Costly Shoe-Track Drilling Practices Using Conventional and Rotary-Steerable Systems Evaluated: A Summary of Lessons Learned, Proposed Best Practices, and Software-Driven Recommendations

Abstract

Drilling operations performed through the shoe-track are generally considered duplicated effort by many operators. Nonetheless, shoe-track drillout is an operation that must be performed on all surface or intermediate casing strings or liners. Slow penetration rates are often experienced, even when drilling through so-called drillable casing equipment. Today's costly drilling operations force operators to attempt to reduce nonproductive operations whenever possible. Therefore, improved shoe-track drillout performance can improve operators' overall drilling cost and schedule. Thus, a better understanding of downhole dynamics is necessary to develop improved drilling procedures. A review of jobs from the North Sea database of cement jobs and shoe-track drillouts revealed that, of the more than 1,200 data points available to the authors, 83% of the drillout times were less than three hours; 70% of the drillout times were less than two hours; and 50% of the drillout times were less than one and one-half hours, with the overall average being 93 minutes. When a single type of cementing casing equipment was drilled in some wells in 30 minutes and other wells in three hours, questions were raised as to what major contributing factors determine actual drillout time. Two case histories are presented with close attention paid to drilling parameters that adversely affect actual weight applied by the bit to the target being drilled. A better understanding of weight on bit (WOB) and weight on target (WOT) is needed to best determine drilling procedures to be used for any given drillout. This paper documents lessons learned from successful drillouts performed with conventional and rotary-steerable drilling assemblies. Software-driven recommendations are provided for improved interpretation of downhole forces applied to the target being drilled. Introduction During the past several years, much progress has been made in fixed-cutter bit designs. Improved technology and manufacturing processes have improved bit performance and reliability to the extent that polycrystalline diamond compact (PDC) bits are successfully encroaching into hard-rock drilling applications. Formations that once were reserved for roller cone bits are successfully being drilled with PDC bits. Additionally, it is becoming more common for PDC bits to be used to drill out cementing plugs and float equipment. These achievements reflect recent improvements in technology and the innovation involved in bit design and manufacture. The aggressive cutting nature of many fixed-cutter bits is designed to maximize bit performance when drilling formations. However, this aggressive nature can cause large debris to be created when drilling through cementing plugs or other cementing casing equipment (Fig. 1). Specifically, the elastomer and phenolic materials commonly used in the construction of cementing plugs and floating equipment tend to tear or fragment into large pieces rather than the typical shearing that occurs when drilling formations. The cuttings created when drilling cementing casing equipment are more significant than cuttings created when drilling formation. In some situations, such debris can become lodged in the junk slot area of the fixed-cutter bit. Therefore, special consideration should be made when determining procedures to be followed when drilling out shoe tracks.

Shoe Track Drillout Analysis: Factors Affecting Drilling Efficiency

“…After" all" changes" have" been" done," the" weak" points" were" no" longer" on" the" cutters," and" the" bit" strength"was"increased"with"70%."" " H." Rogers" et$ al.$ [46]" have" evaluated" shoe" track" drillouts" using" the" conventional" (motor)" and" RSS" (rotary" steerable" system)" drilling" assemblies." They" have" concluded"that"most"float"equipment"and"wiper"plugs"can"be"drilled"out"with"PDC" bit," even" though" their" aggressive" nature" may" cause" large" debris" creation."…”

“…In" deviated" wells," applied" weight" on" bit" is" not" fully" transferred" to" the" well" bottom" due" to" friction" between" drillstring" and" wellbore." Some" authors" differentiate" between" WOB" -" the" applied" force" from" surface,"and"WOT"-"weight"on"target,"the"netto"force"that"reaches"the"well"bottom" " 35" [46]. "It"is"equal"WOB"minus"the"upward"force"acting"from"the"cutting"bed"or"other" obstacles."…”