Advanced Techniques for Mapping Oil-Water Contacts

Abstract Lateral variation of water levels can pose a great challenge to successful placement of horizontal production wells. Continuous identification of water levels has been traditionally achieved by logging old vertical or deviated wells drilled in the area, or by drilling new ones for evaluation purposes. This process is usually costly, time-consuming, and does not resolve the lateral uncertainty between those wells. This paper discusses the effectiveness of traditional and advanced modern techniques for identifying varying water levels, for successfully placing horizontal wells in the reservoir. Traditional techniques to identify water levels based on vertical or deviated well logs utilize resistivity data from logging-while-drilling (LWD) or wireline tools. The results of using different types and frequencies of LWD and wireline resistivity measurements were analyzed. In addition, LWD formation testing data were used for calculating pressure gradients to confirm fluid type and density, as well as estimate formation water salinity. While drilling horizontal sections, evaluation of the oil-water contact (OWC) can be achieved using 1D and 3D inversion from deep and ultra-deep resistivity tool measurements. This technique, using real-time data, provided good estimates of fluid boundary positions. Advanced 3D inversion techniques were also examined to distinguish between the lithology of layers with similar resistivity values. Comparing the different modes and frequencies of LWD propagation resistivity has shown how evaluating water zones in deviated wellbores has several challenges, depending on which resistivity response is used for the evaluation. Calculating pressure gradients with LWD formation testers is shown to be a successful approach although challenges can be faced due to using different drawdown rates compared to wireline testers. For horizontal wells, real-time fluid mapping using deep and ultra-deep resistivity allowed the assessment of lateral variations of the OWC, making it possible to maintain a distance from the water contacts while drilling. The utilization of 3D inversion for resistivity and anisotropy helped to determine the fluid type and lithology at a distance, where anisotropy evaluation was the differentiator for situations where shale and water-bearing sand zones had very similar resistivities. Integrated data from multiple wells allowed mapping of the water level as a three-dimensional surface at a wide multi-well scale. This paper presents an integrated approach to mapping OWCs using traditional and advanced techniques. The data used for single-well and multi-well analysis enabled proactive well placement as well as better planning of future wells.