Deepwater Subsea Completion Benefits From Horizontal Fracture Stimulation
Authors: JPT staff _ 
Published: February 2015

In late 2004, for the first time in history, a deepwater, subsea well was fracture stimulated using hydrajet-based fracturing with no downhole isolation. The well is located in 1,000 ft of water in the Campos Basin, southeast of Brazil. As the stimulated well had two branches abandoned due to drilling problems it behaved like a triple-lateral in terms of stimulation design. The 2.5-day treatment for Petrobras, closely monitored in real time from Duncan, Oklahoma, and Macaé and Rio, Brazil, resulted in five acid fractures created using the ZCA acid system.

Production rate for the first 15 production days following the treatment with Halliburton’s SurgiFrac service approximately doubled the maximum historical rate of this well and was approximately four times the monthly production rate.

As with vertical wells, in horizontal completions underachieving wells are common. This can be caused by many things, such as unexpectedly low permeabilities in the area; however, in horizontal wells, underperformance often is attributable to one or more of the following:

- Permeability anisotropy (especially vertical-permeability limitations).

- Skin damage or near-wellbore plugging of a natural-fracture network.

- Ineffective stimulation techniques.

The third item is especially the case in openhole horizontal wells and even more so in wells that are completed with slotted or preperforated liners. Perforated liners could be deemed the worst-case scenario when attempting to place multiple hydraulic fractures in the horizontal section.

Controlling Fracture Placement

This technology is the first method to resolve the problem of openhole fracture-placement control using dynamic diversion and consists of a combination of three processes—through-tubing hydrajetting, through-tubing hydraulic fracturing, and coinjection down the annulus with separate pumping equipment. An important aspect of this technique is dynamic sealing capability (Fig. 1). Unlike other techniques that require hardware-type packers or plugs or even chemical plugs, this process creates a seal using fluid movement. Packers are generally not used; therefore, the existence of passageways behind liner or through fractures rarely affects performance.

The technique is based primarily on the Bernoulli principle, which states that the energy level of a fluid is generally maintained constant. To accomplish the SurgiFrac process, a jetting tool is placed near the toe of the well and is then used to jet perforate the casing and the formation rock, forming a 4- to 6-in.-deep cavity. Based upon the Bernoulli equation, as pressurized fluid exits the jet-ting tool, the pressure energy is transformed into kinetic energy or velocity. Since the fluid velocity around the jet stream is the highest, pressure in this area is the lowest (the fluid does not tend to “leak” out). Conversely, fluid from the other areas of the well will flow into the jetted area. The fluid contains some abrasives to help the fluid penetrate the steel liner and the formation rock. As cavities are formed by each jet, high-velocity fluid impacts the bottom of the cavity (i.e., velocity becomes zero—an energy change from kinetic back to potential energy, or pressure), causing pressure inside the rock to become high enough to create a fracture. Annulus pressure is then increased to assist in fracture extension. After the fracture is completed, the tool is moved to the next fracturing position and another fracture is placed.