Methods for Enhancing Far-Field Complexity in Fracturing Operations

Abstract

Summary For decades, the oil industry has struggled to overcome nearwellbore-fracture complexity during fracturing treatments, particularly in low-permeability, naturally fractured hard-rock reservoirs. A number of techniques have been created to diagnose and remediate these conditions to enable the extension of created fractures and successful placement of proppant deep in the reservoir. Microseismic-fracture-mapping (MSFM) technology has revealed the creation of far-field complex fracture networks in hard-rock reservoirs during fracture extension. This revelation offers the opportunity to hydraulically connect to a much larger volume of rock, provided that appropriate treatment techniques are applied to ensure the fracture network is adequately connected to the main fracture. Additionally, techniques have been developed and can be applied during the fracture treatments to facilitate and enhance the fracture-network creation. Net fracture-extension pressure analysis combined with real-time MSFM allows for identification of the degree of fracturing-network creation and provides a decisionmaking tool for engineers to modify treatment schedules or apply complexity-enhancing methods on the fly on the basis of desired treatment objectives and rock responses to the fracture treatment. This new approach to fracture stimulation requires a new focus on rock mechanics that includes defining the brittleness of the rock matrix, determining the existence and magnitude of the principal-stress anisotropy, designing the optimum spacing between fractures, and defining the optimum fracture-treatment parameters. Once the completion design is implemented, the designed treatment parameters can be adjusted in real time to meet the objectives of the completion on the basis of actual rock responses to the treatment. These rock responses are measured in real time using net fracture-extension pressure and MSFM diagnostics. Adjustments made to the fracture treatment are varied and include treatment-rate adjustments, proppant concentration, proppant-slug placement, diversion techniques to ensure opening of natural fractures, viscous-fluid spacers, acid spacers, and incremental stop/start pumping schedules. The proppant-concentration adjustments are enabled for immediate downhole changes through a unique coiled-tubing (CT) fracturing process that incorporates liquid/sand concentrate slurries. Examples of actual completion designs of these applications are discussed.