Hamoud Ali Al-Anazi's thesis
by
Hamoud Ali Al-Anazi, MSE
University of Texas at Austin, 1999
Supervisor: Mukul M. Sharma
A pH-sensitive polymer was evaluated as a carrier fluid for gravel packing operations. Several experimental studies were conducted to evaluate the polymer. Rheological data is presented as a function of polymer concentration, pH, shear rate, and temperature. The effects of monovalent and divalent ions on the rheology are also presented. Core flow experiments were conducted on Berea sandstone cores. Fluid loss and filter cake stability were studied at an overbalance pressure of 100 psi. The effectiveness of polymer was compared with that of a conventional carrier fluid (HEC) used for gravel packing. Compatibility of the polymer with reservoir/field fluids was also investigated.
It was found that the viscosity of the polymer is strongly dependent upon the pH of the solution. At higher pH values (>6.0), the polymer viscosity reached a high value that is sufficient to suspend most gravel. Hydrochloric acid breaks this high viscosity to a low value (<5 cp) at pH values below 2. The thickening and thinning with pH was found to be reversible. The effect of temperature on the rheological properties of the polymer was not significant up to 85°C. Compatibility tests showed that the polymer was compatible with most brines (NaCl, NH4Cl, and KCl) used for field applications. Core flow results indicated that the filtration rate was low (<9 ml/hr) compared to that of HEC (106 ml/hr), at an overbalance pressure of 100 psi. The return permeability of the core was found to be 80% and 40% after polymer and HEC treatments, respectively. The invasion depth is also shorter than that of HEC due to the formation of a stable filter cake.
Our evaluation study shows that this anionic polymer would be an excellent non-damaging carrier fluid for gravel packing. It has excellent rheological and suspension properties and is easily broken down with a mild acid wash before flowback.
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