Success of Rigless Multistage Selective Stimulation in Supergiant Tight Reservoirs
Authors: Carpenter Chris 
Published: September 2016

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 171821, “Success of Rigless Multistage Selective Stimulation in Supergiant Tight Reservoirs: Case History From UAE,” by M.A. Fahim, Ali Abdullah, Dalia Abdallah, A. ElBarbary, and H.B. Daghmouni, ADCO, and S.A. Waheed and M. Tawakol, Halliburton, prepared for the 2014 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 10–13 November. The paper has not been peer reviewed.

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), 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.

Naturally, this process works even better with acid as the primary stimulation fluid in a high-solubility carbonate formation. This process provides the ability to perform real-time in- situ mixing—“ real time” meaning that changes downhole can be controlled by surface changes and will occur within seconds downhole.

The HJF technique involves the placement of many fractures in the formation rock. The near-wellbore (NWB) HJF extends the acid wash, also creating many microfractures, minifractures, or even larger fractures, while still performing an acid wash in between them. The large and small fractures will also be etched such that a much larger surface of the formation is exposed, for better production.

A unique tool was therefore designed and built for this purpose. This self-positioning tool was designed to overcome the reaction forces created by the jets. The tool uniquely bends upward into the direction of the jets. The jets are therefore positioned near the target-wellbore wall or the casing regardless of the position of the tool before being pressurized. This will allow HJF to be used in the formation effectively (first perforating the casing, if present). For the HJF processes, this means that Bernoulli effects are maximized because of the small jet distance from the resulting perforated tunnels.