Abstract

A number of robust predictive methods for establishing sanding thresholds have been developed over the past decade. Having identified when the onset of sanding occurs, recent research efforts have focused on determining the rate at which sand will be produced once these thresholds are exceeded. In this paper a new analytic model for predicting the rate of continuous (steady-state) sand production is described. This sanding rate model is consistent with the threshold prediction model, and utilizes as its basis the non-dimensionalized concepts of loading factor (near-wellbore formation stress normalized by strength) and Reynold's number (a function of permeability, viscosity, density and flow velocity). Interpreted this way, the results of laboratory sand production experiments are used to derive an empirical relationship between loading factor, Reynold's number and the rate of sand production. A second empirical sand production ‘boost factor’ incorporates the effects of water production. The derived model is compared with field data from a total of six wells from two fields, for a wide range of flowing conditions. The predictions are a good match to the field data, typically overestimating the field-measured data by a factor of less than four. However, as the model is for continuous sanding only, this degree of overprediction is considered acceptable for field application, as it provides some compensation for short-lived transient sand production at rates higher than steady-state values.

Introduction

Over the past decade considerable research efforts have been expended in developing robust methods for predicting the onset of sand production as a function of rock strength, drawdown and reservoir pressure. The most notable contributions to this area of work have been by Shell; References 1 and 2 provide a good overview of this decade of effort. In recent years, attention has now focused on establishing methodologies for predicting the rate at which sand is produced once the sanding threshold is exceeded. The principal motivation for this work is to determine whether sand production can be managed at surface, or if downhole sand control is needed. There are pros and cons to both approaches - both management and exclusion.

In the sand management scenario, the biggest risk and challenge is being able to reliably estimate the amount and concentration of the produced sand. This is important for sizing facilities sand handling capabilities, as well as ensuring that erosion limits for chokes and surface pipework are not exceeded. From a HSE perspective, this is especially critical in high rate gas wells, as well as in high rate oil wells, particularly where gas-oil ratios are high. From an operating cost perspective, the consequences of severe sand production and choke erosion could be very costly in subsea wells, especially in deepwater. On the positive side, the cased and perforated completion option usually employed with sand management does permit avoidance of producing from notably sanding prone intervals through selective or optimized perforating. Cased and perforated completions also maintain access to the producing interval to shut-off water or to recomplete in other secondary producing horizons. This has allowed significant increases in reserves recovery in a number of fields worldwide.

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