The challenge of the alpha/beta waves gravel packing open hole in offshore Brazil is how to successfully displace the proppant slurry in a large wellbore with a low fracture gradient formation, deep to ultra-deep water depths, and extended reach horizontal section.
Since 2001, job data from more than 72 open hole horizontal gravel packings have been compiled into a database. This paper reviews the well information and the key gravel packing parameters: pump rate, fluid density, injection proppant concentration, inner/outer annulus area ratio, dune ratio, packing rate, packing time and packing efficiency during alpha/beta waves. The engineering implementations and challenges, the best practices and lessons learned for open hole horizontal gravel packing are also summarized. The data analysis yields a better understanding about the open hole horizontal gravel packing in the Brazil offshore and provides a good guideline for future practice. A historical review is also presented showing how the gravel packing methodology has improved packing efficiency and success rate.
Case histories are provided demonstrating how to deploy the single trip system and pack the extended reach wellbore utilizing ultra-light-weight (ULW) proppant under extreme with improved packing efficiency and the success rate.
Introduction
Deepwater exploration and production has developed over the last decade. There is a broadening of the geographic regions for deepwater completions (figure 1). The vast majority of the deepwater reserves are concentrated in the Gulf of Mexico, West Africa, Brazil, North Sea and South East Asia. The potential to achieve significantly higher sustainable production rates, well longevity and cost reduction have been the primary drivers for pursuing most deepwater completions. There have been many different types of completions in deepwater, however, the frac-packs and open hole horizontal completions have emerged as the two dominant completions. Appropriate applications are area dependent. In Brazil, the dominant completion type is the open hole horizontal gravel packing. In the Gulf of Mexico, 60% to 70% of completions are frac-packs. In West Africa both open hole completions and frac-packs are used.
Based on published references 3 to 19, open hole horizontal gravel packing envelops, in terms of depth and the hole departure, are plotted in figures 2 and 3. The latest world record horizontal gravel pack was completed in a well with the departure length of 4206m and a departure ratio of 5 in the Captain Field in the North Sea.13 The open hole horizontal gravel packing completed in the deepest well was in the Campos Basin field of Brazil with sub-sea TMD of 5093m and TVD 3855m.
Typical reservoirs in Campos Basin fields are high permeability turbidite sandstones with low API gravity oil. Generally, these unconsolidated formations are not strongly water driven. A high rate injection was needed to maintain reservoir pressure on these large producers. Several fields in the Campos Basin were developed with a series of horizontal producers and injectors.
More than 200 open hole horizontal gravel packings have been completed since 1998 in Brail 1,2. Current gravel packing technology offers a good option for horizontal well completions where the problem is sand production.
Key issues in project planning and execution of open hole horizontal gravel packing include reservoir study, shale stability study, formation integrity test, gravel pack sand sizing, gravel pack screen selection, workstring design, well displacement, and fluid loss control. The feasibility and success of gravel packing a long horizontal well depends on drilling techniques, drill-in fluids, wellbore clean-up, completions fluids, completion tools, equipment, sand control techniques, software/simulators, pumping schedules and field personnel experience.
Challenges that can jeopardize performance of successful open hole horizontal gravel packing are excessive fluid loss, varying hole geometry that can lead to premature pack termination, hole stability issues leading to hole collapse, and a narrow pressure window between bottomhole pressure and fracture gradient. The beta-wave placement pressure is the main factor in determining the maximum length of a horizontal gravel pack. This pressure is limited by the requirement to install the gravel pack without exceeding formation fraction pressure.
