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Abstract
The matrix/fracture conductivity of a fractured low-permeability reservoir is variable, and its heterogeneity is serious. When carrying out deep profile control measures, it is difficult to inject under the premise of ensuring the plugging effect. According to the characteristics of the fractured low-permeability reservoir in Chaoyanggou Oilfield, the polymer/chromium ion deep profile control system was optimized via a viscosity evaluation experiment, liquidity experiment and oil displacement experiment. The experimental results show that the high molecular weight main agent/low concentration system and low molecular weight main agent/high concentration system can meet the gel strength requirement. The evaluation results of the injection ability and plugging performance of the fractured low-permeability core show that a high molecular weight profile control system is difficult to inject, while a low molecular weight profile control system has a poor plugging performance and high cost after simulated shear. Therefore, the formulation of the profile control system was determined to be a polymer with a molecular weight of 16 million g·mol−1 as the main agent with a concentration of 1000–1500 mg·L−1. As assisting agents, the concentrations of thiourea, NaCl and NaHCO3 were 900 mg·L−1, 800 mg·L−1 and 700 mg·L−1, respectively. The plugging rate of the system was 87.6%, and the resistance coefficient was 19.2. Finally, a fractured low-permeability core model with parallel long cores was designed, and the optimal profile control system was used for the core oil-displacement experiment. Compared with the water-flooding experiment, the plugging rate can be increased by 6.9–8.0%.
Highlights
In fractured low-permeability reservoirs, there are serious contradictions between intra-scale and inter-scale layers
The results showed that adding a small amount of pre-polymer slug before injection of the profile control agent can maintain good cementitious properties and achieve good development [5]
S. et al carried out a pilot test of deep profile control for ultra-low permeability fractured reservoirs in the Yaoyingtai Oilfield, screened the indoor pre-coagulated expanded particle composite plugging agent and formula combination, and evaluated the applicability of the technology by simulating reservoir conditions with different temperatures and mineralization degrees [21]
Summary
In fractured low-permeability reservoirs, there are serious contradictions between intra-scale and inter-scale layers. An experimental study of the core displacement profile control and an oil displacement effect evaluation was carried out, and the formulation of the anionic delayed crosslinked polymer profile control agent with ideal long-term stability was determined [3]. S. et al carried out a pilot test of deep profile control for ultra-low permeability fractured reservoirs in the Yaoyingtai Oilfield, screened the indoor pre-coagulated expanded particle composite plugging agent and formula combination, and evaluated the applicability of the technology by simulating reservoir conditions with different temperatures and mineralization degrees [21]. Studied the migration characteristics and plugging mechanism of gel under fissure matrix conditions and the distribution characteristics of residual oil after subsequent fluid flooding and found that, for multi-fractured reservoirs, multiple wheel profile control can give full play to synergy and improve the profile control effect [26]. The profile control system formula of the low-permeability reservoir was preliminarily determined from the perspective of gelling viscosity
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