LWD Resistivity Tool Application to Horizontal Geosteering in Thinly Bedded Carbonate Reservoir Layers

摘要

Logging While Drilling (LWD) propagation and azimuthal laterolog resistivity tools are utilized to accurately place long horizontal wells within a reservoir unit located near the base of a thick carbonate reservoir. The reservoir unit is comprised of a thin dolostone layer, sandwiched between two, moderately thicker limestone layers. The dolostone has higher resistivity than the two limestone layers. The degree of resistivity elevation varies laterally throughout the field depending on the degree of dolomitization, saturation and porosity levels. When adequate resistivity contrast between the limestones and dolostone exists, geosteering geologists utilize this contrast to direct the well in close proximity to or within the dolostone. This is the preferred method of geosteering in ZADCO for extended reach horizontals with its current drilling rig fleet, which are near their drilling reach capacity. This reduces the use of nuclear source porosity tools and the potential for long fishing operations should a stuck tool in hole incident occur. The history of the field development (e.g. water injection), simulation predictions of water front movement, geological characteristics, surveillance data and petrophysical data in the area of interest are checked to determine the suitability of resistivity tools (only) to geosteering.