Risk assessment of human exposure to radionuclides and heavy metals in oil-based mud samples used for drilling operation.

This study investigates heavy metals and naturally occurring radionuclide materials (NORM) possible presence and pollution rates in oil-based drilling fluids system used to drill an oil and gas well. It also estimates the health risks of the drilling crew due to their exposure to these substances. Measurements from Atomic Absorption Spectrometry (AAS) revealed that, the concentrations of the metals present in the drilling mud samples varied significantly and decreased in the order of Zn > Al > Ni > Pb > Cr > Cu > As > Hg > Cd. Generally, amongst all the heavy metals considered, mud sample C had the highest heavy metal concentration when compared to samples A and B, respectively. When compared with the recommended maximum allowable limits, Cd and Ni were found to be higher than the International Reference Standard by factors of Cd (3 mg/kg) and Ni (50 mg/kg). The cancer risk obtained from this present study are 1.1 × 10-3 and 7.7 × 10-3 for the drilling crew, which is slightly above the acceptable risk range considered by the environmental and regulatory agencies. The concentrations of radioactive substances as obtained from analysis, show that K-40 is the dominant radionuclide in the samples with the highest value slightly twice the standard reference value. The concentrations of Ra-226 and Th-232 activity in the mud samples were found to be lower when compared with the International Reference Level. Also, the X-ray diffraction analysis helped to identify 16 very important/useful minerals in the three mud samples under consideration. The higher elemental concentrations of potassium and aluminum silicate found in sample C can be credited to the elevated heavy metal-content found in the mud samples. Significantly, these exposure risks found in this present study indicate that the potential health risks due to radiological activities may not pose short - but long-term risks to the drillers.

A Review on Polymer Nanocomposites and Their Effective Applications in Membranes and Adsorbents for Water Treatment and Gas Separation.

Globally, environmental challenges have been recognised as a matter of concern. Among these challenges are the reduced availability and quality of drinking water, and greenhouse gases that give rise to change in climate by entrapping heat, which result in respirational illness from smog and air pollution. Globally, the rate of demand for the use of freshwater has outgrown the rate of population increase; as the rapid growth in town and cities place a huge pressure on neighbouring water resources. Besides, the rapid growth in anthropogenic activities, such as the generation of energy and its conveyance, release carbon dioxide and other greenhouse gases, warming the planet. Polymer nanocomposite has played a significant role in finding solutions to current environmental problems. It has found interest due to its high potential for the reduction of gas emission, and elimination of pollutants, heavy metals, dyes, and oil in wastewater. The revolution of integrating developed novel nanomaterials such as nanoparticles, carbon nanotubes, nanofibers and activated carbon, in polymers, have instigated revitalizing and favourable inventive nanotechnologies for the treatment of wastewater and gas separation. This review discusses the effective employment of polymer nanocomposites for environmental utilizations. Polymer nanocomposite membranes for wastewater treatment and gas separation were reviewed together with their mechanisms. The use of polymer nanocomposites as an adsorbent for toxic metals ions removal and an adsorbent for dye removal were also discussed, together with the mechanism of the adsorption process. Patents in the utilization of innovative polymeric nanocomposite membranes for environmental utilizations were discussed.

In-situ remediation of petroleum-contaminated soil by application of plant-based surfactants toward preventing environmental degradation.

Remediation in this study employs the use of green plants and their extracts in enhancing the remediation process of polluted soils. GC-MS & FTIR techniques were employed in determining the constituents of the soil during the investigation. 60 ml of the extracts were applied on 1 by 2 ft segments of hydrocarbon polluted site and observed for two months. The results show that plant extract A significantly reduced the TPHs and PAHs to 5,450 and 126.2 mg/kg, respectively, as compared to those of extract B whose TPH and PAH values are 10,432 and 362.3 mg/kg, respectively. Both plant extracts reduced the total petroleum hydrocarbon compounds significantly when compared to the standard reference PAH and PAHs (4,500 mg/kg and 50 mg/kg respectively). The microbial plate count for the three media shows that the plant based surfactant had a synergy with the identified bacteria in enhancing Phytoremediation of the crude oil polluted site. Novelty statement: This study examined the application of two plant-based surfactants for remediation. These natural surfactants significantly reduced the petroleum hydrocarbon compounds present in the soil within the in-situ observation window. These Herbaceous plant family extracts have a great advantage as an eco-friendly alternative to synthetic surfactants, and they also exhibited an anti-fungi characteristic. The two biodegradable plant-based surfactants also significantly reduced the time that it could have taken for a remediation process.

Dataset on effect of sand grain size and water salinity on oil recovery.

