|Publisher||Society of Petroleum Engineers||Language||English|
|Content Type||Conference Paper|
|Title||Lessons Learned in the Planning and Drilling of Deep, Subsalt Wells in the Deepwater Gulf of Mexico|
|Authors||Charles D. Whitson, Michael K. McFadyen, Texaco, Inc.|
SPE Annual Technical Conference and Exhibition, 30 September-3 October 2001, New Orleans, Louisiana
|Copyright||Copyright 2001, Society of Petroleum Engineers Inc.|
As more deepwater wells in the Gulf of Mexico (GOM) are being drilled for subsalt objectives, salt sections in excess of 6,000 ft. and well depths in excess of 25,000 ft. are becoming common. In order to drill these wells successfully, deepwater operators are required to focus planning efforts on the challenges posed by these extreme salt sections and well depths. Texaco recently planned and drilled two such wells in the Walker Ridge Area of the GOM. Both wells had salt bodies in excess of 10,000 ft. and were planned with total depths below 26,000 ft. The advantages of long salt sections are (1) high fracture gradients within the salt, which allows longer hole sections between casing strings and (2) insulation from typical well control problems associated with permeable formations. Disadvantages include (1) difficulty in predicting the pore pressure and fracture gradient in the sedimentary section below salt and (2) hole deviation and related directional control problems in the salt.
During the planning of these wells, drilling personnel focused on (1) the drilling of non-under-reamed hole sizes in salt for enhanced directional control, (2) use of new technology to increase ROP and directional control in the salt, (3) installation of heavy, longstrings of casing demanded by the long salt sections and (4) formation of contingency plans to account for the uncertain subsalt pore and fracture pressures. This paper outlines the approach taken in the planning of the two wells and discusses the lessons learned during the execution, most significantly: (1) long salt sections can be used to advantage to extend casing points and eliminate well control issues, (2) ROP in salt can be maximized through the use of conventional, non-under-reaming bits, stabilized bottomhole assemblies, and synthetic oil based mud, and (3) a detailed planning and quality control program is required for the successful running of heavy longstrings of casing.
In early 1999, Texaco committed to drilling two ultra-deep, subsalt prospects in the Walker Ridge Area of the GOM. The Loyal Prospect was located in 6,700 ft. of water and the Catahoula Prospect was located in 5,500 ft. of water. Both wells had minimal supra-salt sections (1,400 ft. in Loyal and 2,465 ft. in Catahoula), followed by 11,000 to 12,000 ft. of salt, with approximately 7,000 ft. of objective section below. Both wells were straight holes with Loyal programmed for 27,000 ft. TVD and Catahoula programmed for 26,000 ft. TVD. Two significant advantages were immediately recognized when it came time to plan the two wells: (1) being able to drill two similar wells back to back and (2) having approximately six months to plan the wells before arrival of the rig on the first location.
The rig planned for the two wells was the Glomar Explorer, a deepwater drillship working in West Africa at the time the wells were approved. The selection of the rig resulted in additional planning issues because it had been working overseas for a period of time. First, the national crews had to be replaced with all new crews and second, the wells in West Africa were shallower than the deep GOM wells and, as a result, some of the rig equipment had not been used to its maximum potential. On the positive side, the rig had an excellent safety record while working in West Africa.
|File Size||315 KB||9|