As longer laterals are drilled in the Utica to maximize acreage cover, the stimulation treatments must still establish high pumping rates to effectively treat multiple clusters even within the stages out near the toe area of the lateral. Overcoming this additional pipe friction as well as using various water sources of varying salinity (up to and including 300,000 ppm) with only one friction reducer (FR) polymer product is now possible. An additional benefit of this new salt-tolerant polymer (STP) as the FR additive is its ability to self-degrade with time and temperature to provide significant viscosity reduction for improving well cleanup after the treatment. This paper discusses use of this new STP to successfully place 131 stages in the Utica on a three-well pad in Ohio using various percentages of brine water with the freshwater supply. This is contrasted with traditional FR and guar used in 61 stages on the same pad and 39 stages on an offset pad. The ability to continue operations in the subfreezing temperatures of winter, coupled with the ability to reuse produced water, provides additional benefits to field operations. The use of a single component STP as the friction reduction provider also reduces inventory stock and simplifies on-location quality assurance of material usage. Analytical production simulation confirms improvement in productivity index (PI) and estimated ultimate recovery (EUR) forecast.
Shale reservoirs have low permeability, high fluid efficiency, and low fluid leak-off making these types of reservoirs ideal for hydraulic fracturing. One of the biggest challenges in analyzing unconventional shale reservoirs is that their flow regimes stay in transient flow for a very long period of time. This aspect of unconventional shale reservoirs makes it very challenging to estimate recoverable resources along with reservoir properties such as fracture half length, permeability, drainage area, and fracture conductivity. Conventional decline curve analysis assumes constant flowing bottom-hole pressure, drainage area, permeability, skin, and existence of boundary dominated flow. Most of these assumptions are no longer valid in unconventional reservoirs. Therefore, it is crucial that not only rate, but also pressure and other reservoir parameters are taken into account to properly evaluate unconventional wells and determine the true flow capacity of their reservoir in linear transient flow. This study uses rate transient analysis (RTA) which plots pseudo normalized pressure versus material balance square root of time to estimate the productivity of Marcellus Shale wells. Our dataset is limited to a restricted area located in Greene and Washington Counties, Pennsylvania, with similar reservoir properties such as porosity, water saturation, pressure, and temperature. With limited variation in reservoir properties, the slope of the superposition plot used to calculate AK becomes a good metric for well productivity. The y-intercept from the same plot indicates the completions effectiveness of the well. The slope of the line for a well with zero completions damage intersects the origin. Any completions damage (skin damage) caused by poor completions designs or unfavorable reservoir properties will have a higher y-intercept in relation to the origin in the superposition plot. After performing this analysis on operated wells in the study area located in Washington and Greene Counties, the wells with the most successful completions methods were identified. This knowledge can then be applied for future wells in the same area for optimum production enhancements.
Development of unconventional resource plays traditionally were completed using the "plug and perforate" the method (plug-n-perf). In recent years, however, multi-stage fracturing sleeves have seen growing industry acceptance as an alternative completion method to plug-n-perf and is now being employed with increasing frequency with both cement and openhole isolation methods in unconventional resource plays. This type of system is operated by dropping a ball from the surface that seats in a landing baffle to actuate the sleeve and allow for fracturing of the formation. These balls and baffles often can be removed from the ID of the casing string by milling, post frac to remove possible restrictions. However, there are situations that can affect the successful milling of the balls and baffles. This paper explores the conditions that can affect the ball and baffle millout process of multi-stage fracturing sleeves. Different aspects of the milling process will be reviewed to determine the critical elements that must be taken into consideration when milling the balls and baffles. Specific factors include multi-stage fracturing sleeve dimensions, wellbore trajectory, torque and drag, depth location, mill design, weight-on-bit (WOB), viscous pill sweep frequency, and other milling procedures. The investigation of the millout of 185 multi-stage fracturing sleeves in Eagle Ford Shale well completions will analyze these factors, which then will be contrasted with surface millout testing on over 100 multi-stage fracturing sleeves performed on a custom millout testing machine. The surface testing allowed visual observation of millout processes and real-time changing of millout variables that reduced risk and lowered operating cost. Both sets of data will then be analyzed to illustrate the critical factors for successful millout operations and discuss the solutions to the millout challenges.
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