Optimizing Seepage Field in Ultra-Low Permeability Reservoirs: A Study on Repeated Fracturing in the Hulangmao Oilfield

Abstract

This study explores the mechanisms behind seepage field enhancement in low-yield zones of ultra-low permeability reservoirs, such as those in the Hulangmao Oilfield. The objective is to analyze dynamic characteristics, define effective displacement boundaries, and optimize repeated fracturing parameters to improve oil recovery. The research integrates dynamic analysis, core experiments (start-up pressure gradient and fractured-core flooding), and numerical simulations. A geology modeling–fracture characterization–simulation workflow was established to study fracture propagation and the evolution of the seepage field. Parameters such as fracture penetration ratio and effective well spacing were optimized using experimental data and engineering charts. Core experiments identified an optimal fracture penetration ratio of 0.3–0.45 for effective displacement, with a start-up pressure gradient of 0.62×10−3 MPa/cm. Numerical simulations demonstrated that repeated fracturing improves pressure gradients, increases swept volume, and reduces effective well spacing, enabling secondary effective displacement. Field tests in the Hulangmao block showed an average incremental oil production of 1.55 t/d per well. The study concludes that repeated fracturing, tailored to reservoir permeability and fracture development, enhances recovery by optimizing fracture-network matching with the well pattern. This research introduces an integrated methodology combining geology modeling, fracture characterization, and numerical simulation to optimize repeated fracturing design. It provides practical guidelines for optimizing fracture parameters and well spacing, offering valuable insights for engineers working in ultra-low permeability reservoirs.