Visual Model Study Shows When And When Not To Pressure Wash Open Hole Gravel Packs
Authors: Maly George P. , Vozenilek J. 
Published: December 2007

Abstract
Circulation pressure washing is one of the least understood practices in open hole gravel packing. If indiscriminately applied, it causes packing. If indiscriminately applied, it causes early gravel pack failures as well as considerable loss of productivity.
This paper presents the results of a model study of gravel placement and pressure washing operations in open hole gravel packs. A movie will be presented to demonstrate gravel placement during a gravel packing operation and the interaction between gravel and formation during subsequent pressure washing. pressure washing. WHAT IS PRESSURE WASHING?
Pressure washing, as the word implies, involves a high velocity jetting of fluid through the openings in the retaining liner. This jetting is usually confined to a short vertical interval, separated by two opposed swab cups.
If washing fluids are returned to the surface, we call it circulation pressure washing.

CIRCULATION PRESSURE WASHING
Circulation pressure washing is a common practice routinely applied by many gravel packing practice routinely applied by many gravel packing companies and operators. Unfortunately, it is one of the most misunderstood and misapplied "arts" of the oil industry. A growing body of evidence indicates that it is not only one of the main reasons for early open hole gravel pack failures, but it is also a main cause of an unnecessary loss of oil production. production. In order to shed a little light on the pressure washing of the open hole gravel packs, and pressure washing of the open hole gravel packs, and possibly to clear up the many misconceptions, we possibly to clear up the many misconceptions, we designed and built two visual models. A photograph of the second model is shown in FIGURE 10. photograph of the second model is shown in FIGURE 10. Our models were designed solely to demonstrate visually the near-borehole conditions existing during pressure washing of open hole gravel packs. No quantitative measurements were obtained of permeability changes during pressure washing, and permeability changes during pressure washing, and our results are reported qualitatively from visual examination. Furthermore, this paper will not deal in any depth with circulation pressure washing of perforations for "inside" gravel packing. Although perforations for "inside" gravel packing. Although our study showed detrimental effects from pressure washing of open hole gravel packs, pressure washing of perforations is a very good and very necessary practice under the proper conditions. However, for practice under the proper conditions. However, for successful results with this method, super clean fluids must be used, and the perforations must be cleaned prior to gravel packing.

WHEN AND WHERE IS PRESSURE WASHING USED?
Most operators and service companies use pressure washing when they suspect that only a part of pressure washing when they suspect that only a part of the theoretical volume of gravel is placed behind the screen at the time of screenout. Some operators pressure wash initially, to insure a full pack, pressure wash initially, to insure a full pack, others claim that an open hole gravel packed well cannot produce properly and satisfactorily without pressure washing. pressure washing. Pressure washing received its strongest impetus when operators had to gravel pack some high angle holes from offshore platforms and frequently suffered premature screen-outs. Pressure washing solved-the problem of gravel placement in high angle holes and became a standard field practice. Its use spread throughout the world, and practice. Its use spread throughout the world, and today it is often routinely applied even in relatively straight and simple holes.
PRESSURE WASHING TN HIGH ANGLE HOLES PRESSURE WASHING TN HIGH ANGLE HOLES In high angle holes, 50 deg. or more from vertical, PACKING OCCURS FROM TOP DOWN, RATHER THAN FROM PACKING OCCURS FROM TOP DOWN, RATHER THAN FROM BOTTOM UP as is the case in vertical holes. Consequently, when high angle holes are packed using standard packing procedures, the pack usually bridges first in the top 10–20 feet of the interval to be packed.