Novel Chelation Opens the Door for Redeployment of Sea Water Based Fracturing Fluids in High Temperature Wells.

Abstract

Exploration for unconventional reservoirs has begun in various countries in the Middle East. Widely recognized as the bastion of conventional crude oil and gas production, the area's exploration for natural resources –– in particular unconventional resources –– is in its infancy. The lack of fresh water may derail some of the exploration and production of unconventional resources in the Middle East. One of the solutions is to use the abundant availability of nearby sea water for fracturing treatments. This paper will discuss the applicability of sea water for fracturing fluids for without the need for separate treatment of the water. Rheological data with synthetic sea water as well as source sea water from Saudi Arabia, identification of any potential precipitation and remediation and compatibility with produced water and proppant pack conductivity data, of applicable fluids to show the effectiveness of the systems to the high temperatures of the reservoirs in the kingdom, 325°F will also be presented. The concept of using seawater as a base fluid is not new. Because of the problems associated with substituting seawater for freshwater in polymer-based fracturing fluids, many operators are apprehensive about using seawater for fracturing. There have been noted attempts to mix polymer-based fluids on the fly with seawater, but treatment results have varied widely. Seawater contains dissolved inorganic salts, adversely affecting hydration and viscosity development of polymer-based fluids. High content of calcium and magnesium in seawater can reduce viscosity. These salts also buffer and strongly influence pH control and may inhibit or deactivate certain gel breakers. To gel effectively, polymer fluids need a specific mixing environment with distinct pH windows. Borate crosslinking normally requires a high pH. Rheology and breaker profiles will be shown that provide the desired properties and regain conductivity to establish the non-damaging clean-up of a properly designed fluid. The technology presented uses chemical chelation of the problem ions in the sea water, resulting in the fracturing fluids with enhanced fluid and proppant pack properties, including thermal stability, retained fracture conductivity, pH buffering capacity, scale inhibition and fluid loss control. Further, the addition of the novel additives to the fluid does not interfere with the crosslink delay time and does not complicate the preparation of the fluid. The technology discussed eliminates the need for traditional water treatment and nano-filtration of sea water and associated disposal issues.

Effect of Seawater Ions on Polymer Hydration in the Presence of a Chelating Agent: Application to Hydraulic Fracturing

“…5 The major challenges associated are the high total dissolved solids (TDS), pipes corrosion, scaling potential, and polymer hydration. 6 A typical fracturing fluid contains water, viscosifiers, proppants, friction reducers, biocides, and other additives. Polymer-based viscosity-modifying agents such as poly (acrylic acid), poly(vinyl alcohol), guar gum and its derivatives, cellulose, and poly(acrylamide) are widely utilized.…”

“…Therefore, seawater and produced water can play a significant role in reducing fracturing operation costs . The major challenges associated are the high total dissolved solids (TDS), pipes corrosion, scaling potential, and polymer hydration …”

“…The presence of these ions could delay or prevent polymer hydration. Moreover, they may induce corrosion, cause scale, and reduce gel stability . Both monovalent (Na + and K + ) and divalent (Ca 2+ and Mg 2+ ) ions affect the viscosity and stability of fracturing fluids.…”

“… 5 The major challenges associated are the high total dissolved solids (TDS), pipes corrosion, scaling potential, and polymer hydration. 6 …”

“…Moreover, they may induce corrosion, cause scale, and reduce gel stability. 6 Both monovalent (Na + and K + ) and divalent (Ca 2+ and Mg 2+ ) ions affect the viscosity and stability of fracturing fluids. The divalent ions are the source of viscosity reduction and precipitation, which is stronger with the presence of calcium ions.…”