Lessons Learned of Dual Monobore Completion Well Construction

Abstract Selection of the completion type of a well is based on many factors. Some factors are main justification to select dual monobore completion well for the field development. Excellent conceptual, planning and preparation stages would bring successful well execution. Overall, the well design was executed successfully. However, some lessons learned remain to improve the future well completion execution that to be discussed in this paper. There are four wells completed with dual monobore completion in this project phase. Well completion selection process selected dual monobore completion with the last tubing size is 3-1/2 inch. Some of main factors to apply dual monobore in this field are: many sand gas zones, higher gas rate with dual production strings, remote area with high cost for any work-over operation for changing layer. Any future well intervention will be performed with rigless, wireline operation or coil tubing unit as required. Another new procedure of getting underbalanced condition before perforation is by pumping diesel oil as the last fluid into tubing. This avoids unloading operation with coil tubing unit which costly in remote operation. After drilling and setting the 7 inch production liner below the 9-5/8 inch casing, long string & short string of 3-1/2 inch tubing run together with specific tubing tong. Cement unit pumped cement to surface through the long string to cover all tubing length, however about 20 ft of cement at surface circulate out by inserting small macaroni string, to be able to set pack off seal between tubing and well head, which specifically designed for dual monobore tubing installation. The operation continued with rigless operation for cement log, perforation and flowing the well. Some problems for lesson learned were tubing tong gripping problem, tubing cementing head leaking, tubing restriction inside tubing that near the bottom of the lowest zone perforation, high over pull of the slickline unit, orienting gun perforation length limitation. Mostly the designs of the dual monobore completion were successfully implemented in this project. The cementing operation performed well. Double casing perforation is achieved with the depth penetration gun. Both tubing strings could produce gas as expected. Diesel oil successfully displaced the cement, gave under balanced perforation and returned back to surface on flowing. The dual monobore completion will be applied for the future well campaign.