ABSTRACT:

According to NACE MR0175/ISO 15156 standard, martensitic stainless steels can be used up to 0.1 bar of H2S partial pressure provided that the pH is above 3.5. However, these alloys have been successfully used in Field A up to 0.0145 bar of H2S at pH 3. It was decided to check the possibility of extending the domain of their use up to 0.035 bar H2S partial pressure at pH 3 (Field B conditions) and then up to 0.05 bar H2S partial pressure at pH 3 (Field C conditions). First, SSC resistance of 13% Cr and Super 13% Cr were tested under the conditions of Field C in two different laboratories. 13% Cr and some of super 13% Cr failed but one alloy showed no crack, confirming the suitability of some Super 13% Cr for Field C. Then, SSC resistance of 13% Cr was tested under Field B conditions with and without chloride. For the test without chloride, test samples are placed in both liquid phase (condensed water free of chloride) and gas phase under condensing conditions. No cracking was detected. However in the same conditions but with 500 ppm chloride, samples placed in the liquid phase cracked but no crack was detected on samples placed in the gas phase. For material selection, shut in conditions are generally considered due to low temperature and high partial pressure of H2S but there is no chloride. According to the test results the presence of chloride seems to be the main parameter at low pH values. Paper discusses the results of tests and the limits of using shut-in conditions for material selection.

INTRODUCTION

Field B is currently producing and wells were completed with L-80 grade 13% Cr. However, testing of new reservoirs indicated the presence of unexpectedly high H2S levels.

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