Habibi, Ali (U. of Tehran) | Al-Hadrami, Hamoud Khalfan H. (Sultan Qaboos University) | Al-ajmi, Adel M. (Sultan Qaboos U.) | Al-wahaibi, Yahya Mansoor (Sultan Qaboos University) | Ayatollahi, Shahabbodin (Shiraz University)
Fines migration is the major reason for productivity decline known as formation damage in oil reservoirs. Sandstone formations are sensitive to brine salinity alteration which disturbs equilibrium condition in porous media. Because of nonequilibrium condition fines migration occurs during various operations. Nanoparticles seem to be good candidates to strengthen the attractive forces between fines and pore wall due to very small size, high specific surface area and electrical surface charge.
In this experimental study, several tests were performed using Berea sandstone (8 wt% clays) cores (3 in. length and 1.5 in. diameter). MgO nanoparticles were stabilized in the water uniformly using surface active agent and ultrasonication. Total dimensionless energy of interaction between nano particles in the suspensions was calculated based on the DLVO theory. Various core flooding tests were conducted to determine the effect of MgO nanofluid injection as clay stabilizer at different brine salinities on the cores with the permeability from 600-100 md. The pressure drop across the core was measured.
The results indicated that the MgO nanofluid could fix fines effectively where brine salinity became lower than CSC. Besides, measured zeta potential and total energy of interaction calculation confirmed that repulsive force became dominant at the specific concentration of the complex nanofluid which ensures its stability for long time during core flooding tests.
Thus, MgO nanofluid significantly prevented water shock problem. Also, no significant reduction in permeability was noticed in any of core flood tests.
Fines are loose silica based particles present in the sandstone formation, which can detach and move easily as a result of ionic strength reduction or pH increase of injected fluid. Migratory fine particles can trap at throat levels which lead to permeability reduction of formation. Colloidal and hydrodynamic forces are found to be responsible for the fines detachment and their release from the pore surfaces. London Van der Waals attraction, double layer forces are the most dominant forces in the detachment of fines from porous media based on the DLVO theory (Khilar and Fogler, 1998; Schramm, et al, 1996; Ahmadi et al, 2011). Hibbeler et al, (2003) provide an excellent review on the practical recipes to reduce fines migration.