Minimum cost drilling programs have been available for about 10 years, but only recently have they been utilized to any extent. One of the principal disadvantages of most programs is that they assume rig operating costs are independent of bit weights and rotary speeds. Although the use of minimum cost drilling programs is relatively new, their proper use programs is relatively new, their proper use can effect substantial savings in the drilling operation.
The principal uses of a minimum cost drilling program are in (1) planning the entire well, (2) selecting the proper bit, (3) optimum time to pull a bit, (4) proper weight and speed to meet special conditions, such as extending bit life in order to save a round trip, reducing bit life as a result of changing formations, critical rotary speeds and crooked hole conditions, (5) revising optimum bit weights, rotary speeds, and bit footages on an instantaneous basis during drilling and (6) studying special problems such as the influence of rig costs on optimum drilling conditions.
Minimum cost drilling programs can be economically used with a time-share computer and a teletype terminal. The terminal can be located at the rig or in the office.
Most minimum cost drilling programs in use today are more complex than they need to be. A relatively simple program should be used initially; then, as more experience is gained, the programs can be made more complex.
Since the late 1950's, as evidenced by the published petroleum literature, there has been published petroleum literature, there has been a strong interest in developing mathematical relationships which would describe and, therefore, permit some type of optimization of the drilling operation. Beilstein and Cannon made an important contribution to understanding the interrelationships of some of the more important variables affecting the economics of drilling. Speer later published valuable data which largely supported the observations of Beilstein and Cannon. Within a short period of time a number of analytical methods for describing the drilling operation were published. All of these methods were developed published. All of these methods were developed primarily to study the effects of varying bit primarily to study the effects of varying bit weights and rotary speeds on penetration rates and drilling costs. These analytical methods are now commonly referred to as minimum cost drilling or optimized drilling methods. A true minimum cost drilling program must include all variables influencing the drilling operation. Some of the most important of these variables are (1) drilling rig, (2) crew efficiency, (3) hydraulics programs, (4) type of mud, (5 bit selection (6) bit weight and (7) rotary speed.