RIASSUNTO
Abstract
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.
Introduction
Throughout well lifetime, the activities of drilling, completion, or well stimulation involve the production of various fluid mixtures such as oil, clean-out fluids, and spent acids. The disposal of these fluids has been a persistent challenge to operators due to personnel safety, environmental, and economic concerns. This challenge is even more complicated in offshore environments, where the personnel safety and environmental concerns are exacerbated by the necessity to transport these fluids to an appropriate onshore waste treatment or to disposal facility.
The Regional Organization for the Protection of the Marine Environment (ROPME) regulates discharges from offshore oil and gas facilities under the "Protocol Concerning Marine Pollution resulting from Exploration and Exploitation of the Continental Shelf??. The guidelines of this protocol prohibit the discharge of offshore installation into the sea except one derived from drilling operations. The oil content in this discharge shall not exceed 40 ppm as an average in any calendar month, and shall not exceed 100 ppm at any time. In addition, the discharge points of oily wastes should be below the surface of the sea (The Regional Organization for the Protection of the Marine Environment (ROPME) 1993).
The limitations on the discharge of oily wastes and other regional regulations have resulted in several efforts to develop technologies and techniques that would make oily discharges suitable for offshore disposal such are incinerators, and solvent-extraction systems (Young et al., 1991; Shaw and Slater, 1989; Heilherker, 1989; Des Ormeaux et al., 1988). However, most of these efforts failed to produce environmentally acceptable effluents and were too expensive to use. Other techniques such as cleaning systems for oil-based mud cuttings proved to be operationally and environmentally effective, but they were too slow to provide real-time treatment for produced oily wastes (Malachosky and Lantero 1990). The combination of drawbacks associated with these methods; and expense, employee exposure involved in transfer operations of oily wastes warrant the need for an onsite disposal option.