Offset Well Selection

The drilling engineer is usually not responsible for selecting well sites. However, he must work with the geologist for the following reasons:

  1. Develop an understanding of the expected drilling geology
  2. Define fault block structures to help select offset wells that should be similar in nature to the prospect well
  3. identify geological anomalies as they may be encountered in drilling the prospect well

A close working relationship between drilling and geology groups can be the difference between a producer and an abandoned well.

An example of geological information that the drilling group may receive is shown in Fig. 2-1. The geologists have found significant production from E.B. White #2. Contouring the pay zones has yielded the contour map in Fig. 2-1. The prospect well should encounter the producing structure at the approximate depth as the E.B. White #2.

A Irimetric plot (Fig. 2-2) is useful as a conceptual too!. It adds a third dimension not presented in Fig. 2-1. The drilling engineer can view the projected targets and develop a better understanding of the goal.

Contour Map Normal Fault
Fig. 2-1 Contour map

Maps that show the surface location of offset wells are available from commercial cartographers (Fig. 2-3). These maps normally provide the well location relative to other wells, operator, well name, depth, and type of produced fluids, ¡n addition, some maps contour regional formation tops.

Bit Selection Drilling
Fig. 2-2 Trimetric plot

The map in Fig. 2-3 is defined according to township, range, and section. In some rare cases, a specific township and range may have several hundred sections. This scheme is used throughout the United States except in Texas where the wells are usually located by county and abstract (Fig. 2-4).

Selecting the offset wells to be used in the data collection is important. Using Fig. 2-3 as an example, assume that a 13,OOQ-ft prospect is to be drilled in the northeast comer of Section 30, T18S, R15E. The best candidates for offset analysis are as follows:

Fig. 2-3 Section map illustrating townships, ranges and sections.
Fig. 2-4 Texas map illustrating the abstracts Operator Section (T18S, RISE)

Shell, 15,000 ft


Union of California, 14,562 ft


Huber, 12,521 ft


Exchange, 12,685 ft


Houston Oil and Minerals, 17,493 ft


Although these wells were selected for control analysis, available data from any well in the area should be analyzed.

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