Experimental Study On Rock Drillability Under Bottomhole Pressure Conditions

Raising penetration rate is one of the main technical bottlenecks that we should solve for exploration and development of deep hydrocarbon resources. An accurate assessment of the rock drillability plays a major role in improving rate of penetration and reducing drilling cost in the drilling process. In the past, the extreme value of rock's drillability can be determined at the normal pressure conditions. However, there is the bigger gap between normal and bottom hole pressures. Considering the relation between rock drillability and rock mechanical properties and drilling parameters, some scholars use it to represent rock drillability or to predict the drilling rate. To some extent, these models solve the bit selection and the drilling rate prediction problem. So far, the experimental and theoretical studies of rock drillability can be adapted to down hole pressure conditions are still unresolved issues. The experiments instrument for measured rock drillability under down hole pressure has not yet involved. Otherwise, In order to measure the value of drillability under bottom hole, it is necessary to put forward a test instrument design principles and programs, And launch to the rock drillability test under bottom hole pressure, With a view to forming a rock drillability limit is a realistic evaluation methods under simulated down hole pressure conditions.This thesis is aimed at the tight sandstone in Sichuan Longcang Xujiahe group. Rock mechanics experiments, the experiment of rock drillability test under the condition of bottom hole pressure is launched in this thesis, Hypermesh and ANSYS are used to understand the mechanism of underground rock breaked. the reliability of the instrument. The main research content of this thesis is followed as below:(1) The static rock mechanics experiments is launched in this paper, including uniaxial compressive strength test, uniaxial tensile strength test, triaxial compression strength test under bottom pressure, which establishes the foundation of tight sandstone as a dynamic simulation material in Hypermesh and ANSYS.(2) The experiment of rock drillability test under the condition of bottom hole pressure is launched in this thesis. Under the conditions of confining pressure and confining pressure and column pressure, three ways to deal with rock, including dry-rock, water saturation and oil saturation. And comparative analysis rock drillability limit in the conditions different medium saturation, different micro-drill bit, different bottom hole pressure. And the establishment of a triaxial strength test data speculation mathematical model of the underground rock drillability extremes, Use drillability limit is estimated drilling rate equation Drillability.(3) The simulation of breaking rock with the PDC micro-drill bit under the conditions of bottom hole pressure is conducted by Hypermesh and ANSYS. Compare experiment date with simulation of the drillability limit, the relationship between bottom hole pressure and crushing volume, the comparison of crushing form are analyzed emphatically.All of the researches above contribute to introduction a reliable methods of measurement instruments and experimental for rock drillability in indoor experiment. A mathematical model has been adapted to take advantage of tight sandstone of triaxial test data speculation underground rock drillability.Finally, there are more accurate results for bit types, and guiding engineering practices better.