Does the Presence of Natural Fractures Have an Impact on Production? A Case Study from the Middle Bakken Dolomite, North Dakota
- Michael J. Mullen (Realm Energy) | Jason L. Pitcher (Halliburton Energy Services Group) | David Hinz (Halliburton Co.) | Michael Lynn Everts (Halliburton Co.) | Don Dunbar (Halliburton) | George M. Carlstrom (Anschutz Exploration Corp.) | Galen R. Brenize (Anschutz Exploration Corp.)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 19-22 September, Florence, Italy
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 1.6 Drilling Operations, 5.8.4 Shale Oil, 1.2.3 Rock properties, 5.1.5 Geologic Modeling, 1.12.2 Logging While Drilling, 5.6.5 Tracers, 2.4.3 Sand/Solids Control, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.5 Reservoir Simulation, 4.1.2 Separation and Treating, 5.1.1 Exploration, Development, Structural Geology, 2 Well Completion, 1.12.3 Mud logging / Surface Measurements, 1.6.6 Directional Drilling, 1.6.7 Geosteering / Reservoir Navigation
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During the last 10 years, more than 2,000 horizontal wells have been drilled and completed in the Middle Bakken formation, which is sandwiched between the two Bakken organic-rich shales. Although most of the debate about this reservoir has centered on the lateral length, stimulation treatment, and the number of treatments, little work has been performed to explore the variations of rock properties and the effect of natural fractures along the 6,000 to 10,000 ft lateral lengths.
Maintaining the horizontal well between the two Bakken shales is easily accomplished with only a gamma ray tool. There are, however, two important questions to be addressed. First, is this an optimal practice for well placement? Second, is there a "sweet spot?? layer in which the horizontal well should be placed to increase production?
In a recent well, an azimuthally-focused resistivity (AFR) tool and an azimuthal deep-reading resistivity (ADR) tool were run as a final wiper trip to investigate the location of natural fracture swarms and the variations of rock properties along the 10,000-ft lateral. The goal of this exercise was to test the concept of improving production by using a "smart?? horizontal completion technique, spacing the swellable packers, and locating fracture stages based on horizontal reservoir data. The AFR image log identified more than 839 individual fractures in four fracture swarms. The ADR mapping showed approximately 40% of the lateral in the sweet spot layer. The evaluation of a post-stimulation oil tracer indicates that these sweet spot layers provide 70% of the production after stimulation. If the well had been geosteered to remain within the sweet spot using a smart completion technology, the production modeling suggests that production could have been increased by 20%.
The Bakken formation is part of a petroleum system that comprises five distinct stratigraphic units: the overlying Lodgepole Limestone formation, the upper, middle, and lower members of the Bakken formation, and the underlying upper Three Forks-Sanish formation (Meissner 1978). The upper and lower shale members of the Bakken provide the source rocks for the oil contained in all of these reservoirs. The Lodgepole and Three Forks formations serve as sealing formations, except where fracturing has enabled the Bakken-sourced hydrocarbons to bleed off into porous zones (e.g., the Middle Bakken and the Sanish sand) and charge these formations. The history of the Bakken completions began in the late 1950s with a few vertical completions. The first horizontal Bakken "boom?? in the late 1980s targeted the Upper Bakken shale member for open hole horizontal completions. This program had a short life span because of the high costs of horizontal drilling, low permeability, and completion techniques. The second Bakken horizontal drilling boom began in Montana with the Lyco Energy Sleeping Giant project in the Elm Coulee field. Most of these wells were drilled in the maximum stress orientation to create longitudinal hydraulic fractures. This process simplified the completion and stimulation process. This development began in early 2000. The possibility of performing multiple fracture stages in one horizontal wellbore was technically challenging and risky. During the last 10 years, more than 2,000 wells have been drilled and completed with a variety of completion techniques, making the Middle Bakken play one of the more significant oil plays onshore North America of the past decade. The cumulative Bakken production is approximately 200 million bbl of oil; as shown in Fig. 1, its daily average production is 6 million bbl per month (North Dakota Oil and Gas Division 2010). The success of this program is largely attributed to a combination of technologies: cost-effective horizontal drilling and multi-stage stimulation.
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