Moderate to high-temperature reservoirs frequently require hydraulic fracturing stimulation to be effectively produced. Temperature-stable viscosified fluids are needed to successfully execute treatments in these harsh downhole environments. The evolution of high-temperature fracturing fluids has led to the use of organometallic-crosslinked, aqueous-based guar or derivative guar gels. These fluids yield high viscosities for long periods of time at elevated temperatures and have received widespread application.
Unfortunately, several recent studies illustrated that organometallic-crosslinked fluids can cause significant damage to the permeability of the proppant pack. An industry consortium reported that the proppant pack permeability damage is often greater than 80% when these fluids are applied. Damage of this magnitude dramatically reduces the effectiveness of the stimulation treatment. Delayed breaker systems, recently introduced to reduce the permeability damage, have limited applicability at temperatures greater than 200°F and, where applicable, greatly increase treatment costs.
A guar-based fluid utilizing a new, organically-complexed borate crosslinking system has recently been developed. Laboratory evaluations of this new system demonstrate superior rheological properties at temperatures exceeding 300° F. More significantly, the new fluid has been observed to be much less damaging to the proppant pack permeability than conventional organometallic-crosslinked fluids. Retained permeabilities greater than 85% have been observed, without breaker, at 250°F.
The rheological, proppant transport, fluid loss and retained proppant pack permeability performance of the high-temperature borate-crosslinked fluid are described and compared to conventional fluids. Field case histories are provided to support the laboratory data.