Carbon dioxide (CO2) fracturing has the advantage of creating complex hydraulic fractures (HFs). However, the characteristics of HFs induced by supercritical CO2 (Sc-CO2) in tight sandstones remain unclear. In this study, laboratory true triaxial fracturing experiments were conducted on the layered Chang-7 tight sandstones and the influences of multiple factors were studied. Experimental results showed that the complexity of HFs created by Sc-CO2 fracturing could be significantly enhanced compared with that of slickwater fracturing, but only improved to a limited extent compared with that of liquid CO2 fracturing. Sc-CO2 fracturing tends to induce complex HF network in the case of small horizontal differential stress (less than 5 MPa). However, it is still possible for Sc-CO2 fracturing to generate complex HF network even under a high horizontal stress difference (over 8 MPa). A large pumping rate is conducive to generating HF branches because of the high diffusivity of Sc-CO2. Compared with open-hole completion, perforation completion can induce more HFs in the vicinity of the wellbore and also reduce the breakdown pressure. The obtained results may provide laboratory evidence for CO2 fracturing treatment design in tight sandstone formations.
Experimental Investigation on the Characteristics of Complex Fractures Created by Supercritical Carbon Dioxide in a Layered Tight Sandstone Formation
Li, S. H., Ma, X. F., Zhang, S. C., Zou, Y. S., Qi, S. L., Ge, Q., Li, N., and T. Cao. "Experimental Investigation on the Characteristics of Complex Fractures Created by Supercritical Carbon Dioxide in a Layered Tight Sandstone Formation." Paper presented at the 53rd U.S. Rock Mechanics/Geomechanics Symposium, New York City, New York, June 2019.
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