Abstract
Shell team was tasked to design and execute a complex ~9,000 ft sidetrack from vertical kick off design from a 9-5/8" casing. Goal was to drill and run 7-inch liner and have high quality cementing necessary for well testing phase and data acquisition of this appraisal well. Complexities of this sidetrack can be focused in three main areas. Firstly, drilling and cementing modelling showed torque and drag values were higher than equipment safe operating limits. There was also high risk of pack off due to unstable shales in build section of the sidetrack. Lastly, there has been previous experience of differential sticking risk resulting in stuck liners across the permeable reservoir due to high overbalance required to avoid kicks and for shales stability.
Post drilling during the completions phase, previous sidetracks had issues running the liner run and obtaining high quality cementing operation, due to losing rotation during cementation because of very high torque requirements and risk of fatigue failure which yielded a connection in an offset well and impacted well's integrity. This also complicated the data acquisition and abandonment operations.
This paper describes the Strategy followed to overcome these challenges while improving drilling and casing performance as well as paving the way for successful data acquisition during well testing.
It is usually challenging to optimize all drilling and cementing parameters only based on models which are not always accurate if not history matched properly. The uniqueness of this strategy was in successfully predicting accurate models for torque and drag for both drilling assembly and liner using calibrated friction factors and sensitivity modelling by matching history data to previous models. Fit for purpose solutions were then designed to overcome challenges referenced above. A key novel solution planned was cementing the liner using water displacement which was not trialed previously. Normal procedure in any cement job is to use a similar mud weight as used to drill the hole for displacing cement – because drilling mud was designed to be compatible with the hole section. However, in this sidetrack, reverse engineering of previous sidetracks experiences guided the team to focus on ways of reducing weight of liner string to make it easier to rotate it – and hence the idea of using water. In addition, various modelling strategies for drilling, running liner, centralizing, and cementing it were studied in detail with comparison to previous data.
In results of this paper, torque and drag actual data from drilling, liner run, and cementing will be interpreted. Moreover, cement quality data from logs will be presented showing improvement from previous sidetracks. In consequence this led to high quality data acquisition during well testing due to cross flow prevention with cement, as well as section milling avoidance in abandonment. Key finding was proving techniques to reduce cementing rotation torques to less than half using water displacement and liner roller centralizers. Another conclusion was criticality of using calibrated friction factors to ensure right torque and drag targets are being mitigated. Study also proved success of a method of avoiding fatigue failure in liner by optimizing placement of connections and monitoring rotation against a set limit.
The novelty of strategies presented in this paper is explaining how calibrated modelling, using new technologies, and most importantly how applying innovative cementing strategies like using water to displace cement, can lead to successfully executing a challenging sidetrack Design with high cement quality.
