Drilling Optimization
Authors: Lummus James L. 
Published: December 2007

Optimized drilling techniques, first applied in 1967, have significantly reduced drilling costs, but have not yet reached full potential. Detailed treatment is given to the interactions of the most important drilling variables. Results indicate that better data, more experience, and confidence will result in greater savings in the future.

Introduction
The development of rotary drilling can be divided into four distinct periods: Conception Period - 1900 to 1920; Development Period - 1920 to 1948; Scientific Period - 1948 to 1968; and Automation Period which began in 1968. The major accomplishments of the first three periods, and a prediction of what lies in the future for the Automation Period are shown in Table 1. In reviewing these development periods, the question naturally arises as to the reason for the approximate 30-year lapse between the end of the Conception Period and the start of the Scientific Period. There Period and the start of the Scientific Period. There are a number of reasons that can be given, but undoubtedly the most significant is that major oilfield equipment firms, mud service companies, and operators did not start appropriating the large amounts of money it takes to do high-quality drilling research until about 1948. When we look at the major accomplishments of the Scientific Period, the most productive years are found to be from 1958 to 1968. A productive years are found to be from 1958 to 1968. A measure of the impact of the drilling technology developed during the latter part of the Scientific Period on holemaking costs, as compared with total Period on holemaking costs, as compared with total well costs, can be seen from Fig. 1. Total well costs increased 14 percent from 1958 through 1967, but holemaking costs remained at the 1958 level; i.e., about $4.25/ft. Other costs such as completion. logging, and casing expenditures increased 21 percent. It is estimated that if the extensive drilling research effort of the past 10 years had not been undertaken and had not been successfully reduced to practice in routine drilling operations, a typical 8,000- to 9,000-ft hole would cost an additional $3.00/ft to drill today. This would amount to a savings of approximately $500 million for 1967 alone, which is testimony that the investment in drilling research undertaken by many companies has paid off. Optimized drilling has been one of the most significant accomplishments of the Scientific Period, but it was not introduced comprehensively until 1967, and therefore will not reach its full potential for several years. It is important to realize that optimized drilling would not be possible today without the hard work of numerous researchers who have spent considerable time studying the effects of drilling variables and how they relate to each other.

Definition and Philosophy of Optimization
There is no such thing as a "true" optimum drilling program; invariably compromises must be made program; invariably compromises must be made because of limitations beyond our control that result in something less than optimum. Perhaps it can be explained this way: for years it bas been known that rate of penetration could be increased by drilling with water, by rotating the bit faster, and by increasing flow velocity through jets in the bit. Lack of sufficient mechanical and hydraulic horsepower, however, often prevents the proper balancing of variables to obtain prevents the proper balancing of variables to obtain maximum drilling efficiency.
JPT
P. 1379