Gravel-Packing Studies in a Full-Scale, Vertical Model Wellbore - Progress Report
Authors: Shryock Steven G. , Millhone Ralph S. 
Published: December 2007

Full-scale visual studies in a vertical model wellbore have investigated several gravel-pack completion design factors. Tests were conducted using commercial field-scale pumping equipment. Observations on needed gravel/slot-size combinations, pack stability, early sandout and subsequent settling problems, and outside perforation packing are presented.

Introduction
Gravel packing has been studied in a full-scale, transparent, vertical model wellbore. The first five tests in this program were described in an earlier paper, which detailed the research procedures and initial results. Twelve more tests were conducted in the vertical model wellbore, and the results are included in this report. The work is continuing with studies of deviated well packing.The full-scale model consisted of three 100-ft (30.5-m) concentric tubing strings including an 11-in. (279-mm) ID clear plastic casing, a 5-in. (127-mm) OD liner, and a 2-in. (51-mm) ID tail pipe. Fig. 1 is a schematic diagram of the general arrangement of the wellbore, pumps, tankage, and monitoring equipment. A more complete description of the apparatus is contained in Ref. 1. All pumping, blending, and filtering operations were performed with commercial service company equipment and personnel to simulate field operations.The first five tests were limited to one gravel size and liner (Table 1). The experiments described here used various gravel sizes, slot widths, liner designs, and wellbore geometries to simulate gravel-pack completions. Results from all tests are used in this paper to make conclusions about liner slot width vs. gravel size criteria, conventional and viscous carrier fluids, and various completion design considerations, which will be useful for field application of these studies. Each of these topic areas is treated individually in subsequent sections of this paper.All tests except Test 12 were done using commercial pumping-type gravel-pack units. Pot-type equipment with continuously altered recycling water carrier was used in Test 12. This discontinuous method of gravel delivery yielded local gradations in the pack. These gradations are the result of segregation of particle sizes as each potload of gravel fell through the annulus. Such gradations may or may not be detrimental to sand control. It also was observed that excess waiting time between potloads did little more than prolong the length of the packing job.

Liner Slot Width vs. Gravel Size
The first five tests showed that avoiding liner slot plugging by small gravel particles and fines was critical to the success of placing a gravel pack and obtaining a productive completion. To study plugging further, two liner slot sizing criteria were used: absolute stoppage and bridging.

Absolute Stoppage Design
The absolute stoppage design requires liner slot widths smaller than the smallest specified gravel particle. It was found in the first five tests that a small percentage of "fines" or grains smaller than the specified gravel size range was sufficient to plug these slots.
JPT
P. 1137＾