Role of microorganisms in selective removal of sulfur by Oxidative Desulfurisation and Biodesulfurization Methods approach for Sulfatereducing bacteria

Reusing flowback water and produced water from active wells becomes more and more important intoday’s oil and gas operations to control surface water volumes in order to keep surface waterdisposal costs (reinjection or trucking off the premises) to a minimum – especially in operations thatdo not require secondary lift support. However, reusing untreated produced and flowback wateruntreated in workover and completion operations can promote bacteria growth both above andbelow ground [1].Water produced from oil and gas wells is a perfect environment for sulfate reducing bacteria (SRB)and acid forming bacteria (AFB) due to its anaerobic nature (< 2ppm O2 content) and high nutrientscontent (organics, free iron, etc.). Reuse of water introduces enough oxygen through regularpumping operations to allow aerobic bacteria to grow – mostly slime forming bacteria (SFB). Theoxygen content is high enough for aerobic bacteria to grow but too low to kill anaerobic bacteria.The oxygen content will cause the anaerobic bacteria to stay in a biostatic state which does not killthem but prevents them from multiplying. As soon as the bacteria find an environment that is conducive to their growth, they will becomeactive again and start multiplying. The anaerobic environment in the formation is ideal for growth ofbacteria like SRBs and AFBs. The aerobic environment of the wellbore is conducive for SFBs. Thegrowth of SRBs will not only lead to Health and Safety (H&S) concerns due to increased sour gas orhydrogen sulfide (H2S) production but also to a slow souring of the formation. This also increaseoperation expenses due to added corrosion (H2S pitting, stress cracking etc) in surface andsubsurface tubulars and related prevention expenses. Other challenges in production can be relatedto AFBs (pitting) and SFBs (emulsion like materials may form) [2].