Sand Control Methods Research Articles

Case History of Yakin Field: Its Development and Sand Control

Summary This paper deals with the development of the Yakin field in East Kalimantan, Indonesia, with emphasis on the sand control methods used. Implementation of an effective sand control program ensured the successful development of this field. Gravel-packed wells had substantially lower production decline rates than the initial completions without gravel packs. Control of sand production also has been demonstrated by the lack of production also has been demonstrated by the lack of sand problems during the 4 1/2 years since the sand control program was initiated. During this time there have been no submersible pump failures associated with sand production. production. The successful sand control program was achieved by a well-coordinated and cooperative effort of drilling, reservoir engineering, production research, and service company personnel. Establishment of communication among all people involved, starting early in the planning process and continuing through the rig operations to the process and continuing through the rig operations to the final production phase, coupled with intensive training at all levels of responsibility, on-site supervision, and quality control were important factors in the success of the development program. Introduction The Yakin field was developed as a joint venture between Pertamina and Union Oil Co. of Indonesia within the terms of a production-sharing contract. The field is located approximately 4 miles offshore East Kalimantan. The field was discovered in April 1976 with the drilling of the Yakin No. 2 well. Yakin structure is a north-northeast-trending anticline, bordered on the north by a normal fault and on the west by a reverse fault. The reservoir is of marine origin, ranging in age from late Oligocene to early Miocene. The main sand has a closure of about 250 acres and an average thickness of 60 ft. The crude oil gravity ranges from 13 to 25 deg. API. More complete reservoir properties of Yakin field are shown in Table 1. The field was developed in two major stages. The earlier development, Phase 1, was completed such that oil recovery from the field could be accelerated. Despite some problems associated with rapid development, early Phase 1 completions provided the experience to allow for Phase 1 completions provided the experience to allow for the proper equipment to be ordered and installed in Phase 2. Phase 2 completions designed to control the sand problems experienced in Phase 1 were started in April 1977. problems experienced in Phase 1 were started in April 1977. Drilling and testing of early wells indicated that sand control would be required to deplete the reservoir efficiently. Sand produced during drill stem testing and low recovery of sidewall cores indicated a poorly consolidated formation sand. The initial three wells of Phase 1 were completed without sand control. Two wells eventually sanded out and the other one was produced at a reduced rate to stop the sand production. These three wells later were worked over and recompleted with inside-casing gravel packs. All the subsequent wells of Phase 2 were completed with open hole gravel packs. In Phase 2 were completed with open hole gravel packs. In some completions the gravel was resin-coated. A brief summary of the overall production characteristics of the Yakin wells is included in Table 2 and Fig. 1. Since a sand-control completion is more complex than a conventional completion, a team approach was initiated to ensure a successful job. A successful sand control project requires that everyone involved has a full knowledge and a thorough understanding of the "do's and don'ts" from the planning stage through the actual sand control job to the production stage. JPT P. 23

Performance Review of Phenolic-Resin Gravel Packing

Summary This paper discusses the application of phenolic-resin-coated gravels in forming linerless, behind-the-casing gravel packs as a method of sand control in shallow steam-displacement wells. Laboratory tests were made to determine the effects of steam temperature, flow rate, and pH on the physical properties of the resin-coated sand (i.e., curing, matrix strength, and permeability). These tests, along with posttreatment production history from a 10-well field test, show that phenolic-resin gravel packing is an effective method of sand control. Introduction Getty Oil Co. operates a major steam displacement project in the Kern River field near Bakersfield, CA. Steam is injected continuously into the productive sand via steam injection wells and ultimately breaks through into the producing wells. Many of these producing wells have experienced severe sand problems because the steam carried large quantities of the unconsolidated formation through the perforations.Unique field characteristics, which have discouraged the use of many modern sand-control methods currently employed throughout the industry, include the following.1. Reservoir temperatures generally exceed 120 degrees C and may go as high as 205 degrees C during steam stimulation.2. To reduce the hydrostatic head, the wells are operated in a "pumped-off" condition. Therefore, the sucker-rod pumps must be placed at the bottom of the producing zone.3. Clearance between casing and sucker-rod pumps in many of Getty's 3,000 producing wells is less than 56 mm.These factors prevent running retaining screens for conventional gravel packs and the use of gravel coatings, which are not stable at these temperatures. However, a linerless, behind-the-casing, consolidated gravel pack using a coated gravel that exhibits high-temperature stability is a sand-control method that is compatible with these field conditions.This paper describes the results of laboratory investigations and a field test program on the use of phenolic-resin-coated gravel (PRCG). Laboratory tests investigated the effect of expected field conditions on the physical properties of the PRCG. The results of these experiments were used to define the physical limitations under which these gravels can be used successfully in field applications. The performance of 10 sand-problem wells that were gravel packed using this coated sand is discussed. The results of this entire program show that PRCG can be used successfully to control sand problems in many of the Kern River wells. Theory The material used in these gravel packs consists of sieved, high-quality gravel, of which each grain has been coated with phenolic resin. After placement in the wellbore, the gravel is heated either by conduction from the reservoir or from injected steam. The resin softens as the temperature increases and diffuses to form "necks" between adjacent sand granules. After a finite period of time, the resin thermosets into a hard, inert coating, forming a highly permeable, consolidated gravel pack.The coated gravel does not require preflushes or postflushes to consolidate uniformly when an adequate heat source is available. This becomes increasingly important as treatment interval length increases. JPT P. 221^

