Well ‘A’ is a horizontal well drilled in the primary and productive upper layer of the carbonate reservoir just below 7,750 ft TVD, with lateral length of 3,495 ft. This layer, due to inherent well placement, presented completion and production challenges attributed to low permeability and with limited scope for production enhancement. The asset team required an effective solution to drain reserves from this well and for evaluating future well placements.
Near-wellbore (NWB) acid stimulation technique was preferred over conventional acid fracturing due to low vertical stress contrast and high tortuosity effects caused by lateral azimuth relative to maximum stress orientation. Based on the Bernoulli concept for fluid diversion and using a dual path pumping system, initiation and propagation of micro-fractures was achieved by pumping fluid through tubing and annulus with a controlled pump schedule. A specially designed high-pressure tool was used for creating formation cavity by pumping acid through tubing. Increasing pressure on the bottom of cavity initiates micro-fracture causing annular fluid to be pulled into the fracture and subsequently extending it.
The NWB stimulation was designed and carried out in 50 stages along the lateral. This was followed by 29-stage matrix acid stimulation using 20% HCl and with pulsonix tool for acid placement. Initial well productivity (PI) was estimated at 0.16 STB/D/psi. Post stimulation treatment resulted in a nine-fold PI improvement. Production post stimulation was 720 barrels oil per day (bopd) with 7% water cut (w.c).
The NWB stimulation enabled significant productivity increment with accelerated production. It is customizable enabling design and placement of multiple micro-fractures. Additional hardware for wellbore isolation during treatment is not required. It is economical in comparison to conventional fracturing treatment and could be extended for cased or liner completions in vertical or deviated wells.