had a tendency to be higher at the beginning of the sand production period and to decline with time. In most tests, the decline in sand cuts continued until no more sand was produced. Significant changes in the permeability and porosity were determined in the vicinity of the slot. The changes in the parameters were less significant away from the slot. The largest fractions of the sand (bigger than 500 µm) have an important role in arch/bridge formation. Introduction Cold production is a primary non-thermal process used in unconsolidated heavy oil reservoirs in Alberta and Saskatchewan, Canada. In this process, sand and oil are produced together in order to enhance oil recovery(1–3). A comprehensive review of cold production has been presented by Tremblay et al.(1). Hall and Harrisberger(4) found that arch stability was flow rate sensitive at low confining stress but independent of flow rate at high confining stress levels. They observed that angular sand without compaction did not form an arch. When a moderate compaction was applied, it could lead to a slightly stable arch. A better interlocking of the surface grains was the explanation for this result. For round sand, arching was not observed for a loose or dense pack at low loads. Yim et al.(5) observed that in addition to the flow rate, the arch stability was strongly dependent on the granulometry of the sand and on the size of the perforation. Larger perforations required larger grains to form stable arches. McCormack(6) conducted experimental work with spherical particles to determine the arching/bridging mechanism that influenced the performance of wire-wrapped sand screens. Selby and Farouq Ali(7) showed that sand production increased as the overburden pressure and the fluid flow rate were increased. They also found that spherical small grain sand packs can produce more sand than angular large grain sand packs. Cleary et al.(8) observed that the structure of an arch depended on the stress distribution in a sand pack. The cohesive force was shown to have an important role in arch stability when different hydrocarbons liquids were used.

A better understanding of the flow of sand and oil into slotted horizontal well liners is important for both thermal and non-thermal heavy oil production. The objective of this study was to investigate the structures that might form in and around a slot when sand production stops, and to relate the development of these structures to the porosity and, therefore, permeability increases within the sand pack. The parameters studied were slot size, sand morphology, and grain size distribution. Thin section analysis and X-Ray computed tomography (CT) techniques were used to observe sand packs immobilized with epoxy resin after sand production took place. The results suggest that sand production through the slots can be controlled, depending more on grain sorting than on the morphology of the grains or its average diameter. For a given sand type, sand production behaviour was strongly influenced by thearrangement of the sand grains observed in the vicinity of the slot, including the formation of sand bridges, arches, or plugs. X-Ray CT images showed that non-uniform porosity increases occurred in the pack, specifically in the area near the slot, when sand production took place. The porosity increases were less significant away from the slot. The magnitude of this increase was observed to depend on the quantity of sand produced and on the morphology of the sand. Good agreement was found in terms of porosity change between the thin-section observations and the CT-scanned images taken of the core before thin-section preparation. Introduction Oil producers in Alberta and Saskatchewan have reported high oil recovery for heavy oil reservoirs under cold production using vertical wells, with large sand volumes being produced along with oil(1–4). For horizontal wells, cold production to some extent has not been as successful, due mainly to sand cleanout costs which significantly affect the economics of the operations(5). A literature review(6) indicated that although many studies have been done in the past on different aspects of sand production, they have mainly concentrated on finding effective methods to avoid sand production due to the high operation costs involved. Recent success in cold production has rekindled interest in sand production. Rather than avoiding sand production, the emphasis should be on control and management of the produced sand. Apparatus and Procedure Three different types of experiments were performed for this study: flow experiments using air, thin-section tests, and tests done in a CT scanner. Results from these tests serve to provide quantitative as well as qualitative indicators of sand production behaviour. Coreflood experiments were also performed using synthetic oil; results are reported in another study(6). Epoxy resin was used to solidify the cores for thin-section tests while air was used in the sand production experiments. EPO-THIN ® resin and EPO-THIN ® hardener were used for the thin sections. Sands with three different morphologies were used: 1) Husky sand, obtained from cold production surface collection tanks in the Lloydminster area; FIGURE 1: Particle size distribution curves. Sil-1, Husky, and GBLH sands. (Available in full paper) FIGURE 2: Particle size distribution curves. GBLH, GBLF, GBWBF, and GBWS sands (Available in full paper) TABLE 1: Sand equivalent diameters. (Available in full paper)

Summary The cold-production recovery process, also known as cold heavy-oil production with sand (CHOPS), is a method for enhancing primary heavy-oil production by aggressively producing sand (massively and persistently). It is a successful commercial recovery process in western Canada using vertical (or slanted or deviated) wells. Applications of cold-production technology with aggressive sand production in horizontal wells, however, have not met with commercial success. This paper presents the results of experiments performed to assess the feasibility of applying cold heavy-oil production with horizontal wells using less-aggressive (i.e., controlled) sand-production strategies. Specifically, the effects of slot size, confining stress, fluid velocity, and sand-grain sorting on sand production have been investigated. Preliminary results indicate that slot-size selection is critical for establishing "sand on demand." For proper slot-size selection, it is essential to know the grain-size distribution of the sand—in particular, attributes such as the size of the coarsest fraction of the sand and the sorting (uniformity coefficient) of the sand. For example, it was observed in the sand-production experiments that the critical pressure gradient for maintaining continuous sand production is much lower for well-sorted sands (narrow size distribution) than for poorly sorted sands (wide size distribution). Ultimately, poorly sorted sands may require criteria different from those for well-sorted sands for slot-size selection. Flow rates are also crucial for managing sand production because a critical pressure gradient is required for initiating sand production and maintaining continuous sand production. The critical pressure gradient decreases as the slot width or confining pressure increases. Large permeability increases were observed in the sand-production region. Persistent sand production led to the growth of a channel and/or the presence of a dilated zone that had an elliptic shape.

The cold-production-recovery process, also known as cold heavyoil production with sand (CHOPS), is a method for enhancing primary heavy-oil production by aggressively producing sand. It is successful in vertical (or slanted or deviated) wells in western Canada. In this process, large amounts of sand are produced on a continuing basis along with heavy oil. Attempts at cold production in horizontal wells have not been particularly successful. When sand production has been generated in horizontal wells, these wells have tended to become plugged with sand.This paper presents the results of experiments performed to assess the feasibility of applying cold heavy-oil production in horizontal wells that have been completed with slotted liners using less-aggressive (i.e., managed) sand-production strategies. Specifically, the effects of slot size, confining stress, fluid velocity, and sand-grain sorting on sand production were investigated.The results indicate that slot-size selection is critical for establishing "sand on demand." From the experiments, a correlation between slot size and controlled sand production was found for well-sorted sands. This correlation should allow for the specification of appropriate slot sizes for target reservoirs containing wellsorted sands.In the experiments, when flow rates resulted in low but persistent sand production, channels and/or elliptical dilated zones were created that greatly enhanced the effective permeability near the slot. This observation suggests that producing at low and steady sand cuts for a long period of time might bring two benefits: a way to transport the sand out of the well without causing plugging and the creation of high-permeability channels or zones that can improve production from the reservoir.To summarize, if the appropriate slot size were combined with the right drawdown rates, controlled sand production could be achieved, with attendant significant increases in permeability. This suggests that substantially increased oil-production rates could be achieved from horizontal wells if sand-production rates could be maintained at low but persistent levels.