ABSTRACT:

This paper presents the development of a parametric FLAC3D model of a single PDC cutter interacting with a rock specimen, and the initial numerical tests investigating the effect of various geologic and drilling parameters. This cutter-rock model is designed to support the Extreme Drilling Laboratory (EDL) laboratory currently being designed and constructed at DOENETL and will be used to analyze the influence of: temperature, pressure, formation and mud properties, bit design and drilling parameters on the cutting process and to optimize drilling rate of penetration (ROP) in High Pressure and High Temperature (HPHT) environments.

1. INTRODUCTION

Much of our nation's future supplies of oil and natural gas for our energy needs are expected to come from deep formations in High Pressure and High Temperature (HPHT) environments. Optimizing drilling performance in these HPHT operations is crucial to successful, economic mineral extraction, and is one of the major goals behind the Department of Energy's (DOE) "Deep Trek" program and the primary goal of the Extreme Drilling Laboratory (EDL) currently being designed and constructed at Department of Energy's National Energy Technology Laboratory (NETL). Located within this Extreme Drilling Laboratory is an Ultra-Deep Single Cutter Drilling Simulator (UDS) which is capable of recreating the bottom-hole conditions of an ultra-deep well. To best leverage the valuable unique data from experiments in the UDS machine, a FLAC3D model of a single cutter interacting with the rock specimen (as tested in the UDS) has been developed. A lot of research work has been devoted to modeling the rock failure associated with bits and cutters. Many attempts have been made to understand the mechanisms of rock failure and chip formation under a drill bit. Obviously, rock cutting by bit indentation is a basic process in borehole drilling and an accurate simulation of the rock cutting process can help optimize the drilling operation and the drill bit design. However, the bit-rock interaction is not a simple process. The natural rock properties and failure processes are not as well understood as those for man-made materials. Furthermore, at the bit tip, the effects of high strain rates, confining pressure, pore pressure, etc. greatly complicate the understanding and analysis of the rock failure. In the past, the cutter-rock interaction has been modeled by numerous researchers [6]. Al-Jalil [1] gives a very thorough review of the present state-of-the-art on the physical and numerical modeling of disk cutters. This paper states that plane-strain or axi-symmetric laboratory/modeling test with indentors are not exactly the true 3-D field situation with dynamic normal and rolling forces. With indentors, three zones are observed: crushed (can be modeled like soils and shows dilatancy), inelastic cracking (mostly tensile cracks with greatly reduced modulus) and elastic. Often numerical analyzes in the literature are two-dimensional, with a single interface defined between the cutter and rock, and the effect of only one or two parameters are analyzed [8]. Field and/or laboratory validation of the numerical model is sometimes performed but not often. In addition to finite-element analysis [7], the FLAC code has also been used for numerical modeling of drilling [5].

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