Optimising Offshore Gas Field Development with Large Well Bore Completion

Abstract

During 2008-2009, Saudi Aramco recorded two major nonassociated gas field discoveries in the Arabian Gulf. The initial plan was to develop both fields with deviated extended reach 7" completion wells, which will be drilled from multi-well platforms. Based on the challenging subsurface conditions of the problematic highly fractured shallow horizons, in addition to the thick, highly fractured, and excellent carbonate Khuff reservoir quality, the decision was carefully made to develop both fields with vertical large bore wells completed as monobore with 9⅝" pre-perforated uncemented liner across the pay zone and 9⅝" production tubing to the surface. The large bore wells are planned to be drilled from single-well platforms that can be strategically located around the two fields to allow efficient spacing and depletion to produce initial gas rates up to 300 MMscfd per well.The large bore well design has a potential for maximizing the gas production from each well and reducing the overall field development costs down by 45% by minimizing the number of wells and facilities required without jeopardizing the production, safety or integrity of the development projects.The shallow horizons in the newly discovered fields, along with the targeted Khuff reservoir, are considered to be highly faulted structures with many associated fractures that can continuously cause drilling problems with lost circulation and differential sticking. The newly planned vertical large bore wells tend to reduce drilling problems. Nevertheless, those planned vertical large bore wells are still capable of producing the required high gas rates.The intent of this paper is to highlight the multiple challenges faced during the early exploration and delineation phase of the fields and to share the experience of planning new offshore field development strategies for large bore wells with high reservoir temperature and pressure (T&P). Transforming from the original development plan to the optimized large wellbore completion plan, takes advantage of the excellent reservoir quality and high flow capacity, allowed for many optimization efforts. Such optimizations have changed the entire project strategy to accelerate the official onstream startup date without any compromises.