A study of borehole image data acquired from eight wells drilled as open hole completions into highly fractured basement has identified open and stress-sensitive fracture sets. This information together with seismic interpretations of fault damage zones, production and gas log data has helped to constrain basement targets in the Bayoot Field, Block 53, Yemen. However the dominant productive zones within the basement appear to be within seismically resolvable fault damage zones that should in theory be closed under the present-day stress regime. Sidewall core examination has shown evidence for cement bridging between fracture surfaces and this propping effect is envisaged along these major faults. A dual porosity system is hypothesised whereby open critically stressed fractures act as hydrocarbon conduits into the seismic-scale faults.
This case study of ten oil wells drilled into highly fractured and heterogeneous crystalline basement rocks of the Bayoot Field, Say’un Masila Basin, Yemen, brings together the findings from a wealth of oil field data and shows that a multidisciplinary approach is required for full characterisation. An improved method for targeting hydrocarbons has been established for the study area. This has been achieved by drilling highly deviated wellbores into the upper basement reaches and optimally orienting them to intersect a maximum number of stress-sensitive fractures together with major seismic-scale fault damage zones that are not in direct connection to the local Bayoot Fault.