A blowout is the eruption of underground reservoir fluids to the surface during drilling operations. This has devastating results, which are described by the serious impact on human health, environmental problems, and economic loss. Blowout events are unpredictable due to uncertainty of how they evolve. Blowout risk usually lies with parts of the safety system that are expected to function fully, and prevent blowouts. Fault Tree Analysis (FTA) is a graphical method offering a way to identify Causal Factors (CF) of the safety system failure, and to evaluate the contribution level of each event to blowout. In this study, an FTA model for offshore blowout probability is mapped to a Bayesian Network (BN). This BN-based model is utilized for Probabilistic Risk Assessment (PRA) of hazards, accounting for uncertainty in both safety system failure rates and subsurface formation pressures. To the best of our knowledge, this is the first time all of the commonly encountered safety barriers are combined in a single PRA analysis. The PRA is performed using importance measures of FTA roots. According to results herein, the blowout event is attributed mostly to human error in monitoring safety barriers. Also, blowout events are highly probable due to inability to precisely identify abnormal subsurface pressure zones. Finally, casing failure is found to be the third significant contributor to blowout.


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Estimating reservoir pressure and temperature is one of the challenges of geothermal reservoir engineering. A new proxy model has been developed to estimate reservoir pressure and temperature using wellhead pressure, temperature and non-condensable gas (NCG) amount. An exhaustive set of wellhead data covering a range of possible wellhead pressure, temperature and NCG data is used in a calibrated wellbore simulator, which is then used to create a knowledgebase to train an artificial neural network (ANN) mode...
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Arı, T. Çağrı; Akın, Serhat; Department of Petroleum and Natural Gas Engineering (2014)
Drilling fluid is a fluid mixture that is used in oil and gas drilling operations. Generating hydrostatic pressure, carrying cuttings to the surface and maintaining wellbore stability is essential for a drilling fluid with its other important functions. For low pressure reservoirs, hydrostatic pressure that drilling fluid generated should be low. To achieve that, drilling fluid density should be lowered. However, use of drilling fluids with higher density than required could cause partial or complete loss o...
OZBELGE, TA; SOMER, TG (Elsevier BV, 1994-08-01)
Heat transfer from a solid surface to a fluid-solid suspension in vertical or horizontal transport is of importance in the design of heat-exchangers, driers, fluidized beds, and slurry pipeline reactors. There are fewer studies on heat transfer in liquid-solid flows than on gas-solid flows. In this paper, a correlation for heat transfer to dilute liquid-solid flows in a horizontal pipe is presented. Suspension properties were used to derive the following equation: Nu(s) = 0.202Res0.6Prs0.675(D/d(p))0.092(mu...
An Experimental study of silicate polymer gel systems to seal shallow water flow and lost circulation zones in top hole drilling
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Shallow water flow and lost circulation are frequently encountered problems during drilling top holes of oil, gas or geothermal wells. Plenty of methods have been applied to overcome these problems. Placement of silicate based gel systems is one of the oldest methods to seal such undesired zones. For this study, sodium-silicate based gel system is investigated experimentally. This gel system is deliberately delayed multi-component system mixed as a uniform liquid at the surface but desired to form strong ge...
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Mud solid and filtrate invasion are the most common causes of formation damage during overbalanced drilling (OBD), which is a method of drilling in which the wellbore pressure remains greater than formation pressure. During the past ten years, underbalanced drilling operations (UBD), which can be defined as a drilling method in which the wellbore pressure is less than formation pressure, has been growing due to their applications such as prevention of lost circulation, reduction of filtration lost in natura...
Citation Formats
M. ELSALİH, “PROBABILISTIC RISK ASSESSMENT OF OFFSHORE BLOWOUTS,” M.S. - Master of Science, Middle East Technical University, 2021.