First Successful Application of Multi-layer Bed Boundary Mapping Technology to Achieve Maximum Reservoir Contact in Horizontal Wells in Saudi Arabian Gas Reservoirs

Abstract

Abstract Distance-to-bed boundary technologies have been successfully deployed to geosteer wells horizontal sections for the last 10 years. As the technology is based on the propagation of electromagnetic waves, its preferred operational environment is to be in the resistive reservoir layer, while mapping the adjacent conductive layers. Technology advances have driven the development of a more robust inversion engine, as well as opened the opportunity to acquire and transmit a richer suite of measurements in real-time that are more sensitive to reservoir dip and anisotropy. The evolution has taken the technology from distance-to-bed boundary to multi-layer bed boundary mapping improving the resolution from a simple 3-layer model of up to ~15 ft radially from the wellbore to multi-layer detection in excess of 20 ft. The new inversion engine is also better equipped to resolve for information about the reservoir in the less-favorable environment, such as, conductive target reservoir with resistive adjacent layers. In an effort to maximize reservoir exposure and minimize wellbore stability issues when multiple layers are crossed, a new generation of boundary mapping technology was deployed to help address challenges in thin porous layers within carbonate reservoirs. Since reservoir layers are identified by porosity, and this technology is conductivity-seeking, the basic premise of the well placement approach was to ascertain the relationship between resistivity and porosity on landing, and then proceed thereafter with the appropriate inversion result-based geosteering. The assumption is that the relationship remains the same throughout the wellbore length, otherwise a new well placement strategy would need to be devised in real-time. As the gasbearing target reservoirs are a mixture of calcite and dolomite, it was often found that the more conductive layers were indeed the target porous layers, when compared to the upper/lower adjacent layers (tight and more resistive). However due to lithological heterogeneity, the opposite was also found to be true. While drilling across these targets, there was a clear delineation of the upper and lower layer limits, with the target layer thicknesses in the range of 2-8 ft. Proactive well placement decisions were executed to maintain the trajectory within the target layer, resulting in unprecedented reservoir exposure. Placing a well in a single porous zone will not only bring the benefit of improving production rates, but it will also allow the well to be drilled with properly optimized mud weight resulting in no wellbore stability issues while drilling, tripping or performing casing operations.