Measurement of Permeability at Elevated Stresses and Temperatures

Laboratory measurements of the permeability coefficients of various rock types suggest that the permeability coefficient is sensitive to the temperature and the stress state at which it is measured; the effects become more pronounced as the temperature or stress state is increased. This paper presents a summary of data in the literature to support this statement and describes some laboratory techniques used to obtain the data base.

Laboratory observations indicate that the permeability coefficient is temperature sensitive and that it is affected in many different ways as the temperature is increased. Temperature might be expected to affect the permeability coefficient through purely physical effects such as thermal expansion or thermal cracking. However, a variety of fluid-rock interactions apparently play a role, evidently through pore geometry alteration, which can have profound effects on the value of the permeability coefficient. The changes in permeability coefficients caused by temperature reviewed in the paper were large but not quantitatively predictable.

The permeability of rock is known to depend upon pore dimensions and fracture geometry. Either one, or a combination of the two, can control the measured permeability depending on the type of rock and its stress-strain history. Pore dimensions, particularly the aperture and the fracture width, change with stress so that it is not surprising to find that the permeability coefficient of various rock types can be quite stress dependent. The paper discusses general trends in stress related behavior changes for both low and high porosity unjointed rocks as well as for some jointed rocks.