^^ Subsurface Geologic Methods 



shots run in nonmagnetic drill collars and out through trigger-type sur- 

 veying bits. Magnetic multiple-shot surveys were made in the deeper 

 portions of the well. This well deviated horizontally 6,738 feet at a vertical 

 depth of 5,949 feet. A drift angle varying between 52 and 62 degrees was 

 maintained in the well below 2,500-foot measured depth. 



Offshore leases in the Gulf of Mexico granted by the states of Texas 

 and Louisiana to major oil companies in the last three years have con- 

 fronted engineers with new problems in constructing artificial drilling 

 locations for exploratory wells. As some of the drilling programs already 

 under way are as far as 20 miles offshore and are in water 50 feet 

 deep, the construction and maintenance of such man made islands is very 

 costly. Drilling costs are great; hence the companies carrying on this 

 work are using the best equipment and methods available. Exploratory 

 work must be rushed because of provisions of the leases. Obviously, only 

 one vertical well can be drilled from an island of this type. Some operators 

 have set the island structure on the corner of four leases in order to explore 

 a group of leases from the one point by drilling directional wells. Direc- 

 tional-drilling and well-surveying methods and techniques already tested 

 and proved in other areas are being used successfully to explore and pro- 

 duce the formations discovered. Both shallow and deep structures have 

 been found. Extensive multiple-well directional-drilling programs are 

 under way at the present time. One major company, which has spent one 

 and a quarter million dollars on a structure in 50 feet of water, plans 

 to drill from seven to ten wells from the island to reduce the unit cost of 

 well locations (fig. 269). Directional wells have already attained drift 

 angles of 57 degrees with no bad consequences, a fact which gives assur- 

 ance that well bottoms may be correctly spaced over a large area from 

 one structure. As deeper zones are found, the area that can be covered 

 from an island is increased. Directional-drilling methods make this off- 

 shore development practical economically. 



A question which often is asked when the drilling of a directional 

 well is under consideration is whether there will be any serious pumping 

 difficulties encountered in producing the well. A survey of this problem 

 was made in Los Angeles Basin fields, since a large number of high-angle 

 wells have been pumping there for years. A number of major oil opera- 

 tors and representatives of rod and tubing manufacturers were asked for 

 their actual experience in this matter. Their opinion was that there was 

 little or no difference in tubing and rod wear between straight wells and 

 those drilled at high angles by modern directional-drilling methods. In 

 fact, it was found that several straight wells which had tight spirals or 

 "dog legs" in their courses gave more production trouble than nearby 

 directional wells. One company had made a private investigation of this 

 kind on several hundred straight and deviated wells of their own. Sand 

 content of the oil, drift angle in the well, sizes of rods and tubing, types 

 of pumps used, and other pertinent factors were taken into consideration. 



