What is the Magic of Water in Producing Sand?

Abstract

We performed a comprehensive sand prediction study of several deep, HPHT wells within a large reservoir and the findings revealed that, for these wells, common criteria based on critical drawdown, minimum bottomhole pressure, depletion or fluid velocity failed to predict the outcome by a relatively large margin. All these wells were subjected to relatively high levels of drawdown and also very high fluid velocities and, with the exception of one well, none showed any sanding until water production was encountered. In this paper, we provide a rationale for why water can be highly effective in inducing sand production and we support our argument using advanced numerical modeling. This exercise also ranks the performance of some of the common tools and theories that are conventionally used for sand prediction. We also provide reasons why some of these models do not perform satisfactorily for the cases studied. The originality of the work is in demonstrating that prior to sand production, the dis-aggregated rock (i.e., individual sand particles) around the wellbore is basically held together by the capillary tension which is destroyed by water flow. While the capillary tension appears to be insignificant (as it is in the order of 1 psi or so), it provides a significant resistance against sand mobilization. The importance of this issue has been quantified using advanced numerical modeling. This concept is vastly different from the previous theories that propose water weakens the rock through chemical interaction or changing the relative permeability. Introduction While a great deal of work has been done in the general area of sand production1–15, approaches used to quantify the volumes of the produced sand have faced challenges in the validation process (Class A prediction). In fairness, it is difficult to firmly single out the deficiencies when predictions do not materialize in a consistent fashion as the quality of the input data, monitoring of sanding events as well as the assumptions and physics used for modeling sanding can all be potential culprits. Following up on this line of reasoning, it is not the intention of this paper to prove or refute any previous work done in sand production studies nor to show that our method is universally superior. The primary intention is to provide a deeper insight into the mechanisms of sanding, in general, and water-production induced sanding, in particular. We try to support the views presented using basic fundamentals along with field observations. Significance and Potential Applications Conventional sand production models2,3,15–17 predict the onset of sanding which in practice is presumed to signify large-scale sanding. This single case solution scenario does not give operators options to assess risks and benefits which is becoming increasingly more relevant under the currently optimized completion and production practices. In essence, operators would like to know, at any stage in a well's life, how much sand will be produced (rate and duration) for a given production strategy (e.g., maximum drawdown, effects of bean-up and shut-in cycles, impact of water). By better understanding the role of various variables one is enabled to choose the optimal completion method for the life of the well (which may exclude installation or deferring sand control measures) and quantify the impact of aggressive fluid production strategies in terms of volume and rate of sanding.

North Sea Hannay Field Case History: Perforating Through a Cased-Hole Gravel Pack to Significantly Increase Oil Production

“…The study indicated that initial sand production from Hannay 1 was a result of the removal of failed rock material being flushed into the wellbore with produced fluids (Dusseault, 2002& Vaziri et al, 2002. Analysis of the plastic radius confirmed that the volumes seen at surface correspond to an expected volume of failed rock from the drilling and completion processes.…”

Predicting and Managing Sand Production: A New Strategy

“…As described by Vaziri, et al, 4 failed and disaggregated sand can be held together remarkably well by tiny capillary cohesion forces, due only to connate water, when water saturation is low (i.e., a sand-castle made with damp sand). But when water saturation increases with water influx, this capillary cohesion is extinguished, and sand will enter the well and be produced (i.e., sand-castle collapses as tide comes in).…”

Sand Management in Tangguh Big Gas Wells

“…However, the onset of water is expected to significantly increase the potential of formation sand and/or other solids production (Vaziri et al 2002). Produced water chloride content will continue to be measured weekly and Tangguh wells believed to be closest to the aquifer have been flagged for special surveillance.…”