A review of the stimulation methods used in the Hanifa formation (primarily a combination of diesel-emulsified acid/visco-elastic diverting systems) performed during the first two quarters of 2005 revealed that while initial post-stimulation vertical or deviated well-performance was typically improved, it was also short-lived (Surjaatmadja et al. 2001; Surjaatmadja et al. 2001; Surjaatmadja et al. 2002). All the wells exhibited a gradual loss in productivity after the stimulation treatments. Furthermore, in horizontal wells, the problem was aggravated because there was not enough control of acid placement over long openhole carbonate intervals where permeability or damage contrast existed; requiring a deeper matrix stimulation.
Exploring improved methods for stimulation, a multidisciplinary team composed of Saudi Aramco and service-company representatives were brought together to review various stimulation methods. After looking at conventional hydraulic-fracturing as a method of deeper-formation stimulation than matrix acidizing, it was concluded that over the long open-wellbore intervals, there would not be sufficient control of fracture placement, fracture growth and propagation, and interaction with the natural fracturing present in the Hanifa. Additionally, the typical Hanifa completion strings have completion size restrictions which limit the options for rigless stimulations.
After the review of several options, including coiled tubing (CT) proppant fracs, and stimulation using multiple and discrete mechanical-isolation devices like plugs or packers, the team selected the packerless selective acid fracture (PLSAF) stimulation using CT as the stimulation method most desirable for the limitations intrinsic to the Hanifa formation for the following reasons:
PLSAF with CT offers control of fracture placement in an openhole environment.
PLSAF can achieve multiple treatments without mechanical isolation.
PLSAF can provide moderately deep, controlled fractures with reduced risk to connect the generated fracture with the water sources.
PLSAF was applied successfully in one well during the third quarter of 2005, where ten selective acid fractures were placed along the openhole section. This paper presents the long-term evaluation and benefits of the first regional application of the PLSAF in Saudi Arabia.