Preliminary Results From Full-Scale Gravel-Packing Studies
Authors: Shryock S.G. , Dunlap R.G. , Millhone R.S. 
Published: December 2007

This paper describes gravel-packing research performed in a transparent full-scale model well. Tests were conducted with low-viscosity conventional and high-viscosity gelled carrier fluids. Initial results demonstrate the need for properly sized gravel, and clean carrier fluids and equipment to avoid completion damage.

Introduction

The petroleum industry continues to use gravel packs for controlling sand production from wells completed in unconsolidated formations. To improve the productivity of these completions, recent gravel-packing studies have dealt mostly with the design of a properly sized gravel to restrain formation sand, with the detrimental effects of gravel/sand mixing, and with new completion fluids and placement techniques. Little has been written about placement techniques. Little has been written about the damage mechanisms that could affect the performance of a completed gravel pack before the performance of a completed gravel pack before the gravel contacts the formation sand.This paper discusses these damage mechanisms, as well as the compaction and uniformity of commercially placed gravel packs, as observed in a full-scale research placed gravel packs, as observed in a full-scale research model.

Test Objectives

This research was conducted to improve the application of gravel-pack completion technology for good sand control without losing productivity. Several full-scale experiments were performed to study how various system parameters affect the quality of these completions. The most significant and fundamental parameters concerning the behavior of both the gravel and liner aregravel quality,liner slot size and design,liner centralizers and collars,carrier-fluid viscosity and cleanliness, andpumping rate and carrier-fluid gravel concentration.

The experimental program was designed to investigate the effects ofgravel-size distribution on liner slot plugging;slot width on pack confinement and slot plugging, where the slot size was designed to retain the smallest on-size gravel;mechanical restrictions in the wellbore annulus on pack continuity:carrier-fluid viscosity, pumping rate, and gravel concentration on compaction of the placed pack, gradation within the pack, and wellbore erosion at the crossover port;carrier-fluid cleanliness on liner slot plugging; and (6) crossover port diameter upon jetting plugging; andcrossover port diameter upon jetting damage and gravel shattering.

Test Parameters Gravel

When selecting the gravel, we used only size-range and distribution criteria. Other factors affecting gravel quality (such as angularity, shape, strength, and solubility) were not considered in these first experiments. One size of gravel a 10-20 U.S. mesh [0.0787 to 0.0331 in (2 to 0.85 mm) diameter], was used in these tests. Both commercially stocked and specially prepared blends were purchased, and their grain-size distributions were determined using the Tyler sieve analysis method. Results of these analyses are shown in Table 1. The stock gravel used in Test 1 contained 0.24% grain sizes &gt;10 mesh and 8.0% less than 20 mesh. For later tests, specially prepared gravel was made by rescreening the stock prepared gravel was made by rescreening the stock material to reduce the less than 20 mesh grain sizes to less than 0.9%.

JPT

P. 669