Summary
For decades, the oil industry has struggled to overcome
near-wellbore-fracture complexity during fracturing treatments, particularly in
low-permeability, naturally fractured hard-rock reservoirs. A number of
techniques have been created to diagnose and remediate these conditions to
enable the extension of created fractures and successful placement of proppant
deep in the reservoir. Microseismic-fracture-mapping (MSFM) technology has
revealed the creation of far-field complex fracture networks in hard-rock
reservoirs during fracture extension. This revelation offers the opportunity to
hydraulically connect to a much larger volume of rock, provided that
appropriate treatment techniques are applied to ensure the fracture network is
adequately connected to the main fracture. Additionally, techniques have been
developed and can be applied during the fracture treatments to facilitate and
enhance the fracture-network creation. Net fracture-extension pressure analysis
combined with real-time MSFM allows for identification of the degree of
fracturing-network creation and provides a decision-making tool for engineers
to modify treatment schedules or apply complexity-enhancing methods on the fly
on the basis of desired treatment objectives and rock responses to the fracture
treatment.
This new approach to fracture stimulation requires a new focus on rock
mechanics that includes defining the brittleness of the rock matrix,
determining the existence and magnitude of the principal-stress anisotropy,
designing the optimum spacing between fractures, and defining the optimum
fracture-treatment parameters. Once the completion design is implemented, the
designed treatment parameters can be adjusted in real time to meet the
objectives of the completion on the basis of actual rock responses to the
treatment. These rock responses are measured in real time using net
fracture-extension pressure and MSFM diagnostics. Adjustments made to the
fracture treatment are varied and include treatment-rate adjustments, proppant
concentration, proppant-slug placement, diversion techniques to ensure opening
of natural fractures, viscous-fluid spacers, acid spacers, and incremental
stop/start pumping schedules. The proppant-concentration adjustments are
enabled for immediate downhole changes through a unique coiled-tubing (CT)
fracturing process that incorporates liquid/sand concentrate slurries.
Examples of actual completion designs of these applications are
discussed.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
26 October 2010
- Meeting paper published:
20 September 2010
- Revised manuscript received:
11 January 2011
- Manuscript approved:
14 May 2011
- Published online:
11 July 2011
- Version of record:
10 August 2011
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