Best Practices and Lessons Learned in Open Brazil Hole Horizontal Gravel Packs Offshore
Authors: Farias Rodrigo , Mendez Alfredo , Calderon Agostinho 
Published: October 2008

Horizontal open hole gravel pack (OHGP) completions are increasingly required for the low API gravity oil fields in and near the Campos basin, offshore Brazil. Many successful horizontal gravel packs have been performed in this area, often in spite of increasingly difficult technical constraints on the operation. Critical limiting conditions on successful gravel pack placement include the combination of low fracture gradients, deep to ultra-deep water depths, and extended reach horizontal sections.

This paper describes the lessons learned and best practices developed for offshore Brazil horizontal gravels packs under these severe conditions, supported by data from 20 jobs performed to-date. The analysis yields a better understanding of this type of open hole completion and demonstrates how to achieve a successful treatment under critical limiting conditions. Also discussed are several proven completion practices with application for future completion operations in the scenarios presented.

Introduction

Economic development of deepwater projects demands a minimum number of wells to be drilled and completed in order to effectively drain the reservoir. Heavy oil exploitation makes this approach even more difficult because extended reach wells are needed. Due to the high cost of operating in a deepwater, subsea environment, wellbore intervention must be minimized and completion life sufficient to achieve depletion of the reservoir. Gravel packing of horizontal wellbores in unconsolidated formations has proven to be an effective method to achieve these goals economically in the Campos Basin, offshore Brazil (shown in Figure 1).

Stand-alone horizontal completions have common used to complete long, open hole horizontal wells in unconsolidated formations. However, in most applications the stand-alone devices become plugged or cut out with time. The consequences may be unacceptably low well rates or excessive sand production. Therefore, un-gravel packed screens and slotted liners in horizontal completions have been disappointing.

Typical reservoirs in Campos Basin giant fields are high permeability turbidite sandstones with low API gravity oil. Generally, these unconsolidated formations are not strongly water driven. Due to the need for high rate injection to maintain reservoir pressure, and since large producers are needed for economic development, it was decided to develop several fields in the Campos Basin with a series of horizontal producers and injectors.

Current gravel packing technology offers a great option for a horizontal well completion where sand production presents a problem. The advantages of gravel packing over a stand-alone completion are improved productivity or injectivity and completion longevity.

Offshore Horizontal OHGP Best Practices

While it is important to effectively prevent sand production, it is equally important to do so in a way that does not hinder productivity. The feasibility and success of gravel packing a long horizontal well depends on drilling techniques, drill-in fluids, wellbore clean-up, open hole stability, completions fluids, completion tools and equipment, sand control techniques, software/simulators, pumping schedules and field personnel experience.

Monitoring Return Rate

In the early OHGP's performed with floating rigs, the return rate was monitored through the choke/kill manifold with the annular BOP closed. An extremely high circulating pressure was observed during gravel pack pumping.