Visualization of Sand Structures Surrounding A Horizontal Well Slot During Cold Production

Abstract

Abstract 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)