454 Subsurface Geologic Methods 



logging to choose only those sections to core which contain oil or gas. 

 The procedure is to drill ahead until a significant increase in drilling 

 rate, "a drilling break" indicating a change to a softer, more-easily-drilled 

 formation, is encountered. After two to four feet of the soft formation 

 are penetrated, further drilling is suspended until the mud, which was 

 exposed to this new zone, and the corresponding cuttings are pumped to 

 the surface and samples reach the logging unit for analysis. If oil or 

 gas shows are obtained, cores of the formation are taken. If nothing of 

 interest to the operator is indicated, drilling is resumed until another 

 drilling break is encountered; whereupon, the procedure is repeated. Such 

 a program has an operational advantage in that the information is avail- 

 able a relatively short time after the zone is penetrated. This program 

 allows the operator to core, or, if desired, to make drill-stem tests while 

 the effect of contamination by the drilling fluid is at a minimum. 



Baroid Well-Logging Units also contain complete core-analysis equip- 

 ment by means of which the operator may make determinations of por- 

 osity, permeability, salinity, and oil and water saturations. 



The type of log produced is especially useful in those cases where 

 conditions exist which make it difficult to get good electrical logs. These 

 conditions may apply to an entire area such as the Permian Basin of West 

 Texas. Here it is almost impossible, because of the properties of the lime 

 formation and the high-saline content of the drilling muds, to obtain good 

 electric logs; whereas, the Baroid log gives the operator accurate informa- 

 tion on the oil and gas content of the formations. Similar conditions exist 

 when the temperature of the drilling fluid becomes exceedingly high, as 

 in some of the deep Louisiana wells, or when the chemical treatment of 

 the mud is such that it will interfere with the electrical log. Also to be 

 considered are isolated formations which are difficult to interpret by the 

 electric log. In this category are such formations as the Eocene Wilcox, 

 the Cotton Valley, the Travis Peak, and numerous others. The electric 

 logs taken through these sections do not readily indicate the fluid content 

 of the formation. With the Baroid log, a positive identification of the 

 fluid content is made, thus reducing testing to a minimum, with a resultant 

 decrease in time and money expended on the completion of the well. 



In certain sections of the country some exploratory wells are drilled 

 without taking any cores. After the electrical log is run, sidewall samples 

 are taken to check the possible indications shown on the electric log. In 

 this manner, the wells are drilled with a minimum output of time and ex- 

 pense, but ever-present is the possibility that a productive sand or lime 

 will be missed. This possibility is removed by using the Baroid Well 

 Logging service during drilling. This type of logging can be depended 

 upon to pick up indications of all possibly productive formations, and 

 the fluid content of such formations can be further checked by side-wall 

 cores. 



This exploratory method is particularly useful in areas of abnorm- 



