This paper will review some of the types of applications of hydrajet perforating during the past 8+ years, specifically as they apply to horizontal and highly deviated completions for both oil and gas reservoirs. In many cases this has allowed for more effective fracture placement as well as shorter operational times required to achieve effective multi-stage frac treatments. This can reduce operator costs for the completion or the workover operation.
One method is especially useful when the reservoir has no isolation along the lateral section, whether this is from an open hole method of completion or a work-over of a cemented lateral that has been extensively perforated, referred to herein as Hydrajet Assisted Fracturing (HJAF). Previous traditional methods for application of hydraulic fracturing in this type of well are either ineffective, very high risk, or require installation of costly hardware that also reduces effective wellbore ID.
Conversely, if there are no small ID restrictions, the operator can use the HJAF method which combines hydrajet perforating immediately followed by "hydrajet-fracturing" where all the frac slurry for this stage is also pumped down the tubing and out the jet nozzles. This means that numerous nozzles are being used to achieve adequate injection rates for typical fracture stimulation treatments (~6 to >35 bbl/min). The BHA is moved away from the perfs within seconds to minutes after each zone has been fracture stimulated. When each treatment stage is being pumped, the tremendous energy concentrated at the mouth of the fracture intersecting the wellbore creates a dynamic isolation effect to keep the fluid going into (only) this fracture plane (Bernoulli principle). When the tool is moved uphole and the same operations are repeated at a new location, again the fluid dynamics at the tool face can eliminate the need for mechanical isolation. This lowers risk and shortens completion time. For many years, the most significant limitation with the "hydrajet-fracturing" method was a jetting tool life expectancy of only 150K to 300K lbs of proppant. Since early 2008, new jetting tool designs have increased life to where greater than 1,000,000 lbs of proppant have not caused tool failures. Wells using 10-stage fracturing completions have been completed with a single tool in only a few days of continuous operation.
A newer method employs a CT string only for hydrajet perforating where all frac slurry is pumped down the annulus of the casing. We will refer to this as Hydrajet Perf-Annulus Path (HPAP) fracturing method. A wellbore sand plug is set at or above each fraced location to isolate previous fractured locations, often completing many frac stages in the same day. This method was first used for vertical wells, beginning in 2003, and in 2005 it was expanded to horizontal applications. By mid- 2009, it had been used in about 300 horizontal wells with 3 to 9 stage completion plans. There is no need for expensive, hard to install completion jewelry, risky placement of frac plugs, or time-consuming drilling out of plugs afterward.
Not only do hydrajetted perfs offer large, highly effective and non-damaged perfs, but this method is often employed using very closely clustered perforations at each frac location. This combined effect will usually prevent the common problems of both multiple (simultaneous) fractures growing independently and also avoid near-wellbore tortuosity. Both of these problems often occur after conventional shape-charge perforating. This essentially eliminates the risk of abandoning zones and leaving part of a lateral unstimulated. This method makes higher proppant concentrations easier to place and gives longer fracture lengths. Also, with this stimulation method, the CT stays in the wellbore with the jetting tool pulled up above the perfs while slurry is being pumped into the new set of hydrajetted perforations. In many cases, the CT string can clean out all wellbore sand plugs soon after the final frac stage has been completed, which can be especially important for low pressure gas wells.
The numerous benefits from using either the HJAF or the HPAP method may result in both reduced operating costs and provide better fracture placements, the recipe for a higher Return on Investment!
