Quantifying the skin factor for estimating the completion efficiency of perforation tunnels in petroleum wells

Conventional methods of perforation by shooting (PS) cannot achieve the expected wellbore productivity due to the presence of a region of reduced permeability around the perforation tunnel. Even though this phenomenon is well-known in the petroleum industry, few have attempted to quantify the damage due to PS. This paper quantifies the permeability damage followed by the recommendation of a novel perforation technique. This study has established that permeability of an open-hole is reduced in the range of 30%–75% due to the implementation of the PS technique. In order to remedy this problem, a new perforation technique called perforation by drilling (PD) has been proposed in this paper. To simulate a perforated completion, cylindrical sand samples with varying strength and porosity were prepared. These samples were perforated by the PS, PD and Casting techniques. Perforations created by the Casting techniques are considered to be representative of open-hole perforation tunnels. An important measure of flow efficiency or productivity of perforation completions can be referred to as skin factor (s) and productivity index (PI). In this paper, the performance of the PS, PD, and Casting technique was evaluated in terms of skin factors. Experimental results suggest that the skin factor is reduced substantially when the PS technique is replaced by PD technique resulting in significant improvement in PI. Finally, a mathematical model is used to predict permeability values with various perforation techniques. The mathematical model results agree closely with experimental observation.