The Effect of Perforating on the Performance of Shale-Laminated and Crossbedded Formations

Abstract

ABSTRACT The productivity of a completed well depends, to some extent, on the internal structure of the formation. This internal structure includes shale laminations and current beds of crossbedded units. In order to drill to "target" formations, hundreds of feet of laminated and crossbedded formations are traversed. Optimal shot density distribution is essential for completing these laminated formations. Too low a shot density limits production; too high a shot density wastes money and can cause casing damage. Tailoring the perforating to the minimum number of shots for optimum flow will improve the well's economics. This study used a general-purpose finite-element program to simulate perforated, shale-laminated, and crossbedded formations. A field example was used to investigate the effect of perforating on the performance of shale-laminated formations. The results show that 1) at high shot density, the performance of a laminated formation is practically independent of perforation location; 2) at low shot density, shale/sand distribution controls the performance of shale-laminated formations; 3) the performance of crossbedded formations is not a function of the dip angle of the foreset laminae but is a strong function of perforation length, with the perforation intercepting the laminae. A shale distribution index has been defined and correlated with the productivity ratio of laminated formations. This correlation can be generated for a key well in the reservoir and the results can be used for optimal shot density selection for completion of the key well and other wells in the same reservoir. A summary of recommendations for completing various formations, based on the results of this study and those of other investigators, is presented.