In the pulse technique of permeability measurement, a small pressure pulse is applied to one end of a confined core and the pressure versus time behavior is observed as a small volume of fluid moves through the core. Although a number of papers have discussed its usefulness in measuring low permeabilities of tight rocks, its application to heavy oil systems has not been reported. We have found several new applications of the pulse technique in specialized core tests for heavy oil systems. The main advantage of this technique is that it permits the evaluation of fluid transmissibility with only a minute amount of fluid flow through the core. Thus, possible damage to the core due to migration of fines and clays can be virtually eliminated. In this paper, we review the basic theory and present experimental results for four ifferent applications of this technique in heavy oil systems. These include the following:
In displacement test with tar sand cores, it is often necessary to work at elevated temperatures due to the lack of significant mobility at the reservoir temperature. The minimum testing temperature is generally set in an ad hoc manner, and this can lead to core damage due to high pressure gradients if the selected value is low. This risk can be minimized by establishing the minimum testing temperature on the basis of pulse tests conducted at a series of different temperatures.
The technique is also useful for assessing the extent of core damage resulting from displacement tests for measuring relative permeability. This is accomplished by measuring the total fluid transmissibility at connate conditions by the pulse technique before initiating the displacement tests. A comparison of this value of transmissibility with that calculated on the basis of the relative permeability curves provides an assessment of core damage.
The other applications described in the paper deal with measurements of pore space compressibility and evaluation of the gelling behavior of cross-linked polymers within a porous medium. Examples of" the data obtained in each application are presented, and the limitations of the technique are discussed.
The pulse decay technique was developed by Brace et al.1 to facilitate measurements ofgas permeability in very low permeability granite. Because of its advantages in speed and reliability it has received considerable attention in the literature.2–5. In this technique a small pressure pulse is applied to one end of a confined core, and the pressure vs. time behavior is observed as a small volume of fluid moves through the core. An analysis of this pressure decay behavior is used to determine fluid transmissibility and storage capacity in the core. Although a number of papers have discussed its usefulness in measuring low-permeabilities of tight rocks, its application to heavy oil systems has not been reported. We have found that it isequally useful for permeability measurements with very viscous oils because the oil obility (k/o) can be very low. In addition, we have found several new applications of the pulse technique in specialized core tests for heavy oil systems.