Search

The production performance of waterflood reservoirs with years of production is severely challenged by high water cuts and extensive water channels. Among IOR/EOR methods, weak gel injection is particularly effective in improving the water displacement efficiency and oil recovery. The visualized microscopic oil displacement experiments were designed to comprehensively investigate the weak gel mechanisms in porous media and the numerical simulations coupling equations characterizing weak gel viscosity induced dynamics were implemented to understand its planar and vertical block and movement behaviors at the field scale. From experiments, the residual oil of initial water flooding mainly exists in the form of cluster, column, dead end, and membranous, and it mainly exists in the form of cluster and dead end in subsequent water flooding stage following weak gel injection. The porous flow mechanism of weak gel includes the preferential plugging of large channels, the integral and staged transport of weak gel, and the residual oil flow along pore walls in weak gel displacement. The profile-control mechanism of weak gel is as follows: weak gel selectively enters the large channels, weak gel blocks large channels and forces subsequent water flow to change direction, weak gel uses viscoelastic bulk motion to form negative pressure oil absorption, and the oil droplets converge to form an oil stream, respectively. The numerical simulation indicates that weak gel can effectively reduce the water-oil mobility ratio, preferentially block the high permeability layer and the large pore channels, divert the subsequent water to flood the low permeability layer, and improve the water injection swept efficiency. It is found numerically that a weak gel system is able to flow forward under high-pressure differences in the subsequent water flooding, which can further improve oil displacement efficiency. Unlike the conventional profile-control methods, weak gels make it possible to displace the bypassed oil in the deep inter-well regions with significant potential to enhance oil recovery. [ABSTRACT FROM AUTHOR]

The conglomerate reservoir of the Xinjiang-552 oilfield is characterized by high heterogeneity and complex pore structure. After several years of water injection development, the formation pressure in the reservoir is low and the production per well is poor. The reservoir is difficult to regulate and control and does not meet the conditions for the implementation of the polymer flooding operations. In this paper, the numerical simulation method is applied to optimize the injection-production parameters, including the injection-production ratio, pressure recovery rate, reasonable production rate, and polymer injection timing of the polymer flooding in the X-552 reservoir. The objective of the research is to determine the optimal injection-production parameters and to provide sufficient injection-production capacity for polymer flooding. The front-water flooding technology is applied to ensure the successful progress of polymer flooding in the reservoir. The results show that when the reservoir formation pressure coefficient is 1.0 (the formation pressure is 16.4 MPa), the polymer flooding recovery is reasonably high, the front-water flooding injection time is 5 years, the injection-production ratio is 1.05, and the average annual pressure recovery rate is 0.52 MPa. As shown by the predicted results, the production profile and recovery degree are greatly improved, the development effect is satisfactory, and the goal of the frontal water flooding is achieved. The proposed method can be applied to provide guidance for front-water flooding in conglomerate-type reservoirs. [ABSTRACT FROM AUTHOR]

• The PEG/Fe 3 O 4 /GO-NH 2 nanoadsorbent removed Ca2+ and Mg2+ from oilfield wastewater by 61–70 %. • The nanoadsorbent had relatively high reuse rates of 69–80 % at the fifth recycling run. • The oil recovery significantly increased by 11.8 % when the treated oilfield wastewater was reinjected. The high salinity of oilfield-produced water caused by the presence of metal ions, such as Ca2+ and Mg2+, has a significantly adverse effect on oil recovery. It is crucial to remove these metal ions efficiently before the oilfield wastewater is reinjected down into the oil wells. To address this issue, we prepared a PEG/Fe 3 O 4 /GO-NH 2 nanoadsorbent by aminating GO, incorporating magnetic Fe 3 O 4 nanoparticles and coating with PEG (PEG = poly(ethylene glycol); GO-NH 2 = aminated graphene oxide). We investigated the removal ratios of the nanoadsorbent for Ca2+ and Mg2+. The respective removal ratios for Ca2+ and Mg2+ reached 69.8 % and 61.1 % at 10 min, indicating that the nanoadsorbent was capable of efficiently removing Ca2+ and Mg2+. We also evaluated the reusability of the nanoadsorbent by recycling and reusing it 5 times. At the fifth recycling run, the nanoadsorbent retained relatively high reuse rates (79.1 % for Ca2+, 69.5 % for Mg2+) and removal ratios (69.5 % for Ca2+, 64.3 % for Mg2+), suggesting that the nanoadsorbent possessed relatively high reusability. Oilfield wastewater treated with the nanoadsorbent was employed for oil recovery in core displacement experiments. The oil recovery efficiency significantly increased by 11.8 % compared with untreated oilfield wastewater. Therefore, the PEG/Fe 3 O 4 /GO-NH 2 nanoadsorbent exhibits considerable potential for the treatment of oilfield wastewater to enhance oil recovery. [ABSTRACT FROM AUTHOR]