Tracer Analysis in a Fractured Geothermal Reservoir: Field Results from Wairakei, New Zealand
Abstract/Contents
- Abstract
- Interwell tracers have been used extensively in oil reservoirs to detect reservoir heterogeneities. High permeability production zones can channel a disproportionate amount of fluid between an injector and producer. This reduces the vertical sweep efficiency in waterfloods and causes early breakthrough of water in producing wells. Analogously, tracer analysis is important in determining geothermal reservoir characteristics. Most importantly, it provides a means of identifying cold reinjection water flowing to producer wells. In Japan, rapid interference from reinjection wells has caused thermal drawdown in four of five liquid-dominated fields. Although maintaining reservoir pressure is one motive for total injection of waste water, the reduction in enthalpy and subsequent decrease in steam discharge rates may imply that maintenance of discharge enthalpy is more important. Tracer analysis will be instrumental in identifying the relative importance of the flow paths which make enthalpic reduction possible. Unfortunately, models currently used for oil reservoirs cannot be applied to geothermal system. Oil field models assume flow through porous media. Geothermal reservoirs, however, are usually highly fractured. Since the preferred flow channels of reinjected water will be through intervening fractures between producer and injector, a method of determining the extent and type of fracturing is needed. A tracer model to characterize flow in a fractured geothermal system is developed in this paper. It can be used to: (a) Investigate possible damage from premature reservoir cooling; (b) Determine natural flow patterns within the reservoir; (c) Predict interference from current injection wells; and (d) Plan reinjection programs t o minimize thermal drawdown. Recent field test data from tracer tests in Wairakei, New Zealand, are analyzed and compared. Although the main surface fault system is well identified at Wairakei, determining whether interwell flow is primarily within the fault or through other fractures is important before a reinjection program can be evaluated. This study illustrates how tracers can be used to understand not only the nature of fracture systems, but also their relative influence as preferred pathways for well-to-well flow. It is a vital first step in designing a reinjection program. Failure to recognize preferential flowpaths before reinjection could result in substantial financial losses for the operator and permanent damage to the reservoir. Proper application of tracer techniques can reduce the probability of this damage occurring.
Description
| Type of resource | text |
|---|---|
| Date created | June 1982 |
Creators/Contributors
| Author | Fossum, Martin Peter |
|---|---|
| Primary advisor | Horne, Roland N. |
| Degree granting institution | Stanford University, Department of Petroleum Engineering |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Subject | Stanford Geothermal Program |
| Genre | Thesis |
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Preferred citation
- Preferred Citation
- Fossum, Martin Peter. (1982). Tracer Analysis in a Fractured Geothermal Reservoir: Field Results from Wairakei, New Zealand. Stanford Digital Repository. Available at: https://purl.stanford.edu/kt451cg5736
Collection
Master's Theses, Doerr School of Sustainability
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