Deposit Buildup During Gravel Packing With Viscous Polymer Solutions and Water
Authors: Torrest Robert S. 
Published: December 2007

Torrest, Robert S.; SPE; Arizona State U.

Summary
Large deposits are formed at perforations and on the screen during gravel packing with viscous polymer solutions. The deposits are retained with low packing with viscous polymer solutions. The deposits are retained with low pressure drop and can grow and interact so that much of the annular area is pressure drop and can grow and interact so that much of the annular area is blocked off. Examination of deposit characteristics and the dynamic equilibrium that exists between local buildup and wash away is important for understanding overall buildup, subsequent quality, and response to production. production.

Introduction
Gravel pack buildup and behavior may be strongly dependent on placement conditions examined in recent studies. For example, Shryock and Millhone and others have noted bridging, voids, and incomplete packs when using viscous fluids. Here we summarize a few results from a more detailed discussion of a laboratory study that illustrate some fundamental features of deposit buildup for viscous gravel packing. AQUAPAC, Shell Oil Co.'s aqueous viscous system with Natrosol 250 HHR, a high-molecular-weight hydroxyethyl cellulose (HEC) polymer, was used. Buildup is just one part of a complete study that also should include polymer flow in porous media, slurry dispersal, settling patterns and interaction with the formation, and pack quality and response to production. Comments pertinent to some of pack quality and response to production. Comments pertinent to some of these topics have been presented elsewhere. The best "inside" gravel pack is one that can be placed with reasonable procedures and will maintain its integrity during production. That is, it will not have internal voids or excessive porosity, and will prevent the invasion of formation sand or the development of open flow prevent the invasion of formation sand or the development of open flow channels from the formation to the screen. Typically, the slurry is "pumped away". Then, when viscous polymer solutions are used, deposit buildup inside the wellbore during placement is a prominent characteristic. After the gravel bridges against the formation and fills the perforations, deposits (nodes) grow from the perforation back to the wire-wrap screen. As they enlarge in the annulus, resistance to fluid flow increases, and some of the fluid will be diverted through the wire-wrap screen. Of course, this fluid carries gravel in suspension, so that an annular deposit will form on the screen. Fig. 1 shows these features in an idealized sketch representing deposit buildup in the early stages of placement, with some recirculation or the configuration near the top of the annulus pack after substantial placement. As fluid velocity in the annulus increases because of deposit buildup, there is a tendency for deposit growth to be self-leveling and even for parts of deposits to be washed away. That is, with a steady injection of a viscous suspension, a more or less complicated deposition pattern evolves in the wellbore annulus that is transient in time and position. The nature of the deposit buildups and interaction may lead to variations in the annulus pack porosity, with subsequent adverse consequences for sand control or well productivity. Or, in certain cases, budging of the deposits before complete filling may lead to erroneous sandout indications and inadequate gravel placement. In contrast, gravel packs fill from the bottom of the wellbore annulus upward when using water packs fill from the bottom of the wellbore annulus upward when using water or other low-viscosity fluids.
JPT
p. 325