Perforating Resin-Consolidated Zones for Capacity Improvement

Sand control using epoxy resin consolidation usually is effective, but treated wells fail to produce occasionally. This, paper presents field results showing that through-tubing jet reperforation of wells into the previously resin-consolidated zone can restore production. previously resin-consolidated zone can restore production. Laboratory tests indicated clean, productive perforations and undamaged resin consolidation. Introduction Reservoirs from surface to 8,000 ft and deeper off the Louisiana coast are notorious sand producers. Excessive sand production can result in separation and disposal problems, erode pipe and equipment, damage casing, problems, erode pipe and equipment, damage casing, and shutdown pumps. Sand control is necessary in wells of this type. From 1958 to 1972, when multiple completions were most common, Chevron Oil Co. elected to complete many wells dually with two-stage gravel packs in lower zones and resin consolidation in upper zones. Any selective (single) zones also were resin consolidated. Both sand control methods have proven highly successful. However, in several instances some resin-consolidated zones failed to produce, and acidizing also failed to induce flow. Assuming sand or mud fillup is not blocking the perforations, it has been proposed that unintended dirt or debris injected with the resin and associated fluids may plug perforations or damage near-well formation plug perforations or damage near-well formation permeability. permeability.After all other methods failed to induce flow from these wells, reperforation with through-tubing, jet-perforating guns gave promising results. Field Work Six nonproducing or low-production resin-consolidated wells were reperforated. Two other selected wells were not reperforated because of mechanical problems encountered. The selected wells are located east of the Mississippi River delta in the Main Pass area. The productive section is Upper Miocene in age, with sands and productive section is Upper Miocene in age, with sands and shales deposited in a near-shore marine environment. As the electric logs (Fig. 1) suggest, some sands are massive and relatively clean with porosities of 30 to 35 percent, while others are argillaceous with lower porosity. The eight wells represented two different types of completion. One was the selective zone completion (Fig. 2). Casing was perforated, sand was resin consolidated and packers were placed on single tubing string, isolating the zones at initial completion. Only one zone was produced at a time, starting at the bottom and progressing up produced at a time, starting at the bottom and progressing up the tubing. When moving to an upper selective zone, lower zones were plugged off and a special tubing perforator was used to open the tubing between the packers perforator was used to open the tubing between the packers isolating the selective zone to permit flow. In contrast, when using the reperforation completion technique, the reperforating gun in a selective zone must perforate both tubing and casing. A through-tubing, expendable, capsule-type, jet perforating gun was used. Shot density was four shots per foot, oriented at a 90 degrees angle. Wells 1 and 2 were selective zone completions. The second type was the standard dual completion (Fig. 3). Two strings of tubing allowed simultaneous but separate production from both zones. In our examples, only the upper zone was resin consolidated. To reperforate these zones, the perforating gun was lowered through the short tubing string until it hung free in the upper zone. Only the casing was penetrated. JPT P. 283

