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Abstract A project was initiated in the Wolfcamp shale to reduce the operational complexity and costs associated with hydraulic fracturing. The goal was to use dissolvable diverter to increase fracturing stage lengths while maintaining an average cluster spacing similar to the current completion design without affecting well productivity. To ensure maximum effectiveness, a unique methodology was employed that uses reservoir properties along the lateral to create stage specific diverter strategies. The methodology used to design the diverter strategies begins with understanding well heterogeneity along the lateral. Estimations of minimum in situ stress at each cluster were combined with estimates of pressure increases caused by stress shadow both from previous stages and between treatment clusters to determine fracture breakdown pressures along the lateral. This data was used to selectively segregate the clusters into those that would be treated before diversion and those that would be treated after diversion. Additionally, calculations including hoop stresses and perforation friction were used to ensure pumping pressures remained in a range that increased the probability that clusters designed to take fluid after diverter were not prematurely broken down during the initial pumping treatment. This approach of engineered diversion was applied to three wells located in the Wolfcamp shale of the Midland Basin. The completion incorporated a designed stage length that averaged 315 ft with nine perforation clusters per stage using a single diversion drop. Typical well designs in this field contain stages that are 175 ft in length with five perforation clusters. Thus, this revised design constituted an eighty percent increase in stage length over conventional stage designs. The goal of the treatment was to increase stage length without affecting production. During the treatment of the new engineered diverter stages, there was clear indication that after the first portion of the fracture was completed and diverter had seated on the perforations, the fluid was effectively diverted to virgin rock. This is a positive indication that the stage-specific diverter design was effective. Additionally, when comparing production between the three wells in this study and conventionally stimulated offset wells, there was no appreciable difference in production. This case study represents one of the earliest applications of a fully engineered diversion strategy and will describe how lessons learned during this application can be applied to further improve economics and effectiveness of diverters in horizontal shale plays.
Yang, Xiaoling (CNPC Daqing) | Qiu, Bilan (CNPC Daqing) | Qi, Dunke (CNPC Daqing) | Lv, Deqing (CNPC Daqing) | He, Jian (CNPC Daqing) | Zhou, Shubo (Halliburton) | Wang, Zichao (Halliburton) | Han, Rong (Halliburton)
Abstract A case study is presented discussing a specific completion strategy applied in the Daqing oil field, Block Long26, and the outskirts of tight oil wells. An alternative fracture completion method and enhanced flowback technology were used to develop these tight oil fields. The methodology applied resulted in improved efficiency of the fracture completion strategy and post-stimulation flowback, which reduced operational time and related costs. Optimized fracture cluster spacing length was determined based on the operational time efficiency and engineered fracture completion design. Laboratory testing was performed to select fluid recipes, and field trials were performed for the correlated custom-made microemulsion technology, which enhanced post-fracture flowback to shorten operational time and increase the return on investment ratio and production. Field results and post-fracture completion production are promising. Several post-fracture completion production surveys have been applied in the Daqing field, Block Long26. The most popular completion strategy applied in this field involves using less than three perforation clusters in each fracture stage, applied using multiple, horizontal fracture stages, with longer and (normally) much greater fracture spacing length, thus requiring less fracture cluster treatments along the horizontal laterals. After stimulation, normally, additional days are necessary to observe the oil drop showing; thus, alternative flowback technology is necessary to enhance post-stimulation flowback to help improve the return on investment ratio. Limited entry fracture and/or extreme limited entry fracture technology were part of the intensive fracture cluster completion strategy to benefit fracture completion and production. Field operations involved doubling the current perforation and fracture clusters in one fracture stage. Laboratory methods were used to select the appropriate mircoemulsion additives to form a fracturing fluid recipe to aid oil production and enhance flowback.
