Quantifying Flux-Induced Sanding in Oil and Gas Wells

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ABSTRACT: Following rock disaggregation, sanding in oil and gas wells is principally driven by the fluid flow induced drag forces overcoming frictional resistance of rock aggregates. The empirical Hill-Koch-Ladd (HKL) correlation of viscous drag force to the Reynolds number, fluid flux, fluid mechanical properties and particle size widely used in chemical engineering is employed to assess the flux effect on sanding in this paper. It is illustrated that the viscous drag around the near perforation area is much larger than the pressure drag in the gas flux range commonly encountered in wells and thus its impact on sanding cannot be ignored. The HKL correlation has been incorporated into an existing finite element numerical sanding prediction model within the framework of the Biot’s general consolidation theory to quantify field-scale flux-induced sanding. The improved numerical model explicitly considers both the viscous drag and rock disaggregation with reservoir pressure depletion. It captures many field observations of practical significance including effects of aggregate size, fluid flux, and the overall trend of sanding with reservoir pressure depletion and natural decline of well flow rate with time. One set of field cases presented involves two weak reservoir formations in two fields with distinctly different average particle sizes, gas flux range and sanding responses. It is used to illustrate the numerical model’s capability to capture the effect of rock aggregates size and gas flux. The combined effect of flux and gradual rock disaggregation is demonstrated through another field case involving a strong reservoir formation. The numerical modeling results can be used to better optimize well sandface completion design, and short- and long-term well hydrocarbon production. 1. INTRODUCTION There are two prerequisites for sanding to occur in the field. The first one is that rock needs to be disaggregated from its intact state. Field-scale rock disaggregation is a gradual process and primarily driven by reservoir pressure depletion and sandface drawdown. Xiao et al. (2011) describes a practical approach to approximate field-scale rock disaggregation and corresponding mechanical strength degradation beyond the conventional concept of strain softening and its impact on sanding. The second prerequisite is that fluid flux needs to exceed certain limit. The fluid flux is the fluid flow rate per unit length of completed reservoir formation intervals along the wellbore. Its practical units commonly used include million standard cubic feet per day per foot (mmscfd/ft) in gas wells and barrels per day per foot (bpd/ft) in oil wells, and can be converted to fluid flow velocity in meter per second (m/s) on the sandface through sandface completion geometries, e.g. the perforation density in shots per foot and perforation entry hole diameter (EHD) in a cased and perforated (C&P) completion, along with fluids PVT properties.