Application of a 4D Geomechanical Model to Reduce the Risks of Offshore Field (Russian Federation) Development Throughout the Entire Life Cycle

ABSTRACT: Based on the results of the 3D/4D geomechanical modeling, the influence of the static mud weight on the degree of shear failures of the borehole was shown. Recommendations were made to increase the mud weight to avoid clay shear failures, but at the same time control the equivalent circulation density (ECD) during drilling to avoid fault reactivation. Also the reservoirs layers have experienced a decrease in pore pressure associated with development. As a result, the minimum total horizontal stresses in the far field are reduced due to the "stress-path" effect. Design safe mud weight windows for wells of different orientations for different cases were obtained. Based on the completed 3D/4D geomechanical modeling, several design horizontal wells were successfully drilled. This geomechanical model used in the construction of wells takes into account work with problematic wells of previous years. Thanks to this model, well drilling happened faster and was accompanied by much fewer emergency situations. The predrill model agreed with the postdrill one. The seafloor subsidence and the degree of reservoir compaction are predicted. With the remaining 70% of the total depletion expected over the next 25-30 years, the final subsidence, according to the baseline case, could reach 0.55–0.65 m. 1. INTRODUCTION At the studied offshore field, geomechanical drilling support is an important support for trouble-free oil and gas production. It is used to solve various problems in the process of field development and operation. The objective of this work is to apply the geomechanical model to prevent risks during the construction of inclined and horizontal wells. The main problems is borehole instability of well walls, manifested in the presence of overpulls, tightening, collapsing cuttings on vibrating screens and sticking, were observed in clay intervals with a drilling mud density of 1.18 to 1.33 g/cc (Fig. 1). Most successful wells were drilled in 340 mm and 244 mm sections with a higher drilling mud density exceeding 1.33-1.37 g/cc. In the 178 mm section, elevated gas readings (up to 50%), tightening and landings were mainly observed at a density of 1.13–1.18 g/cc. The number of caverns is smaller than in the upper parts of the section, since the 178 mm section usually exposes sandstones, which are more stable than siltstones and mudstones. To display all drilling events that accompanied the construction of the well, a "stick chart" diagram is used, shown in Fig. 2.