ABSTRACT
The existing plugging removal operation in JZ9-3 oilfield has the disadvantages of small amount of plugging remover, fast injection speed, and short construction time. Under the condition of injection well suction profile reversal, plugging remover is difficult to enter the low permeability part and play the role of deep plugging removal. In order to improve the plugging removal effect, this paper used the physical simulation method to carry out the experimental study and mechanism analysis on the effect of water flooding, chemical flooding, and plugging removal measures of the multi-layer system combination model. The results showed that the recovery of general plugging removal after chemical flooding increases by only 0.70%, while the recovery of 'profile control + plugging removal' increases by '9.34% + 2.59%', and the amount of produced liquid decreases by more than 40%. It can be seen that the combined operation of profile control and plugging removal has dual effects of plugging and dredging and synergistic effect, which not only expands the swept volume, but also reduces the inefficient and ineffective cycles. On this basis, the optimization design and effect prediction of the target well W4-2 plugging removal scheme were carried out by using the numerical simulation method. Recommended scheme: inorganic gel profile control agent volume 13,243.6 m3, produced by the main agent (Na2O·nSiO2), isolation fluid (Water), and auxiliary agent (CaCl2) through multiple rounds of alternating injection into the reservoir. The plug removal agent (K2S2O8) injection volume is 100 m3, the concentration is 0.8%. The post-implementation 'Output/Input' ratio is expected to be 3.7.
ABSTRACT
In this article, we developed a new composite gel for plugging dominant fluid flow channels in offshore oilfields. The composite gel was synthesized by organic and inorganic gel networks interpenetrating into a compact three-dimensional spatial network structure, resulting in a good plugging effect. The performance of the composite gel was evaluated from the aspects of gelling characteristics and gel microstructure, while the plugging effect was evaluated through core experiments. The results showed that the influencing order of each component on gelling was acrylamide > cross-linking agent > urea > initiator > polyaluminum chloride. The initial viscosity of the composite gel was about 5-6 mPa·s, and it had good plugging abilities in different permeability cores. In comparison with inorganic gels (plugging ratio of 77.2%) or organic gels (84.8%), the composite gel system has a plugging ratio of up to 99.5% using a core with water permeability of 4300 mD. Besides, the reservoir applicability of the composite gel was studied, and the results suggested that the composite gel system had good resistance to dilution, mechanical shear, oil corrosion, and aging and could be quickly removed after plugging.
ABSTRACT
To meet the technical requirements of deep fluid diversion in Bohai oilfield, the swelling property, plugging effect, transport characteristics of polymer microspheres, and fluid diversion effect in heterogeneous cores are studied in this paper. There are two kinds of polymer microspheres including core-shell microspheres and traditional microspheres. The instruments used in this study include a biomicroscope, a metallurgical microscope, a scanning electron microscope, and core displacement experimental devices. The results of microscopes indicated that the core-shell microspheres were successfully synthesized, and the microspheres had good hydration expansion effect. The expanded microspheres could attract each other through the electrostatic force of anions and cations to achieve the purpose of coalescence. Compared with traditional microspheres (initial particle size is 3.8 µm), the initial particle size of the synthesized core-shell microspheres is close to 3.3 µm, but the particle size distribution is more concentrated, so the injection performance is close to that of traditional microspheres (initial particle size is 3.8 µm). After 8 days of hydration expansion, although the expansion multiple is small, it can coalesce and enhance the plugging effect, which can adapt to a wider range of permeability, ranging from 200 × 10-3 to 3000 × 10-3 µm2 (200 × 10-3-1500 × 10-3 µm2 for traditional microspheres). Under the same conditions (heterogeneous core), compared with the traditional microspheres, the core-shell microspheres have the characteristics of coalescence. Therefore, its fluid diversion effect is better, and the oil recovery is increased by 5.5%. Nevertheless, there is the "end effect" during the injection process, which weakens the steering effect of deep liquid flow. The results show that the "end effect" can be effectively reduced by alternate injection of microspheres and water. Meanwhile, the effect of deep fluid diversion is improved, and the increase of oil recovery is increased by 2.06%.
ABSTRACT
Establishing an effective displacement system for conventional water flooding development in low-permeability reservoirs is difficult, with generally low liquid and oil production and a worse water flooding effect. Imbibition oil recovery technology has received increasing attention from oil development workers because of its simple operation, low cost, and good oil increase effect. To explore the method and mechanism to further improve the effect of imbibition oil recovery, we study the imbibition and oil recovery effect and its influencing factors in a low-permeability reservoir in the Dagang Oilfield based on evaluation indexes of the adhesion work reduction factor, ratio of capillary force to gravity N B -1, regression analysis of the recovery rate of imbibition, proportional relationship with spontaneous imbibition, and dynamic imbibition effect in crack rocks. Results show that reducing the interfacial tension of the surfactant on the imbibition process has a dual effect. The selection of the surfactant for fractured tight reservoirs should not excessively pursue ultralow interfacial tension, and it should consider the surface wettability environment favorable for imbibition to ensure that a sufficient driving force can be provided. In the initial imbibition stage, the capillary force is large, the velocity of water imbibition in pores is fast, and the oil recovery rate is high; the holding time of the imbibition process is important to imbibition recovery. With the increase in imbibition time, the capillary force weakens, and the imbibition speed decreases to zero. With the increase in injection volume, reservoir pressure, pressure holding time, and imbibition cycles, the oil recovery increases, but the amplification of oil recovery decreases. From the technical and economic viewpoints, the optimal slug size, throughput cycle, and pressure holding time of the target reservoir are recommended as follows: 0.5 PV,three3 rounds, and greater than 96 h, respectively.