In-House Development of Arsenic in Condensate Removal of Offshore Brownfield
Authors: Usawinchai Chanon , Limpanachaipornkul Patara , Watanapanich Supaluck , Sangwattanachai Manisa , Piromchart Taradon , Sangwanna Khunaphat , Chinkiri Kittichai 
Published: October 2022

The key challenges of the impurity specification in condensate production for offshore brownfields are space limitation and production cost. Mercury (Hg) and arsenic (As) are impurities unique to condensate produced from Gulf of Thailand and thus, the additional treatment process is critical to meet PTTEP's sale obligation. Mercury has been successfully removed by filtration, but no proven technology exists for arsenic removal until now. PTTEP – Thailand's national E&P company, has developed the first arsenic-in-condensate treatment for offshore brownfield.

Several techniques spanning a variety of removal methods were tested in-house, beginning from lab scale, and progressing to field trial tests, and eventually prototype. With 90% removal, catalytic adsorption was found to be the most effective in lab trials. The selected adsorbent was integrated into the Arsenic Removal Mobile Unit (ARU) which was designed with modular fabrication for flexibility of installation and relocation for onshore and offshore pilot tests. The results at onshore shall be used in the technical evaluation for installed platform selection. The pilot unit was then relocated for arsenic in condensate treatment at offshore brownfield.

The ARU was installed at an onshore tank farm for a 3-month trial test in early 2021. The objective was to test the performance of selected adsorbent with the different sources of condensate production. The test result showed the very promising result of 74% - 95% arsenic removal efficiency. The removal efficiency varied depending on the form of arsenic in condensate and arsenic concentration which regularly fluctuates. The test scenarios were conducted to see the impact on the removal efficiency and for better bed life prediction once this pilot unit was installed at offshore in Q3-2021. A variety of plant shutdown scenarios with the stagnant condensate flow conditions were tested with the objective of monitoring the effectiveness of the adsorbent after shutdown. A surprising result was that arsenic removal efficiency still maintained at the same level regardless of shutdown scenarios. However, the presence of emulsion which dramatically impacts the removal efficiency of the selected adsorbent. The removal efficiency can be reduced to below 10% when facing with high water content in condensate or emulsion issue. Nevertheless, the removal efficiency will rebound once normal conditions return.

PTTEP is a pioneer in studying of arsenic removal technology from condensate. This success will provide confidence for further ARU investment to support condensate management strategy. This technology also grants environmental benefits such as reducing the generation of impure wastewater from downstream petrochemical plants previously used in As treatment. Ultimately, this technology has the potential to unlock high As reservoirs which present broader implications for the oil & gas industry as a whole.