Abstract

K Field is a gas field located in Saudi Arabia, with production from the Unayzah A reservoir, an unconsolidated sandstone reservoir notable for its comparative depth. The high corresponding bottomhole temperature combined with corrosive gas properties manifests in aggressive in-situ corrosion conditions. Sand control is needed in this reservoir due to the weak rocks and high tectonic stresses. Frac-pack completions have been used successfully for a number of years and typically manifest in a low positive skin. They tend to suffer from condensate banking and flow related skin.

A number of years ago it was decided to use the then novel expandable sand screen (ESS) technology in a long horizontal well to maximise reservoir drainage. This presented many challenges in terms of the metallurgy, the interaction with high stresses and the deployment in a deep hot well. In April 2004 Well K-3 was drilled as a horizontal open hole well and completed with ESS, setting three world records at that time for the hottest and deepest ESS installation and first ever Incoloy ESS system.

The well was shut-in almost immediately after clean-up operations began due to a mechanical failure in the upper completion, and remained shut-in for nearly 3 years. The well was successfully restarted after an upper completion workover.

This paper describes assessment of well performance from a multi-rate production test conducted following successful workover of Well K-3, and benchmarks key performance indices with those derived from analysis of neighbouring wells equipped with alternative sand control techniques.

Introduction

The K field is an Aolean sandstone reservoir with strong sanding tendencies. The field is in the Greater Ghawar area, south east of the super giant Ghawar Field. The reservoir is in the early Permian age (c280My) Unayzah A formation, which underlies the Pre-Khuff carbonates 1. The reservoir is deep at 14800' TVD, with an average porosity of 18%, but with permeabilities ranging up to several Darcies.2 The field was discovered in 1982 and developed in (2000–2004).

The Unayzah formations consist of well developed Aeolean sandstones with associated inter dune deposits. Geological analysis has divided the reservoir into four discrete facies: dune, sand sheet, paleosol and playa. The dune and sand sheets are the main productive reservoir units, while the paleosols and the playa have low porosity and permeability (<1mD) and act as flow barriers. The reservoir has been completed with sub-vertical frac-packs. These provide excellent productivity and sand control, but suffer from relatively rapid depletion due to intersecting only one reservoir unit.

The main challenges to drilling and completing the wells were the relative depth (the K-3 well was at 15100' TVD), relatively high temperature of 320F and the non-hydrocarbon content in the gas composition. Additionally the high horizontal stresses gradient of up to 1.5psi/ft due to Arabian plate tectonics and the nearby subduction zone can cause wellbore stability problems, especially in the shales.

The K-3 well was originally drilled into the Unayzah reservoir on 1997 as a gas producer to a depth of 16,149ftMD. The well was then perforated and tested, before being suspended with cement plugs. In October 2002, the cement plugs were drilled out, and the 7" casing was then perforated. After frac-pack pumping operations were completed, the rig was unable to pull the gravel pack service tools out of the gravel pack packer and after numerous unsuccessful fishing attempts, the well was again suspended. The well was eventually sidetracked and fitted with an ESS in 2004.

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