Volume fracturing technology of unconventional reservoirs: Connotation, design optimization and implementation

The connotation, design optimization and implementation of the Volume Fracturing technique are discussed. The connotation includes five aspects as follows: (1) break up reservoirs to form complex fracture network, and "artificial" permeability; (2) the fracture initiation involving not only single open-fracture but shear failure and slip; (3) "breakthrough" the traditional fracturing seepage theory model, greatly shorten the effective fluid seepage distance; (4) more suitable for highly brittle formations; and (5) multi-stage and multi-cluster perforation mode to improve well productivity. Research shows that: the time required to seep through matrix with 0.000 001 x 10(-3) mu m(2) permeability to fracture for 100 m distance is about more than 100 x 10(4) years, and only Volume Fracturing can realize the "shortest distance" seepage. Cluster spacing optimization, non-uniform stage (cluster) interval and proppant filling mode are the key to achieve Volume Fracturing. Small cluster interval technology, multiple stop-injection construction mode and tip screen-out fracturing technology are the key techniques to realize Volume Fracturing in low brittle formations. Volume fracturing technique has a good application prospect in tight oil (gas), volcanic and carbonate reservoirs, and the further developed "integrated" volume fracturing (based on multi-layer and multi-branch well technology) is the future development direction for unconventional resources.