Disposal of produced fluids, during different well activities, has been one of the main challenges for field operators due to environmental and economical concerns. The limitations on the discharge of oily wastes in addition to other regional regulations have resulted in several efforts to develop technologies and techniques that can be utilized as on-site disposal mechanism. One technique is to re-inject produced fluids into non-productive permeable zones of adjacent wells.
A comprehensive lab investigation was conducted in order to explore the feasibility of re-injecting various produced fluids during different activities such as mudcake clean-out, completion, or well stimulation treatments. This study includes also a detailed investigation of emulsion and scaling potential of various produced fluids mixtures: oil/clean-out fluid, oil/spent acid, spent acid/formation brine and clean-out/formation brine. In addition, a series of coreflood experiments was conducted to assess the effect of produced fluids injection on the initial permeability of core plugs taken from non-productive sandstone formation. These experiments were conducted at reservoir temperature using representative cores and collected produced fluids.
Coreflooding experiments showed that the effect of oil injection on core plugs permeability was mainly constrained by the initial core permeability. In tight cores, K = 25 mD, injection of oil damaged the core by forming external oil filter cake on the face of core. However, in cores with high initial permeability, K > 1 D, nearly 10 PV of produced oil was injected with no observed formation damage. Similarly, clean-out fluids/oil mixtures were also injected with no observed formation damage. In contrast to oil/clean-out fluids, spent acid/oil injection effect on core permeability value was dependent on injected spent acid type. This paper provides the recommendations and limitations of using produced fluids re-injection as a waste management technique.