Cuttings And Waste Injection Disposal Domain Assessment From Shale Gas Fracturing

Millions of barrels of cuttings and waste injected per well around the world in shale formations dictate uncertainties regarding its actual placement and containment. The encompassed down-hole waste volume or disposal domain is defined as those hydraulically induced fractures which accumulate the bulk volume of solids from multiple slurry injections. Despite many of the outstanding milestones achieved by cuttings and waste injection, the subsurface risks involved -- such as breach to surface; intersection with near-by wells or with near-by natural faults; and well plugging -- demand constant assessment to ensure understanding of the process. Limited understanding and characterization of the injection domain down-hole footprint could potentially have a significant environmental impact. Today's understanding of Shale Gas complex fracturing geometry provides alternative means of re-evaluating past assessments around cuttings and waste disposal domains. Past assessments of multiple complex fracturing systems along the lines of the uniform disposal domain and a system of interconnected dendrite fractures with bifurcations are re-visited and evaluated in terms of minimum and maximum stress change in a localized near-wellbore fracture area, and the potential location of fracture opening/propagation or branching from the fracture away from the wellbore. This paper presents a comprehensive review of the waste disposal domain evolution from early developments -- the Mounds Drill Cuttings Experiment (MDCE) by Moschovidis -- to current understanding derived from micro-seismic observations in the Barnett, Haynesville and Marcellus shale gas fracturing. Particular discussion is presented around the presence of fissures in shale formations, together with an alternative assessment of the disposal domain from micro-seismic observations that took place during the MDCE injections. In addition, non-ideal bottom-hole pressure signatures reported in the past from observations during regular cuttings re-injection are re-visited and also re-assessed/re-aligned within a complex fracture domain model. Explanations and understanding of pressure anomalies are discussed. The paper demonstrates that a true level of assurance and risk control can be achieved for waste injection disposal (and shale gas fracturing) built around mapping of the fracture - waste disposal - storage capacity and via proactive integration of pressure monitoring with micro-seismic. Down-hole injection cuttings and waste domain mapping is the valuable information required by environmentalist and regulatory authorities to ensure that fracturing for disposal can be performed in a safe and sound manner