Scale Mitigation Strategy for Fracturing Using Seawater-Based Fluid

Abstract

As part of the continuous efforts to save freshwater resources in the Middle East, seawater-based fracturing fluid offers a high-potential solution to help save millions of gallons of fresh water while developing fracturing fluids for hydraulic fracturing applications. Scale deposition is one of the major technical challenges for fracture stimulations using seawater-based fluid. To understand the scale deposition and mitigation for fracturing using seawater-based fluid, a series of dynamic and static performance, compatibility, and thermal stability tests were conducted. Results showed that harsh scale forms with mixing raw seawater and high total dissolved solids (TDS) tested formation water at higher temperatures under dynamic and static conditions. Scale inhibitors cannot effectively inhibit scale deposition in such harsh scaling conditions because of the issues of compatibility and performance at static conditions. Nanofiltration of seawater is introduced to remove most of the sulfate ions in seawater and help significantly reduce the scaling tendency when mixing with high TDS formation water during fracturing treatments using seawater-based fluid. Combining the nanofiltration technique and scale inhibitor application, the scale issue during fracturing using seawater-based fluid can be effectively mitigated and was determined to be suitable for field application. The scale inhibitor showed good compatibility with nanofiltered seawater. The dynamic scaling tests were successful when the proper scale inhibitor and optimum concentration were used, while the static tests did not form any precipitation. Thermal aging resulted in a color change for all tests, as expected, and the performance of the thermal-aged scale inhibitor was evaluated. This paper provides insight into the scale deposition and inhibition for fracturing treatments using seawater-based fluid at high-temperatures up to 300°F and furthers the effective strategies to address the scale issue during fracturing using seawater-based fluid.

Seawater-Based Fracturing Fluid: A Review

“…Sulfate scales form in seawater when two incompatible waters mix together, such as the mixing of seawater (containing a high concentration of sulfate ions) and formation water (containing a high concentration of barium, calcium, and strontium ions). 30 Scale is formed through two crystallization mechanisms: surface crystallization and bulk crystallization. Scaling is a hybrid of these two systems.…”

“…Formation water and seawater are expected to create barium sulfate, calcium sulfate, and strontium sulfate scales at 300 °F . The sulfate in seawater has an effect on ion pairs due to its high concentration.…”

“…Sulfate scales are formed primarily in seawater by the mixing of two incompatible liquids, such as the mixing of seawater with its high concentration of sulfate ions and formation water with its high concentration of barium, calcium, and strontium ions. 30 In order to overcome the obstacles associated with using fracturing fluid made from seawater, it is necessary to first comprehend the composition of seawater-based fluid. The parts of the various oceans of the world that typically display oil and gas activity are summed up here.…”

“…36 Formation water and seawater are expected to create barium sulfate, calcium sulfate, and strontium sulfate scales at 300 °F. 30 The sulfate in seawater has an effect on ion pairs due to its high concentration. The electrostatic attraction between the charged ions in sulfate allows it to form ion pairs with strontium, calcium, and magnesium.…”

Removal of High-Concentration Sulfate from Seawater by Ettringite Precipitation

“…However, one of the primary challenges is the tendency of scale formation due to the incompatibility between seawater and formation water [2][3][4]. As the seawater usually contains a high concentration of sulfate ions (>4,000 ppm) and the formation water contains very high concentrations of calcium, barium, and/or strontium ions, CaSO 4 , BaSO 4 , and/or SrSO 4 precipitates can be formed when these two uids encounter in the reservoir [5]. e formed sulfate precipitates could lead to severe formation damages, overall reduction in hydrocarbon production capacity, and some other adverse e ects [6,7].…”