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Optimization of Injection into Vapor-dominated Geothermal Reservoirs considering the Effects of Adsorption (1995)

 

Investigator: Roland N. Horne, Stanford University

Keywords:
Reservoir performance, Injection, Optimization, Adsorption, Geysers.

Project Objective:
This research program includes the development of practical reservoir engineering methods to include the adsorption phenomenon in optimization studies of vapor-dominated reservoirs. The investigation has placed specific emphasis on the production and injection characteristics of The Geysers steam reservoir. This analysis will allow improved interpretation of field performance data and aid optimization of future production and reinjection operations.

Approach:
This project concerns the effects of adsorption (and subsequent desorption) of water in vapor-dominated geothermal reservoirs. Prior experimental work in our laboratory has provided an understanding of the magnitude and characteristics of the adsorption phenomenon. The current objective is to apply the understanding of the fundamental mechanisms to simulation models to be used for analysis of field performance and design of reinjection strategies. Core samples from The Geysers have been collected over the past year, with the specific objectives of obtaining a fieldwide understanding of the variability of the adsorption phenomenon and characterizing the relationship between adsorption and rock type.

We are currently investigating the inclusion of the adsorption-desorption data into numerical models used for reservoir engineering performance matching and forecasting. These models will be used to develop an optimization procedure applicable to vapor-dominated geothermal reservoirs in general and The Geysers reservoir in particular.

Project Status:
A large number of measurements of Geysers core materials over the past year have provided an understanding of the overall magnitude of adsorption and the way that adsorption depends on reservoir rock type. Results suggest that adsorption can be characterized by the rock's surface area. There is also indication that adsorption is more prominent within the felsite, although these results are still under investigation. Available numerical simulation models have been evaluated and are now ready to be integrated into the study. Optimization algorithms are in the process of development.

Experiments in earlier years have examined the effects of noncondensible gases on adsorption in Geysers rocks. The results suggested that noncondensible gases have little or no effect on adsorption at The Geysers, however we determined the need to confirm these results using a different experimental procedure. These experiments are ongoing.

Research Results:
The work over the past year has yielded several very important results:

  1. Experimental measurements on The Geysers cores have shown the relationships between different locations and rock types from the point of view of their adsorption characteristics. Surface area is a particularly important indicator variable.
  2. The effects of adsorption on injection and on tracer transport have been analyzed, using analytical and numerical modeling.

Plans:
We will integrate the results on the adsorption characteristics of The Geysers as a function rock type into the injection optimization study. This study will undertake the optimization of injection strategy, considering the effect of the readsorption of the reinjected water.

References:
Correa, A.C., and Ramey, H.J., Jr.: "Theoretical Investigation of Adsorption in Porous Media", to appear in Society of Petroleum Engineers Advanced Technology Series (1995).

Horne, R.N., Ramey, H.J. Jr., Shang, S., Correa, A.C., and Hornbrook, J.W.: "Improving Models of Vapor-Dominated Geothermal Fields: The Effects of Adsorption", presented at the 16th New Zealand Geothermal Workshop, Auckland, New Zealand, Nov. 1994.

Palar, S.: The Effects of Noncondensible Gas and Salinity on Steam Adsorption", SGP Technical Report SGP-TR-149, Stanford University, June 1994.

Satik, C., and Horne, R.N.: "An Experimental Study of Adsorption in Vapor-Dominated Geothermal Systems", Proceedings, 20th Stanford Geothermal Reservoir Engineering Workshop, Jan. 24- 26, 1995.

Satik, C., Horne, R.N., and Yortsos, Y.C.: "A Study of Adsorption of Gases in Tight Reservoir Rocks", SPE 30732, presented at the 70th Annual Technical Conference & Exhibition, Dallas, TX, October 22-25, 1995.

Shang, S.B., Horne, R.N., and Ramey, H.J., Jr.: "Measurement of Surface Area and Water Adsorption Capacity of Geothermal Reservoir Rocks", Transactions, Geothermal Resources Council, vol. 18. (1994)

Shang, S.B., Horne, R.N., and Ramey, H.J., Jr.: "Study of Water Adsorption on Geothermal Reservoir Rocks", to appear in Geothermics (1995).

Contacts:
Roland N. Horne, Sandy Costa
Stanford Geothermal Program
Dept. of Petroleum Engineering
Stanford University
Stanford, CA 94305-2220
(410)723-4745, fax:(415)725-2099
e-mail: horne@stanford.edu