Multilaterals Drilling and Sustainable Openhole Production from Theory to Field-Case Studies

Abstract

Summary Drilling and production optimization are two closely related operations for successful well construction and reservoir management, in particular for multilaterals. Unfortunately, to date, analytical study for the stability of multilaterals has been very limited because of the complex geometry and stress state involved. This work entails a recently derived analytical solution to estimate the safe mudweight window for wellbore stability during drilling and to predict the maximum pressure depletion for a stable junction during production. The presented solution is capable of handling the complexity of the 3D anisotropic state of stress as well as any main-bore and lateral size, inclination, and azimuth. The study shows that the design of multilateral junctions, especially inclination and azimuth of both wellbores with respect to regional in-situ stresses, plays a crucial role in the multilateral-junction stability and the critical pressure depletion to prevent solids production and wellbore collapse. A field case study of an openhole multilateral well drilled in the Khuff-C formation, Ghawar field, Saudi Arabia, is analyzed here with drilling data, core-retrieved rock properties, and pressure-depletion and production estimates. The results showed alternative optimized completions that could have been applied early in the drilling and branching of the laterals. Practical guidelines concerning branching optimization have been established for junction planning and execution. The new analytical modeling has also been calibrated with a published peer-reviewed large-scale experimental program simulating both the anisotropy of far-field stresses and the complex junction geometry with exceptional qualitative and quantitative results.