Perforating a horizontal well in the Marcellus shale is typically performed using bare essential technology. Simple rules-of-thumb for perforation cluster spacing and interval length are applied, most likely derived by trial and error, and rarely validated by methods such as production logging and microseismic monitoring. Conversely, a perforating method that is gaining notoriety is an engineered approach in which perforation clusters are placed in each fracture interval of rocks that have similar properties. The reasoning for this method is that it will ensure equal injection rates and volumes of the hydraulic-fracture treatment into each of the perforation clusters; maximizing reservoir contact and production from each cluster.
The completion engineer might base the perforation design on gamma ray measurements with additional support of a mud log. While these measurements add some clarity to the perforation design, there is no evidence that either of these measurements have a direct impact on the breakdown stress of the rock, which is the primary driving force that dictates flow distribution of a hydraulic fracture treatment. Current logging technology does allow us to measure compressional, fast- and slow-shear, and Stoneley slowness waves in 3D along the horizontal cased borehole. These data can then be used to calculate stress and provide a stress profile along the lateral, which can provide an accurate basis for completion design.
Fluid distribution is predicted by way of both basic orifice-flow calculations and 3D hydraulic-fracture models (using actual stress data) and then verified using observations from microseismic monitoring results.
This paper presents a field case in which production improved using the perforation design method described above vs. one using conventional geometrically spaced perforations. In this case study, the operator made the new design technique part of their standard completion program.