Abstract
This paper describes laboratory and field experiments that were conducted to
compare hydraulic and propellant fracturing techniques in the Mancos Shale of
Colorado. The Mancos is a Cretaceous shale approximately 2,000 feet
thick(1). Although mainly considered a source rock for other
formations, the Mancos is also productive in certain areas. To better
understand how stimulation technologies might be used to commercially develop
the shale, four unique data sets were compared including results from both
laboratory and field hydraulic and propellant fracturing.
The results of this work are presented and include the following conclusions:
the propellant fractures in the block test were constrained by relative
strengths of the strata; the layering of the Mancos shale resulted in better
height containment than expected in field test stimulations, although the
mechanism of containment in the field tests is still not fully understood; and
both propellant and hydraulic fracturing can provide stimulation benefits, but
only when applied in appropriate situations.
Introduction
The majority of all oil and gas wells drilled in North America are completed
with some form of stimulation. Stimulations are used to bypass drilling-induced
damage and increase effective wellbore radii, thus, increasing well
productivity. Stimulation types include hydraulic fracturing, acid fracturing,
matrix acidizing and propellant fracturing. The majority of stimulations
performed worldwide are hydraulic fracture stimulations. Hydraulic stimulations
were first experimented with in the 1940s and the technologies, such as fluid
chemistries and proppant design, have been significantly
improved(2). However, hydraulic stimulations are not necessarily
optimal in all situations; they require the introduction of foreign fluids into
the reservoir which can often cause adverse chemical reactions. Additionally,
there is a substantial added cost to hydraulically stimulating wells, which has
significantly increased in the past few years. Propellant fracturing, a
relatively new technology, is an alternative to hydraulic fracturing. It can be
fairly inexpensive and does not involve pumping fluids into the reservoir. The
process uses a combined solid fuel and oxidizer to create the rapid expansion
of gas to rapidly generate pressure and drive fractures out into the rock.
Unlike explosives, which were used as one of the earliest forms of stimulation,
propellant fracturing causes little plastic deformation of the near wellbore
region, which can be adverse to flow(3). A significant disadvantage
to propellant fracturing is that it does not carry proppant into the fracture.
Instead, propellant fracturing relies upon shear slippage or spalling to
prevent the fracture from fully closing back on itself, leaving a conductive
path back to the wellbore.
Little research has been published on propellant stimulations due to their
somewhat limited applications. This paper describes a unique research project
in which propellant and hydraulic stimulations were tested in the same
reservoir in both laboratory and field tests. The research was conducted at the
Colorado School of Mines, Golden, Colorado, between 2005 and 2007. Laboratory
experiments were conducted on campus as well as at the TerraTek laboratory
facilities in Salt Lake City, Utah, and learnings were applied to field tests
in western Colorado.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
26 March 2008
- Meeting paper published:
17 June 2008
- Revised manuscript received:
5 March 2009
- Manuscript approved:
6 April 2009
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