The system studied in this thesis is called the Low Rise Return system and uses a partly filled marine drilling riser with a variable mud level which is used control the bottom holes pressure.Initially main components of the Low Riser Return System are listed and explained. Then the performance characteristics of the system are explored. Level movements in riser during level increase and decrease at constant mud pump rates are explained along with the effect of mud pump rate on maximum level increase and decrease rates.A simple simulator is then presented that calculates the bottom hole pressure when pump rates are changed. The simulator includes a function that enables it to simulate lost circulation scenarios.The simulator is used to simulate some preferred scenarios. First a pressure increase and decrease at constant mud pump rates are simulated. Then it is shown how a faster pressure decrease can be achieved by temporarily lowering the mud pump rate. Next simulations are shown where changes in mud level are used to compensate for changes in equivalent circulation density as mud pump rates are changed. Finally simulations are run that demonstrate how mud level can be reduced to cure lost circulation scenarios. Results and lessons learned are then discussed.

In 2006 the Petroleum Safety Authority Norway (PSA) performed a well integrity survey. The survey indicated that about 20 % of wells on the Norwegian Continental shelf (NCS) may suffer from well integrity issues. Most of the problems were related to deficiency in annulus safety valve, tubing, cement and casing. Pressure build-up in annulus, i.e. sustained casing pressure, is one of the main indicators of a significant well integrity problem. Increased understanding on the field may help engineers to design wells with better integrity in the future. This thesis describes SCP and its most common causes with emphasis on the relation between casing shoe setting depth and the occurrence of SCP. Primary and secondary barrier is described together with the common practice of choosing casing shoe depth. Formation strength and its impact on setting depth is explained together with a brief introduction of the different formation integrity tests. Generic cases have been studied to determine the relation between unfavorable casing shoe setting depth and the occurrence of SCP. For each case there is a suggestion as how the well may be redesigned so that the risk of SCP is reduced. Information on the theme has been acquired through studying and comparing different papers, booklets, previous reports and reviews concerning the subject. The Norsok standard D-010 and 117 – OLF recommended guidelines for well integrity have also been very informative during the study. To be able to avoid SCP and at the same time improve well design, it is important to properly understand how SCP arises. Changing the casing shoe setting depth to a more suited depth or formation cannot alone eliminate SCP. To eliminate SCP a good conversion between Top of Cement (TOC) and setting depth of the previous casing shoe is required. The best way of avoiding SCP because of casing shoe setting depth is to make a thorough investigation of the underground and carefully choose the setting depth.

Kick Tolerance is an important factor in the industry, that allows drilling engineers to establish several parameters in the development phase of a well, such as casing depths, open hole lengths, etc. It can also be considered a valuable safety factor to prevent well control problems.Several different definitions and calculation approaches were found for this term, and when you have something as dynamic and fast-paced as it is the oil & gas industry it is an important issue, since this lack of standardization leads to confusion and miscommunication.In chapter 3 and 4 the current calculation method, industry approach and knowledge of the term is quickly reviewed. Different kick tolerance software was analyzed in order to outline assumptions, compare results and calculation methodologies. Two main groups were distinguished: VBA macros for Microsoft Excel and standalone applications. The software presented in this work is developed in an attempt to overcome the main difficulties and disadvantages found during the initial analysis of the previously mentioned programs. Well: “Thesis work”, analyzed in chapter 5, presents real data from an exploration well that, when planned, was expected to be an easy to accomplish task by the drilling crew, not at all troublesome. In the original analysis, pre-development, an extremely high kick tolerance was found (≈90bbl or ≈15 m3), and drilling and casing designs were made accordingly. Operations for the 8.5” section where estimated to last 5 – 8 days with a specific budget. Several small kicks were presented during the drilling operations, and about 100m before TD was reached, a gas kick occurred, even though the original analysis showed a high margin before trouble was supposed to be encounter, once killing operations started, it became clear that control was not going to be easily regained, ultimately leading to the abandonment well.Many different reasons could have led to this much trouble, i.e. using data from nearby wells without later updating this information with the real data found for this specific well, not taking into consideration all the factors involved on the calculation, etc. This would have helped readjust different parameters before the incident happened, with high probabilities of a different, and more positive, outcome.

With the increasing number of drilled ultra-extended reach wells and complex geometry wells, the drilling limitation caused by excessive torque and drag forces must be further investigated. The wellbore friction being a main limiting factor in extended reach well needs to be studied with the new developed models.This master thesis presents an application of the new 3-dimentional analytical model developed by Bernt S. Aadnøy in the synthetic test and four real wells. Quite diverse wellbore trajectory and depth has been chosen for a better evaluation and comparison of the model with the measured data. In order to investigate the potential and limitation of the model, torque and drag analysis during the different operations such as tripping in, tripping out, rotating off bottom, combined up/down were investigated. An application of the analytical model for wellbore friction analysis in the actual wells is very time consuming and requires a lot data/input manipulation. As a part of the thesis assignment, it was required to create simplified means for application and testing the analytical model. With visual basic application in Excel a simple torque and drag simulator was created purely based on the analytical model simple solution. Along with the analytical model the master thesis includes Wellplan software for torque and drag analysis in all the included test and actual wells. Along with this, the project has a brief literature study of 3D analytical model and torque and drag concept in general. The analytical model gives a reasonable torque and drag results. Based on comparison between the model and actual measurement, it has been observed that the analytical model simple solution in some cases may not precisely describe wellbore friction analysis. The discrepancy between Wellplan and the analytical model prediction occurs during the tripping in operations. Being a strong function of tension/compression in the drill string the analytical model for more accurate torque and drag prediction requires an application of the complete solution. The main challenge for this model is the complexity of its full application. There is an uncertainty regarding the model application in conjunction with drillstring effective tension. For the actual well application it is time consuming and requires drillstring effective tension analyzing which make the model disable for the real time analysis.The analytical model must be further investigated by application in the real well with good quality of measured data.

To determine the carrying capacity of the drilling fluid, also determine the settling velocities of the drilling cuttlings. To produce the Reynold's number experimentally.

The feasibility and success of petroleum development projects depend to a large degree on well construction costs. Well construction cost estimates often contain high levels of uncertainty. In many cases, these costs have been estimated using deterministic methods that do not reliably account for uncertainty, leading to biased estimates. The primary objective of this work was to improve the reliability of deterministic well construction cost estimates by incorporating probabilistic methods into the estimation process. The method uses historical well cost estimates and actual well costs to develop probabilistic correction factors that can be applied to future well cost estimates. These factors can be applied to the entire well cost or to individual cost components. Application of the methodology to estimation of well construction costs for horizontal wells in a shale gas play resulted in well cost estimates that were well calibrated probabilistically. Overall, average estimated well cost using this methodology was significantly more accurate than average estimated well cost using deterministic methods. Systematic use of this methodology can provide for more accurate and efficient allocation of capital for drilling campaigns, which should have significant impacts on reservoir development and profitability.