USC_Sec_6_SP_3pp_ppt

USC_Sec_6_SP_3pp_ppt - PTE-461 Formation Evaluation Fall...

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1 Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 6: SP Slide No.: 1 PTE-461 Formation Evaluation Fall Semester, 2007 Section 6 Spontaneous Polarization (SP) Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 6: SP Slide No.: 2 What is SP? Electrical potential difference between a stationary surface electrode and a moving borehole electrode A passive measurement A gradient due to changing electrode separation with a superimposed signal due to lithologic variations intersected by the borehole, causing variations in electro- chemical conditions Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 6: SP Slide No.: 3 Background • Observed as early as 1830, over buried metallic sulfide ore deposits • Observed by Conrad Schlumberger during surface equal-potential surveys – Measurable voltage difference in absence of power – Named it: Polarisation Spontané • Observed by Conrad Schlumberger during station logging of boreholes, in the absence of (known) metallic sulfide ore deposits
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2 Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 6: SP Slide No.: 4 Potential SP Mechanisms • Oxidation of metallic Ore Bodies • Movement of brines through the subsurface • Heat flow coupling • Junction potential at interface between brines of different concentrations • Membrane potential due to brines of different concentrations separated by cation selective membranes Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 6: SP Slide No.: 5 Archie’s Equations Assumptions Hydrocarbons are excellent insulators Formation waters conduct electricity Earliest Schlumberger papers noted that sands with hydrocarbons had higher resistivities than same sands with only water or the shales on either side. Archie quantified that relationship Water resistivity is needed to use Archie Equations F = R o R w = a ± ² m I = R t R o = S w ² n Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 6: SP Slide No.: 6 Hydrated Ions In the absence of any electric or pressure fields (gradients) each hydrated ion is surrounded by water molecules In the presence of electrical fields or pressure gradients, water molecule cloud becomes tear shaped, with the blunt end in the direction of movement, and tailing off in the opposite direction
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3 Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 6: SP Slide No.: 7 Onsager’s Conductivity Equations ± is electrical conductivity ± o is conductivity of distilled water ² is the dielectric constant of distilled water T is absolute temperature (°K) ³ is viscosity of water c is electrolyte concentration (eq/L) ´ & µ are arbitrary constants This empirical relationship holds only for dilute solutions ± = ± o ² 82.48 ³ T () 1/2 ´ + 8.20 10 6 T 2/3 ± o µ · ¸ ¹ º ± = ± o ² » ± o + ¼ Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp.
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This note was uploaded on 02/27/2008 for the course PTE 461 taught by Professor Donhill during the Fall '07 term at USC.

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USC_Sec_6_SP_3pp_ppt - PTE-461 Formation Evaluation Fall...

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