GGU-SLUGTEST: Approaches for slug tests in double-porosity media

The slug test in double-porosity media (matrix and joints) is comprehensively dealt with by MATEEN (1983) and MATEEN & RAMEY (1984). Besides the fundamentals after COOPER et al.(1967), they also consider both wellbore storage and an infinitesimal skin zone. The pseudo-stationary and transient interactions between matrix and joints were dealt with.

Beside the transmissivity and the skin factor, this allows the ratio of the storage capacity of joints to the total storage capacity - matrix and joints - and the fluid transfer (ratio of permeabilities) between matrix and joints to be assessed.

The pressure in a slug test in double-porosity media can thus be described as follows: during the initial stage, only the joints are effective. The matrix then begins to feed the joints, a transition phase is initiated. At the end of the test the fluid originates in the complete system of matrix plus joints.

GRADER & RAMEY (1988) developed further the solutions for double porosity. Using this approach, the range of a test can be up to 1000 times the borehole radius under favourable conditions.

KARASAKI et al. (1988) show that the duration of a slug test does not depend on the water volume inserted or extracted, or from the size of the impulse, but is directly proportional to the storage constant and inversely proportional to the transmissivity.