The SP Log in Shaly Sands
- H.G. Doll (Schlumberger Well Surveying Corp.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- July 1950
- Document Type
- Journal Paper
- 205 - 214
- 1950. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 4.2.3 Materials and Corrosion, 4.1.5 Processing Equipment, 5.8.5 Oil Sand, Oil Shale, Bitumen, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 2.4.3 Sand/Solids Control, 4.1.2 Separation and Treating, 5.2.1 Phase Behavior and PVT Measurements
- 4 in the last 30 days
- 388 since 2007
- Show more detail
- View rights & permissions
As a continuation of the earlier paper on the general subject of the SP log, amore complete analysis of certain features of the SP log in shaly sands isgiven. The pseudo-static SP in front of shaly sands is compared, on atheoretical basis, to the static SP in front of clean sands, as a function ofthe respective amount of shale and sand in the formation, and of the relativeresistivities of the shale, of the uncontaminated part of the sand, and of theinvaded zone of the sand.
As a conclusion, the advantage of using reasonably conductive mud in this caseis shown.
The discussion is illustrated by field examples.
The discussion reported in the present paper is based on a theoreticalanalysis, and not on experiment. The field examples, joined to the text, areshown only as qualitative illustrations of the essential results of thisanalysis. Although the hypotheses made in the theoretical developments mayperhaps be somewhat improved, it seems, nevertheless, that the results obtainedaccount reasonably well for the actual phenomena, and give a fair approximationof their order of magnitude.
The paper contains a mathematical analysis of a tri-dimensional distribution ofpotentials and current lines, due to spontaneous electromotive forces arisingat the contact of shales and free electrolytes, as a function of the geometryand of the respective resistivities of the different media involved. It isassumed, although this hypothesis is not proven, that the emf's remain the sameeven if the shale occurs in very thin layers or in dispersed particles.
It has already been pointed out that, all other conditions being the same, thedeflection of the SP log in front of a shaly sand is smaller than opposite aclean sand. When the thickness and the conductivity of a clean sand are largeenough, the deflection of the SP log reaches a limiting value which is equal tothe "static SP" of the clean sand. It is generally convenient to takethe static SP of shale as the reference value or "base line." As aconsequence, and for the sake of abbreviation, the expression, "static SPof a clean sand," is often used to designate the difference between thestatic SP of that sand and that of the shales, which difference is a measure ofthe total electromotive forces involved in the chain mud sand-shale.
|File Size||818 KB||Number of Pages||10|