Horizontal Wells Geosteering and Reservoir Characterization by Using Advanced Mud Logging on the Example of the Terrigenous Reservoir of Eastern Siberia

This paper presents the utilization of advanced mud logging to support drilling of horizontal well on the Ignyalinsky license area of Eastern Siberia. The advanced mud logging complex includes specialized software for recording and analysing geological and technical drilling parameters; technological sensors for registration of drilling parameters with the permissible limits of errors no more than 1%; advanced gas logging by using a high-resolution chromatograph at suction and return lines; geochemical analysis devices for XRF, XRD cuttings analysis and natural gamma radiation analysis of cuttings; the use of cuttings weighing machines to quantify the degree of the wellbore cleaning. This article discusses the application of listed data for geosteering and clarifying the geological model of the reservoir. The lithological analysis of cuttings is carried out on the base of mineral and elemental cuttings composition, which, unlike field data of a standard mud logging survey, exclude the concept of "human factor" during analysing the lithology of cutting samples. The data on mineral and elemental composition of wells were interpreted to clarify the lateral variability of the reservoir and to highlight potential reservoir intervals. Advanced gas logging was used to identify potential reservoir interval in pilot well, and consequently to plan MDT works. Data on elemental composition of cuttings sample from pilot section and from core analysis of nearby exploration wells were used to construct geochemical profile of the reservoir. Furthermore, reference chemical elements were selected to mark the well position in the reservoir: exit above or beneath the target interval. XRF elemental analysis while drilling was used to improve borehole position in conjunction to LWD data. The elemental composition of cuttings of horizontal well were used for facial interpretation, which is not captured by LWD tools. So, ancient fluvial channel bodies were identified on the base of geochemical rock typing, and potential reservoir intervals are suggested. The performed interpretation was verified by the resultsof the multistage hydraulic fracturing.