Sanding at Low Oil and Water Flux in Cased and Perforated Wells in Weak Formations

Abstract Production histories of five cased and perforated (C&P) wells from four oil fields are presented to show that sanding in C&P wells in weak formations is limited and manageable when the oil and water flux is low. That observation is explained through a finite element numerical model that considers the sanding mechanisms at scale. The fluid flux in this paper is defined as the fluid flow rate per foot length of the flow contributing intervals on the sandface and it dictates the fluid viscous drag. A high flowrate well may still have a low fluid flux if its completed and flow contributing intervals are long. Based on the reservoir formation's unconfined compressive strength (UCS) and the average size of individual sand grains (D50), the five wells are categorized into three groups. The Group-1 well has UCS of slightly above 1000 psi and a D50 of 150-250 microns, the Group-2 wells have UCS of 500-1000 psi and a D50 of 150-250 microns, and the Group-3 wells have UCS of less than 500 psi and a D50 of 70-150 microns. Although all those weak reservoir formation intervals disaggregated in the near-wellbore area from the beginning of their production life, there exists an oil-water flux range within which sanding is limited. Given that sanding is triggered once the fluid drag dominated by the viscous drag exceeds the frictional resistance of sand grains, the limited-sanding oil-water flux range increases with D50 as the larger the D50, the higher the frictional properties and the lower the fluid viscous drag. When D50 is below 110 microns, that flux range becomes quite narrow. Also, a sandface gas flow reduces the limited-sanding oil-water flux range, depending on the frictional properties and D50 of sand grains and the gas flux. Those findings are in contrast to a widely held view that sanding in a C&P well in a weak formation with watercut is severe and unmanageable, and thus an active sand control completion is required. The results of this study provide the technical assurance needed to deploy a simpler and more cost-effective non-active sand control completion in low fluid flux wells where an active sand control completion may be economically and/or technically unviable.