Abstract

Drilling and completing extended length horizontal wellbores through low-temperature (<80°F) unconsolidated, high permeability reservoirs presents significant technical challenges and operating complications that can significantly impact initial well performance. Integrating the design and functional attributes of reservoir drill-in fluids with the various completion fluids, and their application processes, can produce significant benefits with respect to well performance.

This paper presents and discusses the technical challenges and issues confronting the design and implementation team responsible for installing the first horizontal openhole gravelpacked completion on the North Slope of Alaska. The gravelpacked horizontal well, 2T-218 was installed in the Greater Kuparuk Area's Tabasco field. The paper presents a case history detailing the fluids integration process and validation efforts utilized to develop and implement the reservoir drill-in fluid and filtercake cleanup treatments applied to the gravelpacked completion.The paper discusses the specific design criteria for the various fluids used in the drilling and completion operation, the design and laboratory testing process to determine the optimum recipes, the results of these lab tests, a summary of each field operation, and provides a synopsis of well performance obtained.

The unique conditions of application for this well in the Tabasco field in Alaska include:

  • Medium to coarse pebbly unconsolidated sand and siltstones

  • High permeability contrast (1000 to 10,000 md)

  • Low Bottomhole Static Temperature (76°F)

  • Low Bottomhole Pressure 6.7-lbm/gal equivalent.

The principle issues with which the team had to deal were:

  • Management of the properties of reservoir drill-in fluids utilized at low circulating and bottomhole static temperatures.

  • Effective hole cleaning properties required for the horizontal section.

  • Drilling fluid losses to the 6.7-lbm/gal reservoir.

  • Wellbore stability and stuck pipe through the unconsolidated sand.

  • The potential for formation damage of the high permeability & low-pressure reservoir interval.

  • Adequate lubricity in order to successfully drill the horizontal section.

  • The ability to degrade the drill-in fluid filtercake from behind a sand exclusion liner and coarse (12/20) gravelpack.

  • The risk of and the methods to mitigate potential corrosive damage to the 13-CR completion equipment in the event of prolonged exposure to the filtercake cleanup treatment fluid.

  • The reaction rate, uniformity, and efficiency of filtercake cleanup treatments.

  • The effect of lubricants with respect to filtercake cleanup treatments and retained permeability.

  • The performance of enzymes utilized in low temperature cleanup treatments.

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