Abrasive fluids have been applied in mechanical cutting and perforating systems for years, the result is a precise cut in any size tubular. In abrasive perforating, the entry hole created reveals no tubular deformation or presence of flow obstructing debris. Consequently, the sand-laden fluid moves past cement, damaged zone or filter cake and into virgin formation. At that instant, velocity generated through the nozzles propagates abrasive fluid into multiple reservoir layers creating numerous pathways. Optimizing the direction of perforations allows for cost effective stimulation through conventional fracturing techniques. Therefore, as an alternative to conventional perforating, oriented abrasive perforating is applied specifically for creating channels to natural fractures.
This paper discusses the development of abrasive perforating coupled with orienting technology for penetrating tubing, casing, drill collars, and drill pipe, all of which is deployed using coiled tubing or jointed pipe in re-completions. In addition to conventional coiled tubing tools, this system utilizes an engineered weight bar connected to a high velocity perforating sub.
This paper begins with the development of this technology and existing perforating methods, then a description of tests conducted with the abrasive perforator and subsequent results. Benefits and applications with applied case histories are also discussed including multiple stage plug setting and perforating as well as pipe recovery, followed by conclusions and recommendations.
Development of Technology
Based on evolving requirements from Oil and Gas Operators, the need to develop a more economical perforating system arose. As wells with larger horizontal sections are completed, the inability to reach zones of interest further substantiates the use of coiled tubing and related tools. This technology was developed from using abrasive fluids to cut tubulars with a motor and high velocity cutting head 1.
Currently, wells are perforated using explosive means such as Tubing Conveyed Perforating (TCP) and Electric line. Although these systems are industry standard, challenges and limitations such as extensive rig-ups, the presence of debris post firing and restricted ability in extended horizontal sections do exist. While both systems have been around for years, their inability to completely orientate perforations is inherent.
To maintain simplicity, this system utilizes conventional thru tubing equipment allowing for jet orientation using an engineered weight bar placed below a free rotating swivel joint as illustrated in Figure 1. The engineered weight bar is eccentric based, allowing for weight transfer to the low side of the tubular as shown in Figure 2. This method of application was referenced from a registered patent, describing single trip wellbore isolation and oriented perforating 2.
Based on pump rate and pressure, orifice selection is crucial to maximize jetting velocity. Hydraulic calculations determining pressure drop and velocity at the exit point allows for precision cutting. For example with one 0.125inch orifice, maintaining a pump rate of 0.5bbl/min at 2500psi produces an exit velocity of 540ft/sec.
The sand slurry is not fully abrasive until it enters the orifice gaining momentum at which point the stage of abrasion commences. The 100mesh particles recommended exhibit less momentum in non-divergent fluid streams and consequently less damage to the inside of the coiled tubing. In a jet stream, smaller particles retain impact/kinetic energy through reduced mutual interference 3.
