The Chang7 group in Ordos Basin usually shows low brittleness index, high differential principle stress and little natural fracture, which makes it difficult to generate complex fractures with traditional high rate hydraulic fracture practice. During a geomechanical test on core samples, complex fractures were unexpectedly found inside the test sample due to fatigue failure after cyclical stress loading below fracture gradient. Based on cyclic stress loading tests on cores and large-scale mockups, a cyclic stress fracturing technology was developed with specific operation procedure, downhole tools and optimized fracturing design parameters to generate complex fractures.

This technology injects high concentration slurry through tubing at low rate and slick-water through the annulus at various pump rate. The annulus injection rate changes constantly based on treating pressure and formation response, to achieve real-time control of bottomhole slurry concentration, in order to cyclically apply pressure on the formation rocks to induce fatigue failure, thus complex fractures are generated inside the low brittleness index Chang7 formation.

In the field trial of 24 wells, the wells fractured with cyclic stress technology showed increased fracture complexity, a 100% increase in stimulated reservoir volume in microseismic monitoring result and achieved 50% higher production than the wells treated by conventional fracturing technology.

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