CASE STUDY

Gas Breakthrough in Horizontal Oil Producer

A quantum leap in understanding the well and reservoir behaviour

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A North Sea horizontal oil producer, supported by two horizontal injector wells and gas lift showed signs of gas production and unstable flow rates. 


Results

  • Free gas identified flowing from the upper two sliding sleeves
  • Increase in gas injection causes an increase in slugging
  • Water injection increased the slugging frequency and a reaction time of 4 hrs observed
  • Water production identified from below the BHA

Objectives

  • Identify source of gas production
  • Determine sweep efficiency
  • Allocate flow
  • Determine source of water

Method

The Ziebel modular electric surface unit safely lowered the sensing rod into the well and pushed it far into the horizontal section. The sensing rod was parked in the wellbore during acquisition.

Firstly the well was shut-in and both DTS and DAS base lines recorded as well as point measurement of pressure and temperature from sensors in the BHA.  The well was then brought on production at 50% choke; 50% gas injection without support by the injector wells. Further sensing was carried out with full choke setting and various combinations of gas support and support from the water injectors. During the final sequence, all wells are shut in and  gas injection stopped.

The analysis of DTS and DAS acquired during each of these sequences revealed identification of gas towards the top of the zone, various flow regimes , including slugging and cross flow and water production from below the sensing BHA.

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