Horizontal Well Placement in a Thin Heterogeneous Carbonate Reservoir, Utilizing Azimuthal Sonic and Resistivity Measurements, a Case Study from Offshore Abu Dhabi

Serry, Amr M. (ADMA-OPCO) | Al-Hassani, Sultan (ADMA-OPCO) | Al-Tamimi, Ibrahim (ADMA-OPCO) | Khan, Owais A. (ADMA-OPCO) | Naseem, Shafiq (ADMA-OPCO) | Mostafa, Hassan (Weatherford) | El Kholy, Mohamed (Weatherford) | Bassiony, Aly (Weatherford)



Proper Well Placement in a thin carbonate reservoir could be challenging due to high geological uncertainty. Using radioactive sources to evaluate porosity & formation dipping is effective, but localized geological and structural uncertainty resulted in a decision to not use radioactive sources in the well.

This paper is a case study illustrating utilizing absolutely sourceless BHA including combination of azimuthal sonic with azimuthal resistivity distance to boundary technology as a highly effective alternative sourceless geosteering method & adds extra formation evaluation values.

Azimuthal resistivity was used for larger scale geosteering, landing the well within the reservoir, and positioning it close to the target zone, while azimuthal sonic was used for smaller scale precision placement within the target zone itself, with steering decisions being based on porosity.

A standard LWD sonic tool would have provided an average response to the formation within the zone of measurement, with the transit time for both compressional and shear effectively corresponding to the fastest route from transmitter to receiver.

The azimuthal sonic tool however, measures the transit time for both compressional and shear slowness in 16 sectors around the borehole. As the drill string rotates, waveform data is acquired in 16 fixed-orientation azimuthal bins. The waveforms are processed to yield azimuthally oriented compressional and reflected shear slowness values, with associated porosity values derived from the compressional data. It is these porosity values that were compared and contrasted to ensure positioning of the wellbore within the narrow high porosity zone.

Borehole images constructed from both compressional and shear slowness data provided clear indication of intersecting beds. Compressional data compared well with conventional images from LWD azimuthal gamma and density tools, and was used to identify formation dip and stratigraphic position of the wellbore.