A History of Sand Control in the Teak Field

In the Teak field, extensive testing over a 3 1/2-year period has resulted in techniques that keep sand production to a trace while allowing the wells to be produced at rates exceeding 5,000 BOPD. As of March 1975, these sand-control methods have enabled production of 44 million bbl of oil from eight unconsolidated sand horizons. Introduction Amoco Trinidad Oil Co. discovered the Teak field, located 25 miles off the east coast of Trinidad (see Fig. 1), in Sept. 1968, and production began from four wells on the Teak A platform in Jan. 1972. As of March 1, 1975, 34 wells had been drilled from three platforms to develop the field. Some type of sand control had been installed in 28 of these wells. Amoco Trinidad has two other oil fields on production - Samoan and Poui - but neither has experienced any significant sand problems. problems. The Teak field is a highly faulted anticlinal structure containing 40 productive fault blocks. The sands and shales in this north-south trending anticline were deposited by the Orinoco River in Venezuela. The Teak field contains 14 oil-productive horizons of Pliocene and Miocene age found at depths ranging from 4,200 to 12,200 ft. The shallowest eight horizons are unconsolidated sands requiring sand control. Starting with the shallowest horizon, these sands are named T, T-1, U, MM-0/1, MM-0/2, MM-1/2, MM-2, and MM-4; the first three of these have the most severe sand problems. The sands are among the finest grained discovered anywhere and are often appropriately compared with talcum powder. As seen in Fig. 2, 10 to 29 percent of the fines will pass through a 0.0017-in. screen opening, which is the smallest screen size used in a standard sieve analysis. Composite sand samples obtained from rubber sleeve cores were used in these sieve analyses. Since rubber sleeve cores can be recovered in a relatively undisturbed state, these samples are considered to be the best for distribution analysis. The sand distributions obtained by sieve analysis were then used to determine the proper size screens and gravel to be used. Based on the sand distributions shown in Fig. 2, initial recommendations called for the use of three sand-control systems. These were an unpacked 0.008- to 0.015- to 0.025-in. triple-wrap screen, a 0.016-in. single-wrap screen packed with 0.017- to 0.033-in. gravel, and a 0.020-in. single-wrap screen packed with 0.040- to 0.060-in. gravel. packed with 0.040- to 0.060-in. gravel. Other methods tested included several additional single-wrap screen and gravel combinations as well as both unpacked and packed triple-wrap screens. The current techniques involve packing 0.020-in. single-wrap screens with 0.040- to 0.060-in. angular gravel in both open-hole and cased-hole completions. Initial Triple-Wrap Screen Completions Two types of sand control were initially used in Trinidad from late 1971 until mid-1972. One type was an unpacked 0.008- to 0.015- to 0.025-in. triple-wrap screen (see Fig. 3) developed by Amoco Production Research Co. and the other was a single-wrap screen with a gravel pack. The theory behind the triple-wrap screen was that the formation would "self-pack" around the screens as the well was produced. The multiple wraps of different gauge openings were expected to bridge the largest sand grains at the outer screen, intermediate size grains at the middle screen, and the smallest grains at the innermost screen. Thus, the 3 or 4 days of expensive rig time required for a conventional gravel pack would be eliminated. JPT P. 972

