The oil bearing reservoirs of the Lekhwair A-North field in Oman consist of layered low permeability chalky limestones of the Lower Shu'aiba and the Kharaib formations. These have been waterflooded since 1992 by a 200 well development project. However, the field is more faulted and fractured than was anticipated prior to full-scale development and prolific early water breakthrough occurred in many producers (~20%), due largely to direct alignment of injectors and producers along the principal orientation of faults and fractures in the field. As a consequence, the waterflood is currently being converted from a vertical inverted 9-spot well pattern to a line drive orientated parallel to the dominant orientation of faults and fractures in the field. This will result in significantly improved reservoir sweep and oil recovery. Although initially disappointing, production from the field is now well on the way to meeting original expectations. Several options were considered for implementation of the crestal pattern conversion. In heavily faulted and fractured areas, horizontal appraisal wells can aid the targeting of vertical infill wells by providing better definition of the local fracture network. Significant water-conductive features (faults) thus encountered can be targeted as natural injection planes by infill injectors, while infill producers can be better targeted with reduced risk of early water breakthrough. In relatively unfractured areas, the expense of such appraisal is not justified because the risk associated with infill drilling is small. Simple geometric pattern infill is adopted in these areas, with appropriate reference to reservoir simulation models. Significant scope for coiled tubing drilling exists for pattern infill activities, with potential cost savings. Identification of unswept reserves and improved mapping of the fault and fracture network has been achieved through extensive use of FMI/FMS logs in horizontal wells, correlation of production attributes, and production history matching using numerical simulation models.

The oil bearing reservoirs of the Lekhwair A-North field in Oman consist of layered low permeability chalky limestones of the Lower Shu'aiba and the Kharaib formations. These have been waterflooded since 1992 by a 200 well development project. However, the field is more faulted and fractured than...