Analysis Interpretation Information
Cover Those Elbows Just as sweaters and coats wear out first at the elbows, so does insulation on pipe elbows —i.e., until the advent of jackets for ells ^ A L M O S T since the first use of insulated lines, maintenance engineers have faced the problem of abuse a n d d a m a g e to insulation. Some years ago, a l u m i n u m jackets to cover insulated .lines got a n enthusiastic reception, b u t ells were n o t included because of fabrication difficulties. If an ell was jacketed, it was a sitefabricated j o b — i n most cases, an expensive process. Because of attachment needs, jackets for ells m a d e u p of m a n y sections proved difficult, if not impractical, to remove and reinstall. T o cover ells, insulation material, plastic enough to apply over chicken wire a n d which hardened with time, came into wide use. This nonmetal jacketed elbow insulation invited abuse from passers-by. Often elbows project into areas which raise chances for t h e m t o b e accidentally b u m p e d with resultant damaged insulation. I n addition, vibration a n d shrinkage help make insulation on ells short-lived without protection. T w o southwestern fabricators of a l u m i n u m have come u p with economical a n d easy-to-install jackets to cover insulated ells. Both companies—Childers Manufacturing Co., Houston, Tex., a n d Preformed Metal Products Co. (Premetco), Shreveport, La.—developed twopiece a l u m i n u m jackets for ells. Precision m a d e , t h e jackets are available in sizes to fit several diameters of pipe, each of which m a y be covered with several different thicknesses of insulation. T h u s , for example, a l u m i n u m jackets to fit an 8-inch nominal size ell covered with insulation from 1 to 3 inches in 0.5-inch increments a r e n o w stock items. T h e jackets (see figure) a r e d e signed to fit snugly over a n insulated elbow and join smoothly with jackets
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covering straight lines. These companies say the jackets have a n internal moisture barrier applied a t the factory. According to Childers, their jackets can be installed with a l u m i n u m sheet metal screws. O n the other hand, Premetco recommends a special adhesive it m a n u factures, although they also say straps or screws can be used. First announced last year, alumin u m jackets for ells have received an even more enthusiastic welcome than straight aluminum jacketing did. " W h y m o t h e r necessity d i d n ' t bring us simple jackets for ells sooner," quips a n engineer, "could go down as one of t h e deeper mysteries of plant m a i n t e n a n c e . " B.F.G.
Isotopes Go Underground A d d another role for radioactive isotopes: underground petroleum tagging IVADIOISOTOPES
are
going
under-
ground—to boost oil production. Used as tracers, they help m a p t h e underground flow of fluids. T h e result: better knowledge of rock formations in oil a n d gas fields. W h e n a n oil field starts to peter out, engineers often inject gas or water u n d e r pressure into the pool to squeeze more oil to the surface.
Two-piece aluminum jackets to cover insulated pipe elbows fit snugly to the insulation and join smoothly with jackets covering straight p i p e
Otherwise more than half the oil might remain locked in the earth. But injection is not enough. T o determine how efficient the secondary recovery process is, it is necessary to know what happens to the injected gas or water—how much is doing the j o b a n d h o w m u c h is being wasted or lost. M a n y types of tracers—fluorescent dyes, boron compounds, ammonia, helium, carbon monoxide among them—have
Injecting radioactive krypton gas into pressurizing well a t oil field. Krypton-85 was pressurized t o almost 1 0 0 times atmospheric pressure so that it would flow into the well VOL. 50, NO. 5
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MAY 1958
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REPORTS a b a n d o n e d mines, quarries, or other reservoirs. T h e stored material can then be identified, should it seep out of the reservoir into adjacent mines or wells or into water supplies a n d homes. Esso S t a n d a r d Oil Co., for instance, tagged 200,000 barrels of oil stored in a n a b a n d o n e d slate q u a r r y with tritiated octadecene. A subsurface leak in the pipeline carrying the oil to storage was revealed when oil with a small a m o u n t of radioactivity showed u p in a water well along its route.
Low-level radioactivity counter at National Science and Engineering Corp. laboratory, c a p a b l e of detecting 2 disintegrations per minute in a standard liter of gas
been used to check underground flow. Most such materials have drawbacks. T h e ideal tracer, for instance, should behave as closely as possible to the material being traced ; it should mix readily with it and flow in a similar m a n n e r through the rock. Moreover, the tracer must be detectable in very dilute concentrations. And it should be both safe to handle and inexpensive. I n m a n y ways, radioactive isotopes fit these requirements. Compounds useful as underground tracers include: krypton-85, tritium gas, tritiated water, and tritiated or carbon-14-labelcd methane. None of these is found in appreciable q u a n tities in natural gas or ground water. And each can be detected in such dilute quantities (one p a r t per trillion or less) that it need add little to the natural radioactivity already present in gas at the output well. I n tagging something as large as an oil pool, it is desirable to use an isotope that is relatively safe, is low in cost (tritium costs about $2.00 per curie), a n d has a long half life (tritium has a half life of about 12.5 years and krypton-85 about 9.5 years), points out Seym o u r Rothchild of New England Nuclear Corp., a leading producer of radioactive chemicals. Some commonly used compounds containing tritium, such as water, methane, and long-chain hydrocarbons, he adds, are now available from stock. 26 A
Often all t h a t is needed in a repressurizing study is a measurement of the time for gas to flow from the injection well ' to the producing well. A single isotope, added as a short pulse, indicates how permeable the underground formation is. Structural barriers show u p , even with relatively crude measurements. W i t h more precise work, the flow of fluid can be m a p p e d in all directions a n d channeling or t u r b u lent flow is detected. T w o or more isotopes provide still more information. I n one comm o n situation, the producing well is surrounded by four outside wells (one at each corner of a square), into which gas or water is p u m p e d . Tagging each injection well with a different tracer shows how m u c h each contributes to oil output. Nuclear Science a n d Engineering Corp. has worked with Carter Oil Co. since late 1956 on such experiments in the Southwest. It injected m e t h a n e into one well, krypton into another, and took samples at seven producing wells in w h a t Nuclear Science claims was the first such project using more t h a n one tracer. Samples are analyzed in a low-level laboratory counter to measure concentration a n d the time needed for a given a m o u n t of pressurizing gas to escape through the producing well. Isotopes can also be used to tag gas or oil stored underground in
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Isotopes have other uses, too, as underground tracers. T h e y can be added to drilling mud to supply a n idea of underground formations and conditions, for instance. And they can b e used to locate gas leaks behind well casings. Use of radioisotopes to answer problems in secondary recovery is still experimental, cautions D . R . Carr of Isotopes, Inc., a company which has been active in the field. Problems of tracer selection and injection a n d sampling patterns must be worked out for each application. T h e isotopes must b e analyzed accurately, too, especially if the sample contains more than one tagged material. O n the other h a n d , Carr claims, the cost of underground labeling is not high. If tritium or krypton is used, only a few h u n d r e d dollars worth of isotopes is needed. Calibration costs run to about the same figure. Carr estimates the total cost for injection may reach a few thousand dollars. Homogeneous labeling of storage reservoirs may run to about $2.00 to $3.00 per million cubic feet of stored gas. Carbon-14 is more expensive (for the same a m o u n t of radioactivity), but even so the cost of the isotope is only a minor p a r t of total injection cost. Because measurement of the tracer normally requires special laboratory equipment, however, it cannot be d o n e a t the wellhead. T h e inconvenience of shipping samples to the laboratory is small, nevertheless. Carr predicts routine use of isotopes for petroleum recovery and storage engineering in the near future. T h e cost a n d trouble involved are slight, he points out, in comparison with the potential savings. {Continued on page 30 A)
