Feasibility study to perform coiled tubing drilling on Gullfaks-A

Abstract

This report is carried out as part of Decision gate1 (DG1) feasibility study conducted for the possibility of commencing coiled tubing drilling to drill slim holes simultaneously with other drilling activities on Gullfaks A (GF-A). A number of wells on GF-A platform has been closed and experienced oil production drop due to different reasons. However there are still small reservoirs with oil left in place which can be drilled through their mother wells to act as producer or injector wells in order to increase oil and gas recovery from this field. This project is carried out to assess and gain extensive understanding of all activities so that one feasible solution is identified to meet the project objectives. Coiled Tubing Drilling (CTD) is utilized first in early 1990s for drilling re-entry wells as this technique made it economically possible to drill inter-bedded formations. Thereafter, these have accelerated the use of coiled tubing (CT) as drilling application. Technical and logistic challenges associated with CTD as well as drilling in mature area have considerable risks that indeed require steps of evaluation to properly understand the task so that prevention and mitigation measures can be set and overall risk picture can be evaluated to make the decision for initiating the concept and then the planning phase. However, CTD operation in offshore environments is still not as widely used as on land operation and still needs in depth studies to evaluate its feasibility due to limited space and cost efficiency. Utilizing previous experiences will enhance the study with lessons learned and positive practices done when drilling with CTD specifically on GF-A platform. Performing CTD as independent operation compared to CTD conducted by utilizing drilling tower on the platform have completely different planning, and special attention must be taken in considerations regarding top side equipment that should to be identified during the feasibility and execution phase. The investigation of these points has made a significant contribution in the final conclusion of this study. This thesis describes the CT as a well service tool that can offer different solutions for different applications. A general introduction to CT surface and downhole equipment supported with Figures is presented to allow better understanding for an inexperienced reader. The CTD represents the core subject of this thesis and presented by first introducing the CTD as a relatively new drilling application with its opportunities and limitations. This is followed by case studies for similar operations held in Norway and from two different places around the world executed by two different operating companies. Variables that impact the drilling operation are highlighted with a guideline to achieve the optimal drilling parameters so that one feasible solution can be met as intended by t this study. As the well integrity importance is crucial for the entire well’s life cycle, the well barrier schematics during drilling operation and proposed plug and abandonment plan are presented in this report. The discussion has also covered the time and cost estimations as well as platform capacity with respect to deck space and people onboard capacity. The people onboard capacity made a significant impact on the final outcome of the feasibility study to perform CTD operation on GFA-A. The new technologies and comparison between CTD and conventional rotary through tubing drilling is outlined to highlight both strength and limitations for both applications so that future drilling operation can be carried out in an optimal way.