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Summary After several incidents of blown port plugs in used and new perforatingguns, a study was initiated to determine the causes of plug perforating guns, astudy was initiated to determine the causes of plug loss. The study included (1) an examination of the swelling characterstics of a heavy-wall, reusableperforating gun, (2) an examination of new guns from which plug loss had andhad not occurred, and (3) construction of a port-plug test cell in which plugloss factors could be studied. The port-plug test cell in which plug lossfactors could be studied. The results of the study identified at least threemajor factors and nine minor factors that could operate singly or jointly tocontribute to plug loss. Introduction In a reusable perforating gun, the screw port or port plug provides apressure seal to prevent fluid entry and completes the alignment system thatholds the individual charges in place. The plugs, as detailed in Fig. 1, arethreaded, hollow "bolts" with an external flat gasket for sealingagainst the gun body and a dome that provides a thin place for jet penetration. When detonated, the shaped charge perforates the dome, minimizing the use ofjet energy needed to perforates the dome, minimizing the use of jet energyneeded to perforate the casing and formation. The spent plugs are replacedperforate the casing and formation. The spent plugs are replaced when the gunis reloaded for the next use. Occasionally, port plugs are lost from the gun. Most plug losses cause no real problem, but experiencing a large number ofblown port plugs is a general indication that something is out of specificationin the construction or operation of a perforating gun. Although blown portplugs rarely cause a serious problem in most wells, they can be quitetroublesome where clearances are small because the port plug is often thickenough to act as a wedge and stick the gun in the well. The industryexperiences numerous stuck perforating guns every year; in many cases, blownport plugs are the cause. This study was undertaken to isolate the variousreasons for blown plugs and to determine methods of quality-control inspectionsthat can plugs and to determine methods of quality-control inspections that caneliminate most of the major causes of blown plugs. Some wells, such as shallowor low-pressure wells, often experience more blown port plugs because of lesshydrostatic pressure on the outside of the gun. In many cases, however, thecause of the blown plug may be the gun or the loading operation. Tests of Port Plugs To determine the stability of and domes of port plugs, 11 batches of plugswere tested in the pressure apparatus shown in Fig. 2. This test cell snowedthe pressurization of the port plugs from either the outside or the inside. Thetest cell was a two-part unit that sealed together to make a pressure cellabove and below the port plug. The inner cell was machined with a 7/8 -in.,12-thread/in. port that would accomodate one port plug and the accompanyinggasket. The outer cell housing screwed onto the inner cell with a dome abovethe plug area that would allow the entire plug to blow out if thread failureoccurred. The pressure-cell support equipment included a surge chamber thatcould be pressured to several thousand psi and then released through aquickening valve into the test apparatus. The purpose of these tests was todetermine how much pressure the individual plugs could withstand before thedome ruptured, the from plugs could withstand before the dome ruptured, thefrom the plugs sheared, or fluid leaked past the gasket. The batches of plugsused in the test (Table 1) had dome thicknesses from 0.056 to 0.108 in., variedfrom aluminum to steel, and included long- and short-thread designs. Two lotsof plugs included hardened steel threads. As Table 2 shows, the major internalpressure release was leakage by the gasket. The gasket was designed pressurerelease was leakage by the gasket. The gasket was designed to hold only a fewhundred psi when the differential pressure was from the inside of the