A Laboratory Investigation of Temperature-Induced Sand Consolidation

Summary Current gravel-packed, slotted-liner completion techniques for wells in unconsolidated and weakly consolidated sandstone are relatively expensive and result in greatly reduced operational flexibility. On the other hand, empirical field evidence (Wilmington, California) demonstrates that sand grains surrounding the wellbore are cemented and consolidated following injection of high-pressure (1,600-psi) steam. Effective sand control results without adverse changes to formation permeability and producibility. Here, sand consolidation mechanisms are exposed by duplicating, in the laboratory, the governing geochemical processes. Sandpacks contain typical per-volume concentrations of concrete resulting from perforating a cased and cemented well. The evolution of sandpack pore and grain struture is determined using scanning electron microscope imaging and compositional analyses. Results show that hot alkaline water injected at rates comparable to field rates indeed results in grain-cementing precipitates. Casing cement plays a crucial role in that it is the source of calcium silicates appearing in various pore-lining precipitates. Conditions for effective sand consolidation are not necessarily formation-specific, and the process can be altered to improve cost-effectiveness, flexibility, and longevity of the completion technique. Introduction In poorly consolidated and unconsolidated sandstone reservoirs, solids are sometimes carried from the formation to the wellbore as oil and water flow toward producers. It is referred to as "sand production." This term is usually detrimental and should be avoided. Operational problems result, including extra wear of the pumping units, shorter pipe lifetime, frequent workovers, loss of well productivity, and waste-disposal issues. Several remedies are available to the engineer. They include production-rate reduction (Penberthy and Shaughnessy 1992), physical barriers (Penberthy and Shaughnessy 1992), in-situ consolidation (Prats and Hamby 1965; Davies et al. 1983; Davies et al. 1997; Davies et al. 2003), and hybrid methods (Penberthy and Shaughnessy 1992; Kruger 1986). No sand-control method is, as of yet, generally applicable. We use laboratory experiments to develop a mechanistic understanding of a novel hot alkaline/steam sand-consolidation technique. This technique has proved effective empirically (Davies et al. 1997). The mechanisms of mineral and grain dissolution, precipitation, and consolidation using Wilmington (Los Angeles basin, California) field cores and quartz sandpacks are described. Field sands are drawn from the productive, heavy-oil intervals (T and D sands) of the Tar II-A zone (Hara 2003). The tools employed are core-scale and beaker-scale experiments, scanning electron microscopy (SEM), and elemental analyses. Additionally, tubing-tail samples recovered from the field are reexamined in light of the new laboratory results. Before proceeding to the experimental details and results, a brief review of the hot alkaline/steam sand-consolidation process is given. This background is foundational, because it underpins the experimental program and interpretation of results. The experimental objectives, apparatus, and procedures follow. Results, discussion, and implications finish the paper.