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Reports: DNI951561-DNI9: Studies of Streaming Potentials Generated by a Two-Phase Flow with Applications to Detecting Water Encroachment towards Oil Wells

Hui Zhao, PhD, University of Nevada (Las Vegas)

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Text Box: . Oil reservoirs with bottom water layers exhibit high oil recovery due to supplemental energy imparted by the aquifer. A large oil production rate may simultaneously drive oil from the reservoir and water from the underlying aquifer towards the lower pressure sink created by the oil well. Typically water moves in a cone shape and such phenomenon is termed water coning referring to the deformation of a water-oil interface which is initially horizontal. Water coning is a serious problem in managing reservoir recoveries since water mobility is much larger than oil mobility in porous rock and water phase may become so dominant in total production to the extent that further operation of the well becomes not economically valuable and the well has to be abandoned. For economic and environmental benefits, solutions have been proposed to prevent or minimize water coning during oil production including artificial barriers, downhole water sink, and injection of polymers or gels. However, in order to control water coning or minimize the impact of unwanted water in oil wells, an effective technique monitoring water flow into oil wells is the first and key step.

The objective of this project is to investigate the feasibility of measurements of streaming potentials to detect water encroachment since when water approaches an initially oil-filled reservoir, it induces changes in the streaming potential.  
Text Box: During this reported period, we made progress in both experimental and numerical aspects of the project. Experimentally, we studied the oil droplet motions in a serpentine channel geometry similar to the porous structure (Fig. 1). At small pressures, the change of the channel geometry does not break the oil droplet and the oil droplet maintains a bullet shape. As the pressure increases, the shear force near the curved surface starts to squeeze the droplet. At even higher pressures, the droplet breaks into two droplets. To measure the streaming potential, we randomly injected oil droplets into a water stream which is driven by a constant pressure and monitored the streaming potential. Our experiments showed that the streaming potential is significantly changed by the presence of the oil droplet in the serpentine channel.

Numerically, we have implemented the phase-field method to track the motion of a droplet suspended in another liquid in the curved surface in the presence of the electric field. The Laplace equation accounting for the electric field has been incorporated into the model. The model is capable of studying electrokinetic phenomena under the limit of thin double layers. The modeled droplet shape shows good agreement with experimental data.

In addition, we also studied the interaction of colloidal particles similar to soil particles at the oil-water interface. We theoretically examined the particle-particle interaction force and compared favorably with reported experimental results (Fig. 2). Due to strong electrostatic forces, particles are stably separated at the oil-water interface. Colloidal particles stabilizes the oil-water interface and prevent droplet coalescing which has an important implication in encroachment.

The ACS PRF Doctoral Investigator Grant has a significant impact on PI's career. The grant helped the PI to obtain many important results to study electrokinetic phenomena and gather preliminary results for his NSF proposal on relevant topics. The project supported two graduate students and one postdoc scholar.