Horizontal wells are commonly used worldwide to improve recovery of petroleum resources. Offshore Abu Dhabi, the carbonate reservoir contains sub-seismic features such as faulting and fractures that impact production and enhanced recovery. This paper is an attempt to identify and link fractures and faults observed near borehole with surface seismic in order to provide insight into their extent, distribution, characterization and implications on the reservoir production. The study resolved structural interpretation uncertainty in the 3D seismic, highlighted the variability in the injected water front advancement, and provided a methodology to link fine scale observation from micro-electrical image logs to intermediate sonic measurements and surface seismic.
Conventional sonic logging is similar to refraction seismic experiments carried out on the earth's surface except that, for the sonic, the source is higher frequency and the source receiver distance and receiver spacing is much closer. This allows the sonic to achieve a higher resolution velocity measurement over a shorter interval.
Sonic logging waveforms can also be processed for reflection information in a similar way to reflection surface seismic. Its higher frequency source thus allows for much higher resolution reflection information tens of feet away from the well.
The structural dip computations from pilot and horizontal image logs were linked with sonic reflections to mark probable fault locations and to construct a geological cross-section, which used to define the different reservoir layers that intersected along the well trajectory. Structural lineaments (faults and fracture zones) within a given reservoir layer were extended away from borehole by utilizing sonic waveforms. Due to small fault displacement (<4 m) the fault was not originally picked on the surface seismic, but overlaying the interpretation on the attributes indicates the possibility of a fault. The results were subsequently validated by injection profile. Mapping these lineaments improved seismic interpretation, which ultimately lead to better well placement and validated existing dynamic data.
