Summary Over the years, a variety of problems with PDC bit design and application has been well documented. The industry has discovered that many of these inherent problems can be explained as being caused by ‘bit whirl’. The goal of most PDC manufacturers and the subject of this paper is the development of a better-performing, ‘whirl resistant’ PDC bit. Similarly, the goal for most operators is the decreased costs which are a direct result of the effective application of such bits. The possibility of decreased cost due to improved performance has led to most operators focusing on their PDC operations in order to lend assistance to the industry and to bit manufacturers in all phases of bit development and application. This paper discusses a cooperative development effort between operators and manufacturer to effectively apply advanced concepts to the design, manufacture and application of a new series of PDC bits in South Texas. The paper describes PDC design concepts such as force balanced cutting structures, asymmetric blade layouts, spiral blade designs, and tracking cutter arrangements. Such design principles are shown to be effective in countering the destructive effects of ‘bit whirl’ and allow the PDC bit to be utilized in harder formations. A presentation of performance data, operational details, and economic analyses concerning the use of these bits in several south Texas fields is given. The cooperative effort between operators and manufacturer to develop the advanced PDC concepts is discussed. Introduction This paper presents the results of a project to develop PDC bits for specific application in the intermediate section of the Wilcox (Lobo Trend) area of South Texas (Figure 1). The overall goal of the project was to improve PDC bit performance and, thus, reduce drilling cost. The project involved a joint development effort between the operators and the bit manufacturer. The operators' drilling departments worked jointly with the bit design and application engineers to develop PDC bits for their specific applications. The direct benefit of a joint development effort to the operators was the significant savings that would be realized as a result of improved bit performance. Over the past decade, it has been well documented how PDC application in the production section of the Lobo Trend has reduced drilling costs by as much as 30%. These savings were first realized in the early 1980's when the standard practice was to displace the water base mud with an invert-emulsion oil mud. The use of oil mud in the production section of the Lobo Trend proved extremely beneficial to the performance of PDC bits. The synergism between PDC bits and oil mud resulted in increased rates of penetration, increased bit life and decreased drilling cost. The cost savings were so dramatic that the use of oil mud and PDC bits in the production section became the standard practice at the time. Recent work has led to the development and current use of an ROP-enhanced water base/terpene mud system in the production section.
IADC Members This paper was selected for presentation by an IADC/SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers or the International Association of Drilling Contractors and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the IADC or SPE, their officers, or members. Papers presented at IADC/SPE meetings are subject to publication review by Editorial Committees of the IADC and SPE. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A. Telex, 163245 SPEUT. Abstract A water-base drilling fluid treated with a special additive has successfully replaced the diesel oil base muds (DOBM) on a series of wells drilled in the South Texas Lower Wilcox formation. Until recently, a relaxed fluid loss DOBM mud was used in this hole interval because it provided improved hole stability and higher penetration rates at favorable economics. The only problem the DOBM mud did not solve was environmental. The cuttings were coated with oil and high salinity brine and therefore had to be treated before they could be disposed of locally. Efforts to find an environmentally safe DOBM mud replacement have resulted in the development of a special additive for water base muds. It offers a significant reduction in total well cost by increasing the rate of penetration and reducing the mud and cuttings disposal costs. This paper will discuss the field development and use of this special drilling fluid additive that provides improved performance characteristics when compared to traditional, economic, environmentally safe water-based mud systems. Over 45 wells have been drilled with this new water-base drilling fluid additive. In some areas, the average rate of penetration, including connection time, has increased 30% over the DOBM average. The rotating hours required to drill an interval from 1500–3000 feet in length with 14.0 –16.0 ppg mud have been reduced accordingly. Total well costs have been reduced by 20 percent. The authors provide data on how to optimize water-base mud formulations, special additive maintenance treatments, mud solids management and bit performance utilized on this successful South Texas drilling program. P. 971^
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