DGeophS Luncheon - Looking for Gas in all the Tight Places

Rulison Field, Piceance Basin, is located on a northwest plunging anticlinal structure near Rifle Colorado.  It produces from tight gas sandstones and coals of the Late Cretaceous Williams Fork Formation.  The best production is associated with a “sweet spot” in the middle of the field where high expected ultimate recovery (EUR) wells are located. The high EUR wells are located near faults. Open fracture sets near the faults exhibit a rigidity contrast with the surrounding rock making the fracture zones detectable with S-wave seismic data, whereas, they are indistinguishable with P-waves.

Connectivity to the natural fracture system is critical to better well productivity and high EUR. Predicting connectivity on the basis of hydraulic fracture orientation and using that to design pattern drilling is not as effective as knowing the actual orientation and lateral extent of the fractured reservoirs and using that to locate wells and design hydraulic fracture treatments. Decline curves show two delivery mechanisms involving wells in the sweet spot; natural fractures that dominate early production, followed by production from the sandstone porosity and storage capacity.  Some wells are capable of producing for decades especially if they have pressure support from the coals through the natural fracture system.  As pressure drawdown occurs in sandstone bodies connected to the Cameo Coal interval it accelerates gas desorption from the coals further sustaining gas deliverability. Fractured reservoir detection and monitoring could change the strategy of well placement from grid drilling to precise target drilling, thus improving the economics of tight gas exploration and development. Reserve growth can be achieved, and recovery efficiency improved, if depleted zones can be avoided and bypassed reserves can be added through precise target drilling.

In our search for gas in all the tight places, multicomponent seismic technology can help us drill the best wells first and guide us in the development of resource plays. Economic thresholds and environmental restrictions will demand the use of multicomponent seismic technology versus a mantra of “drill baby drill”.