guntoward the outside. The plugs in these tests were blown only when the threadedport in the test cell was enlarged, leading to less thread contact. (Results ofovertightening are explained in the sections on guns.) When the threaded portof the cell was near gauge specification, none of the plugs were stripped fromthe vessel. This indicates that, when plugs are properly placed in a well-made, new gun, the possibility of blowing a large number of plugs is small. Blownplugs are usually caused by a problem in one or more of four major areas:the loading operation, the gun, the charge, or the support equipment. By examining the gun and the remaining port plugs, we often can findthe cause of the blown plugs. The following paragraphs discuss several causesof blown plugs. The following paragraphs discuss several causes of blown portplugs. These may not be all the causes, but they are the most port plugs. Thesemay not be all the causes, but they are the most common. Table 3 summarizespossible causes of common problems. problems. Loading Operations. The loadingoperation is the source of two major reasons for blown port plugs. Fortunately, both are easily corrected or avoided with a little knowledge and care. Portplugs are most often screwed in with an electric or air-powered impact wrench. Torque limits are difficult to set because a wide range of gun conditions, fromnew to very worn, must be considered. If the plugs are overtightened, especially in worn guns or in new guns plugs are overtightened, especially inworn guns or in new guns with ports that are too large, the threads on theplugs are extruded (Fig. 3) and severely weakened. When the gun is fired, theplugs can be blown out very easily. When a very large number of plugs are lostfrom a new gun, the problem usually is overtightening in poor-quality ports. Selecting a tightening criterion that will not poor-quality ports. Selecting atightening criterion that will not start a shear of the threads reducesovertightening. This selection can be based on examination of several portplugs after they have been installed and removed. It may also be useful towatch the extrusion of the rubber gasket on the port plug and to stoptightening before the gasket starts to extrude over the top of the plug. Whenplugs are overtightened, the rubber gaskets may have slivers of rubber tom outor extruding from the gasket where the gasket contacts the barrel of the portplug and the sealing surface of the gun. The gaskets must extrude to seal, butin our tests, completely flattening and distorting the gaskets did not improvethe seal's pressure-holding ability. pressure-holding ability. The otherloading-related cause of blown port plugs is misalignment of the charge. Whenthe alignment linkage of the gun, charge, alignment washer, alignment sleeve, and port plug is correct, a good shaped charge will punch a hole near thecenter of the plug and will not clip the throat of the plug. When the charge ismisaligned, the jet will cut part of the throat of the plug, which, in moresevere cases, may weaken the plug to the point of failure. In general, mislignment of charges costs the perforating company a great deal in damagedguns and is usually corrected very quickly. New Guns. When a reusable perforating gun is new, it is unusual to lose morethan one or two port plugs on a gun per run. When a large number of plugs arelost with a new gun, the problem may be threaded ports that are too large tohold the plug securely. When ports are properly sized during gun manufacture, the 7/8 -in., ports are properly sized during gun manufacture, the 7/8 -in.,12-thread/in. holes will normally have an ID of 0.780 to 0.800 in. When theholes are m this range, virtually no plug losses will occur. This was confirmedby the first phase of testing on port plugs with a gauge threaded opening inthe test device. With internal surges of up to 40,000 psi, only gasket leakagewas seen; no plug loss was observed. When the ID of the 0.790-in. port in theplug holder was increased by 0.030 in. to a new ID of 0.820 in., the plug lossrate jumped to 20%.
