In 2010, natural-gas production rates in the USA for March and April were the highest since 1974 (US Energy Information 2010). This is largely related to recent success in exploiting unconventional reservoirs and successful development and implementation of innovative technologies. In Europe, unconventional reservoirs (in particular shale gas) are receiving considerable attention. Basins with potential shale-gas plays exist, as does the infrastructure to transport gas to the end user. In addition, the gas-price scenario is favorable as well. It will be critical to find US analogs and transfer technologies/processes that will facilitate European shale-play developments into economically successful projects. However, the market and challenges in Europe are significantly different from those in the US. The population density is much higher and environmental regulations will play a different role. In addition, the entire industry is set up different with a lot less drilling rigs and other service providers. For different reasons, costs are somewhat higher than in the US as well. This demands optimization from Day 1. Directional drilling of horizontal wells needs to progress toward sweet spots, and the completion and fracturing process must be optimized starting at the first well. Therefore, it is important to understand the technologies that were game changers in the US, identify their applicability in Europe, and implement them properly. This paper discusses two recently developed hydraulic-fracturing processes and a hybrid unit that might have considerable impact on advancing economic recovery of unconventional reservoirs. The first new process is designed for high-pumping-rate, multistage fracturing treatments with low proppant concentration. Highly concentrated proppant slurries are pumped down the coiled tubing (CT), jointed tubing (JT), or combination string, and nonabrasive, clean fluid is pumped down the annulus. In such pumping scenarios, the permanent well tubulars are saved from erosion. The pumping rate can be manipulated in real time to customize the placement and downhole-proppant concentration instantly. In case of premature screenout, a well could be easily reverse circulated and cleaned for the next stage. The combination of downhole mixing and microseismic fracture mapping provides unprecedented control of fracture execution to facilitate branch fracturing. The second new process is a combination of mechanically activated sleeve completions and fracturing of individual intervals, but with a change in the sequence in which the intervals are stimulated. This new method is proposed with a goal of altering the stress in the rock to facilitate (or enhance) branch fracturing and connect to induced stress-relief fractures in a single, horizontal well.
As oil and gas reserves are declining, operators all over the world are now being forced to go to land areas with extreme conditions and deeper into the sea to find more reserves. The reservoirs are getting more complex and well designs are becoming more complicated and costly. The complex reservoirs and extreme conditions require several individual zones to be completed and fractured individually to access maximum reservoir and get the biggest return for the money. Oftentimes, each zone requires a specifically designed fracturing treatment to effectively treat it. A lot of money and time are lost each year when operators try to treat these multizones using conventional techniques. The optimum production rates are not achieved and the reservoir-recovery factor is low, leaving most of the oil and gas unrecovered. Because of the recent drop in oil and gas prices, cost, time, and production are the driving factors causing operators to look for alternate completion and fracturing methods to reduce cost and time without compromising production. Numerous techniques and hit-and-trial methods have been tried throughout the past decade to overcome this problem. Multistage fracturing has offered one of the best solutions to everyone in this tough economic environment. Throughout the past few years, there has been a growing acceptance among both operators and service companies that hydra jet (abrasive jetting) perforating can improve overall well economics for fracture-stimulated wells in many reservoirs. More and more customers all over the world are now using multistage fracturing to access the complex reservoirs and treat wells with complex completions. In a few cases, pinpoint stimulation has proven to be the only way that effective stimulation could be achieved. The pinpoint-stimulation portfolio has evolved throughout the past decade to offer several options to different well conditions and types. This paper presents a detailed review of many pinpoint-stimulation technologies that have been successfully used for treating multizones in complex reservoirs and extreme well conditions in the last decade, either in new wells or in mature fields, to improve the production and reservoir recovery factor. It provides insight to strategies of how these different technologies were applied to different well conditions. Case histories are provided to support the obtained benefits and advantages, and lessons learned are discussed along with recommendations and what to avoid in field operations. Future directions of pinpoint stimulation are also discussed. Multistage fracturing can be performed in different ways, depending on the well design and completions. More and more customers are now designing the well and selecting completions based on the multistage fracturing technique that best accesses the reservoir efficiently. The following multistage fracturing techniques are discussed in this paper: CT applications.Jointed-pipe applications.Sleeve applications.Perf-and-plug applications. Globally, pinpoint-stimulation treatments have been performed on more than 6,000 wells in 18 countries. Multistage fracturing is gaining popularity in the oilfield industry with each successful treatment that is put into the ground. With the use of CT, the task of placing many cuts at multiple places is straightforward and not time consuming. For many wells needing multistage fracture stimulations, significant reductions in nonproductive time (NPT) help reduce well costs, even when more actual fracture stages are pumped. The use of more stages has often provided significant production gains and greater recoverable reserves. In this paper, different techniques for a wide variety of applications and a review of successful evolution of multistage fracturing in the last decade are presented.
