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Abstract Technological advancements have recently been directed toward development and optimization of horizontal completions in unconventional reservoirs, with the ultimate objective of increasing asset performance and value. Unconventional plays are being completed with ever-longer laterals, tighter stage spacing, and high rate slickwater applications designed with increasingly larger volumes of sand to create increased reservoir contact area for greater hydrocarbon recovery. Success is predicated upon overcoming the limited transport capabilities of slickwater. The benefit of higher injection rates employed to enhance proppant transport is soon lost as the lateral velocity declines exponentially with distance from the wellbore, allowing the sand to fall rapidly to the bottom of fractures, resulting in propping only a fraction of the created fracture area. While there are advantages to the use of slickwater and sand for unconventional applications, the transport characteristics inherent to slickwater/sand slurries suggest significant limitations to step-changes in hydrocarbon recovery. Near-neutrally buoyant, ultra-lightweight proppant is a proven solution to make productive the otherwise non-propped area. Several previous studies in parallel plate slot flow models have shown ULWP-1.05 is transported well in slickwater, whereas sand settles rapidly to form a dune even at high flow rates. Such behavior is intuitive given the near-neutrally buoyant ULWP has an Apparent Specific Gravity of 1.05, in contrast to the 2.65 ASG of sand and the 1.0 ASG of water. Two new proppant transport models have recently been introduced, including a slot with multiple fracture branches and, a 3D complex network flow model designed to imitate flow through a lateral wellbore into a complex fracture network. In both, the ULWP-1.05 was observed to be transported near-homogeneously with the fluid to the extremities of the apparatus. Conversely, small mesh sand tended to stay in the lower sections of the models and to deposit prior to reaching the extremities. As a prelude to ULWP-1.05 field application in Permian Basin extended length horizontal wells, proppant transport and fracture conductivity data for the near-neutrally buoyant ULWP-1.05 were used in fracture models to optimize proppant placement for maximizing conductive fracture area, with iterations to optimize well performance in production simulations. A desired outcome of this endeavor is the development and validation of an optimized stimulation design exhibiting materially enhanced well performance. This paper includes analyses and observations from the proppant transport testing, fracture conductivity testing, discussion of the subsequent fracture designs and production simulations, and comparison of the production simulations with production experienced in field applications. Performance of slickwater fracs with sand alone and, with both sand and near neutrally buoyant ULWP are compared. Lessons learned may be used to substantially increase the conductive fracture area of unconventional wells, optimizing production performance and stimulated reservoir recovery efficiency.
Abstract As well construction technology enables ever-longer horizontal reach, the challenge increases for proppant placement in hydraulic fracturing operations. Effectively placing conventional proppants (sand and ceramic) in extended-reach wells requires either high pump rates or high-viscosity fluids and are subject in both cases to early proppant settling and banking. Even when heavily gelled fluids are used, proppant suspensions are subject to particle settling in the presence of vibration, and/or due to fracturing fluids breaking before the fracture closes. Furthermore, the fractures are typically vertical; and in this case the proppant has a tendency to settle in the lower portion of the fractures while the upper portions close in the absence of proppant. This can lead to impairment in the geometry of the fracture and well productivity. Using proppant with much lower densities than that of conventional proppant will provide better transport. Another benefit from these ultra-lightweight proppants (ULWP) is the elimination of polymer damage with the use of low-polymer or slick water fluid systems, enabled by their extremely slow settling rates. Since the mid-2000s, ULWP has been used in over 3000 wells to overcome placement and settling challenges. Taking advantage of low-viscosity fluids, ULWP have been used as nearly neutral buoyant proppant; thus, minimizing settling within the created fracture and leading to a better placement. In this study, the hydraulic treatment and production data of those wells treated with ULWP and offset wells were carefully reviewed. Main production metrics are calculated to evaluate the production performance.
Brannon, Harold D. (BJ Services Company) | Malone, Mark R. (BJ Services Company) | Rickards, Allan R. (BJ Services Company) | Wood, William D. (BJ Services Company) | Edgeman, J. Randall (BJ Services Company) | Bryant, Josh L. (Amerada Hess Corp.)
Abstract Hydraulic fracturing practitioners have long theorized that maximized fracture conductivity could be achieved by creation of fractures with partial monolayers of proppant. Fracturing mechanics and design experts have lamented that fractures filled with partial monolayers of proppant, while highly desirable, were "virtually impossible to achieve". The expert's reasoning was expressed as due to the inability to obtain uniform and complete coverage of the fracture with a partial monolayer, insufficient proppant strength to support the load, loss of fracture width due to proppant embedment and, potentially deleterious non-Darcy flow effects in the relatively narrow propped fracture. Many innovative fracturing products and design techniques have recently been developed and introduced to cost efficiently enhance well productivity. Evaluation of case histories of several wells recently treated utilizing some of these innovations have led to the consideration that perhaps the experts were a bit too hasty. Slickwater fracturing has enjoyed a recent renaissance, in large part, due to the favorable treatment cost economics for the well stimulation benefit achieved using such non-damaging, low viscosity fluids. Slickwater fracturing treatments have historically been typified by pumping large volumes of slickened water at high rate to deploy relatively small volumes of frac sand. A potential shortcoming of slickwater fracturing treatments is the tendency for fracture propagation out of zone due to the high treating rates and, proppant settling below the target zone due to the poor transport properties afforded by the low viscosity treating fluid. Optimization of slickwater fracturing treatments employing recently developed ultra-lightweight proppants to facilitate proppant placement throughout the entire created fracture area has found success. Wells treated with the new proppants using refined placement techniques have been observed to experience extraordinary stimulation increases which are indicative of production through a partial monolayer proppant pack. The observed increases are resulting in payouts in a few weeks or months compared to the years experienced historically with previous methods. The focus of this effort will be a review of case histories of wells treated with new products and placement techniques. Discussion of slickwater treatment design optimization and laboratory evaluation of the ultra-lightweight proppant partial monolayer conductivity and transportability is also provided. Results demonstrate how merging new technologies with old techniques can produce modern, high value results. Introduction and Background Hydraulic fracturing may be characterized as a complex process involving pumping highly pressurized fluid into a well at a rate sufficient to create fractures in a subterranean formation. The fractures provide highly conductive flow paths radiating laterally away from the wellbore, and thereby, a means to increase the productivity of an oil or gas well completion. Proppants are typically placed in the fracture to ensure that the created flow path remains open and thus, conductive, once the treating pressure is relieved. Since the first "hydrafrac" treatment in 1947, hydraulic fracturing has become recognized as a key process in the enhancement of petroleum recovery. Over the past fifty-some years, the industry has directed substantial resources toward gaining greater understanding of the mechanics of fracturing processes and, to the ongoing evolutionary improvement of equipment, products, and techniques to optimize the productive benefits of hydraulic fracturing application.