Summary. Loss of mutual solvents during acidizing can be severe, depending on the type of product. Results showed that some mutual solvents can penetrate deeply into a test formation. Chlorination of mutual solvents by penetrate deeply into a test formation. Chlorination of mutual solvents by HCl was also considered and was found to be minimal when the treatments were designed properly, Introduction The uses of mutual solvents as preflushes and in conjunction with acid have become widely accepted because of their success in preventing and breaking emulsions, sludges, and water blocks. preventing and breaking emulsions, sludges, and water blocks. The original concept of the mutual solvent was that it could effectively reduce the surface tension of acid from 72 to below 40 dynes/cm [72 to 40 mn/ml, reduce interfacial tensions to below 10 dynes/cm [10 mn/ml, and provide solvency for removing oil films before acidizing. With the success of the original solvents, used at 10 to 35 vol% in the acid, came a succession of "micellartype" mutual solvents, intended for use at 1 to 5 %. For many jobs, such as lowering surface tension, these low-concentration surfactant-mixture mutual solvents were very good. In a few cases, however, treating attempts with acid and some mutual solvents used to remove deep damage proved unsuccessful. Although many factors, including fluid placement, compound the difficulty of removing deep damage, it was felt that in numerous cases the acid was reaching the damage but not removing it. A set of tests was designed to duplicate the fluid/rock contact area of the deep-damage problem. The tests involved flowing the treating fluid through a Berea sand-stone core 2 in. [5.08 cm] in diameter and 6 ft [1.8m] long. Berea was selected to provide a homogeneous matrix with representative formation clays. By encasing the core in a fiberglass wrap and using 6-in. [ 1.59-mm] -ID sample tubes to thieve fluid from the interior of the core, we could remove samples of the treating fluid from the core at set intervals and check the fluids for signs of degradation. In the laboratory tests, the surface tension of the acid/mutual-solvent system was often higher in samples taken at the farther sample collection taps immediately after acid breakthrough. This indicates that the concentration of some mutual solvents in the acid was reduced during injection of the acid/mutual-solvent mixture through the sandstone core. Although dilution of the mutualsolvent/acid volume with water from the pore spaces was considered, some of the mutual solvents seemed to be more affected than others. Because the scope of the research was limited to testing for the absence or presence of the mutual solvent through the surface tension level of the treating fluid, the identity of the loss mechanism was not established. Limited testing of other sandstones (Banders, Tubb. and Springer) with higher clay content or a different variety of clay has shown more rapid loss of mutual solvent in a few test cases. For the purposes of this paper, the loss of the mutual solvent within the Berea sandstone will be labeled with the all-encompassing term of adsorption. concern for the amount of chlorination of mutual solvents and other organic compounds by HCl accompanies the increasing use of these materials with HCl. The concern is well founded because a high concentration of some chlorinated organic materials in crude oil can result in damage to refinery catalysts. In some instances, special tests for chlorinated material in the crude oil stream have been devised. Because the only remotely related study on chlorination dealt solely with the reduction of HCl strength by heating with primary alcohol solutions, 10 a more detailed report on mutual solvents was needed. In our tests on attempting chlorination of methyl alcohol, we could not duplicate the data reported in this earlier paper. Our analysis of the methyl-alcohol/HCl products indicated a level of chlorination about even with background readings for methyl alcohol or HCl. Finally, a study of the seriousness of the transfer of the chlorinated hydrocarbon from the acid to the oil was of prime importance. Discussion Tests for Loss of Product. The mutual solvents tested included an alcohol-mixture mutual solvent. ethylene glycol monobutyl ether (EGMBE), and two surfactant-mixture mutual solvents. The alcohol-mixture mutual solvent is a blend of 83% isopropyl alcohol and 17% isooctyl alcohol that is miscible (a single-phase solution) at 35 vol % in a 15 % HCl solution. 4 The EGMBE is miscible in 15 % HCl at concentrations of less than I to more than 30% but is normally used at I 0 vol%. The surfactant-mixture mutual solvents are used at 1 to 5% in acid. Undoubtedly, the amount of mutual solvent initially present will affect the outcome of this type of test. High concentrations of the solvents or mutual solvents are often needed where large amounts of oil, sludge, or emulsions are present. However, not all mutual solvents can be used at high concentrations. Many of the surfactant-mixture mutual solvents can form emulsions at concentrations 15% or greater. Even EGMBE, when used at very high concentrations, may oil-wet the formation or promote emulsions. In one well in a south Texas field, a reduction of 80% of total fluid production was observed after an acid treatment in which 35 % EGMBE production was observed after an acid treatment in which 35 % EGMBE was used mistakenly in the acid. In this