Novel H2S Scavenger Testing Methodology to Meet the Ever-Present Challenge of Simulating Scavenger Application Methods with Laboratory Testing Protocols

Abstract

The design methodology for H2S scavengers relies heavily on developing a test protocol that most closely simulates field applications. These include gas contact towers, direct gas production injection and multiphase treatments, such as subsea umbilical delivery lines to sea floor well heads, hydrocarbon flow lines and sour storage tank treatments. There are very few testing standards and while there are industry accepted methods, the novel methods presented fill the gaps that exist. A thorough review is made of existing test methodologies such as the static gas breakthrough test and the multiphase Parr Autoclave. Each of these has become an accepted, albeit unofficial, industry standard. Novel methods recently developed comprise the "Direct Injection Laboratory Simulator" (DILS) which, as the name suggests, represents a laboratory method of evaluating a direct gas injection application. Also included is a unique modification of the gas breakthrough test, known as the "miniature Ultrafab tower" which simulates a regenerative tower-based system, commonly in operation in the field. The results showed fascinating validation of gas direct injection and dynamic tower interactions. In some cases, the results are as expected and in others fresh insight has been obtained into any observed discrepancy between a scavenger's field performance and how it performs in the laboratory development studies. In the case of the "miniature Ultrafab tower", this ingenious piece of equipment has been proven to accurately simulate the packing typically seen in the gas contactor to enhance gas/liquid interaction as well as provides the ability to continually replenish the tower with fresh chemical during the test using an accurately controlled flow rate from an HPLC pump. These have been shown to be vitally important parameters for accurate lab to field correlation and are uniquely available from this test, for example gleaning the minimum flow rate of fresh scavenger which can control the H2S concentration to the predetermined level; exactly as is done in field operations. This novel apparatus also has a separator chamber where the spent chemical can be collected, analyzed and evaluated, exactly as is done in a field trial for a dynamic contact gas tower. Armed with a new series of test methodologies, the development of H2S scavengers can enjoy a much higher success rate in the all-important transition from laboratory to field. The test methods also give invaluable tools to trouble shooting and investigate unexpected deficiencies in products which have in the past performed as expected. This includes providing a validation method for changes and enhancements desired during the manufacture process and raw material sourcing for chemical scavengers.