High pressure (HP) and high pressure high temperature (HPHT) wells present the most challenging conditions for drilling and well completion operations. During the completion operations of these wells the perforated pay zone may require acid stimulation to remove and clean up debris and therefore permit unrestricted hydrocarbon flow. Also later in the well life carbonate scale may deposit which needs to be removed with a scale dissolver treatment.These chemical treatments are mostly corrosive to steel and can potentially cause significant corrosion damage. Hence there is a need to assess these chemicals prior to application in the well to prevent severe corrosion damage to the wells tubing equipment and liner sections. For this reason laboratory testing of these chemical packages plays an important role in determining their suitability in preventing corrosion damage. In this respect it has been observed that the experimental parameters can heavily influence the test results. Therefore in designing such a screening test program it is not only important to choose the correct test parameters but to also scrutinize the test set-up such that it replicates the treatment application as closely as possible[i][ii]. Another issue regards the inter-laboratory repeatability thus aligning the test set-up parameters is of the utmost importance. For this purpose a testing program was designed and agreed between two Oil & Gas Companies to determine a detailed testing procedure which evaluated the effect of selected experimental parameters when testing a scale dissolver chemical package provided by a major Oil & Gas Industry Chemical Supplier.The corrosion tests were conducted with additive types and quantities recommended by a chemical supplier for use in both the Brazilian and Norwegian Continental Shelf (NCS) offshore areas. Each of the Oil & Gas Companies in turn contracted a specialist laboratory to conduct the test program and their behalf.The metals used for the purpose of this comparison program were high strength Martensitic and duplex stainless steels tubing Alloys namely UNS S41426 17CR (17Cr-4Ni-2.5Mo-1Cu)[iii] and UNS S39274. These Alloys were tested in the 15% HCl – based scale dissolver package at 110°C up to 172 bar for an exposure period of 6 hours.The test results underlined the importance of the test set-up parameters and the need for properly aligning these parameters between laboratories to achieve agreement of test results.In particular it has been shown that critical parameters like the testing pressure solution volume/test specimen area ratio temperature ramp up and cooling times as well as post-test specimen treatment are key experimental parameters to achieve agreement of test results.The initial tests conducted at ambient pressure at the two laboratories resulted in a large variation in the corrosion rates ranging from 27 mm/y to 760 mm/y. Once the experimental parameters were aligned the test results between the laboratories varied less but the difference was still considered unacceptable.The testing pressure; tests conducted at ambient pressure produced corrosion rates considerably higher than those performed at high pressure (up to 172 bars). This was in part attributed to the stability of key protective agents contained in the scale dissolver chemical packages at ambient pressure when tested at 110°C.Once critical testing parameters were aligned and testing was performed at high pressure then good agreement in the test results between the two laboratories could be achieved. Testing at pressures considerably higher than ambient seemingly had the largest impact in reducing the scatter in the test results.Therefore it can be concluded that fine tuning and aligning the experimental parameters aids towards obtaining a better screening approach when evaluating scale dissolver treatment packages.[i] M.L. Walker J.M. Cassidy K.R. Lancaster T.H. McCoy “Acid Inhibition of CRA’s: a review “ NACE Conference 2012 Paper No 19 (Houston TX: NACE 2012)[ii] J.M .Cassidy “Design of a North Sea Acid Corrosion Inhibition System” NACE Conference 2006 paper No 6482 (Houston TX: NACE 2006)[iii] T. Ohe S. Nakatsuka Y. Otome H. Amaya H. Takabe D. Matsuo M. Ueda ” Corrosion Resistance of Newly Developed Super 17%Cr Stainless Steel for Extreme High Pressure High Temperature Wells” Eurocorr 2012 (Istanbul September 2012)

Key words: Martensitic Stainless Steel, 17%Cr stainless steel, Duplex Stainless Steel, scale dissolver packages, well stimulation, deep water, HP