Michael A. Mccabe

Encapsulated Scale Inhibitor for Use in Fracturing Treatments

This paper describes the development and testing of a solid, encapsulated scale inhibitor for use in fracturing treatments. Data from laboratory and field tests are reported. Laboratory testing with a continuous flow apparatus has yielded inhibitor release rates under dynamic conditions. The inhibitor was tested to determine the minimum inhibitor concentration required to inhibit the formation of CaCO 3 , CaSO 4 , and BaSO 4 scales in brine. Laboratory data were used to determine the parameters of a mathematical model to predict the long-term release rate of the inhibitor. Data from a treated well are compared with predictions of the model. Release-rate testing in a continuous-flow apparatus shows that an encapsulated solid derivative of a phosphonate inhibitor has a sustained release profile. Temperature (100° to 225°F) and brine strength have a small effect on the release-rate profile. Coating the solid derivative makes it compatible with metal-crosslinked fracturing fluids. The coating has a short-term effect on the release-rate profile. The composition of the solid derivative has the greatest effect on its long-term release-rate profile. A comparison between the mathematical model proposed to describe the long-term release rate of the inhibitor and actual data collected from a treated well shows a large discrepancy, likely because most of the inhibitor is not in contact with the water being produced from this well.

Controlled Viscosity Reduction and Increased Fracture Conductivity Using a High-Temperature Breaker System

High-temperature fracturing-fluid breaker systems have been used in fracturing operations for the past several years. The advantage of using these systems has been improved fracture conductivity, but there has been an increased risk of poor proppant placement and premature screenouts resulting from early viscosity reductions as the fluid is exposed to high temperatures. In many cases, this problem could only be avoided by adding breaker to the final portion of the proppant stages, essentially improving the fracture conductivity in the near-wellbore region without enhancing the conductivity of most of the proppant pack. This paper highlights innovative research for developing high-temperature breakers that work synergistically with gel stabilizers to maintain excellent gel viscosity. This viscosity allows sufficient time to place the treatment while still providing a more complete break and improved fracture conductivity. Laboratory testing has shown that this high-temperature breaker system can be used effectively at temperatures as high as 350°F without sacrificing early-time fluid viscosity or proppant placement, while still providing dramatic improvements in fracture conductivity. Field production has been analyzed and shows the combined benefits of improved proppant placement and increased fracture conductivities obtained with the application of this technology.

Novel Oxidizing Breaker for High-Temperature Fracturing

A novel oxidizing breaker system has been developed for fracturing fluids at high temperatures. Below 200°F,the system is not active, but above 200°F, the oxidizing system aggressively attacks the polysaccharide backbone of the fracturing fluids, resulting in a complete break of the crosslinked fluids. In the presence of a get stabilizer, an intermediate, reactive oxidizing species is formed. The result of this formation is a delayed, soluble, high-temperature oxidizing system. Controlled viscosity reduction at 200°F to 300°F in crosslinked gelled fluids with and without a get stabilizer will be demonstrated. Testing included Model 50 viscosity profiles, high-temperature static break tests, and conductivity testing. Results from all testing showed the effect of oxidant concentration in producing a predictable, controlled break of the thermally stabilized crosslinked systems. Data were obtained in low-pH and high-pH Zr-crosslinked fluids as well as in borate-crosslinked fluids. The delayed mechanism of the new breaker system provides fluids with excellent crosslinked viscosity properties at early times with predictable, long-term viscosity reductions. Case histories show that the breaker system can be used throughout the treatment in the pad fluid, proppant-laden fluid, and flush. This paper provides data that allow significant improvements in job design. The operations engineer can obtain predictable, controlled get degradation by using the data provided for temperature, get type, get stabilizers, and breaker concentration. The results are optimized treatment designs with rapid fluid recovery, improved proppant-bed conductivity, and increased well productivity.