This research investigates the combined effect of grain size and water salinity on oil recovery. Water flooding experiment was carried out using unconsolidated formation from Niger Delta. Five groups consisting of five samples, were tested for the effective interaction of two factors (grain size and salinity) and how they affect oil recovery. Each group was assigned a particular grain size while the prepared brine concentration was varied within a specified range. The selected grain sizes were obtained from laboratory sieve analyses. For each sand sample, the same concentration of brine used in saturating it was poured into the accumulator and connected to the flooding tube to displace a column of crude oil. The control valve was opened to cause oil displacement. The amount of brine used to displace the crude oil was ten times the pore volume and all the oil in each sample was recovered by the saturated brine solution. Laboratory investigations show that oil recovery was highest for brine concentration of 15,000 ppm; this was also the case in relation to oil recovery and sand grain sizes.

Toxicology of Heavy Metals to Subsurface Lithofacies and Drillers during Drilling of Hydrocarbon Wells.

This study investigates the toxicological effects of heavy metals on lithofacies of the subsurface in a drilled hydrocarbon well as well as, to the drilling crew and people in an environment. The pollution levels of selected heavy metals were considered alongside their ecological effects during dry and wet seasons. The health hazard potential of human exposures to the metals, were estimated in terms of intensity and time using the USEPA recommended model. The heavy metal concentration for each layer decreased across the lithofacies as follows; Layer 5> Layer 4> Layer 3> Layer 2> Layer 1. The average concentrations of the heavy metals present in the samples obtained from the formation zone, varied significantly and decreased in the order of Al> Zn> Ni> Pb> Cr> Cu> Cd> As> Hg. The highest concentration of Al, Cu, and Zn in this present study were within the maximum allowable limits whereas, those of As, Cd, Hg and Ni were all above their maximum allowable limits. Among the transition metals analysed, the maximum mean daily dose of Pb (9.18 × 10-6 mg/kg/d) and Cr (1.42 × 10-6 mg/kg/d) were confirmed susceptible to human carcinogens and environmental toxins. The estimated hazard quotient shows that the dermal pathway is the most likely route via which the drilling crew and people in the environment can get contaminated. The cancer risk values for the Pb (7.72 × 10-4), Cd (1.35 × 10-1), Ni (9.97 × 10-3), As (1.50 × 10-1) and Cr (3.16 × 10-3) are all above the acceptable values. The cancer risk contribution for each metal was in the order of As> Cd> Ni> Cr> Pb. Layer 5 had the maximum Geo-accumulation index for the heavy metals considered. This higher Geo-accumulation index noted at the depth in Layer 5 may be attributed to the effect of water basin with turbidity currents, deltas, and shallow marine sediment deposits with storm impacted conditions. Also, the pollution from lead (Pb) in the dry season was maximum with an Igeo value> 5 for all the lithofacies considered because of the low background concentration of the metal. During the wet season, the heavy metal pollution rate was moderate for Zn whereas, it was extremely polluted with respect to Pb. The ecological risk potential of Pb shows that the associated ecological risks range from 536 - 664 in the wet season (i.e. extremely strong) and 2810 - 3480 in dry season (extremely strong). The high level of Pb pollution found in the area at such shallow depth may be due to the sedimentary folds possibly caused by the full spectrum of metamorphic rocks and primary flow structures at shallow depths. This was used to identify the environmental sensitivities of the heavy metals during the dry and wet seasons.

Assessment of naturally occurring radiation in lithofacies of oil field in Niger Delta region and its possible health implications.

The accumulation and increase in radionuclide activities of NORMs beyond permissible levels, will lead to health hazards and environmental damages if proper measures are not taken to control their occurrence as well as protect the lives of drillers and the environment. Therefore, evaluations and risk assessments of subsurface lithofacies is inevitable in order to protect people and the environment. Lack of existing Federal environmental regulations to address the presence of NORMs in oil and gas exploration activities in Nigeria, gives credence to this study. However, before these regulations can be developed, adequate research knowledge is needed to better understand the occurrence and distribution of Norms in subsurface lithofacies, as well as quantify the hazards posed by these NORMs to the people in the environment. This study then investigates the occurrence of natural radiation in lithofacies of an oil field region in Niger-Delta area using Hyper Germanium (HPGe) detector. Six (6) samples of different subsurface layers of lithofacies were collected during drilling, and analyzed. The results showed that the measured activity concentration of 238U decreased as the depth increased; the activity concentration of 232Th ranged between 11.8 ± 9.29 Bq/kg and 23.1 ± 8.43 Bq/kg, while the activity concentration of 4 K ranged from 161.8 Bq/kg to 245.4 Bq/kg. The estimated radiological risks such as absorbed dose rates, annual effective dose rates, radium equivalent index, external hazard index and internal hazard index were determined. The mean values for the estimated radiological parameters were 12.32 nGyh-1, 15.1049 Svy-1, 44.7720 Bqkg-1, 0.1209 and 0.1318 respectively. The gamma index estimated for the samples used were within the standard values recommended by Unscear, 2000. Significantly, this study reveals a distinctive decrease in 232Th activity with depth within the area under consideration. Based on the compared results, the measured radioactive concentrations and estimated radiological risks were below international reference values.

