Multi-Zone, Single-Trip (MZST) completions have significantly reduced the time to complete deep wells with long intervals and have been successfully used in Lower Tertiary formations in deep-water Gulf of Mexico (GOM) projects. MZST completion can be used to create the interface with the reservoir and to deliver stimulation treatments typically limited to up to single-digit zones. Additionally, the minimum spacing allowed by standard MZST completions limits the treated zone length.
The Lower Tertiary formations encounter high-laminated pay zones, often hydraulically isolated, and with pressure variations across the small spacing length. Therefore, a treatment covering several compartments results in uneven treatment distribution across long intervals. These single-trip systems require a high proppant amount and pressure to complete the sizeable frac-pack jobs required in Lower Tertiary formations. Using ball-activated fracturing sleeves and dedicated fracturing ports, these completion systems allow a larger number of stages over multiple intervals. This method affords more precise placement of stages with reduced spacing down to single-digit feet between zones, a feature that also enables targeting specific pressure characteristics in the reservoir.
Completion selection and well performance analysis were conducted to design a new completion system for production enhancement from Lower Tertiary formations. Design and selection of the lower completion system focused on multi-stage fracturing and potential sand control options, and their impact on production. The following systems were studied to estimate and predict the initial production rates: Multi-Zone Single-Trip (MZST) completion, Large Bore Multi-Zone (LBMZ) completion system and Ball-Activated Fracturing Completion System (BAFCS).
This paper describes a high-level workflow developed for completion design and selection, fracture modeling to generate 3D fracture geometry and fracturing pressures, wellbore design including tubing stress and movement analysis for fracturing treatments and production systems analysis to generate vertical lift performance/inflow performance relationships (VLP/IPR), and to estimate the initial production rates and flowing bottomhole pressure for sand-free production.
The proposed BAFCS used more fracture initiation points (up to 20 stages) in the Lower Tertiary formations when compared to eight individual stages (20 perforation intervals) with MZST and LBMZ completion systems. The more confined fracture geometries were created by using the new proposed multi-stage fracturing system. Predicted BAFCS production rates were higher than those of MZST and LBMZ completion systems. To attain higher production and recovery factors than those achievable with natural depletion, artificial lift options (electrical submersible pumping) were also examined for Lower Tertiary wells.