Increased Well Productivity from Energized Fluid Fracing, in Tight Unconventional Formations
Mark H. Holtz, Ikenna Nwaneri, and Dan Dalton
Praxair, Inc., Houston, TX, [email protected]
The oil industry today is expanding its hydrocarbon resource and reserve base by exploiting very tight (unconventional) formations. The numbers of plays has expanded quickly, with production coming from formations consisting of true siliciclastic shales to carbonate-dominated mudstones. Each of these formations has very low matrix permeability and thus the production is dependent on hydraulically fracturing the rock. Since the well productivity is highly dependent on hydraulically fracturing, the type of stimulation applied is a key parameter to the relative success of a well.
To unlock the hydrocarbons from unconventional formations there are several parts to the completion process such as long reach laterals, well direction, multiple stages, and stage spacing, combined with hydraulic fracturing technique itself. All aspects influence a well’s productivity along with the damage associated with the fracturing process. This damage has a strong influence on productivity. Damage comes from the interaction of the frac fluids in both the induced fractures and from leakoff into the rock matrix. Within natural and induced fractures polymer residue can result in damage. In the formation, damage can occur as fine’s migration, clay swelling, and as capillary and relative permeability water blockage. This fracture and formation damage can be reduced by applying energized fluids such as CO2 and N2 in the hydraulic fracturing process.
Energized Fluid fracing can increase a well’s productivity while using less water. Fracture simulations studies of energized fluid fracing take into account both the geomechanical as well as the petrophysical rock properties. Petrophysical properties include capillary pressure and relative permeability. Including these petrophysical properties models damage associated with injecting water into the rock. By accounting for these fluid –rock interactions the productivity index of well fractured with energized fluids is greater than straight water fracs.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012