Saturation Mapping in the Interwell Reservoir Volume: A New Technology Breakthrough

摘要

Using a coiled tubing (CT) conveyance, data from a crosswell electromagnetic (EM) tomography survey was acquired between two horizontal wells, a water injector and a producer. The survey was conducted in a swept area of a naturally fractured Middle Eastern carbonate reservoir. This article presents the workflow that was developed to integrate the EM survey results with other data to successfully map the interwell hydrocarbon saturations. A slanted well was later landed in the interwell area based on the crosswell survey interpretation results. This new well, which targeted an oil column shown to be bypassed by the water injection in the swept area, is currently on production. The survey established a number of world firsts for the EM technology, including its first deployment in horizontal wells, its first survey of well spacing > 1.3 km, its first data interpretation with full 3D resistivity inversion, and the first 3D apparent water saturation mapping from EM data. The field program included acquisition of an extensive open hole logging sequence in each well prior to the crosswell EM data collection. The crosswell EM survey measured 135 profiles, covering a horizontal section of more than 800 m in each of the two wells. High quality data were acquired for almost all the data profiles, even in a 400 m cased section. The field data were interpreted with a 3D inversion code. The fracture corridors were identified as electrically conductive volumes due to their high water saturation. The less swept or unswept areas were characterized by their higher resistivity due to their lower water content. A resistivity model cannot be used directly for reservoir evaluation, so the subsequent step was to convert the resistivity model into a saturation volume, based on Archie's law. An innovative workflow of petrophysical simulations was designed to define the volumetric distribution of porosity and water salinity based on reservoir simulation scenarios and ad hoc laboratory analyses. Finally, the most probable scenario for the location of apparent water saturation volumes in the interwell reservoir volume was produced. This work demonstrates the critical need for deep characterization in cases of fractured carbonate reservoirs, including any cases where the sweep efficiency is likely to be uneven due to heterogeneities in reservoir petrophysical properties, particularly permeability field variations.