First Application of LWD Deep-Azimuthal Resistivity Tool and Advanced Data Interpretation Software for Reservoir Navigation at West Salym Field in Russia
Authors: Belyaeva Olga , Podberezhnyy Maxim , Zverev Vladimir , Sviridov Mikhail , Mosin Anton , Antonov Yuriy 
Published: October 2016

Abstract
West Salym is a Salym Petroleum Development oil field located in Khanty-Mansi Autonomous Okrug, 120 kilometres south-west of Surgut. The West Salym oil field was discovered in 1987 and was brought on stream in 2004. The reservoirs vary from fluvial/deltaic to shallow marine deposits. The primary development of the central area of the West Salym field is completed. The edge of the field remains undeveloped and potentially attractive.
The edges of the field are presented by a mouth bar and characterized by significant structural formation changes, including unknown formation dips and the presence of local carbonate concretions and stripes. The sand thickness of the target layer is 15 m with a minimum oil height of 1m, caused by structural dip and OWC closeness. In these conditions it is difficult to drain the area with geometrically placed wells within the hydrocarbon-saturated layer based on well correlation and 3D seismic interpretation results. Another challenge is the low resistivity contrast between shale, oil- and water-bearing layers, which complicates reservoir properties evaluation and distinguishability of different fluid saturations. To evaluate capabilities of modern reservoir navigation technology, two horizontal wells (500 m each) were drilled for the first time in the West Salym field, using deep-azimuthal resistivity technology and advanced data interpretation software. Drilling both horizontal wells was improved by pilot holes (well A and D) with standard GR-Resistivity-Density-Neutron logging suite and pressure testing‥
Logging-while-drilling, deep-azimuthal resistivity technology has been used in the field development, contributing to proactive reservoir navigation. This technology provides input for the interpretation of an extensive set of multi-component, multi-spacing and multi-frequency measurements. This data are usually sufficient to resolve the formation properties in the vicinity of several meters from the wellbore and to adjust the direction of the well trajectory. However, due to time restrictions, very simple resistivity models and only the subset of data are often used for real-time interpretation. Moreover, the structure of the data subset is often predefined to provide the maximum depth of investigation, neglecting the quality of formation parameter resolution. In some particular fields it can lead to increased uncertainties during reservoir navigation.
The data interpretation software mentioned in this paper has an excellent performance and enables the real-time processing of the full set of downhole measurements based on multi-layered formation models. This case highlights the first use of this software application in the Russian Federation.
The software is based on the method of the most-probable parameter combination and keeps the optimal balance between the information recovered from the measured data and all available a priori knowledge about the structure. The ability to accurately involve a priori information enhances software capabilities of resolving layers with low-resistivity contrasts. Moreover, inversion software is user-controlled to carefully monitor lateral and vertical changes in the geology.
The advantages of data inversion software ensured successful reservoir navigation in the challenging conditions of the West Salym field. All steering decisions were made according to the consistent and reliable multi-layered formation resistivity model that was constructed in real time during the drilling. A good net-to-gross ratio was achieved: almost 75% for one well and 50% for the other. Expected oil rates are 300 and 150 m3/day. Post-drilling analysis showed that in the case of geometrical drilling without the application of reservoir navigation technology the net-to-gross ratio would not exceed 40%.