Thin-Section and Permeability Studies Call For Smaller Gravels in Gravel Packing

The paper discusses the results of an experimental investigation designed to find the most effective gravel-to-sand size ratio for an effective gravel pack. It was found that a gravel-to-sand size ratio of less than 6, and preferably 4, gives a stable pack. Angular gravel and a uniform formation sand promote the pack stability. The experimental results were confirmed by visual examinations of thin sections. Introduction Two general methods of sand control, bridging and sand consolidation, have been extensively used in oil and gas wells. Bridging of sand grains may be accomplished by the use of screens, gravel packs, or plastic-coated gravel. Gravel packing is one of the more plastic-coated gravel. Gravel packing is one of the more popular methods of achieving sand control for relatively popular methods of achieving sand control for relatively thick sands in unconsolidated sand formations. There are a number of criteria that must be satisfied for a successful gravel pack. Some of these areratio of gravel size to formation-sand size;gravel quality (angularity, shape, strength, size degradability, contamination, and solubility);type and cleanliness of fluids used during underreaming and gravel placement;hole cleanout;gravel-to-fluid ratio;slot size and type of liner or screen; andover-all job planning, supervision, and quality control. Our experimental work was designed to answer the following questions.What is the extent of gravel-permeability reduction as a function of gravel-sand size ratio?What is the effect of gravel angularity on bridging?Under what conditions does and badge on and within the gravel?What is the effect of sand-grain uniformity, defined by the uniformity coefficient of the sand, on the gravel permeability? An accurate screen analysis of producing formations is necessary for correct gravel sizing. The Tyler or U. S. standard screen scale is used for determining the range of formation-sand sizes. A formation-sand sample is washed, dried, weighed, separated, and passed through various-sized screens. The screen sizes are designated in Tyler or U. S. standard numbers for ease in classification. For example, a 6 Tyler screen has 0.131-in. openings. The material is progressively passed through the largest to the smallest screen. The sand on each screen is weighed and a plot is constructed showing cumulative percentage retained vs grain size. percentage retained vs grain size. Sand size is generally characterized by the 10-percentile point of the sieve analysis, or the size of sand particle at its coarsest 10 percent by weight. This does not take into consideration the size of the remaining finer 90 percent when, in fact, the size of these may be a controlling factor. The amount of fines can be defined by introducing another parameter, called the uniformity coefficient or C-ratio, defined as C = D(40)/D(90), where D(40), is the grain diameter at the 40-percentile point and D(90), is the grain diameter at the 90-percentile point. A C-ratio less than 3 describes a uniform or well-sorted sand, while a C-ratio greater than 5 describes a nonuniform or poorly sorted sand. An important consideration in designing a successful gravel pack is to determine the correct gravel-to-sand size ratio. JPT P. 107

Controlling Sand With an Epoxy-Coated, High-Solids-Content Gravel Slurry

A new sand control process, effective in either old or new wells, has been applied successfully in more than 600 wells in Louisiana and Texas. Here are a review of field results and an outline of some important aspects of treatment design such as batch size, pump rate, gravel size, positioning of down-hole equipment, and the pumping sequence of fluids and slurry. Introduction The current emphasis on disaster prevention in offshore wells combined with the need to produce all wells at their maximum efficient rate has increased the need for effective sand control systems that do not cause impairment. A longstanding problem has been that of controlling sand in wells producing sizable quantities of it. In the past, two of the most widely used sand control methods have been gravel packing and in-situ sand consolidation. Although both methods have enjoyed considerable success, they have not always been as effective as desired. Neither method has proved effective more than half the time in treating old wells. The desire for a sand control method that would have the advantages of gravel packing without the susceptibility to shifting has led to the development of a number of processes that call for placing resincoated gravel across the producing interval. Essentially, the gravel is coated with resin at the surface and is carried into place in the well by a carrying fluid; then the resin either is allowed to cure or is flushed with a catalyst solution to effect cure. The Process In this process the gravel is placed as a concentrated slurry in a viscous carrying oil. Either of two internally catalyzed epoxy resin formulations is used to lightly coat the gravel. The slurry of resin-coated gravel is squeezed out be perforations until a screenout occurs or, in some cases, until a predetermined amount of slurry has been placed. In either case, the squeezing of the slurry is usually stopped while there is still enough slurry in the casing to leave a cap of the gravel in the casing above the perforations. In some cases where no screen-out is obtained, several barrels of excess slurry is squeezed and another batch of slurry is pumped into the well. After curing, the resin-coated gravel left inside the casing is drilled out, and the well is returned to production. At the writing of this paper, the new process has been applied in more than 600 treatments. The treated wells generally have been oil wells with perforated intervals ranging in length from 2 to 31 perforated intervals ranging in length from 2 to 31 ft. A few treatments have also been performed in gas wells and water injection wells. All but two of the treatments have been in cased and perforated intervals. One of the two noncased holes treated was a California well in which a slotted liner had failed. The liner was perforated in the area where sand was being produced, and two 10-bbl batches of slurry were pumped produced, and two 10-bbl batches of slurry were pumped to repair the screen. After the treatment, sand-free production was obtained. production was obtained. The treatment results in general have been very encouraging. Between 80 and 90 percent success has been obtained in treating both old and new wells. Naturally, changes in procedure have evolved since the method was first introduced to the field in late 1971. JPT P. 1215

