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

TLDR

Volume Fracturing technique creates complex fracture networks by breaking up reservoirs, initiating fractures through shear failure and slip, shortening effective fluid seepage distance, and employing multi‑stage, multi‑cluster perforation to enhance productivity. The method is achieved by optimizing cluster spacing, stage intervals, and proppant filling, and by using small cluster intervals, multiple stop‑injection, and tip screen‑out technologies, especially for low‑brittle formations. Research shows that only Volume Fracturing can achieve effective seepage over long distances in ultra‑low permeability formations, and it offers strong potential in tight oil/gas, volcanic, and carbonate reservoirs, with integrated multi‑layer, multi‑branch wells as the future direction.

Abstract

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 0.000001 × 10−3 μm2 permeability to fracture for 100 m distance is about more than 100 × 104 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.