An Evaluation Method for Screen-Only and Gravel-Pack Completions

Abstract

Abstract Screen-only and screen with gravel-pack completions have become more commonplace in long horizontal wellbores in poorly consolidated reservoirs. Several of the formations currently being completed pose challenges in selecting effective sand-control screens due to their non-uniform particle size distributions and the large amount of very small particulates. Early screen and gravel-pack studies, from which common scaling factors were derived, did not always contain the smaller particle sizes that are encountered in poor quality reservoirs. Later studies have shown that both the fines content and the uniformity of the sand impact the performance of the completion7–13. This paper presents an evaluation method for screen-only and gravel-packed completions utilizing formation sand samples. The method determines the amount of solids produced through the screen and the change in flow capacity of the screen and formation sand pack with increasing stress. The flow capacity data is useful in estimating production changes as wellbores collapse around the screen and the formation porosity around the screen decreases. The amount of formation particles that pass through the screen or the gravel-pack and screen is useful in estimating the solids production. Data is presented which illustrates the amount of small particles, which can penetrate wire-wrapped and premium screens, along with gravel-packs and gravel-packed screens. Data will be compared for gravel-packs based on conventional scaling factors of 5–6 times the median diameter and other scaling factors. Introduction The planning that goes into the drilling and completion of a horizontal, openhole completion in a soft or poorly consolidated formation includes selection of the drill-in fluid (DIF), the sand-control screen that will be used to restrain the formation and the cleanup system for removal of the drill-in fluid filtercake. Previous papers have addressed DIF selection, DIF maintenance, and cleanup treatment design for maximizing well productivity.1–6 Recently, there have been a number of studies evaluating the performance of sand-control screens in screen-only completions.7–12 When selecting a sand-control screen for use in screen-only completions, numerous design and performance criteria must be considered. Among these criteria are sand retention and plugging resistance (retained permeability). Over the years, sizing guidelines have been developed for slotted liners and wire-wrapped screens that are reported to increase sand-control reliability and plugging resistance under specific conditions.14,15 Unfortunately, the wire-wrapped screens are not well suited as a primary sand-control device in very fine, dirty sands or in reservoirs with widely varying sand quality. For the poorer quality reservoir sands, the new woven-wire or wire-mesh screens (Figure 1) offer the possibility of improved sand-control and plugging resistance. Currently, little guidance is available for sizing these screens with fine, dirty formation sands. Furthermore, defining the minimum acceptable performance with regard to sand retention or plugging resistance can be a difficult task. Often, a screen may be selected based on performance testing because it provided the "least" amount of sand production or the "best" flow capacity with a synthetic sand composition. This selection strategy may be misleading and can unnecessarily limit the number of acceptable screen designs and suppliers. For example, more than one screen in a testing program may have provided acceptable sand retention and retained flow capacity. Conversely, even the "best" of the candidate screens may not have provided acceptable performance for a specific application. To quantify the performance of screens in a specific application, rigorous laboratory tests have been developed incorporating small screen and formation sand samples.