Experimental Study on the Oil Recovery Performance of CO2 Huff-and-Puff Process in Fractured Tight Oil Reservoirs

Abstract

In order to investigate energy supply capacity and oil production contribution of near-fracture and fracture-free zone in fractured tight oil reservoirs, a series of CO2 huff-and-puff tests were designed and carried out in different experimental conditions. A fracture-matrix long-core system was established to simulate the near-fracture zone and matrix zone of tight oil reservoirs. The NMR technique was utilized to identify the microscopic remaining oil of certain core samples. The effects of fracture length, soaking time, depressurization method, and asphaltene precipitation on the oil recovery performance of CO2 huff-and-puff process were evaluated, respectively. The results indicated that the dissolution and diffusion range of the injected CO2 can be apparently increased from both macro and micro aspects through increasing the length or density of the fractures and extending the soaking time; and, during puff period, the slow depressurization method has better recovery effect on near-fracture zone, while the step depressurization method has better recovery effect on distal fracture-free matrix. After CO2 huff-and-puff process, the oil recovery of the medium pores near fracture could be close to oil recovery of the large pores, which is higher than 60%. But, in the distal matrix, the oil recovery of the medium pores was only a little higher than depletion development. The remaining oil of medium pores in distal fracture-free matrix still has great potential to be developed after CO2 huff-and-puff process.

Insights into Enhancing Shale Oil Recovery Postfracturing with CO2 Huff and Puff and Elastic Depletion Development Strategies

“…41 Qian et al studied the liquid production capacity of fractured and nonfractured ends of fractured tight oil reservoirs by changing the fracture length, soaking time, and depressurization method. 42 The results show that increasing the fracture length can improve the recovery rate and the recovery rate of the pore in the core near the fracture end is effectively improved. Bejestani et al studied the effects of porosity and permeability of the rock matrix on oil recovery when CO 2 is injected under different miscible conditions (primary miscible, near miscible, and immiscible).…”

“…The existence of fractures reduces the pore seepage resistance and increases the contact area between CO 2 and matrix pores, which is conducive to the extraction of the crude oil from smaller pores . Qian et al studied the liquid production capacity of fractured and nonfractured ends of fractured tight oil reservoirs by changing the fracture length, soaking time, and depressurization method . The results show that increasing the fracture length can improve the recovery rate and the recovery rate of the pore in the core near the fracture end is effectively improved.…”

Performance Evaluation of CO2 Soaking and Flooding Processes in Tight Oil Reservoirs

“…Shen and Sheng carried out experiments and built a core-scale simulation model to investigate the asphaltene deposition in shale and reported that the CO 2 penetration depth and CO 2 concentration were the dominant factors in asphaltene precipitation. Moreover, the research on asphaltene precipitation on the tight cores during the soaking process mainly focused on permeability reduction. − The microscopic asphaltene precipitation distribution in the pores and its comparison with CO 2 flooding have been rarely studied.…”