Abstract

ZADCO is the first company worldwide to invent, implement and develop a 36"Conductor Deflection Tool methodology for slot recovery techniques in four actual wells. The main objective of this paper on conductor slot recovery utilizing 36"CDT is to share our experiences and findings with the industry. We are confident that we can demonstrate a strong technical justification for using 36" CDT to companies still considering this approach on their projects. In this paper, all the lessons learned and actual findings which were captured during the planning and execution phases will be explained step by step. All the required equipment and operational procedures which relate to the 36"CDT design will be covered in detail.

One of the major reason for the 30" conductor casing to lose integrity is environmental corrosion. Many of wells in ZADCO offshore environment aren't integral for production and all should be plugged and abandoned. Therefore, Slot recovery for those wells which would otherwise be abandoned is the preferred option therefore recycling the platform slot, enabling a new well to be drill to maintain the production profile. ZADCO has developed a new methodology of slot recovery technique using the conductor deflector tool (CDT). It has been designed and modified mainly for shallow water offshore projects. ZADCO is pleased to be the first company globally to invent and implement this technique of slot recovery.

The new CDT technique delivers the following benefits: 1) No further platform modification is required, 2) stress and side forces are not transferred to the platform due to conductor bending, 3) the top portion of 36" CDT should be kept vertically in order to prevent Wellhead deviation. The design detailed will be described later in this paper. To implement the 36" CDT an existing wellbore should be plugged and abandoned and then an existing 30" conductor and inner casings should be cut 3ft above the sea bed and finally 36" CDT will be installed on the old stump of old well to allow new sidetrack well. All related procedures and the process conduct this will be clearly illustrated step by step in this research.

To date, 4 wells were successfully completed with the 36" CDT slot recovery methodology technique. The 36"CDT has proved to be an effective method of minimizing operational time which has delivered substantial well cost optimization. This technique will help to recover most of non-integral wells from temporary P&A back into service again. The 36" CDT has proven the best alternative solution compare to heavy milling operation options which would expose our aging platforms to the high vibration risk due to the milling operation. Based on the lessons learned which have been captured our design has proved the capability of running various sizes of casings 18 5/8", 20" and 24" as a conductors. In this case study the following topics will be covered in detail.

  1. Definition and types of slot recovery techniques available in the market

  2. Brief history of each case and why CDT was the right solution

  3. Description and applications of CDT

  4. Engineering Calculations of the CDT design

  5. Presentation of data & results including the stages of modification.

  6. Future Challenges, recommendations, mitigations and Conclusion.

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