Control of Unconsolidated Sands in Waste-Disposal Wells: ABSTRACT

Sand control methods were first used in water wells, and later, modified methods were applied to oil and gas wells. The most recent application for sand control is in waste-disposal wells. The increasing use of unconsolidated sands as disposal zones has created a need for better sand-control systems. We suggest that the primary causes of sand control problems in disposal wells are: (1) greater completion intervals, (2) intermittent operation of the well, and (3) chemical characteristics of the injected effluent. Therefore, successfully to prevent sand production in disposal wells, consideration must be given to: (1) formation characteristics, (2) completion fluid, (3) type of completion, and (4) completion method. Two universally used methods of sand exclusion, with suggested modifications when applied to disposal wells, are the method of in-place sand consolidation with plastics, and the use of gravel packs in conjunction with sand screens. Sand consolidation has limited application owing to the large completion intervals normally used in disposal wells, and to possible chemical reactions with injected effluent. However, a gravel-packed-sand-screen completion generally eliminates the three primary causes of sand production in disposal wells. Factors of prime importance are (1) the drilling and completion fluids, (2) formation grain size and composition, (3) size and amount of gravel, (4) pumping rate, (5) pressure, and (6) gravel concentration. Field and laboratory data show that the method of gravel-packed-sand-screen completions can be used successfully over intervals as large as 500 ft in unconsolidated Frio sands. End_of_Article - Last_Page 2084------------

Stability of Sand Arches: A Key to Sand Control

Sand production, from a well completed in an incompetent formation without a metal screen, can be attributed to failure of the sand to form a stable arch around the wellbore or over a perforation. This study shows the usefulness of having a sand of high grain strength outside the perforations, and indicates that even a low-strength plastic can provide the restraint necessary to stabilize an arch. Introduction The petroleum industry has used both mechanical and chemical methods for controlling the production of sand from wells completed in unconsolidated formations. In developing sand control methods, mechanical studies have dealt mostly with the design of screens and slotted liners and the placement of gravel packs; chemical studies have dealt with the composition and performance of sand consolidation plastic systems, and techniques of applying them. Little attention has been paid in the literature to the mechanical process of failure of the sand structure around a wellbore and the factors that affect the stability of the formation. Our laboratory has conducted, in the past several years, both theoretical and experimental studies on the mechanics of sand failure. W.M. Ayers,1 in 1965, presented results of his theoretical studies combined with field experience. He discussed the stress field around a wellbore and its relation to the formation stability in terms of the shear strength properties of the sand. The work being reported here was a laboratory extension of Ayers' studies. It was conducted as a basic study of sand control and was carried out. in two phases:elucidation of the failure mechanisms of unconsolidated sands and of the mechanism of stabilization of sands by consolidating plastics, using triaxial strength tests; anda direct study of the arching behavior of sand, or the manner in which sand can form a stable structure spanning an opening. Background Shear Strength of Sand The study of the strength of bodies of granular materials generally falls within the realm of soil mechanics. A widely used criterion for shear failure of soils is the Mohr-Coulomb theory.2 This states that failure will occur when the major and minor principal stresses s1 and s3 combine to produce a critical and characteristic value of the obliquity, which is the ratio of shear stress t to normal stress s in the plane of shearing. The validity of this criterion, which ignores the intermediate principal stress s2, is supported by experimental evidence cited by Bishop.3 The shear strength of a sand may therefore be described in terms of a Mohr envelope and its slope a, the angle of shearing resistance. Shear Strength of Sand The study of the strength of bodies of granular materials generally falls within the realm of soil mechanics. A widely used criterion for shear failure of soils is the Mohr-Coulomb theory.2 This states that failure will occur when the major and minor principal stresses s1 and s3 combine to produce a critical and characteristic value of the obliquity, which is the ratio of shear stress t to normal stress s in the plane of shearing. The validity of this criterion, which ignores the intermediate principal stress s2, is supported by experimental evidence cited by Bishop.3 The shear strength of a sand may therefore be described in terms of a Mohr envelope and its slope a, the angle of shearing resistance.