field, both 10% EGMBE and the 35% alcohol mixture had been used successfully. The drawback to the high concentrations of mutual solvents, of course, is cost. The total mutual-solvent cost depends on both unit cost and the amount used. The surfactant-mixture mutual solvents, also referred to as "micellar acting" or "stable dispersions," may contain small quantities of glycol ether products, long-chain alcohols, and several sur-factants. These products were included in our testing because other cost appeal. Some commercially available demulsifying and surface-tension-lowering surfactants were also tested. Table 1 shows the initial acid strengths, surface interfacial tensions (IFT's), and some IFT data for the acid/mutual-solvent and surfactant/acid solutions. The initial acid strengths of the mixtures reflect the actual strength of HCl in the total solution after mixing. The adsorption tests were carried out with Berea sandstone cores 2 in. [5.08 cm] in diameter and 6 ft f 1. 8 ml long - These cores were wrapped with a triple-thickness fiberglass mat and resin as confinement. SPEPE P. 205
- North America > United States > Texas (0.68)
- North America > United States > West Virginia (0.45)
- North America > United States > Pennsylvania (0.45)
- (2 more...)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.96)
- Geology > Mineral > Silicate > Phyllosilicate (0.77)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Summary A series of perforating tests was run in surface targets to determine whether the conditions of the port plug from a perforating gun could be used as a relative indication of entrance hole shape and perforation penetration. Tests that used centralized and decentralized perforation penetration. Tests that used centralized and decentralized guns in large cement targets showed that a strong correlation exists between casing-entrance hole shape and the shape of the hole in the port plug of the gun. Also, if the charge was misaligned or double-jetted. plug of the gun. Also, if the charge was misaligned or double-jetted. resulting in cutting of the side of the port plug or the gun, target penetration was sharply reduced. Data were also collected on such penetration was sharply reduced. Data were also collected on such influences as gun clearance, charge weight and liner type, multiple casing strings, defective charges, and age of charges. Introduction Much interest has been generated in perforating performance during the past several years after Saucier and performance during the past several years after Saucier and Lands verified the crushed zone surrounding a perforation. The influence of the crushed zone has been perforation. The influence of the crushed zone has been explored by several authors, and its impact on production is generally agreed to be severe. To minimize the effects of this damage and to achieve optimum production, deep, clean perforations have been proved necessary. Although information has been generated on perforation cleaning, the techniques for placement of deep, open perforations are still not completely applied in the field. perforations are still not completely applied in the field. A fieldwide analysis of perforating company performance, such as that by Keese and Oden, is extremely useful, but too often perforating performance cannot be evaluated because of poor data gathering or incomplete information on the charges or other components of the perforating system. This paper presents information on perforating system. This paper presents information on jet-charge perforating performance with respect to penetration repeatability, age of charge, charge penetration repeatability, age of charge, charge misalignment, and the double-jetting effect of a charge malfunction. Charge performance was also tested in concentric-casing-string targets to simulate perforating in overlap sections. The ability of a shaped charge to produce a deeply penetrating hole depends on its ability to concentrate its penetrating hole depends on its ability to concentrate its energy along a single axis--i.e., to produce a single round hole. If one or more elements of a charge are asymmetrical, there may be multiple axes of penetration, and double jetting occurs. Our data indicate that when a charge double jets, an irregular hole is produced in the port plug, the entrance hole in the casing is irregular, and the penetration in the target is sharply reduced. Minor penetration in the target is sharply reduced. Minor occurrences of this interruption of symmetrical firing may cause a pitting effect around the entrance hole (Figs. 1A and 1B). Severe double jetting, which is a gross malfunction of the charge (also illustrated in Fig. 1), caused reduction of penetration from a 22-g charge with an API test claim of 23 in. [58 cm] to an actual penetration of 10.5 in. [26.7 cm] in a 4,000-psi [27.6-MPa] - compressive strength concrete test target. The alignment of the charge in the gun is important for proper standoff distance and to allow the charge to proper standoff distance and to allow the charge to penetrate the thinnest part of the port plug. Charges that shoot penetrate the thinnest part of the port plug. Charges that shoot through the side of the gun or severely cut the port plug both change the standoff distance of the charge. and expend energy from the charge by penetrating extra metal. Although various reasons exist for misalignment, the two most prevalent causes are human error and improper equipment.