Preliminary Theory Of The Wairakei Geothermal Field

By Making Quantitative Comparisons Between Theory And Observations It Is Shown That Hydrostatic Theories Cannot Account For The Pressure Changes Which Have Occurred In The Vairakei Geothermal Field. The Pressures At Three Representative Dates Can, However Be Obtained On The Theory That The Hot Water Flows According To Darcys Law Under The Influence Of Buoyancy Forces Resulting From The Surrounding Cold Ground Water, Allowance Being Made For The Effect Of The Uncased Parts Of The Bores In Increasing The Vertical Permeability Of The Hot Region. According To This Theory A Steady Rate Of Draw Off From The Bores Will Result After A Period Of The Order Of One Year In An Almost Steady Pattern Of Pressure With Depth, The Greater The Draw Off The Lower Being The Pressure At Any Depth. The Ultimate Source Of Most Of The Water Withdrawn Is The Cold Ground Water Surrounding The Hot Region, Which Is Heated By The Hot Rock Through Which It Flows And In So Doing Cools The Outer Parts Of The Hot Region. The Steady Reduction In Width Of The Hot Region Caused By This Lateral Inflow Extends Much Deeper Than The Bottom Of The Bores, And At The 1963 Rate Of Draw Off Will Lead To A Reduction Of 10 Percent In The Radius Of The Hot Region Over A Period Of About 70 Years. This Contraction Of The Hot Region Will Cause A Slow Fall In Pressure If The Rate Of Draw Off Is Held Constant. Egi Reference Number Gl03584

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metadata-date 2014-06-17T12:56:44
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