3D Subsurface Mapping for Precision Re-Engineering of Sidetracks in Faulted Carbonate Reservoirs

Abstract Horizontal Well-A in the North Kuwait Dhabi structure was drilled from the flank towards the crest and parallel with minimum stress, targeting the tight carbonate Najmah Limestone Unit-4. The drilling was complicated by poor seismic data due to the overlying Gothnia salt and lack of offset well. The 3D mapping from UDAR were used to navigate the well and revealed higher dip than expected toward the well azimuth, necessitating an inclination of up to 95 degrees. The well was steered using 3D mapping of Ultra Deep Azimuthal Resistivity (UDAR) to delineate boundaries up to 80 feet above and below the Najmah Limestone, which has a thickness of 60-70 feet TVD. During drilling, the well encountered faults and fractures, causing it to deviate to the top of the Najmah Limestone. Immediate steering corrections were made to return to the target layer. The open faults and fractures led to significant mud losses, necessitating a reduction in mud weight from 16 ppg. However, this reduction initiated the gas start to flow into the well bore. Further strategy is to cement the well and side-track the well to avoid the fault plane. The direction of the sidetrack necessary to be determine in order the steer away from the fault plane in real time. The information of the 3D mapping from UDAR was suggested to steer the well to the right (eastern direction) from the initial well azimuth to get away from the fault plane.