Petroleum (Feb 2021)
New insights into hydraulic fracturing fluids used for high-temperature wells
Abstract
Current interest in deep, low-permeability formations (<10 md) demands accelerated development of high-temperature hydraulic fracturing technologies. Conventional guar systems break down above 300 °F and require higher polymer loadings to maintain thermal stability. However, higher polymer loadings generate more residue and damage to the proppant pack and the formation. To resolve these problems, a variety of high-temperature stabilizers are added to enhance the thermal stability of these fracturing fluids at temperatures above 300 °F. The focus of this work is to: (1) identify those additives that best enhance temperature stability of fracturing fluids and (2) study the rheological influence of incorporating these additives on the fracturing fluid systems.The experimental fracturing-fluid solutions were prepared at a total polymer concentration of 30 and 40 lb/1000 gal. Additives such as synthetic polymer, oxygen scavengers, crosslinkers, crosslinker delay additives, and pH buffers were examined in this work. Hydrated polymer solutions were crosslinked with a metallic crosslinker between 200 and 400 °F. Viscosity measurements were carried out in a high-pressure/high-temperature (HP/HT) rheometer to evaluate rheology and thermal stability.Results show that adding a synthetic polymer and a crosslinker with the slowest reaction rate improves the fracturing fluid thermal stability. Of the three other additives tested, oxygen scavengers showed the greatest enhancement to thermal stability while pH buffers showed the least. Through the addition of high-temperature stabilizing additives, the fracturing fluid in this work was able to maintain a stable performance at temperatures up to 400 °F.Maintaining the thermal stability of fracturing fluids at a lower polymer loading remains a challenge in the industry. This work proposes techniques that can be used to enhance the thermal stability of fracturing fluids. Deeper knowledge about these different techniques will allow for better additive development and application in the field.