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. Introduction 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.
The successful development and exploitation of unconventional reservoirs has relied on innovative technologies, such as horizontal drilling, multistage completions, modern multistage fracturing, and fracture mapping to pursue economic completions. It is important to highlight that economic production in these ultralow matrix-permeability reservoirs relies on conductivity that must be generated through hydraulic fractures and fracture-network systems. Simulations demonstrate that shale reservoirs with ultralow permeability require an interconnected fracture network of moderate conductivity (branch fractures) with relatively small spacing between fractures to obtain economic production rates and reasonable recovery factors. This paper discusses two recently developed hydraulic fracturing processes to improve economic recovery in unconventional reservoirs.The first new process is designed for multistage-fracturing treatments with high pumping rates and low proppant concentration. This method uses the efficiencies of tubing-deployed abrasive perforating. Proppant slurries are then pumped down the coiled tubing (CT) and nonabrasive clean fluid is pumped down the annulus, saving the permanent tubulars from erosion. As a result, the rate down the annulus can be much higher. The pumping rate can be instantly manipulated to customize the placement and concentration of proppant being pumped down the CT. In case of premature screenout, a well could be easily reverse-circulated and cleaned for the next stage. Wellbore proppant plugs eliminate the need for overflushing, and the new approach to fracture stimulation, known as branch fracturing, could be achieved by changing proppant concentration in real time.The second new process uses a combination of mechanically activated sleeve completions and fracturing of individual intervals with a change in the sequence in which the intervals are stimulated. This new method is proposed with the goal of altering the stress in the rock to facilitate branch fracturing and to connect to induced stress-relief fractures in a single, horizontal well.
As oil and gas reserves are declining, operators all over the world are now being forced to go to land areas with extreme conditions and deeper into the sea to find more reserves. The reservoirs are getting more complex and well designs are becoming more complicated and costly. The complex reservoirs and extreme conditions require several individual zones to be completed and fractured individually to access maximum reservoir and get the biggest return for the money. Oftentimes, each zone requires a specifically designed fracturing treatment to effectively treat it. A lot of money and time are lost each year when operators try to treat these multizones using conventional techniques. The optimum production rates are not achieved and the reservoir-recovery factor is low, leaving most of the oil and gas unrecovered.Because of the recent drop in oil and gas prices, cost, time, and production are the driving factors causing operators to look for alternate completion and fracturing methods to reduce cost and time without compromising production. Numerous techniques and hit-and-trial methods have been tried throughout the past decade to overcome this problem. Multistage fracturing has offered one of the best solutions to everyone in this tough economic environment. Throughout the past few years, there has been a growing acceptance among both operators and service companies that hydra jet (abrasive jetting) perforating can improve overall well economics for fracture-stimulated wells in many reservoirs. More and more customers all over the world are now using multistage fracturing to access the complex reservoirs and treat wells with complex completions. In a few cases, pinpoint stimulation has proven to be the only way that effective stimulation could be achieved. The pinpoint-stimulation portfolio has evolved throughout the past decade to offer several options to different well conditions and types. This paper presents a detailed review of many pinpoint-stimulation technologies that have been successfully used for treating multizones in complex reservoirs and extreme well conditions in the last decade, either in new wells or in mature fields, to improve the production and reservoir recovery factor. It provides insight to strategies of how these different technologies were applied to different well conditions. Case histories are provided to support the obtained benefits and advantages, and lessons learned are discussed along with recommendations and what to avoid in field operations. Future directions of pinpoint stimulation are also discussed.Multistage fracturing can be performed in different ways, depending on the well design and completions. More and more customers are now designing the well and selecting completions based on the multistage fracturing technique that best accesses the reservoir efficiently. The following multistage fracturing techniques are discussed in this paper:• CT applications.• Jointed-pipe applications.• Sleeve applications.• Perf-and-plug applications. Globally, pinpoint-stimulation treatments ...
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