Wellbore stability is a critical issue when drilling through tectonically stressed and complex geological conditions. Understanding wellbore stability issues before a well is drilled enables better planning of the drilling operation and helps to avoid borehole failure. This is of particular importance in underbalanced drilling where we are limited with our choice of drilling mud densities. This thesis examines the impact of fluid pressure change on wellbore stability during underbalanced drilling by using a timedependent poroelastic model. The poroelastic behaviour is analysed using numerical and analytical models. The finite element method (FEM) is used for the numerical model. Some simple techniques are developed and implemented to increase the speed and stability of the FEM solution. The common assumptions of plane strain and plane stress are explored. It is shown that the plane strain assumption results in high error while the error for plane stress is low. It is also shown that use of plane strain predicts more instability than use of plane stress and the stability difference is significant. From this it is concluded that the plane stress assumption should be used instead of the commonly used plane strain assumption. A sensitivity analysis is conducted to demonstrate the effect of several variables on wellbore stability during underbalanced drilling. These variables include mean in-situ horizontal stress, deviatoric in-situ horizontal stress, bulk compressibility and permeability. I various ways changes in these variables were shown to change the chance of shear failure, early time tensile failure through exfoliation and late time tensile failure through hydraulic fracture initiation.

Graduation date: 1995

The economics of drilling offshore wells is important as we drill more wells in deeper water. Drilling-related problems, including stuck pipe, lost circulation, and excessive mud cost, show the need for better drilling technology. If we can solve these problems, the economics of drilling the wells will improve, thus enabling the industry to drill wells that were previously uneconomical. Managed pressure drilling (MPD) is a new technology that enables a driller to more precisely control annular pressures in the wellbore to prevent these drillingrelated problems. This paper traces the history of MPD, showing how different techniques can reduce drilling problems. MPD improves the economics of drilling wells by reducing drilling problems. Further economic studies are necessary to determine exactly how much cost savings MPD can provide in certain situation. Furter research is also necessary on the various MPD techniques to increase their effectiveness.

Although the use of compressible drilling fluids is experiencing growth, the flow behavior and stability properties of drilling foams are more complicated than those of conventional fluids. In contrast with conventional mud, the physical properties of foam change along the wellbore. Foam physical and thermal properties are strongly affected by pressure and temperature. Many problems associated with field applications still exist, and a precise characterization of the rheological properties of these complex systems needs to be performed. The accurate determination of the foam properties in circulating wells helps to achieve better estimation of foam rheology and pressure. A computer code is developed to process the data and closely simulate the pressure during drilling a well. The model also offers a detailed discussion of many aspects of foam drilling operations and enables the user to generate many comparative graphs and tables. The effects of some important parameters such as: back-pressure, rate of penetration, cuttings concentration, cuttings size, and formation water influx on pressure, injection rate, and velocity are presented in tabular and graphical form. A discretized heat transfer model is formulated with an energy balance on a control volume in the flowing fluid. The finite difference model (FDM) is used to write the governing heat transfer equations in discretized form. A detailed discussion on the determination of heat transfer coefficients and the solution approach is presented. Additional research is required to analyze the foam heat transfer coefficient and thermal conductivity.

Thesis (M.A.)--Florida State University, 2003. / Advisor: Dr. Dennis D. Moore, Florida State University, College of Arts and Sciences, Program in American and Florida Studies. Title and description from dissertation home page (viewed Mar. 2, 2004). Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 231-236).

Lost circulation and wellbore failure are common problems in the petroleum industry and they increase drilling costs dramatically. Casing drilling in depleted zones helps reduce drilling costs and problems related to lost circulation and wellbore failure. Thus, casing drilling is an important technology to minimize or eliminate conventional drilling problems in depleted zones. This thesis is focused on a study of smear effect in casing drilling in depleted formations. It is based on information about casing drilling and a commercial computer software ABAQUS. The smearing mechanism of drilling solids into the wellbore wall and the effects of parameters that affect the stress distribution around the wellbore wall are studied. Moreover, multiple wellbore cracks are studied to determine their effects on hoop stress distribution and all the results are given at the results chapter of this study. All the discussions about the changing parameters are given in results section. In conclusion, the smear effect in casing drilling can significantly improve hoop stresses around the wellbore and lost circulation problems can be minimized by using casing as a drilling string. These models can be used as a basic tool to understand smear effects in casing drilling in depleted formations. / text

