Summary
When the first frac pack was performed in the Gulf of Mexico (GOM) over a
decade ago, very little was known about the effects this form of sand control
would have on the intended formation. Even less was known about how to optimize
the treatment to obtain the most benefit for the formation. Since that time,
the sand control community has learned a great deal about the effects and
benefits of frac-packing various unconsolidated formations throughout the
world. However, most of the knowledge and design criteria have remained housed
within the minds of individuals and cannot be looked at as a whole to find
trends and fine-tune the design methods currently being used. Another
complicating factor is the number of frac models of varying degrees of
complexity being used within the industry. Therefore, even though thousands of
frac packs have been performed globally, frac-pack redesign methods are still
subjective and differ from individual to individual and from model to
model.
The recent creation of a database that houses selected formation evaluation
test (FET) and frac data along with model-specific parameters allows full-scale
analysis of a large number of jobs pumped in the Gulf of Mexico (GOM). With a
consistent analysis procedure in place, the database, populated with numerous
treatments by engineers working throughout the GOM, can be analyzed
objectively. The data contained in this database include rock mechanics, net
pressures, pumping trend data, tip screenout (TSO) times, and other
variables.
This paper explains the methodology and discusses the results of the
database analysis, using case studies to determine the best method for analysis
of the jobs. Crossplots show the correlation between TSO prediction and actual
events and suggest recommendations for more successful design work in the
future. This paper is meant to give up-to-date guidelines for designing better
frac packs.
Introduction
Within the sand control community, the ability of an engineer to redesign a
frac pack from data generated during the minifrac can sometimes be considered
more art than science. Often the engineer whose job it is to formulate the
frac-pack treatment will use several different methods to arrive at a solution
deemed most correct. Many hours are often dedicated to determining the proper
design for a frac-pack treatment. While often the results cannot be argued
with, it is unwise and possibly a waste of time to reinvent the wheel for every
job. Rather, it should be the goal of the sand control and frac-pack
communities to develop a design method that can determine the most important
parameters necessary to complete the job. This method would be easily
repeatable and could be used throughout the GOM and possibly in other
high-permeability, unconsolidated regions of the world.
The purpose of this paper is to solve the problem previously described. The
goal of the project was to predict TSO events accurately so that the fracture
geometry could be better understood. In fracture theory, the TSO (Ellis 1998)
is the point at which there is no longer any propagation of the fracture
length. Most fracture models treat this as the time at which the first grain of
sand is exposed to the tip of the fracture, impeding any further growth and
allowing net pressure to accumulate and build width throughout the length of
the fracture.
The creation of a reliable standard method for predicting the onset of a TSO
event would enable engineers involved in designing frac-pack operations to
become more uniform in their procedures and provide more accurate results.
Knowing which “knobs” within the fracture model should be manipulated in order
to obtain the most accurate results would be invaluable. This would allow for
much quicker analysis of the data accumulated from the minifrac, thereby saving
expensive rig time. In addition, should multiple engineers be analyzing the
data, a single reliable method would allow a much clearer resolution of any
issues that arise, because everyone should see very similar results. Many
efforts have been made to accomplish this (Dusterhoft et al. 1995). This paper
presents a methodology for developing a database system to track frac-pack
treatment data, identifying the data deemed necessary to build a reliable
model, and procuring that information from various fracture treatments. Case
studies are then presented which prove that the model, populated according to
the recommended procedure, accurately predicts the TSO event in various
situations.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
24 October 2005
- Revised manuscript received:
21 August 2006
- Manuscript approved:
25 August 2006
- Version of record:
20 May 2007
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