Chap. 12] MISCELLANEOUS GEOPHYSICAL METHODS 909 



Since this induration works progressively outward from a point above the 

 field, the mineralized solutions are diverted toward the edge of the field. 

 This is in harmony with the halo arrangement of both characteristic min- 

 erals (see Fig. 12-15) and pseudohydrocarbons, presumably formed by 

 the reaction between these solutions (chlorides?) and organic materials, 

 and with processes occurring near the surface. Methane, hydrogen, 

 ethane, and the heavier paraffin hydrocarbons are diverted in the same 

 manner by the near-surface "plug" into halo arrangement. 



The observations and interpretation of soil and gas analysis surveys may, 

 therefore, be summarized thus : The maximum concentrations of (significant) 

 hydrocarbons occur above the suboutcrop of fissures or high points of subsurface 

 oil and gas traps except where clogging of the reservoir or near-surface forma- 

 tions has diverted them. This diversion is generally outward from the high- 

 point, that is, in down-dip direction. Virtually all results published to 

 date can be explained in this manner. Laubmeyer was first to measure 

 gas concentrations (mostly methane) on the proved German fields of 

 Oberg, Nienhagen, and Wietze, whose maxima, as pointed out before, 

 were shifted outward, away from the centers of known production. Laub- 

 meyer also found maxima (in both hydrocarbon and radioactivity curves) 

 above the suboutcrop of faults. Graf likewise obtained a maximum near 

 the suboutcrop of a fault in the Oberg field with a down-dip shift, and 

 maxima with outward shift surrounding the Pierce Junction dome in 

 Texas. Pirson observed maxima in ethane above fault outcrops in the 

 Woodhull gas field in New York. Sokolov observed that the maxima in 

 methane and heavy hydrocarbons were, in some cases, shifted away from 

 the axis of the anticline of the Malgobek field in Russia. Although 

 Antonov's results appear to indicate a definite tendency to halo arrange- 

 ment, the latter considers the maxima as being directlj^ related to the 

 suboutcrops of the gas formations and faults in this area. He claims to 

 have obtained fairly good agreement between drilling data and calcula- 

 tion, but details on the actual geologic situation are too meager in his 

 article to decide his evidence for or against the halo theory. 



In the Ishimbaev field, however, the area of greatest concentration defi- 

 nitely surrounds the productive area in halo fashion, as pointed out by 

 Sokolov. ^^ The same is true for the Turkiana and the Kala fields.^" 

 McDermott reports that in the Big Lake field (Reagan County, Texas) 

 not only the significant heavy hydrocarbons, but also the pseudohydro- 

 carbons and significant minerals show a maximum directly above the 

 field, which is explained by the existence of a fissure zone in the axis of 



^' Loc. cit. 



'"' Located on the Apsheron Peninsula (east of Baku), the scene of extensive 

 electrical and gravity work. 



