Extreme Multistage Fracturing Improves Vertical Coverage and Well Performance in the Lost Hills Field

Abstract

In an attempt to improve production response, fracturing designs in the Lost Hills field went from a standard 3 to 6 stage design to an extreme 15 to 18 stage design to stimulate approximately 1000' 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 multi-stage 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 further refined as performance and statistical analysis of previous design changes is 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 with over 1 billion barrels of remaining oil in place, even though they were discovered and initially developed in the early 1900's. Thermal 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 1980's, improvements in hydraulic fracturing design and implementation yielded results which justified an aggressive diatomite primary development well program on 2-½ acre producer spacing1. Waterflooding began in the early 1990's to reduce well failures due to subsidence and improve recovery. The 2–1/2 acre development program was completed in 1997, drilling about 60 wells per year. Beginning in 1998, infilling began to reduce production well spacing to 1–1/4 acre 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 due to the encouraging initial results. In 2003, a large waterflood expansion began northward at an accelerated pace with over 100 wells being drilled each year until 2005 when over 200 wells were drilled to complete the north waterflood expansion at 1–1/4 acre producer spacing. As with any finite natural resource, the Lost Hills field's reservoir quality varies. With development area expansion into the north section of the field, and the smaller waterflood infill drilling spacing, wells should have poorer economic results due to interference between wells and reduced reservoir quality. In order to compete for capital, hydraulic fracturing design optimization had to improve production response and/or reduce costs. To accomplish this, statistical (lean sigma) analysis was performed on all previous fracture design changes from 1998 through 2002. The design changes that yielded the best performance and/or reduced costs were incorporated into a 2003 standard fracture design.

An Evaluation of Coiled Tubing Fracturing Compared to Traditional Completion Techniques in Horizontal Wells

“…The hydraulic fracturing treatment fluid slurry is then pumped through the annulus, while a low rate of clean fluid is maintained though the CT. This leaves the tubing with a near-static column of fluid (i.e., dead string), which can be used to accurately estimate bottomhole treating pressure (Hejl et al 2006;Malhotra et al 2015). The difference in treatment fluid flow path from the HJAF method enables the HPAF method to be deployed with CT rather than jointed pipe.…”

Research on the effect of gas nitriding treatment on the wear resistance of ball seat used in multistage fracturing

“…The ball seat is used to activate the sliding sleeve for multistage fracturing of horizontal wells. The performance of ball seat severely restricts the fracturing effect and stages [6]. Generally, ball seat need to be removed by milling for installing oil pipe when fracturing process is completed [7].…”