The cost of managing and treating large volumes of oilfield produced water (OPW) is a key consideration to oil and gas producers. This water contains a complex mixture of inorganic and organic compounds, dissolved or not, that needs to be partially removed before disposal or reinjection. The main quality requirements for OPW disposal in offshore units are related to oil and grease content. For reservoir reinjection (reuse), it is also necessary the removal of total suspended solids (TSS), which need to be nigh absent in order to avoid clogging the reservoir production zones and maintain high injection efficiency. Conventional systems such as dissolved gas flotators and hydrocyclones have difficulties to reach the water quality requirements for reinjection in very restrictive reservoirs. Thus, membrane technology has been pointed as a potential solution for treating efficiently the OPW, removing almost completely TSS and O&G. The results obtained in this study with polymeric membranes indicated that a permeate with very low O&G content was achieved after filtration. Nonetheless, the total recovery of the original membrane permeability was not obtained and therefore, further tests with polymeric membranes were not realized.
Similar results were obtained with ceramic membranes, concerning the permeate quality, however, a much higher permeability (>620L.h−1.m−2.bar−1) was observed. In these tests, the cleaning procedures applied were also able to regenerate completely the membrane. Therefore, after preliminary studies, filtration process with ceramic membranes can be pointed as a potential technology for treating the OPW in an offshore platform, with the advantages of being compact, resistant and robust.
Formation water is a term used to describe a natural water layer that oil reservoirs have. To maintain the reservoir pressure, water is injected and along with that, formation water is brought from the reservoir to the surface during oil and gas production. The cost of caring this large volume of water is an important issue to oil and gas producers.
This water contains a complex mixture of inorganic and organic compounds, dissolved or not, that needs to be partially removed before disposal or reinjection. The volume and characteristics of OPW can differ from well to well and they depend on the kind of hydrocarbons produced and reservoir lifetime. The water disposal depends on the type of installation, injection water availability, facilities for treatment and feasibility for reusing.
The effluent discharge has to accomplish the Brazilian Environmental Agency standards. According to the resolution CONAMA393/2007, in offshore installations, the efluent's O&G content shall not exceed a monthly average of 29mg.L−1. However, in onshore units, the OPW disposal is more restrictive being necessary, in most cases, the salt removal.
The use of treated water for oil recovery enhancement is the preferred option for onshore units. On the other hand, offshore production platforms tend to discharge the OPW into the sea. This choice is made due to the current conventional technologies difficulties to reach the established quality parameters (TSS and O&G content) for reinjection in most of the reservoirs. These contaminants have to be almost completely removed to avoid clogging the reservoir production zones and to maintain high injection efficiency.
Using a higher performance technology, the required water quality for reinjection can be reached and may represent an economical option, replacing treated seawater injection and decreasing or eliminating the use of chemical products, filters and some equipments, such as deaerators and sulfate removal units.