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 >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

Full-scale visual studies in a deviated model wellbore have addressed several gravel-pack completion design factors. Visual observations of the placement process have shown ways to improve deviated-well completion designs and field gravel-packing practices. Factors controlling gravel transport and deposition were viscosity, flow rate and leakoff of carrier fluid, wellbore geometry, and gravity settling.

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＾