Известия Томского политехнического университета: Инжиниринг георесурсов (Nov 2019)
GRAPHIC METHOD OF SELECTING DRILL BITS
Abstract
The relevance of the research is caused by the need to select promising drilling bits at the design stage of drilling technology. This direction is resource saving, minimizing the volume of field trials in the search for optimal technological solutions. The main aim of the research was to develop an improved method for selecting drilling bits from statistical data on the mechanical properties of formations. Objects: identification of drilling bits of different firms and their selection in accordance with the statistical characteristics of the mechanical properties of formations. These issues are poorly understood and cause difficulties in the design of well drilling regimes. Methods: graphoanalytical study of the correspondence of the types of drill bits to the strength characteristics of formations determined by Unconfined Compression Strength and the method of Static indentation of a stamp with a flat base. Results. The International Association of Drilling Contractors (IADC) has developed a single classification in IADC codes for identification of bits of various manufacturers. For domestic drillers a dilemma arose: formations are characterized by hardness according to the stamp and in categories, and the bits are made in accordance with the strength of the formations in the IADC codes. The authors propose a transition to the index of formation strength, expressed in the codes of the IADC of bits. This ensures the uniformity of characteristics for both bits and rocks. Accordingly the authors proposed nomograms for selection of bits on statistical value of toughness of formations in codes IADC, calculated with reliability of 0,95. It is shown that it is possible to select bit similarly when representing hardness of formations in categories. In the case of blade diamond carbide bits, their choice is divided into two stages: the choice of the type of a bit in accordance with the strength of the formation in codes or with hardness in categories and the calculation of the number of blades of the bit, which depends both on the toughness characteristics of the formation, and on the diameter of the bit. To simplify the choice of bits, it was suggested to characterize the drillability of formations of the allocated intervals not verbally (soft, medium and so on), but by their statistical characteristics in IADC codes or in the categories with a given probability.
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