Abstract:
During fracturing treatment for low-temperature, shallow and high freezing point oil reservoirs, the first-line problems are to overcome uncompleted breakdown, uncompleted cleanup of fracturing fluids and cold damages to the formations by injecting cold fluid. To avoid those problems, it is suggested to adopt a new encapsulated heat-generating hydraulic fracturing fluid system as described in this paper. Firstly, two kinds of chemical heat-generating systems were studied and the NH4Cl-NaNO2 system was selected. According to the reaction characteristics of the system, oxalic acid was chosen as a catalyst of reaction and encapsulated using ethyl cellulose and paraffin as coating materials by the phase separation method. Compatibility of NH4Cl-NaNO2-encapsulated oxalic acid with hydroxypropyl-guar fracturing fluid was also discussed in the paper. The results showed that the hydraulic fracturing fluid containing encapsulated heat-generating agents hare a good stability and compatibility. When the fracturing fluid contains 2.0 mol · L−1 NH4Cl-NaNO2, 0.93% encapsulated oxalic acid and 0.08% ammonium persulfate, the peak temperature can reach 78.0°C and the viscosity of residual liquid is 3.12 mPa · s after 4 hours.
