PWRI AND RESERVOIR SOURING

| Compatible or Exacerbating?

SMALL AMOUNTS OF H2S IN THE AQUEOUS PHASE ARE MISLEADING

| Low Solution Gas Ratios Mean High Concentrations in the Gas Phase Will Result

THE LIKELIHOOD OF SOURING

| Khatib and Salanitro (SPE 38795) conclude that all seawater floods have soured. Ingredients required are sulfate (from seawater) and organic acids (from formation water)

RESERVOIR BIOREACTOR - FAVORABLE CONDITIONS

| Favorable conditions are: temperature below 80 deg C, availability of fatty acids (acetate, propionate, butyrate), and sulfate. The presence of sulfate reducing bacteria (SRBs) is a given.

THERMAL VIABILITY SHELL

| TVS has been coined by Bob Eden (Oilfield Reservoir Souring - HES OTH 92 385) as descriptive of the reservoir bioreactor.

CONTROLLING SUBSTANCE

| Since there is an abundance of sulfate in seawater (2800 ppm), and reservoir temperature will be lowered by injected seawater, the level of souring will be controlled by the availability of fatty acids.

PRODUCED WATER

| Produced water is rich in fatty acids; perhaps as much as 1000 ppm. PWRI will ‘feed’ the reservoir bioreactor an enriched fatty acid stream thereby exacerbating souring already underway.

WATERFLOOD CONFORMANCE

| Poor waterflood conformance will worsen hydrogen sulfide production. Cycling of injected water cools the reservoir and expands the bioreactor, breaks thru earlier, etc.

LAYERED RESERVOIRS

| Layered reservoirs will likely be highly heterogeneous; therefore souring will be accelerated. Adding PWRI to this scenario will further increase souring.

NATURAL MITIGATION OF H2S

| Siderite (Iron Carbonate) in the Reservoir Petrofabric Will Scavenge H2S Naturally

POTENTIAL REMEDIES

| Membranes will reduce sulfate in seawater by over 99+% but need to be installed at outset of waterflood. Membranes currently are not oil-tolerant; technology improvement required for use w/PWRI.