Abstract

PDO has successfully installed the longest open hole clad and longest open hole liner with swelling elastomers in a Yibal horizontal oil producer well. The main objective of installing expandable liner combined with swelling elastomers was to efficiently isolate the water producing features/fractures that are dominating majority of the 957m of reservoir section.

This one horizontal well replaces five vertical wells at cost of two vertical wells. In addition to the cost reduction, the surface location construction constraints in the field do not allow drilling five wells from different locations to reach the required targets. Therefore the introduction of such well type allows drilling five well targets from one surface location.

The overall value Drivers for drilling and completing this well with expandable liners/clads with swelling elastomers were as follows:

  • Restore some symmetry to the water flood process for proper surveillance and management.

  • Vertical wells are uneconomic for establishing symmetry as they are only good for targeting oil sweet spots (reduced number of wells as a result).

  • Allow for more & longer perforation intervals.

  • Proper selective zonal isolation.

The bigger ID provided by the expandable tubular allows for running larger OD smart completion to control the production from specific perforation zones.

Initially 305 m of 5–1/2" × 6–1/8", Open Hole Clad was set at TD (2541 m), then a 687 m Open Hole Liner was tied back to the 7" liner.

Based on 6 arm caliper log, both expandable liner and clad were coated with 4mm and 5.5 mm thick swelling elastomer to achieve optimum annular sealing, covering total length of 425 m isolated interval. Initially perforated well with 4 intervals to produce from different zones. There are further 7 ‘blank’ intervals between elastomer sections for future perforations.

The paper covers a brief background of the Yibal field, detailed technical planning and execution phases for drilling and completing the well with expandable technology & application of swelling elastomers.

Introduction

The Yibal field is located in Oman and it is one of the largest oil producers in PDO. The field was discovered in 1963 and brought on stream in 1969. It reached its peak production in 1997 and then encountered a decline The oil of the field is mainly produced from the highly fractured Upper Shuaiba Carbonate formation, located at a depth of about 1256 mSS (1372 mTVDBDF). The Shuaiba formation, in Yibal, is featured with a major network of faults and fractures partially connecting all parts of the field together.

As the field matured up, production wells experienced co-production of oil & water. The rise in the Oil-Water Contact (OWC) and process of water injection contributed into further increase of water-cut in producers. Following decades of production, it proves difficult, to accurately predict the exact location of remaining oil in Yibal. A completion with cemented liners, i.e. a completion philosophy based on selective perforation, has been used for long time. This approach has several disadvantages, e.g.:

  • At the time of completion it is still not clear which fracture will produce water!

  • Intervals with low oil saturation are not perforated and consequently possibly not swept.

  • In this environment of fractures and large losses, cementations often fail. The selectivity that is the main reason for a cemented liner completion is therefore often not achieved.

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