Background:Gas hydrates are considered as a major threat to the oil and gas flow assurance industry. At high pressure and low temperature conditions, gas hydrates form in pipelines and production facilities leading to pipeline blockages, high removal cost, environmental hazards and loss of lives. For a successful prevention of gas hydrate formation, predicting the hydrate formation phase boundary of hydrocarbon fluid composition becomes very necessary. Objective and Method:In this study, computer simulation software called PVTSim was used to predict hydrate formation phase boundary of synthetic natural gas composition of the Keta basin of Ghana at pressure and temperature ranges of 43.09 bar -350 bar and 12.87 °C -27.29°Crespectively. The effect of changes in natural gas composition (N 2 and H 2 S) and the presence of four commonly used thermodynamic gas hydrate inhibitors (methanol, ethanol, diethylene glycol and monoethylene glycol) on the hydrate formation phase boundary is also discussed. Prior to the study, the accuracy of PVTSim was validated with the hydrate formation phase data in literature. Results and Conclusion:Results suggested that the hydrate formation phase boundary decreased with increasing N 2 composition and increased with increasing H 2 S composition, suggesting that, the presence of H 2 S increases the threat of hydrate formation. However, a reduction in hydrate formation threat was observed in the presence of all four commonly used gas hydrate thermodynamic inhibitors with methanol demonstrating the highest inhibition effect.
Drilling mud is used to ensure save and cost-effective drilling operations. In every phase of the drilling operation, contaminants are encountered which directly affect the properties of the drilling mud. The severity of drilling mud contamination depends on the type of drilling mud used, the type of contaminant and the degree of contamination. In most drilling operations, cement contamination occurs one or more times when casing strings are cemented and the plugs are drilled out. Drilling mud is discarded when cement contamination is too high such that it is practically unreasonable to treat it. It is therefore important to monitor the mud's properties against contamination to ensure the basic functions of the mud. To perform effective monitoring of a drilling mud requires proper knowledge of the drilling mud chemistry, properties, and contaminants. This will help oil operators to apply the right control measures and treatment methods during drilling operations. This paper presents an experimental study on the effect of various concentrations of cement contamination on some physical properties of water based mud (WBM). Four mud samples were prepared of which three of them were contaminated with 10 g, 20 g and 30 g of class G cement. Rheological properties at temperatures of 25 • C, 40 • C and 60 • C as well as the pH, fluid loss and density of the mud were determined. The findings showed that the yield point and gel strength at all test temperatures increased as the concentration level of cement increased. However, the plastic viscosity decreased slightly with cement concentration of 10 g and 20 g and further increased with 30 g of cement contamination at 40 • C and 60 • C. The fluid loss, density as well as the pH of the WBM increased gradually as the concentration of cement increased. It is recommended that the effect of cement contamination in WBM at temperatures higher than 60 • C should be investigated.
Conventional drilling fluids such as diesel and mineral oil have posed some environmental and health challenges in their drilling applications but the introduction of synthetic-base fluids over the past two decades has considerably reduced such challenges. In some cases, a bottom hole temperature above 300°F (150°C) can cause significant instability in the rheological properties of these drilling fluids. Vegetable oils or pseudo oils are known to be environmentally friendly drilling fluids, but have not received much attention because of their instability in High Pressure Temperature High (HPHT) environments. The antioxidant potentials of Citric Acid (CA), Red Onion Skin Extract (ROSE) and Propyl Gallate (PG) on the oxidative stability of seven vegetable oils were examined. The additives (antioxidants) were able to protect the stability of the oils up to 250°C which is beyond the range for the 1 st tier of HPHT environment (150 -205°C). Though it was also observed that the peroxide values (PVs) of the oils as temperature increase also increase, it did not follow and defined pattern (no pattern was established). The applications of combined antioxidants improved the stability of the oil samples when compared with using individual antioxidants. The applications of appropriate antioxidants in local vegetables oils (esters) have revealed the potentials geothermal stability of the local esters to with stand the 1 st tier of HPHT environments.
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