A rigless permanent plug and abandon approach
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There are many options to perform a PP&A operation. The goal of this thesis was to look at the opportunities to perform an effective offline PP&A of wells based on cost, time and personnel. After searching through Service Company’s solution to the problem the final conclusion became Weatherford and their pulling and jacking unit. Based on time, personnel and cost this unit provides an offline solution plus leaving the drilling rig by itself to perform other well operations simultaneously. The biggest concern of Statoil is to not have all wells PP&A when production stops at the end of 2016. If operation is still running when the field is no longer producing the average day-rate will increase from 1.1 million NOK to 2.6 million NOK according to calculations performed internal in Statoil. This makes time of performing a PP&A operation the most important number to get as low as possible. A conventional method takes between 45-50 days to finish and 40 days if the conductor does not need to be pulled. This means that if Statoil want to finish PP&A Statfjord A before production stops in 2016 Statoil needs to start PP&A wells in the summer 2012. In addition to the pulling and jacking unit it is suggested to use a coiled tubing unit to perform cementing operations provides a complete package to a PP&A operation. Cementing on coiled tubing has never been done at Statfjord before and this will be a breakthrough when it comes to PP&A in Statoil. Using coiled tubing to perform cementing job is widely used by other operator company with great success. It is now time for Statoil to also take advantage of the possibilities provided by coiled tubing. Using two units instead of one drilling rig will be a more costly operation, but will provide a much faster and effective operation. When decommissioning an entire field it is important not to rush, but have a systematically approach to the operation. One of the most important factors to create the most effective abandonment procedure is to have a scheduled plan of the wells plugging order. Separating the wells into batches and starting with the wells not producing and saving the wells actually producing for as long as possible will create an effective decommissioning operation. This may not be the most effective method by logistic, but will provide a stable income during the operations and overall lower the total cost. Based on experience from other fields, such as the Hutton field decommissioning by BP, shows that training of personnel and planning ahead of the operation is very important for the success of the operation. Making the crew personnel familiar with the facilities on the platform and equipment has proven to be of great value. In addition to suggesting new equipment to perform a PP&A operation this thesis also suggest a new procedure of plugging wells. Many of the steps are similar to the conventional method, but there are two main features to the new procedure. First the 7” tubing and 9 5/8” is cut above the normal pressure zone. Common practice is to cut the tubing a few meters above the production packer, but cutting it above the normal pressure zone will provide much less pipe handling and a much quicker pulling time. In addition to save time and logistical issues cutting the tubing and 9 5/8” casing above the normal pressure zone will remove the need for a BOP for the rest of the operations. Similar to when drilling a well down to this depth without a BOP, a PP&A operation can be performed without a BOP upward from this point. On Statfjord this normal pressure point is at around 1400m depth. The basics steps of the new proposed PP&A operation are with these points in mind as followed: 1. Log cement bonding and tubing condition on WL 2. Cut Tubing on WL 3. Displace well to seawater 4. Set cement plug in tubing by CT 5. Pull tubing by PJU 6. Log 9 5/8” casing by WL through PJU 7. Cut casing by WL through PJU 8. Pull casing by PJU 9. Log 13 3/8” casing by WL through PJU 10. Cut casing by WL through PJU 11. Pull casing by PJU 12. Set surface cement plug and pull conductors by CT Not included in these steps are the setting and pulling of DHSV and mechanical plugs. There is also assumed good cement behind casing showed by each logging run. Contingency plans when cement is inadequate are discussed in the thesis. 1.1 Conclusion Based on the proposed method and usage of the pulling and jacking unit along with cementing on coiled tubing the following results of time, cost and personnel was established; 1.1.1 Time Including the pulling of conductor a conventional method require 45-50 days to complete the PP&A operation. Time of the new proposed method is estimated based on history and internal experience and resulting in a total operation time of 28 days. This means that PP&A operations may start in the last quarter of 2012 and still finish early in 2016 with all 40 wells resulting in a massive cost saving for Statoil. 1.1.2 Cost To calculate the cost of a conventional PP&A method Statoil used historical data and finds an average day-rate to be multiplied with time estimations. This cost estimated day-rate is set to be 1.1 million NOK per day and include all from equipment to personnel. Since the proposed units have never been used before in Statoil the cost calculations for the new method cannot be based upon historical data. Cost calculations have therefore been calculated in details and result showing a day-rate of 2.5 million NOK. This is much higher than the conventional method, but is much more unreliable plus the method takes less time. How much the actual cost will turn out to be is difficult to predict, but as of now the starting point should be 2.5 million NOK per day. 1.1.3 Personnel A normal rig crew working on the drilling rig consists approximately of 35 people. The new proposed method requires only 18 people. This is half of the people required by the conventional method and will create a daily saving of approximately 250 000 NOK per day. During the whole PP&A campaign this will result in major cost savings overall.
Master's thesis in Petroleum engineering