Typically, water-based fracturing treatments consume large volume of fresh water. Additionally, providing consistent fresh water sources is difficult and sometimes not feasible especially in remote areas and offshore. Therefore, several seawater tolerant guar gum-based fracturing fluids have been developed in efforts to preserve fresh water resources. However, none of these fluids meet the current requirements of preventing/minimizing fracture face skin and proppant conductivity impairment especially in unconventional wells in Saudi Arabia. This paper will go provide the process of resolving this issue.
Several experiments, tweaking and design iterations were conducted to tailor seawater-based fracturing fluids. These fluids were designed to have rheological properties that can carry and transport proppant under dynamic and static conditions. The optimized seawater based fracturing fluid recipes were developed such that no chemical scaling occurs when their filtrate is mixed with different formation brines. The tests were conducted utilizing HPHT viscometer, coreflood, zeta potential and aging cells at reservoir conditions.
The developed seawater-based fracturing fluids were optimized, with a viscosity above 200 cP at a shear rate of 100 S-1 and a temperature of 300°F. The use of polymeric scale inhibitors prevented the severe calcium sulfate scaling in mixtures of seawater and formation water at 250 and 300°F. Furthermore, designing a lower pH fracturing fluid prevented magnesium and calcium hydroxide scaling that occurred above pH of 9.5. It was also realized that some common scale inhibitors had negative impact on seawater viscosity due to its inevitable ability of chelating the crosslinker's zirconate ions. The developed seawater-based fracturing fluid was applied for the first time in conventional and unconventional wells in Saudi Arabia and showed very promising results which will be discussed in this paper.