Computational Fluid Dynamics (CFD) as a Tool to Study Cutting Transport in Wellbores

Abstract

Abstract In a drilling operation hole cleaning plays an important role. Improper hole cleaning can lead to problems like reduced penetration rate, torque and drag increase, and increase in pipe sticking potential. Cutting transport in a wellbore is a complex problem affected by several parameters such as mud density, cutting size and density, rate of penetration and mud circulation rate. Researchers conducted experiments with different setups representing annulus flow in a limited number of hole sizes to investigate the contribution of several physical and operating conditions. Due to time and cost involved in the construction and conduction of the experiments all reported studies are limited to physical model dimensions and operating parameters. In this study, we introduced a new approach to determine the parameters affecting cutting transport in any wellbore. This method utilizes a Computational Fluid Dynamics (CFD) software program. The effectiveness of selected program was determined by simulating successfully results from an experiment reported in literature. Presented in this study are the effects of cutting and mud properties on the cutting transport efficiency for vertical and horizontal wellbores. This approach eliminates the need for expensive laboratory setups and can be used to study unlimited number of physical and operational conditions in any wellbore. Introduction Cutting removal is one of the critical components of drilling operation. Faster the formed particles are displaced by the drilling fluid better the penetration rates due to contact of bit with fresh formation surface. Adequate circulation rates needed to displace cuttings formed. At the same time proper mud properties must be maintained to avoid problems such as stuck pipe and increased torque. An important mud property affected by cuttings is the density but this change is not uniform throughout the wellbore and can lead to problems. The interaction between particles and drilling fluids is a complex problem and existence of different wellbore conditions further complicates any prediction for adequate hole cleaning. The study of cutting transport has been a general interest to several researchers1. Initial studies were conducted with experimental setups to investigate the drill cutting transport in the annular sections of a wellbore2,3,4,5. Experiments were also conducted for directional and horizontal wells to study the transport characteristics and the parameters affecting the cutting transport6–14. Some of the research included theoretical models to describe the two-phase solid-liquid flow process7. The use of a CFD model is proven to be a successful tool in many areas of fluid flow15,16,17,18. More applications of CFD exist in the design and manufacture of drill bits and the related bit hydraulics19,20,21,22. Researchers simulated drilling conditions to visualize velocity and pressure gradients for different wellbore and bit geometry. Recent advances in computer hardware and increased capabilities allow researchers to investigate more complex problems.