Specific fluid requirements for successful coiled-tubing fracturing applications

The recent success of coiled-tubing fracturing in shallow wells has increased interest in using coiled tubing for fracturing deeper and hotter wells. Industry efforts now need to focus on understanding what properties a fracturing fluid must possess to carry proppant successfully at high rates through coiled tubing, frac ports, and perforations and into these deeper formations. The key performance requirements of a coiled-tubing fracturing fluid for deeper wells are low frictional pressure loss and adequate proppant-carrying capability after exposure to high-shear zones and high temperatures. This paper summarizes the results of pilot- and field-scale testing that led to the development of an optimized coiled-tubing fracturing fluid. Results show that polymer-based fracturing fluids can be controllably delayed to have low frictional pressure loss through the curved coiled-tubing unit and straight tubing. However, results also show that fluid stability can be reduced significantly when the fluid is pumped through small-diameter tubing followed by high-shear zones such as frac ports and then by perforations. Results demonstrate that correct fluid choice and fluid optimization are required to meet proppant-transport requirements. For coiled-tubing fracturing to be successful, the fluid and treatment-design recommendations should balance frictional-pressure-loss limitations with fluid-stability limitations.