Successful Deployment of High Risk Monobore Completion in Fracture HPHT Unconventional Reservoir Using Floatation Technology Enhances Well Accessibility
Authors: Elzeky Moataz , Varma Esha , Emam Aly , Al Hammadi Aref Hussain , Al Hadidy Khaled , Nunez Ygnacio , Azher Muhammad , Abdelghany M. M. 
Published: November 2024

Major Challenges while planning HPHT well in unconventional reservoir. The required mud weight to drill is 22ppg. were high torque, friction-factors. Well torque and drag simulations showed that planned completions were not deployable without rotation of the string and the deployment of the frac string required a very low friction factor that could only be reached by Oil based mud(OBM) or rotationwas huge impact. This paper describes the detailed key factors design criteria to deploy these risky completions.

To drill cost-effective wells in a multi-disciplinary team was formed to review the design of unconventional wells and propose a cost-effective solution. Because of the complicated nature of the frac wells, they often use compression on the string to force it down which results in an excessive force which induces helical and sinusoidal buckling. The requirement of very low friction factors to deploy frac string with high mud weight; the new technology of floating the string, rotation of the string with low friction centralizers was introduced. The engineering design for the same was worked with risks of well control were mitigated.

The well was a pilot to put concept to floatation inorder to deploy frac strings to Target depth(TD). The actual friction factor for Fluid systems with mud weight 20ppg and above is 0.45-0.5. The well architecture is complex and challenging due to its very short vertical section to landing point. This requires negative displacement to achieve the well objective with high dog leg severity per 100ft of 5 and above. The deployment of frac string can be achieved only by floatation or rotation. Rotation requires a high torque connection that directly impacts the well AFE. The floatation collar comprises of high-pressure glass disk that allows trapping air below the disk. The concept of flotation is to reduce drag and Friction factor of the frac string with the open hole which allows smooth deployment to TD. It is deemed necessary to use this technology along with low friction composite centralizers. The drilling fluid was customized to provide smooth ECD and circulating pressures targets to avoid increasing the risk of dynamic induced loss of circulation. The premium lubricant reduced the friction factor by 0.01. The cost of this technology is negligible compared to the risk associated with failure to deploy frac string.

This was a new concept put to test which was the most cost effective with several new ideas and technologies being used. This novel idea bagged savings upto 6MM $ cost by avoiding use of expensive high torque connections and systems. This concept will be applied to all future wells.

This paper presents and discusses the first installation of completion floatation technology in the UAE for a high-risk unconventional HPHT well. Due to the nature of those unconventional wells in the UAE, many challenges are related to landing the frac completion to target depth. This well is a part of a pad drilling with a plug and perf completion. The operator objective is to run the 5-1/2 inch frac completion to target depth (21,000 ft) without inducing any buckling in the string. The operator previously faced a lot of difficulties running the frac plugs in a later stage as the buckling was preventing the coiled tubing to pass through those buckling area. Torque and drag calculations showed that it's not possible to run the completion to planned depth with the available casing. Additionally, the high amount of friction factor showed it's impossible to deploy the completion to the planned depth.

There are few options to mitigate those risks which will impact the well cost and delivery significantly. Those changes require a major change in casing design and also replace the current mud to oil based mud.

Above left hand figure, well calculation example showed a lock up depth at 17,000 ft which results in losing the last 3000 ft unreached and completed. Moreover, a helical buckling is created in both vertical section and the horizontal section as well.

After careful study and investigating innovative solutions to complete the wells successfully, the decision was taken to implement a pilot trial for floatation collar along with the frac completion string. By utilizing the floatation collars, almost all the challenges are addressed and all risks are mitigated. The floatation collars technology deployed in this campaign are intervention less single cycle valve. This design uses a tempered glass package barrier that breaks at a predetermined calculated pressure. This design was chosen carefully so it leaves a full bore internal diameter and with no moving parts in the tool design.