University of Calabar

Alkali surfactant polymer (ASP) flooding technique is deployed in the oil industry to enhance oil recovery (EOR), especially in aged reservoirs. Microorganisms have been found to utilize the polymer constituent as a nutrient source to accelerate steel corrosion. This work aimed at examining the contributions of microorganisms, sediments, and polymer degradation to the overall corrosion behavior of steel pipes used in ASP flooding system via electrochemical, microscopic, and spectroscopic characterization techniques. The results demonstrate that rust deposition significantly influenced the steel's electrochemical behavior in the SRB-containing ASP solution; driving internal polarization and potential difference with the bare metal thereby establishing a galvanic interaction to accelerate steel corrosion. After 14 days of testing in the SRB environment, the steel covered by rust deposits recorded the most severe localized corrosion of all samples under examination, whereas pitting severity significantly reduced on the bare steel and the sand-deposited coupon. Factors such as sediment conductivity, film development, and microbial activities played crucial role in exacerbating steel corrosion under the rust deposits in the SRB-inoculated ASP solution.

Tidal creeks are characteristic features of coastal wetlands. As transport channels, they play a major role in determining the contaminant status of biologically sensitive back-barrier ecosystems. This role will vary in different tidal creek sub-systems, the two most common and genetically related being herein referred to as estuarine and inlet creeks. In the S.E. coast of Nigeria, both creeks have one channel end linked to the mesotidal Qua Iboe River estuary but differ in that the estuarine creek channel also directly opens to the ocean. The implication of hydrodynamic variations in these creek types to contaminant longevity is the focus of this investigation. Of the ten flow and water quality variables evaluated over 50-day successive simultaneous half-hourly tidal cycle monitoring, the inlet creek and river estuary displayed ebb-asymmetry in 80-90 % of the variables at frequencies of >50-70 % and 76-93 %, respectively. By contrast, the estuarine creek indicated flood-asymmetry in 70 % of the variables at frequencies in the 56-64 % range. With the exception of pH, variables in both creeks showed time series patterns related to lunar tidal forcing variation. Creek tidal excursion length ratios suggest an average of 210 % longer import transport distance of contaminants in estuarine creek as against 170 % longer export distance. The averaged import- to-export distance ratios of 1.23, 1.02, and 0.5 indicated by the estuarine creek, inlet creek and the river estuary, respectively, suggest a decreasing contaminant retention tendency in consonance with their residual velocity and net salinity patterns.

Empirical-based vulnerability ranking of coastal aquifers to ocean-emanating influxes at tidal frequencies is not in public domain. Dynamic pattern analysis of coastal aquifers in microtidal and mesotidal settings of the Nigerian coast shows groundwater level oscillation to be mostly sinusoidal as their contiguous surface water body counterparts. This, in concert with sinusoidal conductivity change patterns, suggests periodic intrusion and expulsion of ocean-borne contaminants out of the aquifers at tidal frequencies. The contrasting water level oscillation amplitudes, water level rise/fall rate and flood/ebb duration ratios form the basis for a simple conceptual model of coastal aquifer vulnerability ranking outlined. The asymmetric water level rise rate and flood duration as well as very high tidal cycle-mean groundwater to surface water conductivity ratio of microtidal aquifers suggest poor flushing potentials and thus higher long-term vulnerability to ocean-borne pollutants when compared with the mesotidal counterparts.