Experimental Characterization of Oil/Gas Interface Self-Adjustment in CO 2 -Assisted Gravity Drainage for Reverse Rhythm Reservoir

Haishui Han, Xinglong Chen, Zemin Ji, Junshi Li, Weifeng Lv, Qun Zhang, Ming Gao and Hao Kang
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Haishui Han: Research Institute of Petroleum Exploration and Development, PetroChina Company Limited, Beijing 100083, China
Xinglong Chen: Research Institute of Petroleum Exploration and Development, PetroChina Company Limited, Beijing 100083, China
Zemin Ji: Research Institute of Petroleum Exploration and Development, PetroChina Company Limited, Beijing 100083, China
Junshi Li: CNPC Advisory Center, PetroChina Company Limited, Beijing 100120, China
Weifeng Lv: Research Institute of Petroleum Exploration and Development, PetroChina Company Limited, Beijing 100083, China
Qun Zhang: Research Institute of Petroleum Exploration and Development, PetroChina Company Limited, Beijing 100083, China
Ming Gao: Research Institute of Petroleum Exploration and Development, PetroChina Company Limited, Beijing 100083, China
Hao Kang: Polytechnic College, Hebei Normal University, Shijiazhuang 050024, China

Energies, 2022, vol. 15, issue 16, 1-16

Abstract: Worldwide practices have proven that gas-assisted gravity drainage can obviously enhance oil recovery, and this technology can be especially effective for reservoirs with a thick formation and large inclination angle. For the successful implementation of this process, a key technology is the stable control of gas–oil interface during gas injection. For a detailed exploration of this technique, a three-stage permeable visual model was designed and manufactured, with permeability decreasing from top to bottom, thus, a reverse rhythm reservoir was effectively modeled. Then the experiment concerning CO 2 -assisted gravity drainage was carried out with the adoption of a self-developed micro visual displacement device. This study mainly focused on the micro migration law of gas–oil interface and the development effects of CO 2 -assisted gravity drainage. According to the experiments, CO 2 fingering somewhat happens in the same permeable layer from the beginning of gas injection. However, phenomena of “wait” and “gas–oil interface self-adjustment” occur instead of flowing into the next layer when the injected CO 2 reaches the boundary of the next lower permeability layer through the dominant channel. By the “gas–oil interface self-adjustment”, the injected CO 2 first enters into the pores of the relative higher permeability layer to the greatest extent, and thus expands the sweep volume. Futhermore, in the process of CO 2 injection, obvious gas channeling occurs in the low permeability layer directly connected to the outlet, resulting in low sweep efficiency and poor development effect. After connecting the core with lower permeability at the outlet, the development indexes of the model, such as the producing degree of the low permeability layer, the oil recovery before and after gas breakthrough, are significantly improved, and the recovery degrees of the medium permeability layer and the high permeability layer are also improved, and the overall recovery factor is increased by 12.38%. This “gas–oil interface self-adjustment” phenomenon is explained reasonably from the two scales of macroscopic flow resistance and microscopic capillary force. Finally, the enlightenments of the new phenomenon are expounded on the application of gas-assisted gravity drainage on site and the treatment of producers with gas breakthrough in gas injection development.

Keywords: heterogeneous reservoir; gas injection; gas–oil interface self-adjustment; seepage resistance; reverse rhythm (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
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