Status, Experience, and Inspiration of Unconventional Resources Hydraulic Fracturing Technology

Abstract

Abstract China's recoverable tight/shale oil resources amount up to 32 billion barrels, and 92% of the newfound proven reserves are low/ultra low permeability or unconventional reserves. Complex sedimentary structure & geological conditions, deeper reservoir burial and worse reservoir characteristics, fast decline, low recovery and high cost these all make it very hard to develop these kinds of reservoirs. In this paper, we firstly introduced the geology and reservoir characteristics of unconventional tight/shale oil and tight/shale gas reservoir, compared with North America, the organic-rich shales in China are characterized by large burial depth (about 65% of the shales with a burial depth > 3,500 m), complex surface conditions, and variety of types of organic-rich shale. These characteristics determine that the resource characteristics of these shale oil and gas are different from those of the widely developed in the United States. We summarized the past 30 years’ progress of hydraulic fracturing technology, from vertical well acidizing, vertical well hydraulic fracturing, and horizontal well multi-stage multi-cluster hydraulic fracturing. Small well spacing, dense cutting and 5-6m length per clusters is the optimal artificial fracture spacing for this kind reservoir via Geo.-Eng. integrated fracturing design. Extreme Limited-Entry (XLE) perforation design, 3-8 perforation holes per cluster is best for equilibrium artificial fracture initiation, 6-8 clusters per stage and over 85% fractures can be opened via downhole cameral monitor. P’N’P completion method and soluble well downhole plugs, saving non-pumping time and reducing fracturing costs. Multifunctional fluids and reusable low-cost variable-viscosity slickwater, featured with imbibition mechanism and increase oil recovery. Low-cost quartz sands wildly be used to reduce costs. Factory style hydraulic fracturing mode, increase the fracturing efficiency and reduce on-site organizational costs. The integrated technologies have been widely applied in unconventional wells. Application of the integrated technologies and the experience can be references for the development of similar marginal reservoirs.