Possibility of Another Sidetrack thru 9-5/8" Casing

Request your technical experts’ comments regarding the condition of the existing 9-5/8” casing and the feasibility of attempting another sidetrack.

The key findings from the USIT survey are summarized below:

• At 3,628.7 ft: Complete loss of casing wall thickness (100% wall penetration). Behind this point is 13-3/8” casing and cement. Please see the attached schematic.

• From 6,583 to 6,780 ft: Severe metal loss at multiple depths. See attached files.

• From 7,020 to 7,090 ft: Sinusoidal response, interpreted as drill wear.

• General casing condition: Drill wear across the logged interval, with several joints classified as Grade 3.

In view of the above, we would appreciate your technical input on the following:

1. Sidetrack Feasibility: Please advise or comment whether another sidetrack can be attempted through the existing 9-5/8” casing, considering its reported condition.

1. Technical Recommendations: Please provide any additional recommendations, operational limitations, or precautions that should be considered before proceeding with another sidetrack.

Operational History and Repeated Casing Obstructions:-

During ST-2, the 8-1/2” hole was drilled to 12,823 ft. While running in hole with the rotary assembly, an obstruction was encountered at approximately 8,460 ft inside the 9-5/8” casing. Casing clean-out was subsequently performed using taper, flat-bottom, and insert-bladed mills across the 8,460–9,224 ft interval (764 ft). Open-hole conditioning was then carried out using rock and PDC bits down to 12,823 ft, after which drilling resumed to 12,845 ft before deployment of the RSS directional assembly.

Subsequent survey correlation confirmed an accidental sidetrack of the 8-1/2” hole (ST-3) within the 9-5/8” casing from approximately 8,450 ft. A 6” bit with an 8-1/2” string mill was then deployed to regain access to the parent hole, and the operation was successful. Subsequently, ST-4 was drilled to 13,412 ft.

However, during a subsequent losses situation, an obstruction was again encountered at approximately 8,430 ft, at nearly the same depth as the previous events. This time, attempts to regain access to the parent hole have been unsuccessful.

The repeated occurrence of obstructions at approximately 8,430–8,460 ft, despite previous successful clean-out and recovery operations, raises serious concerns regarding the integrity and stability of the existing 9-5/8” casing.

would appreciate your assessment of whether the existing 9-5/8” casing joints above these proposed kickoff depths can withstand further tripping operations and potential losses/gains during drilling, considering the observed metal loss, drill wear, and Grade 3 classifications.

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