Experimental study and field test of CO2 fracturing mechanism

SU Weidong; ZHOU Ran; YE Wenyong; LI Yong; DU Yan; ZHANG Chengwu; HE Xinyan

doi:10.12055/gaskk.issn.1673-3177.2025.01.006

Natural Gas Exploration and Development >

2025 , Vol. 48 >Issue 1: 50 - 56

DOI: https://doi.org/10.12055/gaskk.issn.1673-3177.2025.01.006

OIL AND GASFIELD DEVELOPMENT

Experimental study and field test of CO₂ fracturing mechanism

SU Weidong ^,¹^,² ,
ZHOU Ran ¹^,² ,
YE Wenyong ¹^,² ,
LI Yong ¹^,² ,
DU Yan ³ ,
ZHANG Chengwu ¹^,² ,
HE Xinyan ¹^,²

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1. Drilling & Production Technology Research Institute, CNPC Chuanqing Drilling Engineering Company Limited, Deyang, Sichuan 618300, China
2. National Engineering Laboratory for Exploration and Development of Low Permeability Oil and Gas Fields, Xi’an, Shaanxi 710018, China
3. Sichuan Yuesheng Energy Group Co., Ltd., CNPC Chuanqing Drilling Engineering Company Limited, Chengdu, Sichuan 610066, China

Received date: 2024-07-03

Revised date: 2024-10-31

Online published: 2025-03-04

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Abstract

To reveal the fracture initiation mechanism in CO₂ fracturing, experiments and tests were conducted with small-sized and large-sized rock samples, and large-scale fields through large-scale physical simulation experiment of CO₂ fracturing, X-ray diffraction (XRD) detection, rock mechanics testing, rock sample CT scanning, and interpretations of water hammer pressure response and downhole microseismic fracture monitoring during on-site fracturing. The results are obtained in five aspects. First, supercritical carbon dioxide (SC-CO₂) has an extremely strong capability of filtration and penetration in rocks, and the area of the artificial fractures it causes is much smaller than that formed by conventional hydraulic fracturing. Second, CO₂ has a significant dissolution effect on calcite and dolomite in rocks, leading to a decrease in the Young’s modulus, shear modulus, and compressive strength of rocks, and an increase in rock brittleness index. Third, affected by the CO₂ soaking, the fracture surface formed after rock rupture is relatively rough and poorly integrated. Such fractures show a good conductivity even without proppants, achieving self-propping of artificial fractures. Fourth, the instantaneous pump-off pressure of CO₂ fracturing exhibits small-amplitude and long-duration fluctuations, and its pressure conduction behaviors are distinctly different from those of conventional hydraulic fracturing. Fifth, the mixed fracturing mechanism of SC-CO₂ fracturing provides a good explanation for the phenomena of less acoustic emission signals in physical simulation experiments of CO₂ fracturing, and fewer microseismic events in field tests, proving the rationality of the mixed fracturing mechanism. It is concluded that the fractures initiated by CO₂ fracturing, with no proppant added, can achieve good stimulation performance, proving the rationality of the self-propping theory of CO₂ fracturing.

Key words： CO₂ fracturing; Fracture initiation mechanism; Large-scale physical simulation experiment; Rock mechanics; Dissolution effect; Self-propping; Mixed fracturing

Cite this article

SU Weidong , ZHOU Ran , YE Wenyong , LI Yong , DU Yan , ZHANG Chengwu , HE Xinyan . Experimental study and field test of CO₂ fracturing mechanism[J]. Natural Gas Exploration and Development, 2025 , 48(1) : 50 -56 . DOI: 10.12055/gaskk.issn.1673-3177.2025.01.006

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