Plug and abandonment, milling operations and simulations

Abstract

During plug and abandonment, there can be a need for removing casing to ensure that a proper cement barrier can be set. The conventional method for doing this is by performing milling operations. Conventional milling operations are very time consuming, costly and also involves major HSE aspects. New technology for performing milling operations are developed with the purpose to perform this operation more safe and efficiently. During milling operations huge amounts of swarf is generated. By milling a section of 50 meters, one can actually generate 4 tons of swarf! The swarf which is basically metal cuttings from the milled casing has to be transported away from the platform site. Some platforms have their own swarf handling units while others don’t. Swarf may cause a lot of damages to equipment, and people and during transportation it may be self-­‐firing. Roughnecks have to use special gloves when working with swarf due to its sharp edges. If one can improve the milling operations or implement better alternatives for removing casing it will be beneficial both economically and for HSE considerations. Alternative technologies to milling exist; this will be further discussed in this thesis. The pro and cons with this alternative technology will be discussed, as well as the technology development within the milling operations. To get the overall picture this thesis starts with a description of P&A, and some important terminology that it is important to have in place. Then the governing regulations from NORSOK D010 are presented with respect to P&A. The newest revision of NORSOK D010, rev 4 that was published in June 2013 is later compared with the previous revision of NORSOK D010, rev 3. The latest part is more academic with some simulations in Matlab. For the simulation part an existing steady state two phase model is implemented. This steady state model is modified for its intended use. The purpose with this modified model is to study the ECD effects during milling operations. Different parameters such as the slip ratio and the mill rate will be adjusted, and the results will be visualised in excel. Steel has a large density and for large concentrations of swarf there can be a problem related to fracturing of the well. The model (programmed in Matlab) will be used to study the effects of different milling rates. The results are discussed to see the trends.