Injection of E&P wastes into a deep geologic repository has become increasingly important from both economic and technical perspectives - it can provide a long-term containment of the injected waste. There have been instances where problems have developed with injection - problems that can be costly in terms of remediation. This is especially true as waste injection projects become larger and more challenging. Multi-million barrels of drilling and production wastes have been injected into individual wells raising questions about where do the injected wastes go and why can so much be injected into a single formation. There are a number of inconsistent theories and analytical models for explaining the large storage mechanisms. A laboratory study was carried out to try to clarify these diverse models and to offer understanding on storage mechanisms for increased assurance. Drill cuttings slurries and produced water were injected, separately and commingled, into a highly permeable and weakly consolidated rock. Two experiments are summarized in this paper - one with cuttings-laden slurry only and one with cycled injections of cuttings and simulated produced water. Key observations included the following:local formation heterogeneity controls solid deposition and containmentsignificant near-fracture plugging (tip and flanks) for the lean, small particle slurry tested would advocate modification of conventional simulators to reflect leak-off degradation with increasing throughputsequential small volume injection falloff cycles can be processed to represent evolving reduction in fluid lossstimulation fracturing technologies can be applied to diagnose injector performance, especially tip plugging These findings and conclusions offer the potential for refinement of models for E&P waste injector risk management and increased waste containment assurance. Introduction Injection has become an accepted method of handling cuttings from drilling operations. Injection can be an economically favored option. In most instances, cuttings slurry is introduced into a target formation at pressures above those required to create, propagate or reinitiate a hydraulic fracture. The geometry of the created fracture system is likely much more complex than rudimentary fracturing models would suggest. Among other factors, the geometry of a fracture system depends on the evolution of internal filter cake due to filtration processes which is similar to the generation of the external or annular filter cake that is familiar to drillers and hydraulic fracturing specialists. While the processes of filtration and slurry dehydration are qualitatively intuitive, physical modelling has been developed to improve fracture geometry prediction - with application to cuttings injection, dilute slurry processes such as produced water reinjection, and concentrated injection associated with wellbore strengthening processes.
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