Abstract
Current drilling practice allows the drilling of wells whose horizontal drain sections maximise reservoir contact by remaining within a single productive zone. The well path may include sharp azimuth changes, which increases friction drag along the wellbore and precludes access and egress by conventional intervention techniques. This paper aims to demonstrate that a low weight, low friction and high strength carbon composite rod can reach the toe of even the most challenging profile of well.
A carbon composite rod of small diameter and containing an embedded electrical conductor is used in combination with standard tractors to deploy logging or other intervention tools into challenging wells. In such wells, the limiting factor for well intervention is the friction drag of the deployment system along the wellbore, especially where azimuth changes. The light weight of the rod combined with its extremely low friction coefficient means that drag is reduced to a minimum allowing access to TD while also ensuring safe retrieval without exceeding safe working load.
The carbon composite rod system has been used on a number of interventions that provide proof of concept for combined operations with a tractor in horizontal well systems. In each case the well and BHA was extensively modelled using the proprietary software designed specifically for the carbon composite rod system. In one case the objective was to maximise the payload that could be conveyed rather than the absolute depth achieved. Following extensive modelling including tractor performance, a toolstring measuring 459ft and weighing 7,260lbs was selected and run successfully in a horizontal well. The predicted behaviour compared very favourably to the data recorded during the job, confirming the accuracy of the models.
For an extended reach well where the objective is to obtain production and reservoir data all the way to the toe, the relatively small size and weight of the logging tools means that achievable depth is increased. A number of wells with challenging profiles that had never been successfully logged post completion were modelled using the latest software and operational parameters derived from recent experience. In each case, it was predicted that TD could be achieved and that the string could be safely retrieved from the well.
Demonstrating the convergence of predicted and actual performance of the carbon composite rod under a number of scenarios gives confidence in the validity of the models incorporated in the simulation software. Using these models to predict the performance in extended reach wells, especially in the cases where there are significant azimuth changes, will allow planning for rigless interventions where access or successful retrieval has been impossible up until now.
