Application and Improvement of Ultradeep Fractured Reservoir Effective Stimulation Reservoir Volume Technology

The ultradeep fractured reservoirs in the Kuqa Piedmont exhibit complex natural fracture systems with significant developmental heterogeneity, posing substantial challenges for effective reservoir stimulation. A systematic investigation of natural fracture activation mechanisms reveals their critical role in forming efficient fracture networks. Integration of the single weak plane theory with Mohr-Coulomb failure analysis demonstrates that hydraulic fracture net pressure dynamically controls natural fracture opening. Under ultrahigh closure stress, activated natural fractures provide limited hydrocarbon flow pathways, whereas tensile-opened fractures with high-strength support exhibit substantially enhanced conductivity. These conductive fractures, combined with hydraulic fractures, form the primary seepage network that serves as the fundamental framework for significantly increasing the effective stimulated reservoir volume (ESRV). This study investigates weighted-fluid fracturing and composite acid fracturing technologies for ultradeep fractured reservoirs. Results demonstrate that increasing bottomhole net pressure while reducing reservoir fracture pressure during stimulation activates natural fractures through tension, enhancing reservoir permeability by 5-8 times and substantially expanding the ESRV. This approach significantly reduces operational risks and complexity, enabling more efficient and safer stimulation of ultradeep fractured reservoirs. To enhance the development of ultradeep fractured reservoirs, a field test employing combined weighted fracturing technology was conducted in Well BZ19. The treatment utilized composite salt and calcium chloride that weighed fluids of varying densities, resulting in successful stimulation outcomes. Key factors affecting ESRV were analyzed and optimized to significantly expand the stimulation range, providing critical technical support for exploration breakthroughs in such challenging reservoirs.