New, Delayed Borate-Crosslinked Fluid Provides Improved Fracture Conductivity in High-Temperature Applications

Abstract

Abstract 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 peck. An industry consortium reported that proppant peck. An industry consortium reported that the proppant peck 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 permeability damage, have limited applicability at temperatures greater than 200F 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 300F. 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 250F. The rheological, proppant transport, fluid loss and retained proppant peck 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. Introduction Evolution of High-Temperature Fracturing Fluids Many reservoirs require hydraulic fracturing stimulation to be effectively produced. Borates were among the earliest crosslinkers used to increase the viscosity and proppant transport capabilities of aqueous, guar-based fracturing fluids. Borate crosslinked fluids have been utilized with success since the late sixties in low to moderate temperature reservoirs. However, with the development of reservoirs with temperatures greater than 200F, the conventional borate-crosslinked fluids were found to provide inadequate rheological stability for successful treatment execution. The early development of high-temperature fracturing fluids emphasized maximization of the thermal stability of the rheological properties. Titanium and zirconium crosslinking fluids were identified for their ability to provide stable bonding in high temperature environments. Stabilizers such as methanol and thiosulfates were subsequently added to further enhance the high-temperature stability of the organometallic-crosslinked fluids. Studies documenting the detrimental effects of the high shear sensitivity of organometallic-crosslinked fluids led to the development of delayed crosslink technology. P. 215