Controlled Injection of Sand Consolidation Plastic

Abstract A new placement system for sand consolidation plastic has been developed to increase success ratios and to extend use of plastic to sands with variable permeability, dirty sands and long or discontinuous completion intervals. Plastic sand consolidation fluids are distributed uniformly through a series of fluid flow control modules with each module covering 2 ft of completed interval. Active modules can be separated by blank spacers to cover a number of individual completed sections in a total interval of 50 ft. Further development is in progress to cover longer intervals. Equipment operation, perforation control and completion program recommendations are discussed. The system has been used in about 75 completions covering up to five individual sand members in total intervals up to 41 ft. Successful plastic sand consolidation has been obtained in many sands where other sand control methods were unsuccessful. Use of the new plastic injection system improves development economics in sand problem areas in three important ways:better fluid injection control increases completion success ratio,greater placement reliability permits reduction in chemical cost and pumping time andone-trip coverage of discontinuous zones significantly reduces completion cost compared to a series of individual packer settings. Introduction Achieving uniform placement of injected fluids into the formation around the wellbore has long been a problem. Success of nearly every injection process is directly dependent upon the degree to which uniform placement is achieved and plastic sand consolidation processes are no exception regardless of chemical and procedural differences. All such processes should provide adequate distribution of consolidating materials around the wellbore to achieve success. Assuming a good cement bond and clean perforations, poor distribution of injected fluids is due principally to permeability differences that occur throughout a formation interval. The composite log with core analysis data (rubber sleeve core) in Fig. 1 shows permeability variations that occur in a typical offshore Louisiana well in Miocene sediments. Note that variations of several hundred millidarcies occur within relatively short increments of the total interval. The lithology column in Fig. 1 is of particular interest because it shows how the grading from claystone to silt to sand takes place over short distances in the geologic column. These thin siltstone and claystone sections may not be seen on conventional logs, but they affect fluid injection patterns and point up the need for plastic sand consolidating processes that are not adversely affected by clays. To reduce the effects of permeability variation, most successful plastic sand consolidation efforts to date have been limited to comparatively short intervals. Review of an article on plastic sand consolidation results in 1959 and an article on the subject as recently as Feb., 1966, discloses that the greater number of successful plastic sand consolidation jobs have been accomplished within intervals of 10 ft or less. Longer intervals were consolidated with separate straddle operations or with a staging procedure. For example, the well shown in Fig. 1 could be consolidated with three separate treatments using retrievable squeeze tools and bridge plugs. Results of attempting to straddle too long an interval are shown in Fig. 2. Consolidation of discontinuous intervals presents a problem. This condition is indicated in the well log shown in Fig. 3. This log shows an interval some 40 ft long containing five productive sand stringers ranging from 1 to 4 ft in thickness. The successful consolidation of these sands might require five separate straddle operations with previously available methods. In summation, a need existed for better control of sand consolidation fluid injection throughout long producing intervals, including discontinuous sands, and preferably in a one-round-trip operation. Solutions to these problems wouldpermit a reduction in the amount of plastic required,permit the consolidation of long intervals,permit economic consolidation of discontinuous intervals.lower costs andincrease success ratios. Development of improved injection control equipment was a necessary part of research to provide an improved plastic sand consolidation system. Closely related work to develop an improved sand consolidation process has been presented. JPT P. 487ˆ

