Significant challenges have been addressed in the application of gel-based materials for permeable carbonate matrices with multi-modal pore systems. Different from near wellbore treatments, this study focuses on a large slug microsphere injection aiming at deep fluid diversion. The objective is to demonstrate the efficiency of the microsphere injection in carbonates in comparison with that in sandstones by conducting a series of coreflooding displacement tests. Numerical simulation studies were carried out to capture response in different wettability regimes.
Coreflooding tests were conducted to study the potential of oil production that can be achieved through microspheres suspended in a polymer solution. Two sets of microsphere systems, with a median size of 0.05 and 0.3 μm in injection water, were used in this study. The tests were conducted at 95°C and 3100 psi pore pressure. The injection procedure started with waterflooding, followed by 1 pore volume of microsphere injection then post waterflooding. Effects of core mineralogy and microsphere particle size on incremental oil production were investigated. The coreflooding displacement processes including microsphere injection were simulated using UTCHEM simulator.
The effectiveness of microspheres, which are smaller than the pores/throats of the porous media, relies on the amount of microspheres injected. The coreflooding displacement with one pore volume of microsphere injection demonstrated significant incremental oil production in carbonate and sandstone core plugs, compared to polymer flooding only. The results showed that higher oil production came from higher differential pressure, which can be attributed to disjoining pressure and pore channel plugging incurred in the porous media. The microsphere injection had higher oil production in the oil-wet carbonate cores than the water-wet sandstone cores with similar permeability. It was supported by the differential pressure data that indicated that microspheres reduced the permeability in carbonates more effectively than that in sandstone cores. Moreover, microsphere injection with larger particle size yielded higher oil production. The experimental results were well matched by the fluid-flow simulator. The simulation results revealed that microsphere injection had a quick and lasting response on oil production, compared to polymer flooding. The simulation results also support our findings that the performance of the microsphere injection is more effective in oil-wet carbonates than in water-wet sandstones.
This work provides an insight of microsphere injection effectiveness in terms of achieved microsphere size, incremental oil production, rock type; and reveals the applicability and durability of such injectant in oil-wet carbonate reservoirs at harsh reservoir conditions, namely high temperature and high salinity.