The article describes the successful experience of geosteering while drilling wells with a long horizontal completion in the Upper Jurassic deposits. The article deals with the issues of geology of the object, the structure of the section of the target sediments, also example of reservoirs discrimination is given. Reservoirs in the section of the Upper Jurassic sediments are interlayers 0.5–3.0 m thick, which can be clearly distinguished according to geophysical studies of wells and cores. A well test field experiment conducted to substantiate the position of the reservoirs in the section is described. The choice of the target interval for drilling long horizontal boreholes in order to maintain the stability of the wellbore and obtain maximum oil inflows is validated. The goal was to support the drilling of horizontal shafts in the target interval of Upper Jurassic sediments with a thickness of 3-5 m. In the conditions of the impossibility of attracting high-tech logging complex for horizontal shafts, a method of geosteering in Upper Jurassic deposits using GR and rock cuttings during the drilling process has been developed. The high degree of characterization of the Upper Jurassic deposits by the data of core studies made it possible to identify indicator elements, the changes of which are most contrasting in different interlayers. Based on the analysis of drilling results, a series of conclusions was made. The proposed technique was tested in the process of drilling 9500 m of horizontal shafts and its high information content and reliability was confirmed. This technology is not expensive and can be implemented on any field after equipping the station for geotechnical well testing with portable devices for determining the elemental composition of rocks. To replicate this technology to other fields, it is necessary to study the reference sections of target sediments from the point of view of layer-by-layer changes in the elemental composition of rocks.
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