Before pumping valuable natural gas into the ground, gas storage operators look for reservoirs that will accept, hold and release gas most efficiently.  Therefore, they target high-quality (porous and permeable) zones that are well sealed and not overly complex or compartmentalized.  Nonetheless, these remain natural rock formations, and operators often find that the wells do not behave as planned.  In addition to unexpected variations in reservoir character and geometry that impact well performance, gas may escape the field through unknown conduits or migrating to poorly-understood areas from which it can not be extracted.

To improve the understanding and operation of gas storage reservoirs, the NETL's Oil and Natural Gas Program is working with gas storage operators to demonstrate the importance of utilizing the advanced reservoir modeling, visualization, and simulation techniques that are commonplace in gas exploration and production operations.  For example, advanced geologic modeling conducted at NETL for a depleted sandstone storage reservoir in southwestern Pennsylvania revealed severe and previously unrecognized reservoir heterogeneities throughout the field.  Reservoir simulation based on the updated geologic characterization, then allowed investigation of selected options for improving the performance of the field.  Ongoing work, conducted in association with Lawrence Livermore National Laboratory, is applying artificial neural networks (ANNs) to the problem of optimizing storage reservoir management.  The ANN will make it feasible to quantitatively assess tens of thousands of possible management scenarios, including programs focusing on well remediation and the addition of vertical and/or horizontal wells in various locations within the field.

A key component of the work in storage reservoir management is the demonstration of the benefits of installing horizontal wells in existing storage fields.  Horizontal wells not only reduce the number of wells needed to operate a reservoir, but greatly increase the rates at which gas can be injected and withdrawn.  The increased deliverability gives operators greater flexibility in meeting peak demands.  To date, horizontal wells have been attempted in two of three fields studied.  The first, drilled into a carbonate reservoir in Indiana in 1997, has demonstrated deliverability more than 3 times greater than the best existing vertical well, even though the well attained a minimal 310 feet of lateral section. Additional horizontal wells are planned for the field.  The second, drilled in the Pennsylvania reservoir mentioned above, encountered drilling problems that resulted in no horizontal section.