Low-Permeability Measurements: Insights
- Sandra Profice (Total CSTJF) | Gerald Hamon (Total CSTJF) | Benjamin Nicot (Total CSTJF)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- February 2016
- Document Type
- Journal Paper
- 30 - 40
- 2016. Society of Petrophysicists & Well Log Analysts
- 6 in the last 30 days
- 610 since 2007
- Show more detail
Recent studies have reported unacceptable discrepancies (up to several decades) between intrinsic permeability (kl) measurements from different laboratories. These discrepancies could be explained by (a) the diversity of experimental procedures, since no standards of measurement have been clearly defined for poorly permeable samples, and (b) the validity of interpretative models which, are rarely available.
This paper first presents the results of an experimental study comparing: (1) Values of the intrinsic permeability kl from step-decay (gas), pulse-decay (gas), and steady-state (both gas and liquid) tests; (2) Values of the Klinkenberg coefficient (b) from step-decay and steady-state tests; (3) Values of the porosity (ø) from step-decay and pycnometry tests.
On a homogeneous material of ultralow permeability (pyrophyllite), different techniques achieve similar results no matter which property is being measured (kl, b or ø). Moreover, the accurate prediction of the gas flow behavior by interpretative models relying on the Darcy-Klinkenberg equation highlights that gas flow in tight rocks is still viscous flow slipping at pore walls. These conclusions were checked for hydrocarbon-bearing rocks by repeating the study on shale.
The paper then provides the results of steady-state and unsteady-state measurements performed during a round-robin test. Pyrophyllite plugs were successively characterized by four laboratories, which selected their methods and experimental conditions but had to work on the whole as-received plugs and at a given effective pressure. It arises from the round-robin test that a satisfactory agreement of kl estimations from different laboratories requires a proper definition of the experimental procedure.
Over the past 10 years oil and gas shales have become a topic of real interest due to the large amounts of hydrocarbons they could potentially produce. Their characterization is a challenging task since these unconventional reservoirs have tight pore throats (a few tens of nanometers) and low permeabilities (from microdarcies to nanodarcies). Consequently, shales require careful identification of reliable methods to identify their one-phase flow properties.
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