Granite basement drilling in Vietnam is well-known for challenges such as slow penetration rate, strong drill string vibrations, and multiple bit runs required to finish the section. A 3,217 m length 3D horizontal basement section was successfully drilled in 2017 by applying a new drill string optimization method in combination with using axial oscillation friction reduction tools (AOT), reaching total depth (TD) at 6,280 m measured depth (MD). This run represented the longest 3D lateral well drilled in Vietnam at the time (please reference the SPE-191872-MS). Based on the success of that project, Thang Long Joint Operating Company planned to drill a new well with a longer reach to farther targets as per subsurface objectives to extend the record to a planned 3,543 m 3D horizontal granite section hitting three reservoir targets. The directional plan included building inclination from 19° to 88°, turning from 97° to 57° azimuth, and then turning horizontally from 57° to 16° azimuth, with planned TD at 6,768 m MD.

With the field-proven drill string optimization method from the offset well, a torque and drag model was built for the subject well in order to understand the difficulty and feasibility to reach the well TD. This model was used for drill pipe selection and configuration, as well as AOT planning purposes, and it was continuously updated in real-time throughout the well. A newer and more efficient version of the AOT technology was introduced to help increase the effectiveness of the friction reduction to help reach the planned TD. From the modeling results, drilling to the planned TD was considered achievable, even when applying worst-case scenario drilling conditions.

In terms of trajectory and timing, the actual drilling operation was well-matched with the planning. The selected drill string designs using single AOT systems and dual AOT systems performed as expected and were instrumental in achieving the planned TD. A total of 15 roller cone insert bits and steerable motor BHA's were used to drill the section. From 5,509m MD, due to the high drag condition, dual AOT systems were utilized to aid in weight transfer to the bit to drill to the well TD at 6,768m MD; the longest 3D horizontal basement section drilled in Vietnam to date.

The success of the project once again proves that axial friction reduction technology is a reliable technology for drilling the granitic basement in Vietnam, on time and within budget.

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