Local and international companies are focused on an aggressive gas exploration campaign in tight high-pressure and high-temperature (HPHT) sandstone formations. In all of the current cases, the prospective HPHT tight-gas producing layers were discovered at depths below 20,000 ft where normally the stress and temperature are extremely high in addition to the very low reservoir permeability conditions. For HPHT tight-gas formations, fracture stimulation is a required step to define the reservoir fluid and evaluate productivity.
The extreme stress and temperature conditions are the main challenges of performing fracture stimulations in HPHT environments. In high-temperature conditions, fracturing fluids especially need to be stable, induce minimum damage, and have good proppant transport capabilities.
In HPHT tight-gas formations fracture stimulation (375°F and 1.1 psi/ft at 20,000 ft), where the temperature and stress conditions exceed existing fracturing fluids application limits, there are also limits from working pressure capability of the available pumping equipment. For this need, a new high-density fracturing fluid (HDFF) was introduced to the industry. Extensive laboratory evaluation was performed to design a new HDFF and to identify a regional supplier for the high-density brine (12.3 lb/gal) used as the base fluid to mix the new crosslinked fluid. The new fluid system was successfully mixed and pumped in the field, enabling the fracture stimulation treatment of a HPHT well at lower surface treating pressure, lower horsepower, safer working environment, and using conventional 15,000-psi rated fracturing equipment. Without having this new fracturing fluid the fracture stimulation treatment would require 20,000-psi rated equipment, which is not normally available in the area.
This paper summarizes the extensive fluid qualification testing, well conditions, and lessons learned from the first field applications of the new high density fracturing fluid system in Saudi Arabia.