A tight gas carbonate reservoir with no oil rim in a supergiant onshore gas field in Abu Dhabi was targeted for stimulation during a field review to increase field production. It became necessary to look at selective fracturing-stimulation techniques that could be applied riglessly and allow contribution from the nonproducing zones. This paper describes a unique engineering approach, the hydrajet-fracturing (HJF) technique, successfully executed for this purpose.

HJF Technique

When HJF tools are used to perforate and fracture wells (Fig. 1 above), a jet nozzle accelerates fluid to a very high speed (greater than 600 ft/sec). With the assistance of abrasives in the fluid, the jet erodes a perforation within the rock. As the perforation achieves sufficient depth, stagnated fluid flow creates a much higher pressure at the tip of the perforation. With a sufficient perforation surface area, a fracture will be initiated from the tip. It is therefore important to note that this is the only method that initiates the fracture from the perforation tip.

As the fracture extends from the perforation tip, it is possible that the total flow rate achieved by the jets will not be sufficiently high to extend the fracture significantly. In this situation, the HJF process allows subsidizing the stimulation flow from the annulus, which is pumped from the surface at a rate required to increase the fracture size significantly. In general, this annulus fluid is a clean fluid that is compatible with the fluid from the tubing, and is mixed downhole in the process.