The reservoir to be described in this paper is a thinner and more poorly developed reservoir overlaying one of the major reservoirs onshore Abu Dhabi. The total reservoir thickness is about 50 feet, but it is subdivided by tighter intervals into four separate subunits. Core data have shown that the bottom of these four subunits, while being the thinnest, has the best permeability.
The field development plan calls for peripheral water injection and mid-flank production by means of horizontal wells. The permeability is known to degrade towards the flank of the field to such an extent that it materially reduces the injectivity in the peripheral injectors. The injectivity achieved controls the number of wells required.
To minimize the required number of injectors it is thus important to maximize the length of the well in the best quality subunit. This requires geosteering the well in the basal bed, which has the highest permeability, but a thickness of only 4–5 feet.
To date six horizontal wells have been drilled in the formation, in one of which a distance-to-boundary resistivity tool was run. This paper reviews the lessons learned from the geosteering of these wells and the results of the distance-to-boundary tool. It also presents a comparison of the success of geosteering of the wells to the nearby geological complexity.
The geological complexity at six proposed locations to be drilled in 2007 is examined. Based on their complexity, in comparison to that of the previously drilled wells, recommendations as to the optimum LWD suite are made. This particularly includes a discussion of whether or not the use of a distance-to-boundary tool is justified. It is concluded that it is possible to risk rank the proposed wells and that such a tool is justified in some but not all of the wells.