Abstract: Control of Microbial Souring of Oil in a Porous Media Column

Mark Reinsel

Oil reservoir souring is a major problem in industry due to H₂S toxicity, corrosion, plugging, and sulfide concentrations in natural gas. Reservoir souring was simulated in Berea sandstone columns and cores using native mixed microbial consortia from two oil fields. Similar souring activity was seen with both consortia growing as a biofllm in columns and cores at 60°C. Most of the souring activity occurred at the beginning of the columns. This simulated injection well souring, in which sulfate-reducing bacteria, sulfate and carbon sources, are all available at the well bore. Biomass and precipitated iron sulfide accumulated uniformly along the column length and caused plugging. More plugging was found in systems with lower initial permeabilities, and most of this plugging was due to iron sulfide precipitation.

Several novel methods were discovered to inhibit souring in the columns and cores. Addition of 10 ppm nitrate stimulated both native consortia to quickly and completely inhibit active souring, and 5 ppm maintained the inhibition. Nitrite was produced at 80-100% of the nitrate level added through incomplete denitrification by nitrate-reducing bacteria, and nitrite was found to be the inhibitory agent. Direct continuous addition of 10-12 ppm nitrite also inhibited souring; but pulse addition was found to be more effective than continuous addition at the same total addition rate. In the 20-hour residence time of the reactor, 10-20% of the nitrite was consumed. Nitrite addition appeared to decrease plugging in the core system. Removal of nitrate or nitrite allowed souring to resume after t had been inhibited for as long as three months. Nitrite was a more effective and longer lasting inhibitor than was glutaraldehyde, a biocide routinely used in oil fields and other industrial applications.

AAPG Search and Discovery Article #90952©1996 AAPG Rocky Mountain Section Meeting, Billings, Montana