Injector needs stimulation, but fluid leaks into natural fractures
In the Korchagina field in the Caspian Sea, Lukoil-NVN operates
extended-reach oil producer and water injection wells. Over time, injectivity
fell in one of the disposal wells. Without another option for disposal, the
operator had to shut in oil production from two nearby wells.
The water wells are drilled and completed in two zones—a naturally
fractured carbonate reservoir and a sandstone formation—which created
stimulation challenges. The operator injected a citric acid-based fluid to
stimulate the well, but the fluid leaked off into the natural fractures,
leaving 1,000 m untreated. Another option was needed to distribute the
stimulation fluid uniformly along the wellbore.
Fluid and particle diversion improves stimulation uniformity
Schlumberger designed an OpenPath Sequence service comprising a diverted
matrix acid treatment to stimulate the carbonate formation and a filtercake
cleanup treatment for the sandstone formation.
For the carbonate formation, the design used VDA acid with 15% HCl. It
develops viscosity as it spends in the formation, which is adequate to divert
treatments with small permeability variations. To improve diversion in the
naturally fractured area, the fluid was blended with degradable fibers and
multimode particles that create temporary mechanical blocks in thief zones. The
combination effectively forces stimulation fluids to flow into
lower-permeability rock. Hydrocarbons or solvents break the fluid, and the
particles dissolve with time.
For the sandstone formation, which was treated in a separate operation,
MSR remover was used to dissolve the hydrocarbon filtercake and damaging
Treatment improves injectivity, and oil production resumes
After the full carbonate zone was treated, the injectivity index was
88.6 m3/d/atm—an 823% improvement over the zone’s prejob
injectivity index of 9.6 m3/d/atm. After treatment of the sandstone
zone, the zone’s injectivity increased 32% from 37.2 to 49
m3/d/atm. As a result, Lukoil-NVN restarted production from the two
nearby oil wells.
For more details about the well and operation, see SPE-189027.