Successful Impact of 3D Seismic Attributes in Planning and Drilling Directional Wells in Clastic Reservoir of Greater Burgan Field in Kuwait

Abstract

Abstract Channel sand reservoirs very rarely have layer cake geometries and are generally characterized by sand bodies/lenses with limited horizontal and vertical continuity. Significant lateral changes occur in reservoir thickness as well as reservoir properties and lenses are often stacked at different stratigraphic levels. The reservoir sands in the greater Burgan field show similar variations both structurally and stratigraphically. Navigating a wellbore in such complex channel sand reservoir requires precision geo-steering technology with two major requirements: Detecting reservoir boundaries with dip information for structural steering. Mapping multiple layers above and below the target layer for stratigraphic positioning. Detecting reservoir boundaries with information on layer dip and anisotropy can immensely help to forward plan trajectory as per formation changes and this require a good knowledge and study about the seismic data and offset wells information. 3D seismic data immensely help in placement of all kinds of wells, especially designing and fine-tuning a meticulous trajectory for Deviated and horizontal wells. Attributes made with seismic cube data, namely Structure and coherency volume, can image major to minor faults, which are generally viewed on slices of major formation tops. There are various other attributes like Impedance, Vp/Vs, Porosity and sand probability map, which can indicate possibility of sweeter part of reservoir. Depth of various major formation tops are predicted quite accurately within the limit of seismic resolution from Velocity model or Depth-Migrated seismic volume. These depth predictions immensely help in designing trajectory and landing the well in the actual desired zone of reservoir at the desired angle. During Geo-steering also, in spite of all the tools of drilling contractor at their disposal, the seismic data help to guide the drillers to steer in the right direction, if drilling team is out of track from the good part of reservoir. Overlaying such a well in the seismic section directly gives the predicted depth throughout the well trajectory, which helps to design the Deviation survey parameters. The paper will explain a special attribute called Ant-trak, which not only shows the major faults, but also very minor faults and sometimes, fine geological features, which cannot be seen in seismic section or slices. This attribute is taken on Burgan-Third sand top surface. All the major NW-SE faults can be seen. Over and above, some minor faults are also seen in it. PSTM seismic data and the other structural attribute which able to show together, faults very clearly. Such a blended surface gives an enhanced display of faults in the area of study including very minor ones, which help to design the survey. By using different Seismic Volume and Surface Attribute analysis, we mark the major faults trend and extracted many structural features in the study area. We try to deal with different attribute parameters and use offset wells data logs near to each planed horizontal well in the area which help us to have more control during geo-steering horizontal wells.