Design of Gravel Packs in Deviated Wellbores

Abstract

This paper describes a new technique for improving the effectiveness of gravel placement between the screen and the wellbore in deviated wells. This technique can be used to predict whether a set of design conditions leads to a complete gravel pack that fills the entire annulus of a wellbore, or to an unstable, incomplete gravel pack that leaves voids in the annulus. The design procedure was used to gravel pack several high-angle wells successfully. Introduction Sand production from unconsolidated formations long has been a source of completion problems. Millions of dollars are spent throughout the world each year to achieve effective sand-control measures. Millions more axe spent each year to remedy many originally successful procedures that fail before the reservoir is depleted. procedures that fail before the reservoir is depleted. Maximum reliability of initial sand-control practices is essential, therefore, particularly offshore and in remote locations where operating costs are high. The most widely used sand-control technique involves placing a screen in the wellbore and packing gravel placing a screen in the wellbore and packing gravel around it. The screen is sized to retain the gravel and the gravel, in turn, is sized to retain the formation sand. This technique has proven effective, especially when formation properties allow open-hole completions. In spite of properties allow open-hole completions. In spite of this success, many gravel-packing procedures have less than desirable effectiveness because of unstable or incomplete placement of gravel around the screen. This is particularly true when the wellbores are deviated. As a particularly true when the wellbores are deviated. As a result, there is considerable incentive to develop gravel-packing techniques that have both high initial success ratio and the ability to provide sand-free production for sustained periods of time. Gravel packs in deviated wellbores need special design considerations. Recent gravel-packing studie's have shown that the wellbore angle has a dramatic effect on gravel placement - high angles can lead to unstable, incomplete gravel packs. In spite of the need to know the factors that control gravel placement in deviated wellbores, little has been published on the relationship between the fluid mechanics of gravel packing and the final distribution of gravel in deviated wellbores. This is a serious limitation because high-angle wells can be gravel packed effectively when the design conditions are packed effectively when the design conditions are selected correctly. Observations made while gravel packing a small-scale laboratory wellbore model are discussed in this paper. Then, the process by which gravel is transported in deviated wells is described. Finally, the development of a new design technique is reported that can be used to predict whether a set of design conditions can lead to a predict whether a set of design conditions can lead to a complete gravel pack that fills the entire wellbore-screen annulus, or to an unstable, incomplete gravel pack that leaves voids in the annulus. Gravel-Packing Apparatus The dynamics of gravel transport in deviated wellbores can be studied most effectively when the process can be visualized. The experiments described here were conducted in two transparent Lucite wellbore models: a small-scale, 3-in. (7.62-cm)-ID model that was 10 ft (3.05 m) long, and a full-scale, 5 1/2-in. (13.9-cm)-ID model that was 20 ft (6.09 m) long. Fig. 1 shows the details of the small-scale model. A 1.9-in. (4.83-cm)-OD wire-wrapped screen with 0.012-in. (0.305-mm) slots was centered inside the Lucite tube. A stainless-steel tube with 1/2-in. (1.27-cm) OD was placed inside the screen to simulate the tailpipe. JPT P. 109