Flow of Polyacrylamide Polymers in the Near-Wellbore-Region, Rheological Behavior within Induced Fractures and Near-Wellbore Area

Abstract

The economics of polymer solution injection projects are dependent on the improvement of displacement efficiency over waterflooding, the injectivity of polymer solutions, and reduced lifting costs associated with oil production and reduced water cut. High molecular weight polyacrylamide polymers show shear-thinning behavior when measured in a rheometer while they show shear-thickening behavior in cores.Micromodel experiments were used to investigate the rheological properties of polyacrylamide polymers at the high flow velocity conditions occurring in the near-wellbore region of wells. The results show shear-thickening characteristics. In addition, some plugging of the models by polymers was observed despite filtering of solutions. Also, core flood tests were performed. For the core-flood tests, severe degradation of the polymers was observed for high flow velocities.The data gathered from the experiments was used to interpret the results of a polymer solution injection test performed in the 8 Torton horizon reservoir in Austria. Shear-thickening behavior of the polymers would lead to very high well-head pressures. Through introduction of the degraded polymer viscosity data obtained from the laboratory experiments, the injection pressure observed in the field is explained.The field test showed that after a first phase of polymer solution injection under matrix conditions, a second phase with injection above the formation parting pressure (FPP) exists. To investigate the polymer rheology during this phase, micromodel experiments with various fracture geometries were conducted. The results show that within the induced fractures, polymer solutions show shear-thinning behavior and no substantial degradation of the polymers is seen. Owing to the low flow velocities through the fracture planes into the formation, also within the formation, no severe degradation of the polymers is expected.Hence, high molecular weight polyacrylamide polymers should be injected above the FPP when high flow velocities are expected in the near-wellbore region and such injection is permissible.

Chemical enhanced oil recovery and the role of chemical product design

“…In porous media and in viscosimeters at high shear rates, HPAM solutions have been well-documented to show shear thickening after a critical shear rate (also called dilatant, pseudo-dilatant, and pseudo-viscoelastic behavior). Thus, the resistance factor increases with increased flux for moderate to high fluid velocities, which was observed and reported by Seright [211][212][213][214][215] and several authors who studied the rheological and viscoelastic behavior of polymer solutions in porous media and/or high shear rates [28,196,[216][217][218][219][220][221][222][223][224][225]. At low velocities in porous media, a mild shearthinning behavior has been reported [151,219,[226][227][228], while different papers report also Newtonian or near-Newtonian behavior [212][213][214][215].…”

Mechanical Degradation of Polymers During Injection, Reservoir Propagation and Production - Field Test Results 8 TH Reservoir, Austria

“…van den Hoek et al 2012, Manichand et al 2013, Zechner et al 2015. For these conditions, no severe degradation was measured in laboratory experiments in fractures (Zechner et al 2013). Generation of fractures decreases the flow velocities and hence degradation of polymers.…”

Polyacrylamide degradation and its implications in environmental systems

“…45 Thus, limited mechanical degradation is expected during pumping of PAM through chokes, valves, and fractures where flow rates are low; degradation should be higher during flow through near-wellbore areas and perforations where velocities are much higher. [58][59][60] Mechanical degradation of PAM is enhanced at high salinity due to changes in polymer rigidity as a result of polymer complexation with ions. 61 Chemical degradation of PAM that leads to chain scission involves activation of the polymer by free radicals, 42,[62][63][64][65][66] most commonly hydroxyl radicals generated in the environment from the Fenton reaction, 62,65 interactions between oxygen and dissolved Fe 2+41,42,62,67 or other transition metals, and sulfate radicals through persulfate activation.…”