No abstract

TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractThe post-yield material performance of 70 and 80 ksi yield strength carbon steel and high-strength corrosion resistant alloy (CRA) coiled tubing (CT) has been investigated experimentally to evaluate its response to a sour environment following plastic bending straining induced during coiled tubing operations. Although this investigation was specifically targeted for under-balanced drilling of sour wells, the results obtained can also be interpreted with respect to CT work-over operations. The four different types of laboratory testing performed were low cycle corrosion fatigue (LCCF), NACE proof ring tests, double cantilever beam tests (DCB) and slow strain rate tests (SSRT). Full-body CT specimens were used for the SSRT and LCCF testing procedures and only SSRT test results are presented for a specific CRA material. The test environments consisted of aqueous H 2 S, H 2 S/CO 2 , varying pH and the standard solution specified by NACE for determining the relative propensity for HIC and SSC. Tests were also performed using the NACE solution treated with an H 2 S corrosion inhibitor. This paper presents the key findings from the carbon steel CT testing, the preliminary data for the experimental CRA CT and the basis on which these materials were evaluated for under-balanced drilling applications. Both 70 ksi and 80 ksi carbon steel grades were found to be fit-for-purpose for sour wells in accordance with certain qualifications discussed. A preference for the lower strength, 70 ksi CT has been identified when CRA materials are not being considered. For carbon steel, the low cycle fatigue (LCF) life in a noninhibited sour environment was reduced to between 15% to 20% of the life in air depending upon the pH level. With the application of an H 2 S corrosion inhibitor, the LCF can be increased significantly to about 2/3 of the life obtained in air. The results of this research are currently being implemented for a revised issue of Industry Recommended Practises for Critical Sour Under-balanced Drilling-Drill String (IRP 6.3).

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAs oil and gas well servicing operations involve increasingly larger coiled tubing (CT) sizes, the ability for extending their useful or working life becomes of increasingly greater economic importance. Not only do larger tubing sizes exhibit inherently lower fatigue lives, but also their replacement cost is considerably greater. Efforts are underway elsewhere for developing CT repair strategies for recovering some of the CT fatigue life that has been reduced due to dents and other damage or degradation of the tubing. Such local repair methods, however, have both material and practical limitations. The capability to remove finite section(s) of tubing that has been damaged or expended a greater percentage of its working life, would be of significant benefit rather than force the retirement of the complete tubing string. Removing sections of excessive ovality and subsequent replacement with new sections without discarding the complete tubing or the ability to extend the CT string length, are further examples of the benefits of performing reliable on-site girth-welded connection(s) in coiled tubing. This paper describes the weld procedure specification (WPS) under development at BJ Services. The procedure utilizes an orbital tungsten inert gas (TIG) welding process equipped with a full-function "Magnatech D-Head". The welding sequence consists of a fine stringer bead technique for maximum grain refinement and a strategic control of heat input, preheat and interpass temperature control. Mechanized systems for tubing ovality removal, reaming of internal ERW seam weld flash and girth-weld edge preparation, are utilized to their fullest extent to maximize repeatability of the weldment integrity and minimize reliance on welder skill and quality of workmanship. Preliminary test results obtained indicate that the low-cycle plastic fatigue life of these mechanized girth welds can be increased by at least 100% compared with what is generally attainable from manual TIG girth welds in coiled tubing.

