The Diatomite reservoir at the giant Belridge field, California, has been undergoing water injection for pressure maintenance to mitigate reservoir compaction and improve oil recovery. Accurate placement of injection water across this 1500 feet thick reservoir is essential for balancing voidage and reducing in-situ compaction. However, monitoring injection profile using conventional Radio-Active Tracer (RAT) technology has been a challenge due to the inability to access wellbores for logging because of scale build-ups and casing deformations.
Field tests with Fiber-Optic Distributed Temperature Sensing (DTS) confirmed that the technology had the potential to replace the RAT for continuous monitoring of injection profile. However, moving from a successful pilot to full field implementation faced numerous challenges both technical and economic.
To begin with, the wellbore had to be free of any restrictions for logging, stimulation, or workover activities. This meant that the fiber needed to be deployed outside the casing and cemented in place without creating a micro-annulus. The fiber and its control line also had to be installed in a way that would permit perforation for completion without damaging the fiber. Another installation challenge was to pull the control line and fiber through the wellhead mandrel, and secure the fiber from damage during rig move-out, and installation of the well-head and injection manifold.
After these technical challenges were overcome, the operational challenge was how to make the whole installation procedure simple and fast enough to be integrated into Aera's lean manufacturing style of drilling process that takes less than three days to complete a well from spud to rig release.
After resolving the technical and operational issues, the remaining and bigger challenge was how to make the acquisition and interpretation of this new DTS technology for monitoring of injection profile cheap enough to be incorporated in a "low-cost" environment where a producer makes less than 20 BOPD. With the potential for hundreds of injectors to be surveyed and analyzed each year, the cost breakthrough came when Aera decided to acquire its own profile surveys and develop its own software for processing and interpreting the data.
A five-well permanent installation pilot followed by a 30-well survey acquisition program, and eventual development of data processing/interpretation software were successful in meeting the technical and economic challenges. The injection profiles from over 70 injection strings with DTS fibers are now being routinely surveyed and the interpreted results are being pro-actively used for waterflood surveillance and optimization. A 60-well per year program is currently in progress with plans for continued expansion in future years.
This paper shows how innovative ideas and persistence can overcome technical and economic hurdles that often make new technologies unfeasible for old fields. The learnings from this project have potential application in converting low-cost brown fields to the digital oil fields of the future.