Rheology of Polyacrylamide-Based Systems Under Near-Well Bore Conditions
G. Chauveteau (Institut Francais du Petrole) | R. Tabary (Institut Francais du Petrole) | N. Kohler (Institut Francais du Petrole)
Excessive water production adversely affects the economics of oil and gas producing wells: being generally responsible for both a rapid productivity decline and an increase in operating costs caused by the handling and treating of large quantities of water.
To face these problems and to extend the lifetime of the wells, different treatments were proposed such as injection into the water producing zones of cements, resins as well as organic or inorganic strong gels. These treatments effectively stop the flow of all fluids in the treated layers, but require zone isolation for their placement.
More recently systems were developed to reduce selectively water production without significantly affecting the flow of hydrocarbons. These so-called “permeability modifiers” are based on the use of either single high-molecular-weight water soluble polymers, generally polyacrylamides, or of “weak” gels obtained by addition of a crosslinker. Their placement is performed over the entire perforated interval. In this paper are described some basic characteristics of the rheology in porous media of these permeability modifiers. Experimental Neutral and partly sulfonated polyacrylamides of high molecular weight (5.106 < Mw <8.106 daltons) were dissolved in water containing 20 g/L of NaCl and 50 ppm of NaN3 as a stabilizer. pH value was kept constant between 6.5 and 6.8. The fraction of acrylate groups was around 1%. while sulfonation degree was 5, 13 and 25%. In the experiments aimed at investigating gel formation in flow through porous media, a zirconium complex, which reacts with acrylate groups, was added immediately before injection.
Polymer solutions were injected at constant flow rate in Vosges sandstone cores (0.24 < k < 0.40 m2) at 60 C. Differential pressure transducers were used to monitor pressure drop across the cores. Adsorption was estimated from the difference in effluent concentration profiles between the first and the second polymer front.
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