Abstract

In many open-hole completions in unconsolidated reservoirs, the preferred method of sand control is a conventional gravel pack across sand exclusion completion screens. To date the gravel pack options available for horizontal or highly deviated wellbores have been the use of brine-based gravel pack carrier fluids or the use of viscous gel packs using alternative path screen technology. The first option, using brine as the carrier fluid, has limited applicability because many reservoir intervals have brine-sensitive shale that, if not stabilized, can disrupt the gravel deposition during the alpha-beta (a-b) packing process, especially in long intervals. The second option, using alternative-path screens and viscous carrier fluids, overcome the shale destabilization issues but not without a compromise in the quality of the pack or the higher price tag.

A third option is now available that utilizes a new, solids-free, invert emulsion gravel pack carrier fluid. This option overcomes the issue of shale destabilization and interupted gravel deposition often associated with brine packs because it avoids the exposure of water-sensitive shale to aqueous fluids.

This paper provides the design details of a carrier fluid that overcomes the technical hurdles of a conventional brine-pack operation as well as the fiscal limitations associated with alternative path technology. Included are the planning and execution details of a 5-well, back-to-back gravel-packing operation from an offshore platform in the Bualuang Field, Gulf of Thailand whereby successful gravel deposition occurred on each well using a invert emulsion system as a carrier fluid. The results presented of this case history sequence clearly demonstrate a world class break-through and triumph for the oil industry.

Introduction

There are numerous options available to operators to complete wells in unconsolidated sand reservoirs. The commonly used methods of completing these types of wells included stand-alone screens, expendable screens, alternate path screens, and conventional stand-alone sand screens accompanied with an annular gravel pack. Although each of these methods of sand exclusion are effective, it is commonly accepted that gravel packed screens extend the life of a reservoir with fewer screen failures.1

Gravel packing is routinely used as a method of sand exclusion in unconsolidated wells. Some wellbore conditions make brine-based carrier fluids a poor choice for this type of solution due to the presence of brine-sensitive formations.2 Many reservoirs require a high degree of inhibition, lubricity and wellbore stability, a pre-requisite that is seldom possible with brine-based carrier fluids. Furthermore, many operators choose to maintain optimum wellbore conditions by selecting an invert emulsion drilling fluid to drill the reservoir. Invert emulsion drilling fluids are not only easy to maintain, they are inherently inhibitive and lubricious whether the reservoir interval is sand, shale or a combination of sand and shale sequences.

Gravel packing with brine-based carrier fluids after drilling the reservoir with invert emulsion mud systems has been successful in a few applications2; however, most operators have avoided this approach because of potential problems that may result from contact of the brine with the invert emulsion filter cake or fear of the brine carrier fluid will destabilizing shale intervals. To avoid the risk of destabilizing the wellbore with brine-based carrier fluids before and/or during the gravel packing process, especially in long gravel pack intervals (>500 ft), a solids-free invert emulsion gravel pack carrier fluid (IEGPCF) has been developed.3 Numerous challenges were overcome to design and maintain the quality of system at the rig-site and mimic the historical performance of brine-based carrier fluids in clean, non-shaly, unconsolidated sand reservoirs. Other challenges, primarily logistical in nature, were studied in detail to ensure good project coordination and success.

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