New High-Temperature Seawater Based Fracturing Fluid Results in Significant Production Increases in China Offshore Oilfield

Abstract The paper presents the development of a high temperature fracturing fluid system and its application in offshore China that delivered significant increases in oil and gas productions. The key contributing factors include a novel, dual organic boron and zirconium crosslinker, and fast hydrating polymer that allow the use of seawater and continuous mixing operations. Fracturing treatments using such fluid system resulted in up to 4-fold increase in production. Fluid thermal stability, potential precipitation of divalent cations such as Ca2+ and Mg2+ in seawater and operating space limitation are some of the technical and logistical hurdles to be overcome for large scale offshore hydraulic fracturing operations. The development of the dual organic boron and zirconium crosslinker combines the advantages of two crosslinking chemistry that provided fluid with shear stability at the near wellbore and thermal stability inside the fracture. The salt precipitation is prevented by controlling the fluid pH and use of chelating agent. The use of rapidly hydrating guar derivatives enables the continuous mixing and pumping operations. Seawater in China typically contains around 400 mg/L of Ca2+ and 1300 mg/L of Mg2+ and total dissolved solids (TDS) of more than 33,000 mg/L. The organo-boron/zirconium complex crosslinker is able to promote fluid crosslinking at pH between 8 to 9, effectively preventing potential precipitation of calcium and magnesium salts, which occurs above pH 9.5. Equipped with a fast-hydrating guar derivative, the seawater fluid is stable up to 180° C (356° F), the highest temperature among the same family fluid known in the open literature. Core flow tests indicated less than 14% fluid damage to the formation. The seawater-based fluid has been successfully applied in 5 wells in offshore China. The reservoir ranges from 10 to 50 mD in permeability, 10-15% in porosity, an average depth of 3300 m and BHST of around 135 °C. The hydraulic fracturing treatments using the seawater-based fluid, coupled with fracture geometry-control technology, delivered 1 to 4-fold increase in oil and gas production.