It has long been accepted that one of the most cost-effective strategies for completing a horizontal shale gas well is to pump several fracture stimulation treatments along the lateral with each treatment contacting several perforation clusters spread out over a few hundred feet. Typically, these clusters are placed geometrically from toe to heel with the same distance between clusters and no other consideration as to the location of these perforations.
While this process simplifies the design of the completion, there are indications that this can be ineffective in contacting the maximum amount of reservoir. The fracture treatment will tend to follow the path of least resistance; intervals where stresses are the lowest will be preferentially stimulated over intervals that have higher stress concentrations. This effect was very clearly seen in a recent stimulation campaign performed in the Marcellus shale. During the fracturing treatments on several laterals, large gaps in microseismic events were observed where some perforation clusters appeared to take little to no fluid. Outlined in this paper is one particular example where even with use of a very aggressive limited-entry perforating technique, which uses perforation friction pressure to help distribute flow equally to each perforation, microseismic monitoring still showed 35% of the clusters receiving no fluid.
To improve stimulation coverage, two completions were designed using data acquired from horizontal well logs. Interpretations of lithology and stress along the wellbore allowed perforation selection in these wells using a newly developed software platform in such a way that the induced fractures were afforded the best chance of distributing equally along the lateral. Microseismic monitoring obtained during the stimulation of these wells clearly indicated significantly better fracture coverage. Additionally, stimulation treating pressures were reduced by targeting lower stressed sections, resulting in less difficulty placing proppant.