Warm-Air Coking - A New Completion Method for Unconsolidated Sands

Abstract A new well completion technique has been used to prevent the production of sand into wells producing oil from an unconsolidated sand formation. The laboratory development of this method of sand consolidation, known as "warm-air coking", is described. Warm air injected into an unconsolidated sand saturated with a heavy crude oil causes the oil to be oxidized. Continued oxidation of this very viscous oil forms an insoluble coke of resin which cements the sand grains together. Ignition of the coke-forming residue is prevented by proper control of the injection rate and of the temperature-increase rate of the injected air. Reservoir oils having cokable heavy ends provide the most satisfactory source of coke, but specially compounded oils or suitable crude oils not native to the formation could be injected to replace the reservoir oil. Usually crude oils having gravities of less than 20 deg. API contain a sufficient amount of heavy ends. Several wells producing from unconsolidated reservoirs containing heavy crudes have been satisfactorily treated with this method. These wells have produced sand-free oil over an extended period of time and have high productivity indices. Introduction The prevention of sand production concurrent with the oil from unconsolidated reservoirs has been a major problem in some areas. In many cases, the sand control problem has been solved by the use of mechanical devices such as screens, perforated liners and gravel packs, or by consolidating the sand around the wellbore with a plastic which is injected into the formation. The advantages and disadvantages of these methods and their success in combating sand production have been discussed by several authors. As pointed out by Hower and Brown, mechanical devices in the wellbore do not leave the casing clear for multiple completions, while sand consolidation with plastics has been only partially successful. In reservoirs producing low-gravity, viscous oil, the conventional methods are only moderately successful because they sometimes do not prevent sand production and frequently require remedial work during the life of the well to maintain the productivity at a satisfactory level. This is more pronounced when the formation contains a wide range of particle sizes, including clays and silts. This paper presents a new sand-control method known as the warm-air coking sand consolidation process. It was developed to prevent sand production from unconsolidated sand reservoirs producing low-gravity crude oils. Sand consolidation is accomplished by the injection of heated air into the formation around the wellbore until the crude oil becomes oxidized into an insoluble resin or coke. Details of the laboratory development and a description of the equipment are given. The results of several field tests of the method are summarized. Two obvious requirements of any sand-control technique are that sand production be prevented and that the oil productivity be maintained. Other desirable features are that the completion lasts the life of the reservoir without remedial work and that no obstruction be left in the casing. It was believed that these requirements might be satisfied if the sand surrounding the wellbore could be cemented with coke. The coked sand would need sufficient permeability to provide the required productivity and enough strength to withstand the pressure gradients created by the flowing fluids and the weight of the overburden. It is well known that crude oils, especially those having a low gravity, form coke when heated to high temperatures. When an unconsolidated sand saturated with an oil containing heavy ends is heated to the coking temperature the coke formed binds the sand grains together. Several methods of heating to form coke in sand-oil mixtures were tried in the laboratory and the most satisfactory appeared to be the injection of heated air. The use of air as opposed to an inert gas enhances the formation of an insoluble binder in two ways. JPT P. 367^

Large - Scale Laboratory Investigation of Sand Consolidation Techniques

Abstract Large-scale sand consolidation tests were conducted in an effort to determine the reasons for the successes and failures of this method of sand control. Several different consolidating materials were used in treating both clean and bentonitic sands that were packed in a chamber having a capacity of 3.3 cu ft. The results were essentially the same for all of the different consolidating materials. The data show that low-viscosity consolidating materials pumped at a relatively slow rate gave the best results. Where the formation has produced sand, the treating fluids can compress the formation, thus permitting the channeling of fluids to another horizon. Pressure-packing these zones before attempting to consolidate is recommended. Sands containing more than 4 per cent of water-swelling clays are not good candidates for consolidation. It is indicated that loose sand, particularly when it is bentonitic, can be fractured during the placement of the treating fluids. Introduction Sand production in oil and gas wells has plagued the industry for many years, and numerous cures for this problem have been suggested. Most methods have been successful to a certain degree, but the great variety of well conditions that exist in the different areas has magnified the problem and limited the successful use of the various systems. Four review papers present a wealth of information concerning the degrees of success that have been obtained by the different sand-control methods. The bridging of sand grains by the use of gravel packs and screens has been quite successful. However, these methods do not leave the casing clear for all types of multiple completions, and the cure does not last for the production life of the well in some instances. The control of loose sands by sand consolidation with resins has never been as successful as desired. It has always been hoped that such a treatment would eliminate all sand problems for the life of the well, but initial applications, starting in the middle 1940's, were only moderately successful. Lott, et al, reported a success ratio of approximately 50 per cent and made the following conclusions: The highest percentage of successes were obtained where:Consolidation of a zone was made at the time of initial completion or prior to the production of sand.The interval treated was less than 12 ft in length.Between 30 and 50 gal plastic/ft of producing interval was displaced through the perforations. REASONS FOR SAND CONSOLIDATION FAILURES Our own experiences in the field of sand consolidation point toward the following conditions as the major reasons for the failure of sand consolidation attempts.Mud-plugged perforations and mud invasion of the formation.Sand in the casing covering all or part of the perforations. This sand could be either formation sand or one of the coarser sands used as propping agents in hydraulic fracturing.Holes in the casing.Channels behind the casing.Attempting to treat too long a perforated section.Too high a percentage of water-swelling clays in the formation.Formations that have produced sand. Recent attempts were made to treat perforated sections ranging from 10 to 30 ft, in wells that have produced sand, by using a straddle packer that was raised and lowered through the perforations as the consolidating material was being pumped. In most instances, the pressure required to pump fluid into the formation varied considerably as the tool was raised and lowered. This suggested the possibility that significant differences in permeability were present or that only part of the formation had produced sand. There were times when a sudden break in pressure indicated that a fracture was being formed. Research conducted several years ago concerning the problem of the control of water in air and gas drilling indicated that shale sections could be fractured quite easily. In addition, it was determined that it was easier to pump fluids into shale bodies by fracturing the shale itself, or the interface between the shale and sand, than to pump into a fluid-saturated formation. Formations that produce sand are usually adjacent to shale bodies and frequently have shale streaks of various thicknesses interbedded in the sand. JPT P. 1221^

