A Practical Method for Evaluating Rig Performance
Authors: Sheikholeslami Bahram A. , Miller James D. , Strong R.E. 
Published: December 2007

This paper introduces a practical method of calculating rig efficiency incorporating both mechanical performance and the performance of the contractor's personnel. By developing a concept called "contractor-controlled time" (CCT), the effect of the rig crew on various drilling operations can be included in the efficiency calculation. Several example calculations of rig efficiency involving actual field data are presented. This paper also addresses the effective cost of a rig to the operator based on efficiency and the normal fixed costs of the drilling operation. This new approach to rig efficiency can be applied to development drilling areas, with some limited application elsewhere. The results of this study have provided a means of comparing rigs and determining which is the most efficient and cost effective. The results also can pinpoint those operations where a particular rig is inefficient. This information provides a method of evaluating rigs on a uniform and consistent basis.

Introduction

The concept of drilling rig efficiency has historically been associated with a rig's mechanical capability. Generally a rig's size, mechanical condition, horsepower rating, and maximum load have been considered by many as determining efficiency. This concept of efficiency has ignored the rig crew and their ability to perform routine drilling operations.

This paper describes a new method of evaluating drilling rig efficiency incorporating performance of the contractor's personnel and mechanical capability of the rig. Efficiency is calculated on the basis of the time it takes a rig to perform various drilling operations. An inefficient rig costs the operator or contractor both time and money. This paper also presents a method to calculate daily rig cost based on efficiency. Equations for rig efficiency and adjusted daily rig cost are included with a comparison of rig efficiencies.

The concepts and equations discussed in this paper provide a practical method for both operator and contractor to evaluate and compare drilling rigs.

Theory

A complete evaluation of drilling rig efficiency should include the effect of contractor personnel on the overall drilling operation. To account for rig crew influence, the time required to perform the component drilling operations directly controlled by the rig and crew is used as a basis for evaluating overall rig performance. Rig efficiency is then a function of both the rig and rig crew's mechanical and operational ability. The theory implies that any rig should be able to equal the optimal or fastest time - if a particular rig is as efficient - both mechanically and operationally.

Drilling a well involves many individual operations influenced by the contractor, the operator, and outside sources. This paper identifies the operations directly controlled by only the rig and rig crew. The time required to perform these operations is defined as "total contractor-controlled time" (TCCT) (see Relationship 1, Appendix A). Appendix B lists the contractor-controlled categories used in this study and defines them as they relate to CCT. Routine operations such as rigging up and down, nippling up and down, cutting drilling line, and lubricating and repairing the rig are controlled directly by the rig's design and condition, and the crew's experience and ability. Drilling, trip, and connection time have also been considered in this study as CCT.

As a basis for comparison, rigs were selected from various drilling areas (Fig. 1), with total depth and geology essentially the same for each well. This equalizes drilling, trip, and connection time between wells. Additionally, these drilling areas were standardized such that the drilling program was the same for each well. Drilling parameters such as hole configuration, bit type, weight on bit, and rotary speed are therefore essentially identical. This normalizes operator and outside influence on the drilling, trip, and connection time. Following these basic assumptions, drilling, trip, and connection time becomes a function of the rig and rig crew's ability to carry out the drilling program.

It is important to note that any CCT associated with trouble or nonroutine drilling operations is not included in the TCCT relationship. It is recognized that TCCT is not limited to the categories listed in Appendix B. However, for the sake of uniformity and to provide a fair comparison, nonroutine operations have been ignored in our analysis.