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Extensive Geothermal Exploration and Development Experience from Regional Studies through Property Development

Temperature Build-Up

Temperature Build-Up, Geothermal Well Evaluation

Monitoring borehole temperature build-up via successive temperature logging runs, allows estimation of the stabilized subsurface temperature profile during open-hole operations.

The extrapolated temperature profile (dark blue) above was sufficient to evaluate the potential of this intermediate temperature hole, during open-hole operations, without waiting nine – twelve months after running casing to obtain a stabilized temperature profile.

Temperature Tool Calibration Problems

Temperature Tool Calibration Problems

The two “stabilized temperature profiles” above were from two different temperature logging contractors.

The differences between these two versions of truth could make or break this particular property at a very early stage in its development.

After review of all pertinent data (including calibration records) and re-logging the temperature hole with freshly calibrated equipment, it was determined that the Contractor

A tool had failed. Had a second vendor (contractor B) not been brought in to log this temperature hole, the prospect could easily have been abandoned prematurely.

Fractured Vesicular Basalt Geothermal Reservoir

Proper selection of wireline measurements and display easily highlights a fractured vesicular basalt reservoir.

The above composite log suite is from a geothermal well drilled into a fractured vesicular basalt reservoir. The log suite consists of a dual (crossed X-Y) caliper, dual induction, micro-spherically focused log (DIMSFL), spontaneous potential (SP), gamma ray (GR), borehole compensated (BHC) sonic, formation density compensated (FDC), and compensated neutron log (CNL).

Track 1 contains the X & Y calipers, track 2 contains the GR and SP, track 3 contains the DIMSFL resistivities, track 4 contains the BHC inverted to velocity, and track 5 contains the FDC & CNL.

The reservoir starts at about 760 ft. At that depth, the resistivities, GR, and BHC velocity all drop and the FDC/CNL overplot switches to a clay type cross-over.

The interpretation is that the fractured vesicular basalt reservoir rock has been leached by the geothermal fluids, resulting in argillic alteration of the basalt.

There is also an approximately -60 mv SP anomaly. This was due to the fact that the well was logged while pumping 1,600 BPD water down the “kill line” to cool the well so that conventional, or non-hostile environment logs (HEL), could be run. This very high water input, resulted in a large streaming potential build up across the filter cake opposite the reservoir.

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