Strategies of Scale Management for Using Seawater as Fracturing Fluid

摘要

Continuous efforts are made to save freshwater resources in the Middle East, and using seawater-based fluid for fracturing has a high potential to save millions of gallons of freshwater in hydraulic fracturing applications. Scale deposition is one of the major technical challenges for using seawater as fracturing fluid. To understand scale deposition and the means for its mitigation when fracturing using a seawater-based fluid, a series of dynamic and static performance tests, compatibility tests and thermal stability tests were conducted. Results show that harsh scale forms when raw seawater is mixed with formation water having high total dissolved solids (TDS) at high temperature under both dynamic and static conditions. Scale inhibitors cannot effectively inhibit this scale deposition due to issues of brine compatibility and the performance at static conditions. Tests were then run using nano-filtered seawater. The filtration removes most of the sulfate ions in seawater and significantly reduces the scaling tendency when mixing the filtered seawater with high TDS formation water during fracturing. By combining a nano-filtration technique with scale inhibitor application, the scale issue during fracturing using the filtered seawater-based fluid can be effectively mitigated and the fluid made suitable for field application. The scale inhibitor showed good compatibility with nano-filtered seawater. The dynamic tests were passed when the proper scale inhibitor at an optimum concentration was used, while the static tests did not form any precipitation. Thermal aging resulted in a color change for all tests, as was expected, and the performance of the thermal aged scale inhibitor was also evaluated. This article provides insight into scale deposition and its inhibition when using seawater-based fluid for fracturing at high temperatures up to 300 °F, and it furthers the effective strategies to address the scale issue raised by using a seawater-based fluid.