Ahmed F. Jubralla, Saif Al-Omran
QGPC's first experience with this technology was for increased injectivity in an upper Jurassic reservoir which is comprised by alternating high and low permeable layers. The first well drilled in 1990 offshore was an extreme success and the application was justified for fieldwide implementation. Huge costs were saved as a result. This was followed by 2 horizontal wells for increased productivity in a typically tight (< 5 mD) chalky limestone of Cretaceous age. A fourth offshore well drilled in a thin (30 ft) and tight (10 - 100 mD) Jurassic dolomite overlaying a stack of relatively thick (25-70 ft) and "Watered Out" grain and grain-packstones, (500-4500 mD) indicated another viable and successful application.
A similar approach in the Onshore Dukhan field has been adopted for another Upper Jurassic reservoir. The reservoir is 80 ft thick and is being developed by vertical wells. However, permeability contrast between the upper and lower cycles had caused preferential production and hence injection across the lower cycles, leaving the upper cycles effectively undrained. Horizontal wells have resulted in productivity and injectivity improvements by a factor 3 to 5 that of vertical wells. Therefore a field wide development scheme is being implemented.
Initially the planning and the design of these wells was based on models and information extrapolated from vertical or at best deviated wells. It is being realised that such models are in fact inadequate and have to be used with care. 3D seismic and the imaging tools, such as the FMS, reconciled with horizontal cores have assisted in understanding the lateral variation and the macro and micro architectural and structural details of these reservoirs. Such tools are essential for the optimum design of horizontal wells.
AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France