3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Tribology of drill bit material in deep oil drilling process: variation of weight on bit (WOB) and bit rotating speed(2019) Seloanyane, MatsoloThe oil and gas industry is faced with great challenges when it comes to the drilling process due to a shift in drilling shallow onshore layers, to deep and ultra-deep offshore layers. The depletion in the onshore oil and gas reserves has resulted in the need to explore alternative reserves, to meet the constantly increasing energy demand. Due to increased drilling depth, the drilling equipment faces challenges of increased torque and drag, which lead to friction and wear, as a result of complicated drilling environments. These challenges eventually lead to serious equipment failure, resulting in increased production costs. It is therefore of paramount importance to find different combinations of drilling parameters that will give the highest production rates at minimum costs while also paying attention to strict environmental and safety regulations. In this research, different drilling parameters such as weight-on-bit (WOB) and drill bit rotating speed, including different drilling environments such as dry and wet environments were studied, to determine how their different combinations affect the coefficient of friction (COF), when used in three different rock types; Fine-grained Arkose sandstone, Coarse-grained Arkose sandstone and Quartzite. In dry environments, varying the WOB and drill bit rotating speed greatly affects the COF. Higher speeds and low loads resulted in reduced COF while low speeds and high load portrayed increased COF. For wet environments, different nanoparticles were used in water-based and oil-based fluids. The oil used was environmentally friendly and biodegradable vegetable oil named castor oil. The nanoparticles (NPs) of bentonite, attapulgite, sepiolite and cellulose nanocrystals (CNC), were used as additives in drilling muds, to reduce the COF. These NPs were successful in the reduction of COF, but they performed better in the oil-based fluids than in the water-based fluidsItem Investigation of the use of nanomaterial surfactants for oil emulsion drilling muds for deep-hole conditions(2018) Kgwete, Maele NomaThe challenges faced by recovery methods for the extraction of oil and gas from reservoirs are related to existing drilling operations. Consequently, the muds become susceptible to poor heat transfer, disintegration, gelation, pipe sticking, poor cleaning ability, and poor lubrication. The challenges in drilling operations at high temperature and high pressure (HTHP) conditions can be mitigated when rheological properties are controlled and monitored. This research focusses on the investigation of the use of nanomaterial surfactants for oil emulsion (OBM) drilling muds in order to address the challenges in HTHP conditions. Emulsion drilling fluids with and without nanoparticle were prepared. ZnO nanoparticle was selected for this research based on its unique thermal stability properties. The drilling fluid package comprised 100 g of distilled water, 1 wt% of NaCl, 1 wt.% of CaCl2, various amount of surfactant (Triton® X-100 or DTAB) and + 6 wt.% of bentonite. The surfactant concentration varied from 0.25 to 1.25 % with 0.25 intervals. To evaluate and compare the contributions of surfactants and nanomaterial, the prepared drilling fluids were subject to rheological and filtration test. The results showed that DTAB surfactants-based drilling mud with ZnO nanoparticle showed a more stability compared to Triton. The decrease in viscosity with DTAB did not have a significant impact of the filtration loss in the presence of ZnO nanoparticles. The drilling fluids showed a dilatant and shear thickening behavior. The filtration test showed that 1 % of surfactant loss minimal amount of fluid and ZnO nanoparticle reduced the fluid lost capacity. The emulsion contained DTAB as surfactant and ZnO nanoparticle performs better in terms of retaining water and/or liquid in the mud; therefore, making it suitable for drilling at HTHP conditions.Item Experimental assessment of heavy crude oil production using emulsion flooding(2017) Sehlake, Portia BoitumeloIn many crude oil exploitation oil cannot be produced using its own natural drive after many years due to pressure depletion. In order to maintain the reservoir pressure and optimize the oil production, secondary oil recovery methods are usually used i.e. water injection, gas lift and reinjection of natural gas. Although, secondary oil recovery methods increase hydrocarbon production by about 35 - 45 %, they do not provide a definitive solution due to continuous pressure decrease and the excessive amount of water required. An alternative recovery technique known as tertiary recovery or enhanced oil recovery is usually used at this stage and focuses on increasing the mobility of the oil. Chemicals such as surfactants, polymers and nanoparticles are injected to improve recovery. These chemicals help improve properties of the injected fluid and its interactions with the rocks. Surfactants are well known for reducing interfacial tension formed between oil and water and polymers for improving sweep efficiency. Moreover, addition of nanoparticle is said to further reduce interfacial tension between water and oil and help reduce the capillary pressure. This study looked at emulsion stability of crude oil with cationic surfactants and non-ionic surfactants. The objective was to analyse how stable the solution with surfactants only is and also how the stability is affected by temperatures, nanoparticles and stirring mechanism. It further investigates which surfactant type is best suitable to stabilise emulsions and whether or not the combination of surfactant and nanoparticle can provide a more stable emulsion than surfactants only In the study, experiments were conducted to test emulsion stability based on temperature variation, water to oil ratios differences and droplet size formation. Cationic dodecyl trimethyl ammonium bromide (DTAB) and non-ionic Triton®X-100 surfactants were used; nanoparticle zinc oxide (ZnO) was later added into the two types of surfactants aqueous solutions and emulsion stability tests conducted. Temperature was raised from 250C to 60C to look at the effect this will have on emulsion stability. Water/ Oil ratios were analyse the effect/impact the different ratios had on emulsion stability. Droplet size distribution was analysed using a microscope to see how tight the emulsions are. The experimental results suggest that cationic DTAB is not a good candidate for emulsion stability especially at 600C. The potential application of non-ionic surfactant Triton®X-100 alone gave better stability. Addition of nanoparticle ZnO to DTAB did not help stability and when ZnO is added to non-ionic surfactant Triton®X-100 the stability was good at all temperatures but did not last for a longer periods vs having non-ionic surfactant Triton®X-100 only , suggesting that Triton®X-100 is best suitable to keep emulsions formed stable and further microscopic work supported this finding.