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Results
Corrosion As A Side Effect During Nitrate Treatment Of Produced Water And Aquifer Water Injection
Beeder, Janiche (Hydro Oile & Energi, Research Centre.) | Andersen, Tore Roberg (Hydro Oile & Energi, Research Centre.) | Liengen, Turid (Hydro Oile & Energi, Research Centre.) | Drønen, Karine (University of Bergen) | Torsvik, Terje (University of Bergen)
INTRODUCTION ABSTRACT Nitrate treatment is well documented as a mitigation method for reservoir souring, however, field trials have indicated that increased corrosion could be a possible side effect of nitrate treatment. This paper describes results from offshore side stream test rigs and laboratory investigation where a mixture of produced water and aquifer water was treated with nitrate. A corrosion rig was developed where the different combinations of produced water and Utsira aquifer water were investigated with respect to corrosion and microbial activity under offshore conditions. Corrosion increased when nitrate was added in combination with CO2, from 0.01 to > 1 mm year. The microbial community changed when nitrate was added, and the presence of H2 consuming bacteria indicates that a cathodic reaction could be a possible corrosion mechanism. During reservoir souring sulfate-reducing bacteria (SRB) convert sulfate into sulphide, causing reservoir souring. When produced water is reinjected (PWRI) the potential of reservoir souring increases due to the increase in nutrients (carbon source) for bacterial growth. Water from the Utsira aquifer is used as injection water to maintain the reservoir pressure in some oil fields in the Norwegian sector of the North Sea. At some of these fields, aquifer water is used as injection water from day one (i.e. Oilfield A, and Oilfield C), but at Oilfield B, seawater was used as injection water for the first three years followed by the use of aquifer water. The oilfields have in addition produced water reinjection (PWRI). The aquifer water is low in sulfate (<5 mg/l), however, sulfate reducing bacteria (SRB) were detected. Nitrate has been used with good results to eliminate activity of SRB and to reduce corrosion in oil fields with seawater injectio. To investigate whether the same positive effect of nitrate injection could be obtained in produced water and aquifer water, a field trial was carried out in two offshore stream test rigs. Addition of nitrate to a mixture of Utsira aquifer water and produced water gave an unexpected high corrosion rate on carbon steel, up to 4 mm/year. There were only minor differences in total bacterial counts, and number of SRB and nitrate reducing bacteria (NRB) in the rigs treated with and without nitrate. To investigate the mechanisms behind the unexpected high corrosion rates obtained at Oilfield A, a laboratory corrosion rig was developed, where produced water and aquifer water from two other oil fields, Oilfield B and Oilfield C were investigated . Experimental procedure OFFSHORE SIDE STREAM TEST RIG Two side stream test rigs were hired. The rigs were connected to the water injection system downstream the injection point for corrosion inhibitor. The sidestreamrig was designed to investigate corrosion on carbon steel and microbial growth. Samples for microbial analysis were taken from the water outlet and as biofilm on the bioprobes. Nitrate was added to one of the rigs. The other rig was operated without nitrate addition.
- Europe > Norway (0.87)
- North America > United States > Texas (0.48)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Disposal/Injection (0.91)
ABSTRACT The candidate waters available for secondary recovery of oil in West Kuwait oil fields are all high in salt. Total dissolved solids (TDS) of an aquifer water is 239,000 ppm (chloride, 146,000 ppm). Effluent water varies, but TDS can reach 241,000 ppm (chloride, 151,000 ppm). Candidate materials for tubulars for secondary injection were tested for MIC attack at high salt concentrations. N-80 and L-80 steels, and three FRPs - phenolic, vinyl ester and epoxy resin were tested in the two water types. A mixed bacterial consortium (including SRB) from a natural Mediterranean marine environment was habituated to high salinity and used as the inoculum. All steel coupons were attacked. Ranking from most to least corroded was as follows: L-80 effluent water > L-80 aquifer water > N-80 effluent water > N-80 aquifer water, indicating that N-80 was more corrosion resistant than L-80 and effluent water was more corrosive than aquifer in these experiments. There was no evidence of attack of the vinyl ester or epoxy based FRP coupons by microorganisms. The surface gel coat of the vinyl ester and epoxy materials did not change in appearance and was not attacked or damaged by the bacteria. No conclusions could be drawn about the phenolic material. Although it did not appear damaged to the naked eye, the gel coat was so fragile that it was attacked by the chemicals and procedures required to examine the coupons in detail. INTRODUCTION Secondary recovery is becoming increasingly common in oilfields around the world as oil stocks dwindle and prices rise. Introduction of SRB and other microorganisms in injection water for secondary recovery has been associated with significant problems of souring, loss of injectivity, plugging and corrosion in fields that had previously been trouble free and sweet. The potential for MIC, therefore, increases significantly with secondary recovery operations and must be considered in any program of water injection. There are various factors that affect the degree of souring and corrosion in secondary injection systems. Mineralogy of the formation rock is one factor in SRB contamination. Siderites, iron-bearing minerals, can act as a barrier to H2S production by sequestering sulfide, increasing the time before production souring occurs. The composition of the indigenous microbial community is a second factor. Competitive exclusion of SRB by other, less harmful bacteria can reduce sulfide production. Encouraging beneficial bacteria has been used successfully to mitigate problems associated with SRB. Another significant factor in potential for contamination of wells and equipment is the quality of the injection water. In West Kuwait, all potential source waters are high in salt. One question that has arisen is whether brines will support growth of SRB and other bacteria. Brines are described as waters higher than typical sea water in dissolved inorganic salt. One aspect of this study was to investigate the growth of marine bacteria in brines. Candidates for injection water for secondary recovery in West Kuwait oilfields are all high in total dissolved solids (TDS).
- North America > United States (1.00)
- Asia > Middle East > Kuwait (1.00)
- Geology > Mineral > Sulfide (0.54)
- Geology > Sedimentary Geology > Depositional Environment > Marine Environment (0.34)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.90)
- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5505/13 > Halfdan Field > Maastrichtian Formation (0.99)
- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5505/13 > Halfdan Field > Danian Formation (0.99)
- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5504/16 > Halfdan Field > Maastrichtian Formation (0.99)
- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5504/16 > Halfdan Field > Danian Formation (0.99)