Donald G. Hill, Ph.D., 

R.Gp., R.G., R.P.G.

Consulting Petrophysicist

"The World is my District"


California Registered Geophysicist No. 170

California Registered Geologist No. 6043

Kentucky Registered Professional Geologist No. 1624

Texas Licensed Professional Geophysicist No. 6289

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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Contact:  Donald G. Hill at: Cell/Business Phone:  +(925) 437-5748,   FAX:   +(309) 420-7354,   Home Phone:  +(925) 947-1541  


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