Abstract
One of the most serious oilfield problems is scale deposition, particularly when two incompatible waters are involved. The control of scale deposition in high-pressure/high-temperature (HP/HT) wells has been challenging because most scale inhibitors lose effectiveness at high temperatures as a result of molecular instability. Hence, in the context of adapting to the continuous challenges of the oil and gas industry, along with the need to preserve freshwater resources in the Middle East, an in-depth study of the scaling results of mixing fracturing fluid developed using nanofiltered (NF) seawater with formation water containing high total dissolved solids (TDS) under HP/HT conditions is discussed.
A series of dynamic experiments was performed using a DSR-6000 dynamic scale loop at 330°F and 3,000 psi. Additionally, static experiments were conducted at room temperature and 330°F for 2 and 24 hours, respectively. For both dynamic and static tests, two mixing ratios were tested: 80:20 and 50:50 mixtures of NF seawater:formation brine. The 80:20 mixing ratio represents the worst-case scenario according to scale advisor software results. Moreover, regained core permeability at 300 and 330°F and retained proppant pack conductivity tests were also performed.
Results demonstrated that, for dynamic scale loop testing, the lowest concentration of scale inhibitor tested (250 ppm) achieved the passing criteria along with all higher concentrations for both mixing ratios. The static tests were also successful, with no precipitation formed. Regained core permeability was in the range of 77 to 89%. Finally, retained proppant pack conductivity result of 56% indicated good cleanup properties for NF seawater.
