Generally, perforating equipment is separated from fracturing and stimulating tools. The perforating gun is deployed either on tubing or wireline into the well and fired on designated depth. After the perforating gun is retrieved out of the wellbore, the fracturing string is run into the well and frac pump including frac blender/other equipment are prepared on the frac site. Fracturing operation is then announced to increase the permeability and drainage radius of the well. The stimulating procedures usually is an alternative to replace expensive fracturing operations.
Some oil and gas wells need better passage to stimulate the reservoirs. A hydraulic fracturing without injecting any proppant into the reservoir is run and is followed by stimulating procedures. The stimulating chemical can reach a bigger volume of the reservoir pores through hydrofracture.
The main purpose of fracturing is to apply a pressure that exceeding the stress strength of the formation. Either liquid or gas can be used as a transmitter medium. Liquid as a fracturing fluid is well known in the industry. The pressure from the fracking pump is controlled on the surface. The operation uses high pressure line and frac pump to anticipate high fracturing pressure and pressure losses. The fracturing length is measured based on the volume of injected fracturing liquid. The length can be more than 50 ft.
The idea comes up to combine the tools for perforating, fracturing, and stimulating in 1 downhole tool and do the job simultaneously. The perforation is done as usual by using shaped charges. For fracturing, gas is used instead of liquid since high-pressure gas can be generated by oxidizing a propellant. The stimulating fluid can be introduced concurrently with or after fracturing. The tool can be run on wireline, slickline, tubing, or coiled tubing. This method eliminates high-pressure equipment on the surface. It also increases perforation diameter and depth which will enhance well productivity.
Figure 1 shows a downhole tool on depth which is the combination of perforation gun (for perforating), propellant section (for fracturing), and carrier (for carrying stimulation fluid). Two packers are used to isolate other parts of the casing from the pressurized fluid. Figure 2 shows the perforating step and Figure 3 shows fracturing and stimulating processes.
Recommended reading and an example of coiled tubing for automotive: