The Effect of Surge Flow on Rock Permeability during Underbalance Perforating

by
Naeem S. Al-Shehri, MSE

University of Texas at Austin, 2002
Supervisor: Mukul M. Sharma

In this thesis, an experimental set-up and procedure have been developed to simulate surge flow that occurs during underbalanced perforating. A series of underbalance surge flow experiments were performed on outcrop Berea sandstone cores and Texas Cream limestone cores to investigate the damage that occurs due to surge flow and the effect of various parameters such as underbalance pressure, core length, lithology, fluid saturation, and the use of chemicals such as clay stabilizers.

Analysis of the results show that: the magnitudes of the permeability reduction observed in experiments conducted with both Berea sandstone and Texas Cream limestone are relatively small and should not be of major concern when using underbalance surge pressures of up to 1,800 psi. Some evidence of fines migration was observed in our experiments. Fines were collected in the effluent during and after surge flow. In the Berea sandstone experiments, the reduction in permeability in general increased with the surge pressure from 600 psi to 1,800 psi. It was found that longer cores generally show a larger reduction in permeability up to a core length of six inches. The salinity of brine plays an important role in determining the permeability reduction. Reducing the salinity from 3% wt. to 1% wt. doubled the damage observed in sandstone cores. Virtually, no damage was detected in all the limestone cores. Cores at connate brine saturation showed no reduction in permeability after surge flow. This suggests that fines migration occuring when the brine phase is mobile becomes a primary mechanism for formation damage during surge flow. The results of this study suggest that the mobilization of native fines during surge flow causes only a relatively small amount of damage in sandstone and limestone formations. Additional tests with other kinds of sandstones and limestones and in radial geometries need to be conducted to confirm this conclusion.

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