Summary
A process has been developed to evaluate drilling fluid cost performance for
a wide range of planning, intervention, and quality improvement activities.
Meant to be universally applicable, the innovative process permits comparisons
between similar and dissimilar wells drilled in the same or different global
regions. It also can be used to contrast drilling fluid cost performance with
operator-driven quality indicators to classify wells for front-end loading
requirements for planning and to monitor actual-versus-planned performance
during drilling.
Methods normally used for drilling performance are not well-suited for
benchmarking drilling-fluid performance. The approach introduced in this paper
is based on a simple ratio that compares mud cost of a well to a corresponding
technical limit. The technical-limit relationship, which uses a profile index
to characterize well complexity, was derived empirically from a large internal
database representing a wide assortment of well types, drilling conditions, and
locations.
This paper describes the development and implementation of this process.
Several case studies are presented to demonstrate specific applications.
Although the process was developed strictly for internal use, full
implementation details are provided to encourage its use by others in the
industry involved with service-quality initiatives.
Introduction
Drilling is an engineering process fraught with complexity and variability
that make global benchmarking efforts difficult. As such, performance
comparisons mostly have been done on a well-by-well, actual-versus-plan basis.
Recent industry service-quality programs implemented to address trends
involving multiple drilling projects have met with varied success. Most seek to
correlate drilling costs to key performance indicators (KPIs), individual
drilling metrics, and parameters that integrate several KPIs and metrics into a
single index. The Dodson Mechanical Risk Index (MRI), for example, is a de
facto standard that considers well depths, mud weight, number of casing
strings, and various key drilling factors (KDFs) weighted by their projected
impact on drilling difficulty (Dodson 2000; Williams et al. 2001).
Successful benchmarking of drilling fluid costs has been more elusive.
Consider the data scatter shown in Fig. 1, where mud costs are plotted versus
total depth for 12,257 wells drilled between 1998 and 2005. This became a
concern when mud-cost benchmarking was assigned a high priority for an internal
service-quality management initiative. One of the objectives was to develop a
universal process to facilitate comparisons between similar and dissimilar
wells drilled in the same or different global regions under radically different
drilling conditions. For example, the process should be able to compare
drilling fluid cost performance on a 10,000-ft land well to one drilled in
10,000 ft of water.
The data in Fig. 1 were obtained from an internal database of conventional,
deepwater, HTHP, and highly directional wells drilled under a broad range of
downhole conditions by numerous operators in 57 countries. Drilling fluid costs
ranged from less than $5,000 to over $15 million for an average of $232,500
(net present value of money was not considered). Maximum and average depths
were 31,753 ft and 9,628 ft, respectively. The majority of extreme mud costs
occurred in the Gulf of Mexico where massive lost circulation had to be
tolerated in some sub-salt wells. Very high mud costs also were experienced in
West Africa, the North Sea, and CIS.
Attempts to correlate mud costs to the more inclusive MRI were unsuccessful,
primarily because of the indices on which KDFs focused: drilling rather than
fluids, offshore rather than global, and critical rather than generic wells.
Correlations improved when KDFs were replaced with common drilling fluid risks
such as lost circulation, stuck pipe, wellbore instability, torque/drag, hole
cleaning, barite sag, and others. The economic impact of these risks, however,
varied greatly between different regions and well types. Moreover, the required
data were difficult to extract and quantify.
Development of a new complexity index that retained some aspects of the MRI
led to a different approach for benchmarking mud costs. The analytical method
was integrated into a Quality Element Deployment (QED) process to address a
wide range of drilling fluid planning, intervention, and quality improvement
issues. Additionally, it made it possible to contrast drilling fluid cost
performance with operator-driven quality indicators, to monitor
actual-versus-planned performance during drilling operations, and to classify
wells for front-end loading (planning) requirements.
This paper focuses on the development and implementation of the QED process.
Case studies involving different drilling environments are presented to
illustrate useful applications. Although the process originally was developed
strictly for internal use, full implementation details are provided in order to
encourage its use by others involved with service-quality initiatives.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
27 June 2006
- Meeting paper published:
24 September 2006
- Revised manuscript received:
9 November 2007
- Manuscript approved:
14 January 2008
- Version of record:
20 June 2008
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