Creating multiple zone stimulations in complex reservoirs presents unique challenges for the completion engineer. Effectively stimulating each individual pay interval using separate fracturing treatments can be costly and time consuming. Historically, efforts to stimulate multiple zones usually consisted of casing fracs with limited entry perforating and using sand plugs to separate zones, or tubing fracs with retrievable bridge plugs and packers. The challenge was to rethink the approach to this technology and develop more cost effective and efficient solutions. Those efforts have resulted in a new approach called pinpoint stimulation.
New pinpoint stimulation methods have resulted in reduced cycle time for operators. This means doing multiple service operations in a single trip to the well. If performed individually, perforating, fracturing, setting isolation plugs, and cleaning out the wellbore for each interval can add days or weeks to a completion, delaying production-to-sales and increasing overall costs. Now, we perforate, fracture stimulate, and clean out with a single trip to the wellsite. Each treatment stage is customized for the intervals treated and many more intervals can be stimulated economically. Pinpoint multistage fracturing is available in 16 different processes for many types of well completions.
In this paper, we present different techniques for a wide variety of applications and provide actual treatment data and results including recent case histories from Russia.
Since the first commercial hydraulic fracturing treatment was performed by Halliburton in Velma, Oklahoma in March 1949, the industry has relied on multistage fracturing to help maximize asset value. Selectively stimulating individual intervals in the wellbore can help to keep operating costs low, reduce time to initiation of production, and improve ultimate recovery.
One of the first experimental fracture treatments on record is reported to have been a four-stage pinpoint stimulation in July 1947 in the Kansas portion of the Hugoton field, which targeted four limestone gas pays at depths ranging from 2,340 ft (713 m) to 2,580 ft (786 m). That stimulation job was conducted in four separate hydraulic fracturing treatments (stages), each of which involved pumping 1,000 gal (3785 L) of napalm (thickened gasoline) through jointed tubing equipped with a cup-type straddle packer, followed by 2,000 gal (7570 L) of gasoline with 1% gel breaker.
Selectively fracturing individual zones with a series of treatments was the only option possible at the time because of the equipment limitations. The available equipment was not capable of pumping the high rates, volumes, and pressures necessary to stimulate large sections of the wellbore. That began to change in the 1950s as the introduction of better casing and tubular products, more powerful pumps, and more capable wellsite equipment combined to enable operators to reach deeper, larger oil-and gas-bearing strata. By the mid-1960s, the primary method used to stimulate gas wells in the Hugoton field was to hydraulically fracture long sections of the wellbore, frequently encompassing several intervals in a single treatment, by pumping large volumes of low-cost, water-base fluids at very high rates. This reflected an industry-wide trend toward large, high-volume fracture treatments targeting several intervals in the wellbore and away from strategies allowing the selective treatment of individual intervals in a well.