Miscellaneous Subsurface Methods 627 



sand dipmeter levels, SP and resistivity, now have been recorded in wells 

 throughout most of the major oil provinces in the country and in many 

 foreign fields. It seems advisable to analyze these data and to describe 

 their application to some of the problems that have been encountered in 

 exploration and development work. 



The hole assembly, about 25 feet long, is shown in figure 326. It 

 consists of a mandril to which are attached three hard-rubber arms spaced 

 120° apart; in the center of each arm and positioned on the same plane at 

 right angles to the axis of the instrument is one of the three recording 

 electrodes. Attached to the electrode unit is a photoclinometer, which 

 determines photographically the orientation of each of the three SP or 

 resistivity curves and gives the drift and azimuth of the well bore. Spring 

 guides above and below the photoclinometer-electrode assembly serve to 

 keep the device centered in the hole and to prevent it from turning. 



The curves are recorded photographically at the surface on the 

 standard electric-logging recorder. Figure 327 is a record of a typical dip- 

 meter level. 



AREAS OF APPLICATIOIN 



Those regions where the geologic section is primarily sand and shale, 

 i. e., California or the Gulf Coast, are best suited for the use of the SP 

 dipmeter. The spontaneous potential here in general shows sharp, well- 

 defined anomalies at formation boundaries, which give definite dip deter- 

 minations. Likewise in these areas a series of bedding surfaces between 

 sand and shale can usually be found at any depth in a well where a dip 

 determination is needed. 



The resistivity dipmeter, on the other hand, has proved of utility in 

 such areas as west Texas, the Mid-continent, and the Rocky Mountains. 

 The numerous resistivity anomalies between, for example, shale and lime- 

 stone found in most wells in these areas provide satisfactory levels for 

 dip determinations at almost any position in a well. 



Field Procedure 



Dipmeter surveys are made with the same cable and, as noted above, 

 surface-recording equipment used for electric logging. Common practice 

 is to make the dipmeter run immediately after the electric logging. 



The dipmeter levels must be chosen, as described later, from the elec- 

 tric log. The assembly — electrodes, photoclinometer, and spring guides — 

 is lowered to the base of the shallowest level and a photoclinometer pic- 

 ture taken. This picture determines the orientation of the elctrodes and the 

 curves, as well as the drift and azimuth of the well bore at the base of the 

 level. The curves are recorded to the top of the level, and a second photo- 

 clinometer picture is taken. The latter gives the orientation of the elec- 

 trodes and the curves, as well as the drift and azimuth of the well bore at 

 the top of the level. After this step, tlie assembly is lowered to the base 



