Abstract: How Clean Should Our Water Be? Reservoir Engineering Perspective on Water Quality in the Long Beach Unit, Wilmington Field

HARRIS, RANDALL, THUMS Long Beach Co., Long Beach, CA

Facilities Managers in the Long Beach Unit are actively working to determine the optimum treating processes for produced water. With numerous water quality improvements already in effect, including increased data gathering and monitoring, and more planned, the water is cleaner. The question is - how clean does this water need to be to maintain injectivity, reduce stimulation expenditures, and reduce injector equipment failures? A study was made to reevaluate water quality specifications, aligning them with reservoir pool requirements.

Relating water quality parameters to reservoir variables is often labeled "impossible" in the technical literature. This is primarily due to the numerous formation damage processes taking place during injection, including solids plugging, scale deposition, plugging from corrosion byproducts, rock wettability changes, microbiological problems, facilities upsets, etc. The large number of reservoir variables, and the inaccuracies often found in the data, also cause difficulty. Only a few models are available, only for solids plugging, and almost all require reservoir-specific testing.

A solids plugging model was found in the paper "Water Quality for Water Injection Wells", by Rochon, Creusot, Rivet, Roque, & Renard (SPE #31122, 1996). This model did not require special laboratory tests. The model cannot account for all the formation damage processes occurring in Long Beach Unit injectors, but solids plugging is believed to be the most important factor.

Injection well case histories were also evaluated. Combining the results from the case histories and the model allowed us to establish the cost of maintaining specified levels of suspended solids. Facilities operations estimated plant costs to maintain water quality at different solids levels. Combining this information allowed us to determine what was the most economically efficient way to run the water facilities.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California