This paper was prepared for presentation at the 47th Annual Fall Meeting of the Society of Petroleum Engineers held in San Antonio, Tex., Oct. 8–11, 1972. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by who the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Equations for steady-state flow of aqueous foam in circular pipes were formulated from laboratory and pilot-scale experimental data. pilot-scale experimental data. These equations were incorporated into a mathematical model of foam circulation in oil wells. The model was tested in two oil wells, and predictions were satisfactory for predictions were satisfactory for engineering calculations. Accuracy of the model may be increased further by accounting for liquid holdup during foam circulation in large-diameter wells. Introduction Aqueous foams have proven effective and economic as circulating fluids in well cleanout and drilling operations, and are becoming increasingly important for a wide range of oil field work. Information on the flow behavior of foam in oil wells is important for designing and conducting these foam operations. Previous work on foam rheology by David and Marsden pertained to capillary tubes only, and validity of results in oil field-size systems is not known. Mitchell measured flow characteristics of foam in tubes up to 0.1 inch in diameter. Results were used by Krug and Mitchell to develop a calculation method for circulation of foam in oil wells, but no field-scale experiments were reported to demonstrate accuracy of their predictions Work published by Wenzel et al. was for larger pipe sizes, but the foam was drier pipe sizes, but the foam was drier than that normally used in oil field applications. The foam flow equations presented herein have been tested in field-scale systems. These equations should improve the industry's ability to design and conduct oil field foam operations.

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 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＾

A discussion of remedies for many placement problems that are caused by gravity segregation of fluids in the wellbore, particularly in stimulation or workover jobs involving small treatment volumes. Three examples are given to illustrate theoretical and experimental models to find remedies for several typical fluid placement problems. Introduction Success of stimulation and workover jobs involving acid. solvents, inhibitors, or other chemicals often is determined by how well an operator understands and can control fluid placement in a completion interval. Sometimes, it is desirable to place a uniform volume of fluid into each part of the completion, while other times it is better to place nearly all of a chemical into only a portion of the completed interval. For example, uniform acid placement probably is necessary for damage removal in placement probably is necessary for damage removal in an interval completed above the water contact, but in a well with potential bottom-water production, carefully controlled acid placement is required so that only the upper part of the completion is stimulated. Although critical to job success, in most low-cost stimulation-workover jobs, little or no foresight is give to fluid placement. Unless mechanical control methods, placement. Unless mechanical control methods, such as packers, can be justified, it is normal to assume a uniform treatment profile. However, such an assumption is only a matter of convenience, because uniform treatment profiles seldom occur. Actual treatment profiles depend on the well completion geometry, formation characteristics, fluid properties, and treatment volume. When a treatment involves a sequence of fluids, as in sand consolidation, the coverage profile for each of the fluids depends on the foregoing factors, plus the profiles of each of the preceding fluids. This paper is presented to call attention to the need for more consideration of placement profiles in increasing stimulation-workover job success. Results from experimental and theoretical studies of placement profiles of sequentially injected, immiscible fluids with different densities and viscosities are described. Experimental studies were performed in a laboratory glass model of a wellbore having three in-line, equally-spaced perforations. Theoretical studies were done using a multilayer, perforations. Theoretical studies were done using a multilayer, radial computer model of a wellbore-completion interval and a surrounding formation, limited by the assumptions of an openhole completion, zero crossflow between formation layers, and radial plugflow in each layer. Variables surveyed include density, viscosity, and sequence of fluids; wellbore configuration and tubing tail position; and formation permeability, pressure, and porosity profiles (Fig. 1). profiles (Fig. 1). Gravity Segregation Whenever two immiscible fluids with different densities are placed in a container, such as a wellbore, they tend to separate. This separation, called gravity segregation, occurs wherever the degree of agitation is less than that needed to disperse the fluids. Our studies show that wellbore gravity segregation is one of the most important factors controlling placement profiles of fluids in the formation around a wellbore. Fig. 2 illustrates why gravity segregation is so important. When a fluid is injected into a well filled with another immiscible fluid (Fig. 2), it tends to rise or fall according to its density and that of the in-wellbore fluid. The injected fluid accumulates at one end of the completion interval, and an interface forms between the two fluids. As the volume of pumped fluid increases, it displaces more of the initial in-wellbore fluid, and an interface moves away from the accumulation point. JPT P. 1657

This paper focuses. on prevention of well completion damage through proper choice of working fluids, pressure balance, and lost circulation material. Field applications are described, and damage prevention is advocated wherever possible. Extensive references are provided for those seeking greater detail on low-density fluids, clear fluids, and nondamaging lost circulation material.