Abstract
In order to evaluate the displacement effect of four kinds of injection media in tight oil sandstone, water, active water, CO2, N2 flooding experiments were carried out in laboratory. Online Nuclear Magnetic Resonance (NMR) spectrometers combine the advantages of NMR technology and core displacement experiments. In the displacement experiment, NMR data of different injection volumes were obtained and magnetic resonance imaging (MRI) was carried out. The results showed that micro and sub-micropores provided 62–97% of the produced crude oil. The enhanced oil recovery ratio of active water flooding was higher than that of conventional water flooding up to 10%. The recovery ratio of gas flooding in micro and sub-micropores was 60–70% higher than that of water flooding. The recovery ratio of CO2 flooding was 10% higher than that of N2 flooding. The remaining oil was mainly distributed in pores larger than 0.1 μm. Under the same permeability level, the remaining oil saturation of cores after gas flooding was 10–25% lower than water flooding. From MRI images, the displacement effects from good to bad were as follows: CO2 flooding, N2 flooding, active water flooding, and conventional water flooding.
Highlights
In the face of the continuous growth of world oil and gas demand and the decline of conventional resources production, tight oil resources with great potential have gradually become burning issues in global petroleum exploration and development [1,2,3,4]
The pores were divided into nanopores, micro-nanopores, sub-micropores, and micropores according to pore radius [44,55], which were 0.05, 0.1, and 1 μm
The distribution of pore radius was analyzed by Nuclear Magnetic Resonance (NMR) data which was acquired from the 16 cores saturated with simulated formation water
Summary
In the face of the continuous growth of world oil and gas demand and the decline of conventional resources production, tight oil resources with great potential have gradually become burning issues in global petroleum exploration and development [1,2,3,4]. China has abundant and plentiful tight oil resources [5], most of which are continental deposits, unlike the United States, where they are marine deposits [6]. The development difficulty of tight oil reservoirs in China is different from that in the United States. China has carried out tight oil reservoirs development in Ordos, Songliao, Santanghu, and Junggar Basin [6].
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