Abstract

With exploration moving into deeper waters, deserts and plateaus, operators and contractors will continue to face complex technical and financial challenges. After various advantages of slim-hole drilling, especially great reduce of cost, are well known, slim-hole drilling has become an important technology and been applied extensively. However, existing three-cone bits and PDC bits can not satisfy the requirements of slim-hole drilling owing to limited structure and short life. So, Southwest Petroleum University (SWPU) has developed a new slim-hole bit, named disc one-cone bit, which combines one-cone bit with disc bit. This new bit will have expansive application prospect in deep drilling, ultradeep drilling and slim-hole drilling because of its less torsion, higher bottom-hole coverage coefficient and longer bearing life.

During the development of new disc one-cone bit, it is very important to ascertain the arrangement and the structural size of disc tooth reasonably according to its rock-breaking mechanism. However, the factors to affect bit rock-breaking efficiency are more and restrict each other. If laboratory experiment is carried out to research a kind of new bit, it will be long period, much cost and only under very simplified conditions. Therefore, computer simulation has important technical and economic value during studying the new bit. This paper discusses rock-breaking mechanism and kinematics simulation researches of disc one-cone bit emphatically.

Introduction

Recently, the demands of efficient small diameter bit are more and more owing to the rapid development of slim-hole drilling technology. When the diameter of existing three-cone bit is as small as 152.4mm, namely 6in, its performance will be bad owing to limited structure, low reliability, short life and low efficiency. It will say nothing of the smaller diameter. Because of the restriction of structure and working principle, small diameter PDC bit can not be used under a lot of conditions owing to lack of adaptability in some complicated formation, great torque and the difficulty to clean and cool its teeth. So, it is reasonable option to develop efficient and small size one-cone bit1. It will not only have the advantages of both three-cone bit and PDC bit, but also mend their shortages. It has unique advantages on structure and rock breaking principle so that it is more applicable to the very hard and plastic formation than three-cone bit and it can work efficiently in some complicated formation, where the PDC bit is not adaptable2–3. As a result, one-cone bit with fine performance and low cost is the substitute of three-cone bit and PDC bit in deep drilling and slim-hole drilling4.

However, along with the exploration and development of oil and gas constantly, the geological condition and natural environment faced with by the drilling operation get more complex and worse, so that the difficulty of exploration and development is increasing and the more requirements are put forward to drilling tools. Though one-cone bit has been developed in recent years5 and it has solved the drilling problem of partial complex formation, it does not yet satisfy the demands of the drilling because its teeth are worn seriously during drilling2, 4. Therefore, it is the one of important tasks in drilling to develop a kind of new bit which has long life, high drilling speed and great drilling footage in some complicated formation6.

According to analysis, the rock-breaking efficiency has important relationship with tooth structure and arrangement of teeth. Tooth surface of bit contacting the formation directly has serious influence on the working performance of bit. Therefore, the structure, shape and arrangement of teeth on the bit will directly affect the drilling speed and the rock-breaking efficiency. Owing to lack of fundamental change on the tooth surface structure of bits in the past tens of years, the drilling speed has nearly not been raised in some special formations. So the new structure of tooth surface must be sought according to the new knowledge for rock-breaking mechanism so as to raise the drilling speed and drilling footage under special environment and some special formations7, 8. The disc bit is just the bit with brand-new tooth structure9.

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