Gravel Packing Horizontal Wellbores with Leak-Off Using Shunts
Authors: Jones L.G. , Tibbles R.J. , Myers L. , Bryant David , Hardin Jim , Hurst Gary 
Published: December 2007

L.G. Jones (Lloyd Jones & Associates), SPE, R.J. Tibbles (Schlumberger Dowell), SPE, L. Myers (Mobil Equatorial Guinea Inc.), David Bryant (Mobil E&P U.S. Inc.), SPE, Jim Hardin (U.S. Filter/Johnson Screen), & Gary Hurst, SPE, (STIMLAB)

Because of the abnormal length of most horizontal wellbores, they present an exceptional challenge for gravel packing. Previously, the only way to gravel pack a long horizontal wellbore in a permeable formation was to seal off the wellbore from the formation to such an extent that substantial circulation could be maintained during the entire packing operation. While this approach has shown limited success, it necessitates the removal of the filter cake after the job is completed, which can be both difficult and expensive.

In this paper, equipment and procedures are described which allow gravel packing of long cased or open hole horizontal wellbores using alternate path shunts, without requiring circulation. The design methodology, procedures and evaluation have been developed with information obtained from studies using a series of physical wellbore simulators ranging from 150 to 500 feet in length. The simulators are described and results from the simulator studies are presented. Two case histories are included. The advantages of the new methodology are that it permits removal of the filter cake before or during the gravel packing operation and allows modest fracturing while packing, if desired.

The pumping techniques and apparatus used in alternate path gravel packing have been extended here to allow gravel packing of long, open hole horizontal wellbores with or without substantial leak-off. Modest fracturing is possible, if desired. The major pumping change is the use of gels that suspend the proppant during the entire job. The major apparatus changes are the use of larger exit ports from the shunts and use of a shroud over the screen and shunts to act as both a protector and centralizer.

The pumping and apparatus design changes are based on results of experiments performed with wellbore simulators ranging from 150 to 500 feet in length. Description of the experiments and results are provided below.

Two case history of the first field applications are presented. Total solids placement was 150% of the calculated annular volume of the 500-foot horizontal wellbore, suggesting that some modest fracturing took place. Productivity index for the well was 21, resulting in a production rate of 12,000 bbl/day from a formation with modest permeability thickness.

Introduction

Gravel packing of horizontal wellbores in unconsolidated formations is appealing because a tight gravel pack stabilizes the formation face. This will prevent movement of formation sand to the sand screen and permit use of a normal screen, which won't be plugged by the few fines that move through the gravel pack.

While gravel packing in cased horizontal wellbores has been used in places like the North Sea since 1991, Open hole horizontal well gravel packing has been difficult to accomplish because fluid leak-off along the horizontal interval dehydrates the slurry, leading to early annulus bridging and sand-out with long unpacked intervals. Numerous studies have explained and documented the weaknesses and strengths of using either gels with good carrying capabilities or low viscosity fluids, such as water, for high angle and horizontal well gravel packing.

Horizontal water packing requires enough fluid velocity to maintain turbulent flow along the top of the wellbore to move the sand downstream. P. 739^