Radiological and toxicity risk exposures of oil based mud: health implication on drilling crew in Niger Delta.

Naturally occurring radioactive materials (NORMs) and the presence of toxic metals in drilling fluids/their additives have raised research interests in recent times owing to the risks associated with the exposure times for drillers of petroleum wells. In this study, two drilling fluids A and B were formulated, while two other Mud Samples C and D were obtained from drilled shale and shale-sand formation zones. All four fluids were collected and analyzed for the presence of radioactive and heavy metals. Lead (Pb), mercury (Hg), cadmium Cd), zinc (Zn), chromium (Cr), aluminum (Al), arsenic (As), nickel (Ni), and copper (Cu) were detected in the mud samples. The heavy metal contents of the mud samples are in the following decreasing order of magnitude Hg > Pb > Cd > Cr. In Samples A-D, Hg, Pb, Cr, and Cd were found to have significant concentrations, and the concentrations of these metals increased in the mud samples after they were used for drilling. The concentration of Hg was above the permissible limit. Also, the concentrations of Pb, Cu, As, and Al found in Mud Samples A and B can cause skin irritations over long-term exposures, while Cd, Hg, Zn, and Ni present in the samples were within levels that can cause lung infections or immune breakdown when ingested over long periods. The quantities of Cd, Hg, and Cu detected in Mud Samples C and D can cause skin irritations over long-term exposures, while those of As, Zn, Ni, and Al were seen to have the potential to cause dermal infections/diseases. Based on the results obtained, the cancer risk for the drilling crew lies within 1.1 × 10-3 - 7.7 × 10-3 HQ. The highest dose rate, radium release, and external hazard index were obtained for Mud Sample C whose radium equivalent was judged to be far below the critical safe limit for the drillers. The radium equivalent activity for the two field mud samples (C and D) were estimated to be 27.467 and 22.978 Bq kg-1, respectively, which is the maximum activity obtained for the analyzed samples. The maximum radium equivalent activity for Mud Sample C was estimated as 27.48 Bq kg-1 with a corresponding external hazard index of 0.7. Based on the analysis, there is a significant correlation between the concentration of heavy metals and the radionuclides found in the mud samples.

Application of non-uniform film thickness concept in predicting deviated gas wells liquid loading.

Liquid loading causes undesirable occurrences such as premature death of wells, as well as significant reduction in production. However, most available models consider vertical wells and only a few focus on deviated gas wells. In order to reduce the impact of liquid loading on gas production, gas well load-up should be diagnosed at its early stage so as to proffer adequate solution. Unfortunately, most gas wells will experience liquid loading at some stage or point in their production life. Therefore, it is of utmost importance to predict liquid loading at the early life of such wells in order to develop apt liquid management strategies as corrective measures. Liquid film flow reversal concept has been identified as one of the major concepts responsible for the occurrence of liquid loading in deviated gas wells. This study develops an improvement on Chen's liquid loading model. The model specifically introduces the concept of non-uniform film thickness around the pipe wall, as against previous works which considered uniform film thickness. A modified friction factor is also introduced to account for large film thicknesses around the pipe wall. Results from the model were compared with those of previous models, and data from published literature was used to validate the new model. The new model gave accurate predictions for 11 of 12 unloaded wells while for the loaded wells, the estimated data gave accuracies for 29 out of 30 loaded wells. This then implies that the new model is accurate for predicting liquid loading in deviated gas wells. •Predictions from the new model show a good improvement over existing models.•The uniform film assumption made in Chen liquid loading model was modified, and a different interfacial friction factor was applied.•The method proposed in this study introduces the concept of non-uniform film thickness around the pipe wall as against previous works which considered uniform film thickness.

Development of an automated drilling fluid selection tool using integral geometric parameters for effective drilling operations.

Modern-day climate and environmental factors are largely responsible for the different geometric characteristics exhibited by formation zones/petroleum reservoirs which makes them highly selective with respect to their adaptation to drilling fluids. However, recent advances in drilling technology, such as, the development of an appropriate drilling fluid automation system carried out in this study, have shown prospects for tremendous improvements in well performance with a subsequent reduction in well dormancy/shutdown. Based on the mud density calculations from the simulation and field measurements, it is evident that the novel drilling fluid selector system has a characteristic algorithm that is suitable for predicting the performance of drilling fluids within limits of accuracy as high as 95-99% for wellbore sizes/diameters and depth, in the range of 8-16" and 0-15,760 ft which is a good step towards attaining a fully automated drilling operation.