FEA Modelled MSE/UCS Values Optimise PDC Design for Entire Hole Section

Abstract

The value of the mechanical specific energy (MSE) concept to analyze drilling efficiency and bit performance is well established. Recent operator-driven research has concentrated on predicting and maximizing rate of penetration (ROP). The specific energy ROP model has been successfully implemented in numerous high-cost/high-profile environments. To further advance the mechanical specific energy (MSE) concept, an engineering team is developing a methodology to optimize polycrystalline diamond compact (PDC) bit design for the entire hole section based on modeled MSE and unconfined compressive strength (UCS) values.Traditionally, PDC design engineers adjust cutter density/size, back rake, blade count and nozzle placement to optimize the bit for a specific application. The goal is to maximize ROP and total footage capabilities by minimizing damaging vibrations (axial, lateral, torsional) in a predetermined series of formations. Generally, the selected design has the least potential for vibration across all lithology types. PDC bits can generally drill a homogeneous formation without issues, but when transitioning zones or penetrating interbedded/unexpected formations vibrations can lead to performance degradation and cutter damage.The industry requires a method to unify bit efficiency throughout the entire section on a meter-by-meter basis. To calculate a bit efficiency factor (E m ), engineers are utilizing a sophisticated, integrated, dynamic engineering modeling system. They start with a meter-by-meter correlation between actual borehole lithology and a digitized rock library (UCS). MSE is then calculated using the modeled drilling parameters, torque, and ROP. The resulting two curves are then standardized by calculating the mean value of MSE/UCS fraction to derive a hard value bit efficiency factor. By overlapping the two curves, design and field engineers can identify lithologies that have the optimum correlation then compute the mean efficiency factor for the interval and use it as baseline for the entire hole section.In the test case study a 38m thick shale section offered the best match, yielding a median efficiency factor. Using the fixed median efficiency factor, engineers designed and optimized a PDC bit for the entire 16-in. hole section instead of each specific formation. The resulting ROP was significantly improved, as is documented in a case study that will be presented.

Drilling Performance Optimization Based on Mechanical Specific Energy Technologies

“…Given the bit had a certain mechanical efficiency in the actual drilling process, Dupriest, Cherif and Amadi defined a mechanical efficiency on the base of Teale model [5,10,13].…”

“…However, this is a controversial issue due to the bits' mechanical efficiency depending on a variety of factors, and it may vary greatly from the assumed 35%. Cherif argued that the mechanical efficiency were 26-64% instead of 35% [10]. In directional and horizontal drilling, the MSE values may eventually become several times the formation CCS due to torsional friction.…”

“…The total mechanical work done by the bit in 1 h can be estimated as Please note that every bit has a mechanical efficiency for drilling when it is produced. The mechanical efficiency is mainly related to the bit's cutting structure and exists all along the drilling process [10,11]. Given the mechanical efficiency of the new bit, the mechanical work required to break the rock drilled in 1 h can be nearly expressed as…”

“…Then numerous investigators were motivated to develop more accurate models. These models include those presented by Pessier and Fear [7], Dupriest and Koeteritz [5], Armenta [8], Mohan et al [9], Cherif [10], Mohan et al [11] and they have been widely used in bit selection, drilling efficiency quantification, drilling performance monitoring, drilling performance optimization, ROP improvement and so on. Although the MSE obtained from these models are more and more precisely model the actual downhole drilling in vertical wells, currently there are few effective MSE models to precisely model the actual downhole drilling in directional or horizontal wells due to the majority of field data is in the form of surface measurements.…”

Optimization of Drilling Parameters by Analysis of Formation Strength Properties with Utilization of Mechanical Specific Energy

“…Since this parameter used in the diagnosis of instability during drilling operations was valuable. Drilling engineers are always by applying different weights on bit, speed of rotation and mud flow rate within the range of normal operation [6] [7] [8] [9]. They try to minimize the amount of mechanical specific energy and maximize the penetration rate of bit on the formation.…”