Gravel Packing Highly Deviated Wells With a Crosslinked Polymer System
Authors: Underdown D.R. , Das K. , Nguyen H. 
Published: December 2007

Summary
One of the major problems associated with gravel packing highly deviated wells is the successful transport of the gravel to the zone to be gravel packed. Conventional gravel-packing fluids allow the gravel to fall to the packed. Conventional gravel-packing fluids allow the gravel to fall to the low side of the tubing in long, highly deviated wells, which can cause duning. This can result in premature sandouts and an unsuccessful gravel pack. Mechanical means, such as baffled and oversized washpipe, have been pack. Mechanical means, such as baffled and oversized washpipe, have been used in an attempt to solve these problems. Gravel-packing fluids made with crosslinked polymers have been used to transport gravel to help eliminate the duning and premature sandout problems. The polymeric systems commonly used are hydroxypropyl guar (HPG) problems. The polymeric systems commonly used are hydroxypropyl guar (HPG) and carboxymethylhydroxyethylcellulose (CMHEC) crosslinked with metal ions such as Ti4+ and Al3+. However, these polymeric systems can cause severe formation damage because of residual solids left in the formation after gravel packing. Now a crosslinked polymeric system that exhibits substantially less formation damage than other crosslinked polymer systems has been developed and used in the field. The system is formed by cross-linking hydroxyethyl cellulose (HEC) with a heavy metal ion under proper conditions of pH and mixing. proper conditions of pH and mixing. Field applications of the crosslinked HEC gravel-packing system have shown that it can be mixed easily in the field and is unaffected by fluids usually found in wells before gravel packing. The wells gravel packed with this system were drilled onshore but completed offshore with a maximum deviation of 800 [1.4 rad] and an average deviation in the production zone of 650 [1.1 rad]. Daily average productions from these wells show expected production with little or no sand production. production with little or no sand production.

Introduction
Gravel packing oil and gas wells to exclude formation sand from produced fluid has been used as a completion technique for the last 40 years. Over the years, the technique has undergone significant improvement. Various fluids--such as brines, gelled oil, and viscosified brine--have been developed for the transportation of gravel to the producing interval. The brine systems are commonly viscosified with HEC. This water-based, viscous fluid system can carry a high concentration of gravel (up to 15 lbm/gal [1797 kg/m3] fluid), significantly reducing the rig time needed for gravel packing. The good gravel suspension characteristic of the system also allows low pump rates, which minimize the mixing of gravel with formation sand, crushing of the gravel at the crossover port, and plugging of slots in a slotted liner or wire-wrapped screen. plugging of slots in a slotted liner or wire-wrapped screen. Fluids viscosified with HEC have good gravel-suspending characteristics; these fluids, however, show a definite and finite settling of gravel, which may create problems-such as premature sandouts--in deep and/or highly deviated wells. An ideal fluid for such applications would show little or no settling of gravel so that a high concentration of gravel can be transported through tubing at any angle. The fluid also should exhibit adequate fluid loss to ensure compact packing of gravel against the formation face. The system should break completely to the consistency of water over a predesigned time interval and should leave no residual solids to ensure a complete pack and to minimize formation damage. Gravel-packing fluids viscosified with HEC have become widely accepted for gravel packing wells deviated up to 750 [1.3 rad]. Good gravel-carrying properties, favorable rheological characteristics, and minimal formation damage make HEC-based fluids more usable for gravel packing than any other polymer-based fluids. Other types of viscosified packing than any other polymer-based fluids. Other types of viscosified carrier fluids that could be used for gravel packing include brines viscosified with HPG, carboxylmethylcellulose (CMC), CMHEC, and xanthan gum (XC) polymers. The major drawback to the use of these polymers is that residual polymeric material trapped in the formation can cause severe formation damage. Gravel packing wells that have highly deviated completions requires a gravel-packing fluid with special properties. The main difference in the fluid needed for gravel packing these wells and that needed for conventional wells is the need for a zero gravel-fall rate. A gravel-packing fluid that has a zero gravel-fall rate would ensure that the gravel is carried to the production zone for gravel packing and would not allow gravel to fall out on the lower side of the tubing, causing duning and premature sandout. One of the ways to achieve a zero gravel-fall rate with a polymeric gravel-packing fluid is to crosslink the polymer. polymer. JPT
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