Mechanisms of Sand Production Through Horizontal Well Slots in Primary Production

Abstract

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.

Sand on Demand: A Laboratory Investigation on Improving Productivity in Horizontal Wells Under Heavy-Oil Primary Production—Part II

“…The pressure at the entrance of the slot ( p slot ) must be calculated in order to calculate (dp/dL) 11,slot . A detailed description of this calculation can be found in Meza-Díaz et al (2003).…”

“…In a previous experimental investigation using synthetic and idealized materials (Meza-Díaz et al 2003), differences observed in sand-production behavior were attributed to differences in grain-size distribution. The SW/ EGD ratio (SW/D i ), particularly for the D 99.9 diameter, was identified as an important parameter in sand production through slots.…”

Sand on Demand: A Laboratory Investigation on Improving Productivity in Horizontal Wells Under Heavy-Oil Primary Production

“…An analysis of the sand-production data from the previous air tests indicated that there was no obvious trend between sand production and the sorting of the sand (as represented by the uniformity coefficient) or between sand production and the sandgrain morphology (Meza-Diaz et al 2003, 2004. This is shown graphically in Figs.…”

“…The results of previous sand-production experiments using air as the working fl uid (Meza-Diaz et al 2003, 2004 were used to guide the selection of the range of slot widths for the experiments reported in this study. The air tests provided sand-production data across several slot sizes for various sands that possessed different grain-size distributions and morphologies (shapes).…”

Restimulation of Unconventional Reservoirs: When Are Refracs Beneficial?

“…• Although counterintuitive, spherical proppants have been found to be more stable in laboratory tests examining the flowback of particles into horizontal-well slots (Meza et al 2002;Meza-Diaz et al 2003).…”