Induced polarization method and apparatus for distinguishing dispersed and laminated clay in earth formations
AssigneeShell Oil Company
InventorsHarold J. Vinegar, Monroe H. Waxman
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Abstract
Logging means and methods are disclosed for distinguishing between dispersed and laminated clay in earth formations. A wireline apparatus is employed consisting of a multifrequency induced polarization logging tool operating at extremely low frequencies, combined with other logging tools which measure the total amount of clay in the formation. A determination is then made of the fraction of the total clay content in the formation which is due to laminated clay.
Claims43
A method for distinguishing dispersed and laminated clay in earth formations, comprising:
- measuring the dispersed clay content of at least a portion of such an earth formation by means of an induced polarization measurement;
- measuring the total amount of clay in the same earth formation;
- and
- combining the results of said induced polarization measurement and said total clay measurement to determine the fraction of the total clay content in the formation which is due to laminated clay.
A method for distinguishing and separately measuring dispersed and laminated clay in earth formations penetrated by a borehole, comprising:
- measuring the dispersed clay content of a portion of a borehole by logging the portion of the borehole with a multifrequency frequency domain induced polarization logging tool operated at at least one frequency less than 1 Hz;
- measuring the total amount of clay in the earth formation adjacent the same portion of the borehole using an SP log and the equations:
- ##EQU13## where E=diffusion potential between sand/shaly sand and adjacent shale beds,
- T=temperature,
- F=the Faraday,
- R=molar gas constant,
- t.sub.Na.sup.hf =Hittorf electrical transport number for sodium ion in aqueous solution,
- R.sub.w =geometric mean water resistivity (equal to the reciprocal of water conductivity, C.sub.w),
- m and .gamma..sub..+-. =molality and mean ionic activity of sodium chloride electrolyte solutions,
- m.sub.1 and m.sub.2 =molalities of mud filtrate and formation brine, respectively,
- B=in-phase equivalent conductivity of the clay exchange cations, and
- (Q.sub.v).sub.T =total clay exchange capacity per unit pore volume;
- combining the results of said induced polarization log
- and said total clay measurement from said SP log to determine the fraction of the total clay content in the formation which is due to laminated clay;
- performing said steps at a plurality of depths in the borehole;
- and
- recording the results of said combining step to produce a log thereof.
Apparatus for distinguishing dispersed and laminated clay in earth formations, comprising:
- induced polarization measuring means for making an induced polarization measurement of the dispersed clay content of a portion of such an earth formation;
- total clay measuring means for measuring the total amount of clay in the same earth formation;
- and
- combining means coupled to said measuring means for combining the results of said induced polarization measurement and said total clay measurement to determine the fraction of the total clay content in the formation which is due to laminated clay.
Apparatus for distinguishing and separately measuring dispersed and laminated clay in earth formations penetrated by a borehole, comprising:
- a multifrequency frequency domain induced polarization logging tool operated at at least one frequency less than 1 Hz for logging a portion of the borehole to measure the dispersed clay content thereof;
- an SP logging tool for measuring the total amount of clay in the earth formation adjacent the same portion of the borehole, using the equations:
- ##EQU18## where E=diffusion potential between sand/shaly sand and adjacent shale beds,
- T=temperature,
- F=the Faraday,
- R=molar gas constant,
- t.sub.Na.sup.hf =Hittorf electrical transport number for sodium ion in aqueous solution,
- R.sub.w =geometric mean water resistivity (equal to the reciprocal of water conductivity, C.sub.w),
- m and .gamma..sub..+-. =molality and mean ionic activity of sodium chloride electrolyte solutions,
- m.sub.1 and m.sub.2 =molalities of mud filtrate and formation brine, respectively,
- B=in-phase equivalent conductivity of the clay exchange cations, and
- (Q.sub.v).sub.T =total clay exchange capacity per unit pore volume;
- means coupled to said logging tools for combining the results of said induced polarization log and said SP log to determine the fraction of the total clay content in the formation which is due to laminated clay;
- and
- means for recording the results of said clay fractional determinations to produce a log thereof.
Dependencies are inferred from the claim text.