Elimination of Scaling Potential of Seawater in a Downhole Environment through the Innovative Use of Nanofiltration and Scale Inhibitor

Abstract

Seawater-based fracturing fluids provide greater flexibility when designing stimulation treatments for offshore environments by reducing delays in stimulation vessel scheduling and using an, essentially, unlimited supply of seawater, opposed to fresh water. Because seawater has a higher ionic strength than traditional fresh water, lower viscosity is observed from guar-based polymers. By comparison, the seawater can produce scaling precipitates when sulfate ions contact the calcium, barium, and strontium ions in the formation. The formed sulfate precipitates could lead to formation damage in the form of scaling, pore throats being clogged, and an overall reduction in production capacity. This paper presents an innovative polymer-based scale inhibitor (SI) to mitigate scaling issues from seawater with 4,000 mg/L sulfate when mixed with 200,000 mg/L total dissolved solids (TDS) formation water. From static bottle tests with seawater, 74% strontium sulfate inhibition was achieved at 300°F. To eliminate sulfate scaling issues, a nanofiltration (NF) membrane-based technique was used to filter seawater. The SI performance was tested by both static bottle tests at different mixing ratios and dynamic tube blocking tests at 300°F. Following static bottle tests, the key ion concentrations were determined using inductively coupled plasma (ICP) spectroscopy. Zero scaling was achieved by adding 300 mg/L SI. The fracturing fluid was prepared using a zirconate-crosslinked derivatized guar. The rheology of the fracturing fluid was measured with and without SI to investigate its influence on crosslinking and proppant carrying capacity at 300°F. High magnesium in the seawater consumes hydroxide ions and affects pH control. To obtain a stable fracturing fluid, the pH was optimized to minimize magnesium precipitation. Coreflooding experiments confirmed the addition of SI does not cause additional formation damage. Using NF-seawater in conjunction with proven SIs can provide effective treatment of seawater-based-fracturing fluids. The separation technique (NF) and chemical solution (SI) complement each other to neutralize scaling issues completely. This technique minimizes freshwater usage in fracturing, which can enable significant savings for offshore operations time and cost.

Seawater-Based Fracturing Fluid: A Review

“…Because of its high salt content, seawater affects the viscosity accumulation in a different way. This results in a high ionic strength, which has a negative impact on the reservoir and the fluid’s rheology and can harm the formation …”

“…Before injecting the fluid into the reservoir, seawater can be nanofiltered to remove impurities before being used in the fracturing process. Researchers have shared several field applications of nanofiltration. , While the results reveal that the formation brine is compatible with nanofiltration technology, the necessary equipment and facilities take up a lot of room. This presents an additional challenge for locations with little available space, such as those located offshore.…”

“…In order to reduce the scaling propensity during fracturing treatments utilizing seawater-based fluid when combining with high TDS formation water, the nanofiltration (NF) of seawater was introduced. , It was discovered that the scaling issues during fracturing with seawater-based fluid may be effectively minimized by combining nanofiltration with the use of scale inhibitors, and it was determined that this combination is suitable for field applications. Nanofiltered seawater has been found to work well with scale inhibitors and is able maintain its rheological qualities for extended periods of time at temperatures as high as 350 °F. , In one study, it was found that no scale inhibitor was needed to produce negligible precipitation in mixtures of NF seawater and formation water.…”

“…This results in a high ionic strength, which has a negative impact on the reservoir and the fluid’s rheology and can harm the formation. 38 …”

“…This results in a high ionic strength, which has a negative impact on the reservoir and the fluid's rheology and can harm the formation. 38 It is important to note that seawater-based fracturing fluids can be improved by either adapting existing fracturing fluids or creating a new fracturing fluid that can efficiently control polymer hydration, cross-linking, additive compatibility, and breaking performance within the intended temperature range.…”