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Rawwater Urges Operators To Make Unexpected Souring ‘Expected’ As Shut-In Oil Reservoirs Are Brought Back Online

As the ongoing rise in oil price makes it increasingly attractive for decommissioned and shut-in assets to be brought back into service, Rawwater the leading oilfield reservoir souring control specialist, urges operators and service companies to ensure that reservoir souring evaluation is completed as part of the due diligence process.

“The costs and risks associated with opening up previously shut-in assets and brownfield sites, in terms of reduced yield and equipment maintenance are well documented,” comments Rawwater’s Senior Research Scientist, Matt Streets. “What is less appreciated, however, is the effect of shut-ins on subsurface hydrogen sulfide (H2S) sour gas generation, with unexpected topsides souring control having the potential to run into many millions of dollars.

Bottle testing“When an oilfield reservoir is shut in for any given period of time, reheating occurs, slowly taking the asset in question back to formation temperature,” adds Matt Streets. “Depending on the temperature and pressure within the asset, a likely outcome is the continued downhole activity of sulfate-reducing bacteria during this period of shut-in and rewarming. Upon the recommencement of production, many operators observe sudden and unexpected appearances in H2S. By including a relatively inexpensive desktop souring study at early decision gates, the degree of sour gas production on reopening an asset can be forecast, as can the time period until pre-shut-in H2S levels resume.”

Following operational shutdowns, significant microbiological hydrogen sulfide production (often referred to as an ‘H2S burst’) is frequently observed at the resumption of extraction, with different water injection treatment strategies being used to varying degrees of success. Rawwater’s DynamicTVS© (Thermal Viability Shell) predictive oilfield souring modelling tool helps make the unexpected ‘expected’, by giving operators and service companies the insight to make informed decisions regarding the degree and duration of increased souring and necessary treatment strategies.

Only recently Rawwater, in association with a service company, completed a major study into the effect of operational shut-downs on sour gas production. For this study, Rawwater investigated microbial sulfide generation under different periods of shut-in, both in the presence and absence of a specific water treatment chemistry.

“Our findings bring important new levels of understanding to the forecasting of oilfield reservoir souring, and will enable operators to factor in the effect of shut-in periods in their calculations,” concludes Matt Streets. “At a time when barrel prices are at a record high, this knowledge will help ensure operators avoid costly unexpected surprises and can more accurately calculate the value of shut-in assets.”