This thesis was stimulated by the requirement to decommission offshore steel structures in the North Sea Offshore Oil and Gas Industry, but applies worldwide, where Oil and Gas production has ceased. It initially shows the UK Government assessment of the scale of decommissioning in the UKCS where there are several hundred structures with associated pipelines, risers and wellheads that have to be cut into sub-structures and individual pieces and then removed. Factors other than cessation of production drive the sequence and timing of structural decommissioning, such as the price of oil &gas and what new development might require already installed infrastructure. The nature of decommissioning of underwater steel lattice structure of offshore oil platforms called ‘jackets’ and underwater infrastructure is briefly discussed with the focus on cutting. The comparison of the performance of different underwater cutting tools currently most used in decommissioning is investigated with respect to two new underwater cutting techniques not only in terms of speed of cut but also in terms of deployment time and infrastructure requirements. A number of mainstream cutting tools and deployment systems are briefly introduced to provide a background, showing the range of tools preceding those investigated in more detail in terms of cutting and deployment efficiency. During the initial cutting research it was considered that fibre lasers had developed sufficiently in terms of power density, size and cost to be applied to underwater cutting. They were considered to have potential benefits over other underwater cutting techniques due to the continually increasing power density at the cut and have the advantage of a small envelope due to the small size of the potential cutting head The potential footprint of the laser head was envisaged to be similar to that of the rotating electrode arc tool therefore the deployment issues investigated might apply to both. The later development There is little published information on underwater cutting by laser particularly for the Oil and Gas Industry except for application to cutting rock for drilling. Research has been biased towards the nuclear industry using manufacturing techniques for surface treatment and cooling to reduce stress cracking. Fibre lasers are expensive to buy and logistically difficult to rent therefore it was considered that 1.2 kW CO2 laser at the University of Aberdeen (UoA) could be employed in obtaining an insight into the cutting and deployment issues concerned. Thus, the author designed, built and tested an underwater laser cutting head that would interface to the CO2 laser and would work at different orientations, fully submerged underwater in a tank. The trials were designed to assess the relationship of cutting parameters and performance at three orthogonal attitudes underwater, (beam downward, horizontal and upward pointing) to represent the orthogonal approach to horizontal and vertical primary axis tubular members, that comprise a jacket’s construction. The cutting parameters and their effects were then analysed to determine trends, behaviour and technical issues. Although an underwater laser cutting system could use a fibre laser, the CO2 laser enabled preliminary tests to be carried out and the viability of a cutting head to be explored. In the conclusion the design and performance of the laser cutting head is assessed with respect to the performance of other main-stream underwater cutting tools developed earlier. Offshore deployment of the laser cutting head is also discussed. Recommendations for future research and development work, to enable the realisation of underwater laser cutting, are presented.

No description available.

Directional drilling has become a popular construction method used by municipalities, contractors and engineers alike for the construction of new subsurface pipelines while minimizing impact on the surrounding community. Pressurized drilling fluid is used during the advancement of the borehole through granular materials to maintain borehole stability throughout the drill path. It is believed that failure of the soil surrounding the borehole is controlled by the shear strength of this frictional ground and this influences the maximum allowable mud pressure that may be applied to the borehole. While there have been a number of theoretical studies, there have been few if any experimental investigations to examine the efficacy of the proposed design equations. The basis of this research considers a horizontal directionally drilled borehole and compares the analytical findings with those obtained from a series of smaller and larger-scale laboratory experiments for a uniformly graded sand and layered sand - sand and gravel case. The analytical solutions are considered reasonable for hydrofracture during pullback, but may not be directly applicable to blowout during pilot borehole drilling such as the model researched in the experiments. During the experiments the downhole mud pressures were continuously monitored and observations of composite drilling fluid and sand material were made. Smaller-scale experiments were carried out to determine the response of the horizontal stresses resulting from internal pressurization acting on the sidewalls of the test cell. During the larger-scale experiments, the surface displacements were measured to better understand the influence of an increase in the soil volume with surface displacement. iii Through the course of the research, physical information has been collected regarding the changes that a clean sand undergoes when in contact with a drilling fluid, the ability of a borehole to resist internal loading, and the effectiveness of the various analytical models currently used to estimate the peak allowable internal fluid pressures. In addition, physical data has been collected regarding the displacement of a surrounding material during the introduction of drilling fluid into a horizontally drilled borehole / Thesis (Master, Civil Engineering) -- Queen's University, 2008-07-25 14:16:41.951