Abstract The economic success of stimulated wells may be defined by the Return on Fracturing Investment (ROFI): the well performance relative to the cost of the hydraulic fracture stimulation employed. Hydraulic fracture deliverability is largely defined by the effective fracture area, which is that portion of the created fracture area exhibiting sufficient conductivity contrast within the productive reservoir interval. Previous studies demonstrating that stimulated well performance can be improved by increasing fracture conductivity have generally addressed characteristics of the proppant pack: optimized proppant properties, increased proppant size, increased proppant volume, and minimized damage to the created fracture permeability. Improving overall fracture area has typically been addressed by employing larger treatments and proppant volumes. Thus, previous approaches to enhancing fracture deliverability have resulted in increased stimulation cost, which, unless accompanied by a similar scale of increase in well productivity, has negative implications on ROFI. The decades-old theory of increasing fracture deliverability by placing proppant in partial monolayers (PMLs) rather than multi-layer packs was resurrected in 2004 with the introduction of ultra-lightweight (ULW) proppant. The theory states that a partial monolayer exhibits conductivity equivalent to 15 to 20 layers of proppant in a packed fracture, which equates to a difference in areal proppant concentration of greater than 20X. In addition to enabling placement in a partial monolayer, the transportability of ULW proppant has been shown to provide greatly increased effective fracture area. Case histories of PML fracturing treatments have consistently illustrated stimulated production increases well beyond expectations, effectively validating the productivity benefits of the process. The focus of this paper is to characterize the ROFI implications of PML designs using ultra-lightweight proppants in comparison to typical packed fracture designs using conventional proppants. Advanced fracture modeling will be used to illustrate the effects of fracture conductivity (proppant type, concentration, & damage) and effective fracture area on well performance. Normalized stimulation costs of the respective designs will be assessed against the resultant fracture deliverability and projected ROFIs. Introduction Proppants are placed in the fracture to provide a preferential pathway to the wellbore once the hydraulic treating pressure is relieved. Successful well stimulation requires that these created fracture pathways provide permeability orders of magnitude greater than the reservoir matrix permeability. The proppant placed in a fracture is perhaps the most vital part of a fracture stimulation treatment since it provides the connection for hydrocarbons to flow between the reservoir and the producing wellbore 1.
Abstract Hydraulic fracturing is more popular, due to its revolutionary impact in the US oil industry, especially in unconventional reservoirs. This paper first presents the analysis of hydraulic fracturing treatments in 56 vertical and horizontal wells in the Wolfcamp and Spraberry formations of the Permian Basin in West Texas. Intrinsic treatment strategies and operational methodologies used by different operators in the Basin were evaluated with the goal of extracting and deducing insights into criteria that characterizes operational virtuosity. The evaluation focused on: proppants types and amounts, fluid types and volumes, treatment rates, well productivity and treatment cost. The second part presents the application and integration of these best practice concepts in the re-designing of hydraulic fracture treatments in a case study well already stimulated with available treatment data. Vertical wells were studied with 25 wells with over 150 treatments in both formations, 18 horizontal wells in the Spraberry formation with over 200 treatments, in Midland sub-basin and 13 horizontal wells in horizontal Wolfcamp in Delaware sub-basin. The Spraberry formation is very fine-grained sandstone, siltstone and carbonates with shales. The Wolfcamp is a complex formation divided into A, B, C and D, mostly limestone, with interbedded organic-rich siltstones. Empirical and statistical analysis using correlations and analysis of variance were used to identify and distill the best practices that actively and positively increase the production rates and decrease the production costs in each of these formation and well types. These results were then integrated in designing optimal hydraulic fracture treatments for these formations in the case well. Log analysis was done with industry standard software for accurate interpretation of the target formations and determination of rock mechanical properties used in the hydraulic fracture design software. Mined data and analysis showed that operators merely replicate designs from similar wells and formations. This practice increases the errors, costs, and reduces expected productivity. Results show that the use of 20/40 white proppant is not economical, while the use of 40/70 white proppant is recommended in both formations. Crosslinked gel creates more complex and wider fractures, but it increases cost drastically, while slickwater was amenable to treatment costs and production rate, but more volume will be needed for the treatments, hence, the use of hybrid fluids are recommended. The original design used 20/40 white sand, the total stage cost of the treatment was 707,236. In the new treatment design, 40/70 white was used instead; all the scenarios evaluated gave a reduction in cost with $100,000. These results are applicable in enhancing optimal hydraulic fracture treatment designs for these formations in the Permian Basin. Also, they serve as templates for other basins with similar formations. These results will be made better by continuous improvements with integration of field results.