Settgast, Randolph R. (Lawrence Livermore National Laboratory) | Izadi, Ghazal (Baker Hughes Incorporated) | Hurt, Robert S. (Baker Hughes Incorporated) | Jo, Hyunil (Baker Hughes Incorporated, Applied Numerics LLC) | Johnson, Scott M. (Lawrence Livermore National Laboratory, Applied Numerics LLC) | Walsh, Stuart D. C. (Lawrence Livermore National Laboratory) | Moos, Daniel (Baker Hughes Incorporated) | Ryerson, Fredrick (Lawrence Livermore National Laboratory)
Design decisions for the layout and properties of perforation clusters in a hydraulic fracture stimulation job are typically based on idealizations that treat the fractures originating from each cluster identically. However, simulations of multi-clustered hydraulic fracturing stages have shown that some perforation clusters may be rendered ineffective due to an increase in confining stresses (i.e. stress shadow) induced by hydraulic fractures originating from neighboring clusters. Two methods to counteract the effects the inter-cluster hydraulic fracture interaction are using non-uniform cluster spacing, and varying the frictional properties of the perforation clusters themselves as investigated in , . In this work, the authors present a method for the evaluation of the effects that cluster spacing and frictional properties of perforation clusters have on the propagation of hydraulic fractures during a stimulation stage. This approach is done through the application of the hydraulic fracture simulation capabilities of the GEOS simulation framework, developed at Lawrence Livermore National Laboratory. GEOS provides a hybrid Finite Element Method/Finite Volume Method that fully couples the mechanics of rock deformation, the flow of fluid through the crack, and fluid flow through the rock matrix. This capability allows for the development of a method for the optimal design of hydraulic fracture stimulation staging that relies on basic engineering principles. For a given set of site properties, multiple simulations are performed with variations in cluster spacing, cluster configuration, fluid properties, and pumping pressure/rate.
Horizontal shale wells present the challenge of generating large, high-density fracture networks, reflecting the sub-microdarcy permeability of the formations drilled by these wells. The goal is to create the largest fracture network volume to maximize ultimate recovery, because the fracture network volume in these wells has been shown to correlate strongly with the production level. However, as the network becomes too large for a given wellbore access point, the relative benefit of size diminishes. This is because of the low fracture conductivity, which creates large pressure drops within the network and makes it difficult to drain distant portions. And the effect is exacerbated by the inability to move water or liquid hydrocarbon through a large complex network (Mayerhofer et al. 2006).
Through near 3000 horizontal producing wells on University Lands in the Permian Basin, we have performed a series of case studies to systematically investigate the most critical parameters to maximize well performance and the value of field development. In addition to summarizing multiple study results, the paper concludes and elaborates that the effective cluster spacing is the most critical parameter that we may be able to control and can influence the most in the unconventional reservoir development.
The paper first shows three observation cases of perforation cluster spacings and their corresponding well performance. To understand why the effective cluster spacing is so vital to well performance, we then illustrate the fundamental theory to understand the pressure propagation timing and depletion patterns in different reservoirs. We compare the mechanistic modeling results of pressure depletion and corresponding recovery efficiencies with different effective cluster spacings by multiple modeling approaches, including single-porosity model, and dual-porosity model, which has validated our case study results and is very insightful for us to optimize perforation cluster spacings.
We then discuss the possible reasons of often-observed well interference. With a large data sample, the paper illustrates the good correlation between well performance and completion effectiveness. The paper presents the EUR and NPV evaluation results of different field development case histories, such as between tight cluster spacing and wide cluster spacing. We will also briefly discuss the current technologies and practices to improve cluster efficiency in the completion process.
Based upon the multiple case studies, theory investigation, and rigorous modeling, we have concluded that the effective cluster spacing is the most critical factor to influence well performance and the field development value.
The workflow illustrated in the paper can be used for operators to systematically optimize their cluster spacings as well as field development plans. To maximize the value of developing unconventional reservoirs, it is vital to optimize cluster spacing and cost-effectively achieve tighter effective cluster spacing.