(274a) Converting Low-Pressure Natural Gas to Foamed Stimulation Fluid: Defining the Operating Envelope

As part of a Department of Energy (DOE) sponsored program, an optimal thermodynamic pathway to transform natural gas (NG) into pressurized NG suitable for use as the internal phase in a foamed fracturing fluid has been already identified. Use of NG foamed fracturing fluids has the potential to reduce the amount of water requirements for stimulation and pose benefits for productivity in water-sensitive formations. This study aims to extend the investigation to determine key reservoir features where using a NG foam fracturing fluid may be advantageous. We provide a comparative analysis, using validated models, to determine the advantages of using natural gas foams relative to conventionally used slickwater, linear gel and crosslinked fluid.

A full 3D reservoir model in a shallow Fayetteville Shale formation has been constructed. Fundamental laboratory and pilot field tests data have been collected for NG foam fluid properties for numerical modeling. Rheology, friction and leak-off properties of the fracturing fluids have been incorporated in creating a numerical model. A 3D-complex hydraulic fracture simulation model incorporating 1D and 2D particle transport models have been utilized. Numerical reservoir simulation of over 50 different sensitivity scenarios has been incorporated for fracture modeling as well as gas production evaluation. Owing to lower density than conventional liquid column, NG form fluid are likely to result in higher surface pressure. Therefore, NG foamed fluid for deeper sections of the Fayetteville formations has been modeled at various degrees of pressure loss per feet to determine the operational depth limits of NG fracturing fluid application in the area.

Reduced pump rate with NG foamed fracturing fluid leads to a lower frictional pressure loss in tubing without compromising the ability to place the desired amount of proppant in the formation. In recent flow loop experiments, non-Newtonian shear-thinning NG foamed fracturing fluid exhibits a higher effective viscosity that allows for effective transport of the proppant. Modeling results indicate that proppant placement is at least 10% farther in the hydraulic fractures than with linear gel and slickwater. Economic evaluation of NG foamed fracturing operations reveal that NG foam fracturing fluid improves economic returns by over 12% as it lowers the water handling, transportation and disposal costs for the operator while achieving superior productivity. Water sensitive and clay rich layers have shown greater production potential with NG based foam fracturing fluid than slickwater, linear gel and crosslinked fluids.

Although foamed fluids were first reported to be used in 1960s the usage of nitrogen and carbon dioxide foams has not been widely practiced due to cost, complexity, and unproven production benefits. Use of NG foamed fracturing fluid is not widespread either, but this study attempts to identify specific regions and reservoirs where use of these fluids may lead to economic and long-term production benefits. We believe that use of natural gas foams is likely to provide long-term sustainable benefits in areas where water procurement and disposal costs are high, where natural gas may be available from a central processing facility via pipelines and where the reservoir is relatively shallow and contains clay-bearing minerals.