Steady-State Stress-Dependent Permeability Measurements of Tight Oil-Bearing Rocks
- Shreerang S. Chhatre (ExxonMobil Upstream Research Company) | Edward M. Braun (ExxonMobil Upstream Research Company) | Somnath Sinha (ExxonMobil Upstream Research Company) | Matthew D. Determan (ExxonMobil Upstream Research Company) | Quinn R. Passey (ExxonMobil Upstream Research Company) | Timothy E. Zirkle (ExxonMobil Upstream Research Company) | Alex C. Wood (ExxonMobil Upstream Research Company) | Jeff A. Boros (ExxonMobil Upstream Research Company) | Daniel W. Berry (ExxonMobil Upstream Research Company) | Sergio A. Leonardi (ExxonMobil Upstream Research Company) | Ryan A. Kudva (ExxonMobil Upstream Research Company)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- April 2015
- Document Type
- Journal Paper
- 116 - 124
- 2015. Society of Petrophysicists & Well Log Analysts
- 5 in the last 30 days
- 501 since 2007
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Permeability plays a key role in determining the optimal well spacing for a tight-oil reservoir. Currently, the industry practice is to measure permeability after crushing these tight oil-bearing rocks. Permeability on crushed rock samples may not represent the in-situ properties.
In this work, we present a steady-state method to measure effective liquid permeability on intact core plugs from tight oil-bearing rock under reservoir stress conditions. We image the samples using CT scanning to evaluate their physical integrity. We measure the permeability while injecting a liquid and applying backpressure to compress and dissolve gases. We flow a liquid, which is miscible with the remnant oil in the sample, and thereby perform permeability measurements on as-received samples, consequently avoiding the time-consuming step of cleaning such low permeability samples. We can flow multiple pore volumes of the test liquid through a tight rock in a few days to weeks. We can accurately measure steady-state effective liquid permeability for tight-oil core plugs from a few microdarcies to tens of nanodarcies. The permeability loss over time at constant net confining stress (i.e., “stress creep”) is significant and this creep can last for a few weeks.
The steady-state permeability strongly depends on the applied net confining stress and the stress history. Large permeability declines are observed as the applied stress is increased, and little recovery occurs as the stress is relieved. We validated the measurement technique by using a set of capillary standards that are not stress-sensitive and for which the permeability could be calculated using Darcy’s law.
IntroductionIn the past few years, oil production from tight oil-bearing rocks and shales in the US has increased from less than 1 million B/D in 2010 to more than 3 million B/D in the second half of 2013 (Wagener, 2014). Commercially viable initial oil-production rates are achieved by a combination of hydraulic fractures and natural fractures in such tight reservoirs. However, once the fractures are depleted, the production needs to be supported by the flow of hydrocarbon from the rest of the reservoir to these fractures.
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