Summary
In an attempt to improve production response, fracturing designs in the Lost
Hills field went from a standard three- to six-stage design to an extreme 15-
to 18-stage design to stimulate approximately 1,000 ft of net pay. The previous
standard designs were becoming borderline economic, and if development was to
continue, then either production response had to improve or costs had to be
reduced. Previous emphasis was placed on reducing fracture-treatment costs by
pumping fewer stages and lower proppant volumes, but the cumulative production
response decreased as a result. Previous tests using an increased number of
fracture stages did not improve economics because of the increased fracturing
costs and minimal production increases. When a new coiled-tubing fracturing
technique was implemented to perform multistage jobs at reduced costs and the
stage count per well was increased, production response and economics improved.
This paper will discuss the differences in job execution, analysis of vertical
fracture coverage using surface and downhole tiltmeter data, and cumulative
production response from the different designs tested. Both treatment and stage
design with this fracturing technique are being refined further as the
performance and statistical analysis of previous design changes are
completed.
Field-Development Setting
A large part of California’s oil production occurs in several San Joaquin
Valley giant fields that have heavy oil or low permeability. These fields
remain highly oil saturated (several have more than 1 billion bbl of remaining
oil in place), even though they were discovered and initially developed in the
early 1900s. Thermal enhanced oil recovery (EOR), waterflooding, and/or
hydraulic-fracturing techniques are now applied to these fields.
Lost Hills is one such field; it was discovered in 1910, remains largely
undepleted, and is currently near all-time high production rates because of a
combination of hydraulic fracturing and waterflooding. Beginning in the late
1980s, improvements in hydraulic-fracturing design and implementation yielded
results that justified an aggressive diatomite primary-development-well program
on 2½-acre producer spacing (Wilt and Morea 2004). Waterflooding began in the
early 1990s to reduce well failures caused by subsidence and to improve
recovery. The 2½-acre development program was completed in 1997, drilling
approximately 60 wells per year. Beginning in 1998, infilling began to reduce
production well spacing to 1¼ acres in the waterflooded area, and this program
continued until it was completed in 2004. In 2001, a 5/8-acre infill pilot was
installed, with the pilot being expanded in 2004 because of the encouraging
initial results. In 2003, a large waterflood expansion began northward at an
accelerated pace, with more than 100 wells being drilled each year until 2005,
when more than 200 wells were drilled to complete the north waterflood
expansion at 1¼-acre producer spacing.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
28 June 2006
- Meeting paper published:
24 September 2006
- Revised manuscript received:
2 May 2007
- Manuscript approved:
17 August 2007
- Version of record:
20 December 2007
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