Experimental Studies Of Rock Drillability And Rock Mechanics Of Deep Well-bore

Fast drilling in deep stratum is a technical difficulties in deep or ultra-deep well drilling, which is the key limiting the development of deep well drilling. Study on Rock mechanics of deep well-bore, especially on rock drillability and rock anisotropy are preconditions of the one technical difficulties. Only if we grasp regularity of drillability, can we select bit type and optimize parameters and increase drilling speed. Prediction and calculation of drillability of rock in the bottom of deep wells, however, is regarded as an important but unsolved problem in the drilling circle. So based on experiment, the dissertation study rock regularity of drillability in deep layer through study of rock mechanics property in deep layer. In addition, the current method to assess the rock drillability needs coring , laboratory experiment and test. Because of need of plenty of scene coring and the problem of economics and technology, it is impossible to conduct coring for the entire formation ,and it is difficult to establish an continuous section map ,and it is impossible to reflect change of rock propery in asymmetry layer and high temperature and high pressure condition of underground rock, which can result in many problem in bits selection and usage. So according to acoustic logging dat, the dissertation proposes a new method of prediction of rock drillability. The main contents of this dissertation concluded as follows:Firstly, Based on studying of the worldwide drilling conditions of deep well and development history,expression methods and problem existed, rock mechanics and key techniques in deep and ultra deep well was analyzed and discussed, the study of rock regularity of drillability was carried out.Secondly, Distribution regularity of confining pressure in deep well bore is systemically studied. The status of primitive pressure is analyzed and the calculating method of primitive earth stress is provided; the status of confining pressure in direct well, the essential equation of confining pressure is set up, and distribution regularity of confining pressure is studied; the status of confining pressure of deviated well bore is analyzed in details, distribution regularity of confining pressure in deviated well is got, which settles the foundation of study on rock drillability.In addition Rock drillability under confining pressure of deep well bore is studied for the first time. The quantitative relation between rock mechanic parameters and confining pressure is set up by laboratory experiment. The calculating method of rock drillability under different confining pressures by analysis on rock drillability.Finally In new expression method of rock drillability, the quantitative relation between rock drillability and acoustic velocity in deep layer was established though analysis of the relation of rock drillability of deep well bore and acoustic velocity, which a method of predicting rock drillability was established by using acoustic velocity.