Abstract

In today's competitive environment in the oilfield, the enduser must choose the very lowest-cost material that will meet the technical needs of the application. This requirement is passed on to the manufacturer, who must use materials that are appropriate yet still meet economical criteria. Another factor has been the expansion of field development into deeper, more corrosive environments, increasing the demand for corrosionresistant alloys (CRAs) at a time when the demand and cost for stainless materials has increased. In expandable sand control systems, an added burden to the manufacturer is that this new technology must compete with existing non-expandable screens that are low-cost to manufacture with commodity-type raw materials. 13Cr is one such example; it is the first choice in a CRA for the base pipe in conventional sand screens. Although 13Cr is one of the least costly of the CRAs, it does provide the necessary corrosion resistance in mild H2S environments under a variety of chloride/temperature conditions. However, it lacks the ductility needed for 20 to 25% expansion as a solidexpandable. 316L (UNS S31603) is a commodity CRA material with sufficient ductility and strength for use as an expandable screen base pipe; but its corrosion resistance is often questioned, particularly its resistance to chloride stresscorrosion cracking (SCC).

This paper provides the data necessary to establish a performance envelope for S31603 and discusses the potential application of the material in several projects. Thus, S31603 is shown to provide a cost-effective CRA material for base pipes in sand-control screens.

Introduction

In expandable screen systems, the capability exists for the screen to be expanded against the borehole ID, virtually eliminating the annulus around the screen and the need for gravel packing. Also, this increases the sand screen surface area, thus reducing pressure drop across the filter and increasing production rates. Because of its high strength, the expanded screen can provide superior support to stabilize the borehole, which then minimizes the potential for sand production.1 Finally, expandable screen can provide a larger production ID than is normally possible with traditional screens. The challenge with the expandable concept has been to provide not only materials that can maintain integrity in the more corrosive environments now being developed but also materials that provide the economic feasibility to allow them to be competitive in today's marketplace.

The base pipe of a conventional, non-expanding sand screen is simply a pipe that has been perforated to allow fluid to flow in from the surrounding wellbore. The basic concept behind 'solid expansion' of a screen system is simply to expand this perforated pipe down hole, and thereby, only slightly reduce the collapse strength as a result of having increased the diameter and reduced the wall. In contrast, a slotted pipe that has long thin slots cut lengthwise in the pipe has very little collapse strength after expansion. Therefore, while slotted pipe is easy to expand, it is also easy to collapse, and thus, is unable to prevent the wellbore from caving in.

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