EinfiihrungIn einer Reihe von Veroffentlichungen (1-17) wurde gezeigt, dad die WeiGblechkorrosion in schwach sauren Medien durch die Gegenwart von Nitrat erheblich beschleunigt wird. Dies wird oft beobachtet bei Konserven, wie Spinat, Tomaten, Bohnen, SutXkartoff eln und anderen Gemusen oder Friichten, welche sowohl -naturgemad oder durch Dungung verursacht -hohe Nitratgehalte (10-23) (bis zu einigen Tausend mg pro kg Frischgewiht) als auch betrachtliche Nitritgehalte (21-24) (bis zu einigen 10 mg/kg) aufweisen. Mitunter ist die Wirkung des Nitrats auf die Entzinnungsgeschwindigkeit von unladrierten Dosen erstaunlich: Johnson (10) beobachtete starke Entzinnung bei Tomaten nach 3-4 Monaten und Iwamoto, Komura und Maeda (11) bei Mandarinen fast vollstandige Entzinnung nach 3 Monaten. unter normalen Verhaltnissen sollte die unladrierte Konservendose bei solchen schwa& sauren Medien (pH 4-5) ca. 2-3 Jahre bestandig sein.Die Mehrzahl der vorher zitierten Untersuchungen (1-17) befagten sich mit dem Nachweis der Wirkung des Nitrats als Korrosionsbeschleuniger ; das Ziel unserer Arbeit war, einen Einblick in den Mechanismus dieser Wirkung zu gewinnen.1.1 R e d u k t i o n d e s N i t r a t s Unter normalen Bedinguagen, z. B. bei Konservierung von schwach saurem Gemuse in WeiSblechdosen, schiitzt das Zinn das darunterliegende Eisen dadurch, da13 es durch Komplex-Bildung mit der jeweiligen organischen Saure und seine relativ hohe Wasserstoff iiberspannung als sich auflosende (,Opfer-")Anode auftritt, wobei der kathodische Vorgang, die Wasserstoff abscheidung, wahrscheinlich hauptsachlich an den freiliegenden Eisenoberflachen, die auf Grund der porosen Natur der Zinnschicht vorliegen, stattfindet (25). Der Gesamtvorgang verlaufk hier langsam wegen der geringen Geschwindigkeit der Wasserstoffentwicklung auf den verhaltnismadig kleinen freien Eisenoberflachen. Wenn in der Losung aber Substanzen vorhanden sind, die bei den am Zinn auftretenden Potentialen reduzierbar sind, kann auch das Zinn gleichzeitig als Kathode dienen, womit der Gesamtaustausch erhoht wird und das Zinn sich schneller auflost. Eine solche Substanz ist das Nitrat. Einen eindeutigen Zusammenhang z w i d e n Nitratgehalt und Zinnauflosungsgeschwindigkeiten fanden Horio, Iwamoto und Komura (6), Board und Holland (7) und Farrow, Lao und Kim (8). Der Mechanismus der elektrochemischen Reduktion von Nitrat ist no& nicht vollstHndig geklart. Polarographische Untersuchungen haben gezeigt, dai3 reines Nitrat am Quedrsilber nicht leicht reduzierbar ist. Die katalytid e n Wirkungen des Uranylions (26), des Molybdations (27-30) und der Seltenen Erden (31, 32) sind bekannt und wurden fur verschiedene analytische Zwecke angewandt (26, 32, 33, 34). Die technische elektrochemische Reduktion von Nitrat an verschiedenen Metallen (vor allem zur Herstellung von Hydroxylamin) gab Anlai3 zu einigen Arbeiten (35-45), in denen besonders die Bedingungen, unter welchen Produkte wie Hydroxylamin oder Ammoniak auftreten, geschildert wurden. Seit einiger Zeit haben sich Schmid und Mitar...

Oil and gas well drilling using coiled tubing (CT), in general, is continually increasing. Because a significant portion of this drilling activity could involve critical sour environments, the industry and regulatory bodies have recognized a lack of adequate guidelines for under-balanced drilling of wells containing hydrogen sulfide. Drilling using coiled tubing (DUCT) in critical sour wells is currently not permitted pending the development of such guidelines. A key element of safe and reliable drilling operations in sour wells, is the materials integrity of coiled tubing when subjected to a wet hydrogen sulfide environment. Considerable laboratory testing and investigation of small-scale, standard NACE test specimens, has already been performed, primarily through a prior joint industry project6 (JIP). These tests did not show unequivocally that coiled tubing steels could be used in sour environments without protection by corrosion inhibitors. Considerably more laboratory testing is indicated. A combined industry effort is required that will compile all laboratory test results from which must evolve a meaningful and practical set of operational guidelines for use with actual full sized drill strings and associated equipment. This paper presents the background to these developments, a review of the materials problem, discusses results from new a new testing method and additional laboratory specimen testing that is required to address any deficiencies or lack in essential data. Analogous to the development of CT fatigue life predictions, full-scale "corrosion fatigue" testing under representative loading and sour environments, is proposed. A methodology is required to integrate the materials response from these test results into the actual systems response of a CT drilling string operating in sour wells. For readers unfamiliar with the technical issues of corrosion fatigue we included extensive appendices giving information related to CT chemistry, metallury and service conditions in sour environments.