Ch. 31] LATTICE CONTROL OF CORRELATION PROFILES 575 



where within the interval being mapped will result in thinning that is 

 not indicative of the true thickness configuration. Isopach (thickness) 

 maps are usually of much value in determining progressive changes in 

 shore lines. 



LATTICE CONTROL OF CORRELATION PROFILES 



Once the principal directions of shore-line trend become known in a 

 general way through the method outlined above, the next step is to 

 establish a series of correlation profiles, several of which should be as 

 nearly parallel to the shore line as possible and several normal to it. 

 The spacing and number of profiles depends entirely on the size of 

 the area, number of reliable logs available, and the complexity of the 

 stratigraphy. In many areas six-mile spacing of profiles along town- 

 ships and ranges should be sufficient. Two such series of profiles will 

 naturally intersect each other at wells common to both and at ap- 

 proximate right angles. The result is a lattice control of the stratig- 

 raphy of the entire area. Many details of stratigraphy can be gleaned 

 only from closely spaced wells, especially where sands are lenticular, 

 where unconformities are present, or where the structure is complicated 

 by faulting. These and other significant details can be worked out by 

 "tying in" all well logs which do not happen to lie on a profile into 

 the nearest profile log that occurs in a shore-line direction with respect 

 to the log in question. In many portions of the Mid-Continent an ac- 

 curate lattice control can be established by using a combination of 

 electric logs and sample logs. Drillers' logs and scout-ticket strati- 

 graphic information then can be correlated readily. In such an area 

 as the Appalachian Basin, where electric logs are almost non-existent, 

 one must rely solely on sample and drillers' logs. This is difficult at 

 best, but has one advantage in that nearly all wells are drilled with 

 cable tools, hence the better sample material. In such an area consider- 

 able discrimination must be exercised in the selection of representative 

 logs for the lattice profiles. Visual comparison of numerous closely 

 spaced logs, especially logs of wells in a pool, facilitates the selection 

 of the proper logs. Careless or generalized logging usually can be de- 

 tected readily. 



Sections that have dog-legged trends are probably the least in- 

 formative profiles to be found in the literature, for under certain con- 

 ditions they may be parallel, diagonal, and normal to the shore line and 

 pass in and out of the same facies several times. A sand body in one 

 well with no apparent lithologic counterpart in the wells on either side 



