The exploration and production of oil and gas involve the drilling of wells using either one or a combination of three drilling techniques based on drilling fluid density: conventional overbalanced drilling, managed pressure drilling and underbalanced drilling. The conventional overbalanced drilling involves drilling of wells with mud which exerts higher hydrostatic bottom-hole pressure than the formation pore pressure. Unlike the conventional overbalanced drilling, underbalanced drilling involves designing the hydrostatic pressure of the drilling fluid to be lower than the pore pressure of the formation being drilled. During circulation, the equivalent circulating density is used to determine the bottom-hole pressure conditions. Due to lower hydrostatic pressure, underbalanced drilling portends higher safety risk than its alternatives of conventional overbalanced drilling and managed pressure drilling. The safety risk includes frequent kicks from the well and subsequent blowout with potential threat to human, equipments and the environment. Safety assessment and efficient control of well is critical to ensure a safe drilling operation. Traditionally, safety assessment is done using static failure probabilities of drilling components which failed to represent a specific case. However, in this present study, a dynamic safety assessment approach for is presented. This approach is based on Bow-tie analysis and real time barriers failure probability assessment of offshore drilling operations involving subsurface Blowout Preventer. The Bow-tie model is used to represent the potential accident scenarios, their causes and the associated consequences. Real time predictive models for the failure probabilities of key barriers are developed and used in conducting dynamic risk assessment of the drilling operations. Using real time observed data, potential accident probabilities and associated risks are updated and used for safety assessment. This methodology can be integrated into a real time risk monitoring device for field application during drilling operations.

Dynamic safety risk analysis of offshore drilling

A borehole-stability model that uniquely couples the mechanical and chemical aspects of drilling-fluid/shale interactions was developed. The model allows the user to determine the optimum drilling parameters (e.g., mud weight and salt concentration) to alleviate borehole-stability-related problems with oil- or water-based drilling-fluid systems. Chemically induced stress alteration based on the thermodynamics of differences in water molar free energies of the drilling fluid and shale is combined with mechanically induced stress. These two potentials are coupled by use of the framework of poroelasticity theory to formulate the physiochemical basis of this borehole-stability model

Borehole-stability model to couple the mechanics and chemistry of drilling-fluid/shale interactions

https://isiarticles.com/bundles/Article/pre/pdf/46561.pdf

Safety and risk analysis of managed pressure drilling operation using Bayesian network

On-chip two-phase cooling of datacenters: Cooling system and energy recovery evaluation

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Application of aluminium oxide nanoparticles to enhance rheological and filtration properties of water based muds at HPHT conditions

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Improved Bottomhole Pressure Control for Underbalanced Drilling Operations

A new comprehensive, mechanistic model that allows more precise predictions of wellbore pressure and two-phase flow parameters for underbalanced drilling (UBD) is proposed. The model incorporates the effects of fluid properties and pipe sizes and, thus, is largely free of the limitations of empirically based correlations. The model is validated against actual UBD field data and full-scale experiments in which the gas and liquid injection flow rates as well as drilling fluid properties were similar to those used in common UBD operations. Additionally, a comparison against two different commercial, empirically based UBD simulators shows better performance with the mechanistic model. Introduction It is generally accepted that the success of UBD operations is dependent on maintaining the wellbore pressure between the boundaries determined by formation pressure, wellbore stability, and the surface equipment's flow capacity. Therefore, the ability to accurately predict wellbore pressure is critically important for both designing the UBD operation and predicting the effect of changes in the actual operation. Because of the complex nature of the hydraulic system of UBD operations in which two or more phases (liquid, gas, and solids) commonly flow, the prediction of pressure drop and flow parameters, such as liquid holdup and in-situ liquid and gas velocities, are performed mainly with empirical, two-phase flow methods. The Beggs and Brill 1 correlation is the most popular among the current, commercial UBD simulators. However, it is recognized by the petroleum industry that most of these empirical correlations were developed from experimental databases, thereby making extrapolation hazardous. 2 Moreover, the Beggs and Brill 1 correlation has been shown to overpredict or fail to predict bottomhole pressures for both vertical and horizontal UBD operations. 3 , 4 Since the mid-1970s, significant progress has been made in understanding the physics of two-phase flow in pipes and production systems. This progress has resulted in several two-phase flow mechanistic models to simulate pipelines and wells under steady-state as well as transient conditions. Consequently, mechanistic models, rather than empirical correlations, are being used with increasing frequency for designing multiphase production systems. Based on this trend of improvement, the application of mechanistic models to predict wellbore pressure and two-phase flow parameters seems to be the solution to increasing the success of UBD operations by improving such predictions.

A New Comprehensive, Mechanistic Model for Underbalanced Drilling Improves Wellbore Pressure Prediction.

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John Rogers Smith

Papers

Improved Bottomhole Pressure Control for Underbalanced Drilling Operations

A New Comprehensive, Mechanistic Model for Underbalanced Drilling Improves Wellbore Pressure Prediction.

Diagnosis of Poor PDC Bit Performance in Deep Shales.

Evaluation of Alternative Initial Responses to Kicks Taken During Managed-Pressure Drilling

Simulations Comparing Different Initial Responses to Kicks Taken During Managed Pressure Drilling