Horizontal wells drilled in unconventional gas reservoirs are often completed by combining multiple perforation clusters in a hydraulic fracture treatment stage. Each treatment stage is typically prevented from communicating by using an isolation plug. It is a challenge to design a limited entry completion that comprehensively ensures that all perforation clusters are equally stimulated within a treatment stage (Miller et al, 2011, Mcdaniel et al, 1999). Slippage or failure of isolation plugs have also been known to occur during treatment execution and in many cases, these failures are discovered only after the well stimulation has been completed. This paper presents three case studies in the Marcellus Shale where real-time microseismic Hydraulic Fracture Monitoring (HFM) was used to evaluate the behavior and development of the induced fracture and a need for the corrective intervention was observed. In one of the cases, an innovative corrective action was implemented and microseismic results show that the intervention was successful.

This study shows how real-time microseismic monitoring can been used for not only evaluating fracture geometry and azimuth but can also be used as a diagnostic tool for observing operational failures in completion tools as well as making real-time changes to completion design in order to improve completion efficiency. Some of the potential failures that may be diagnosed using HFM analyzed in this study include loss of isolation between hydraulic fracture stages, breach in casing integrity, poor cement bond in annulus and confirmation of plug ball seating.

The first case study describes a hydraulic fracture treatment where the real-time HFM interpretation was useful in identifying a failure in the isolation plug between completion stages. This observation during the treatment execution was later confirmed by tagging the depth of the plug during coiled tubing operations. A production log was also run in the well and showed limited production contribution from the stage with the plug failure. The other two case studies address the use of real-time HFM interpretation to identify undesired fracture growth into an already stimulated region. Subsequent intervention by using an isolation plug between perforation clusters as a means of diversion was implemented in one of the cases.

These examples clearly show how real-time microseismic monitoring can be used to adapt conventional completion designs to the dynamic nature of completion operations in the field. The paper also highlights the innovative use of an isolation plug as a diversion mechanism during fracture treatment.

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