Gravel Packing Controls Unconsolidated Sand in Venezuela Field

Abstract Sand control has been the major problem encountered in producing oil from the unconsolidated Miocene sands in the Lagunillas area of Venezuela. One of the first completions developed to prevent excessive sand production was the combination oil string in which pre-perforated casing was employed. In most cases this method was unsuccessful in controlling sand and was replaced in 1951 by a special slotted liner completion. The slotted liner technique has been effective in controlling sand and in obtaining high volume producers in the Bachaquero sand member. However, as a satisfactory completion depends upon the ability to wash the well into production outside the liner, this technique will soon become obsolete because of the declining reservoir pressure in the Bachaquero field. A program to evaluate gravel packing as a replacement for the slotted liner technique (see Fig. 1) and to provide a sand control method for use inside existing pre-perforated completions was initiated in April, 1956. Forty-three wells have been gravel packed in the Lagunillas Dist. through Sept. 25, 1957, with two jobs considered as failures. Thirty of these wells are producing at an average rate of 520 B/D of 12 to 180 API gravity crude as compared to 268 BOPD for the average offset well. Eight wells are awaiting installation of production equipment and are expected to be satisfactory producers when opened to production. Various problems concerning fluids, liner slot sizes and loss of gravel to the formation have been encountered. Solutions to these problems have been found and procedures for both open-hole and inside gravel packs have been developed that can be applied with confidence to the sand control problems that exist in the Bolivar coastal fields. Introduction A program to evaluate the applicability of gravel packing as a sand control method to wells in the Lagunillas Dist. was initiated in April, 1956.

A Proven Method for the Control of Incompetent Sand Formations

Abstract A sand control process has been developed and field proven in the Gulf Coast. The mechanics of the application involve the use of a gel oil (or gel acid or gel water) as a vehicle to carry sand into or against the formation which has, or is expected to, produce sand. This process is carried on beneath a squeeze tool in order to cope with pressures which might otherwise be unsafe. This process makes it possible to pack a formation without mud or water contamination. After the formation is satisfactorily packed, the packing sand is held in place by a screen liner or sand consolidation plastic. Work has been done to determine the most effective packing sands and gravel. Results of this work are analyzed and tabulated. Introduction Sand control problems in the Gulf Coast are as old as oil production in this region. Several sand control methods have been developed; however, there have always been a few wells which defied any sand control measure. It was on wells of this type that the work described in this paper was initially done. Many variables must be considered when the problem of sand control arises. Virtually all sand control measures are dependent on the bridging of formation particles against some screening mechanism placed in the well. This forms a filter which limits the movement of other formation solids into the well bore. Certain basic information is desirable when preparing a sand control program:formation sand grain analysis;variations in sand size in individual zones;formation or producing interval thickness:mechanical hookup of well;subsurface depth of producing zone;degree of cementation of formation;lithology;well fluids to be produced (viscosity);bottom hole temperature and bottom hole pressure;quantity of fluid production; andsand control measures previously used and their success. Some of this well information is difficult to obtain in the Gulf Coast region, due to the difficulty of recovering cores from the poorly consolidated formation.