Integrated Approach to Drilling ERD Wells with the Innovative Reservoir-Scale Mapping While Drilling Technology on Korchagina Field
Authors: Shtun S. , Golenkin M. , Shtun A. , Shtepin D. , Shabalinskaya D. , Makhambetov A. , Sadykov L. , Ocheretyanyy A. , Khakov A. , Fitsner A. , Shirshov A. , Zakharov I. , Gorshenina O. , Kuzakov V. , Pyankov K. , Vasilyev D. 
Published: October 2015

Abstract
Integrated approach with geological, geomechanical and petrophysical support is vital for successful extended reach drilling (ERD) in Yuri Korchagin field.
Geological structure, represented by anticlinal fold, is characterized by variable formation dipping at the flanks. The field development is performed with the wells drilled from a stationary platform, located at the field crest. The main factor, determining the approach to the field development, is the relatively small thickness of the oil rim of 19.9 m, limited by fluid contacts. Hence, the objectives of planned net to gross ratio (NTG) and production rates can only be achieved by drilling ERD wells with the average measured depth of 4000 to 6500 m.
It is hardly possible to precisely forecast structural behavior based purely on well to well correlation and seismic interpretation. Frequent lateral lithology variations and presence of faults represent additional uncertainties. Therefore, successful placement of the horizontal section within the target formation requires not only understanding of the position of the wellbore within the structure, but also real time evaluation of reservoir properties and fluid saturations.
In order to reduce uncertainties in this complex geological environment, the innovative reservoir-scale mapping while drilling technology was utilized for the first time in Yuri Korchagin field. This technology provides an extensive set of deep directional electromagnetic (EM) measurements and has the radius of investigation, exceeding 30 m TVD from the wellbore. The inverted EM measurements are graphically represented as the 2D vertical section along the wellbore with the multiple layers resistivity visualization. The innovative technology, thanks to its large radius of investigation, enabled forecasting and detailed understanding of structural behavior of the target formations, confirmed the oil water contact (OWC) depth and allowed for detection of the faults and their displacement magnitude. Based on the interpretation of the data, obtained with the reservoir-scale mapping technology, the 3D geological model of the field was updated and refined, which served supplementary exploration purpose.
At the greater depths, the risk of drilling accidents, associated with narrow safe mud weight window, is increasing. The "well to formation" equilibrium state is impossible without thorough geomechanical modeling and interaction with geology and engineering departments involved in drilling operations. The integrated support approach and utilization of the innovative reservoir-scale mapping while drilling technology enabled achieving excellent results. The record 8005 m MD well with 4895 m MD horizontal section was drilled. The horizontal section was drilled in a single run, mostly as a result of minimization of drilling in prone to collapse shaly intervals. The NTG achieved 88.5%, the record value in this field.