California Consortium Identifies Techniques To Control Excess Water Production

(Tech Connections Column, April 2004, American Oil and Gas Reporter)

Managing produced water has been a focus for PTTC. Last year we developed a concise Produced Water Manual that presented solutions for the Mid-Continent, although many are applicable across the United States.

Causes of excess water production and appropriate solutions do vary with geological environment. The turbidite environment of California’s Los Angeles Basin is a prime example. This environment is characterized by large intervals of alternating sand/shale sequences, and is quite similar to turbidites encountered in the Gulf of Mexico. Saturations in sands can vary widely, and any sand, regardless of depth, can be wet. Wells are typically completed in multiple intervals throughout several hundred feet of the formation. With the absence of fluid entry survey data, operators typically don’t know the nature and contribution of individual zones.

PTTC’s West Coast Region is working in a consortium that has received funding from the Department of Energy’s PUMP (Preferred Upstream Management Practices) program and the California Energy Commission. Operators are sharing sufficient data for results to be representative of LA Basin operations. Results confirm that water control efforts are generally economic, but more case studies are needed. Data are also clear in that operators need to focus more on diagnosing the problem(s) responsible for high water production.

Participants in this study contributed data from seven fields (six waterfloods and one natural water drive), whose combined production represents 60 percent of California’s District 1 production. There were 12 producing zones represented in the seven fields. Data were summarized for 67 producers and 60 injectors, and the performance of 17 water control treatments was evaluated.

The three leading reservoir engineering/geology factors contributing to excess water production are thief zones, faulting, and wet sands imbedded in producing intervals. The leading mechanical/completion factors are slotted liners (including gravel packs), length of open interval, and inclusion of wet zones. Both producers and injectors were classified as either “good” or “bad,” and numerous parameters were compared to identify differences and similarities in the good and bad wells.

The average cost of the water control portion of the treatments evaluated was a little more than $25,000 (total job cost with additional work averaged $73,000). Average payout was seven months. These data establish that water control efforts are generally cost effective. Economic factors that were perceived to lead operators to take more action with water control solutions were increased electrical costs and better economics for the solutions employed.

Correctly diagnosing the cause(s) of excess water is the single most important factor in a water control program. One must learn the impact of local geology on forming thief zones. One must also know the effectiveness of completion and well bore interaction with the reservoir. One must discern whether there are single or multiple problems. If multiple problems exist, does one dominate? Can and should multiple problems be addressed in a solution? Is problem flow dominated near the well bore or deep in the reservoir?

Solutions fall within three general categories: existing well bore interventions, pattern reconfigurations, and designer well bores. The appropriateness of a given solution depends on where the problem lies within the matrix.

An effective way to trace channeling is to apply chemical tracer surveys. These surveys often identify complex injection water flow paths in waterflood operations. Chemical tracer slugs, using different tracers for each injection well, are injected in precise amounts over a set period into each well’s injection stream.

The presence and concentration of tracers in produced water from nearby producers or other producers thought to be influenced by injection are measured. Sampling periods are set so as not to miss the injection water/tracer slugs. The arrival times and concentrations of tracers at different producers reveals much about fluid flow paths. Rapid arrival at high concentration indicates thief zones or very poor sweep. It is not uncommon for tracers to bypass producers near injectors. Multiple tracer arrival peaks can confirm movement through different intervals.

Fluid entry surveys apply in problematic high water-cut wells, evaluating idle wells, and monitoring waterfloods. When planning fluid entry surveys, one must consider mechanical issues such as available tool sizes, clearance checkpoints, wellhead issues, downhole issues, and potential problems. There are equipment differences for rod-pumped and submersible-pumped wells.

For injection wells, once profile data are available, there are two key questions. Are the zones taking fluid contributing to production? If not, isolate them and treat the offending zones. Do the zones not taking fluid have potential to contribute to production? If they can, stimulate them after offending zones have been shut off.

Concerted efforts to correctly diagnose excess water production will lead to cost effective solutions. There are no magic bullets, but there are solutions. Do you have the time to save your money?