The effects of well interference between existing producing wells and newly stimulated wells (commonly known as "frac hits") are of growing concern as full-density development accelerates across all the North American shale plays. Strategies to mitigate the negative effects of such interference are becoming increasingly important as frac hits become more frequent. This case study presents a second-generation active well defense project involving four new wells and six offsetting legacy wells in the Bakken and Three Forks formations located in the North Fork Field, McKenzie County, ND. The operator has experienced numerous examples of stimulation interference in this field as its development operations have progressed into the full-density phase. Stimulation interference is defined as any increase in pressure occurring in a well as a result of stimulation activities in an offset or nearby well. While such interference has not necessarily had a lasting effect on legacy production, it has in some cases resulted in the need for costly remediation due to the migration of solids into the legacy laterals. The well defense efforts described herein are intended to minimize the need for post-stimulation remediation in legacy wells by preventing solids migration.
Normally, the optimization of hydraulic fracturing performance is limited to pre-job modeling and analytics. A design is determined for a particular well or project and applied without significant change during the course of the stimulation. Performance results are collected during the job and then analyzed after the fact, with the primary purpose of designing for the next project. Significant design improvements can be made by evaluating stage performance in real-time as the well is being stimulated. Unfortunately, real-time analytics are difficult because the immense of volume, variety, and velocity of the available data. The typical frac fleet captures metered data from as many as one hundred measurement points simultaneously on a second-by-second basis. This means that for a single stage, the comma-separated values (CSV) files containing the recorded channels often include over one million discrete data points. Utilizing these large files (approximately 5 MB) with typical off-the-shelf software can be time-consuming. The manual process of file acquisition by analytical staff alone can often exceed the time available between stages. While these files are an invaluable resource, they are often left untouched until long after a job is completed, if they are ever used at all. Cloud-based analytics greatly shorten the acquisition and utilization timeline, making near real-time analysis possible. While the challenges involved in utilizing "big data"; for actionable analytics are frequently discussed, the technology and approaches described in this paper are relatively new to the field of real-time stage management. This paper introduces a novel and highly effective approach in the field of hydraulic fracturing optimization. The history of CSV analysis is presented along with examples of specific types of beneficial stage analytics.
The effect of horizontal well spacing on stimulation performance and well results is of keen scientific and economic interest to the industry. The objective of this paper is to demonstrate these effects in a grouping of five horizontal Wolfcamp wells drilled in a down-spaced configuration where inter-well distances were reduced from 1320′ to 660′. The subject project is located in Ward County, Texas, on a 640 acre lease. A stand-alone Wolfcamp A2 zone well (legacy well) was drilled on the project acreage in late 2016 followed by the drilling of four development wells directly offsetting the legacy well in mid-2018. The four development wells were spaced 660′ apart as opposed to the existing norm of 1320′. This paper presents various pressure, microseismic, tracer, and production data collected during and following the zipper stimulation of the four development wells. This rich data set yielded significant information about the drainage characteristics of the legacy well, the effect of pressure depletion on fracture geometry, the nature of fracture driven interactions (FDI) in down-spaced wells, and the inter-relationship of these factors in their effect on production results. Active well defense was performed in the legacy well and results from these defense operations is also reported. Inter-well spacing of 660′ between wells in the same zone resulted in significantly diminished production results compared to the base case resulting in lowered projected rates of return for the well group. Depletion in the legacy well resulted in larger fracture geometries in the nearest development wells, but not in wells 990′ away. This resulted in larger stimulated volumes in the nearer wells but also diminished oil production. The inferential conclusion is that localizing stimulation energy in the near vicinity of the treated well yields improved well results. Concerning FDI, the data indicate that wells within 660′ of each other are likely to interfere with each other, while the opposite was true for wells that were 990′ apart.
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