Extending Life of Mature Oil Wells with Various Type of Siphon String Application in Offshore North West Java

Abstract

Offshore North West Java (ONWJ) field has been producing since 1971 with multi-stacked layers, solution gas to weak water drive mechanism, most of wells are completed with dual strings and gas-lifted. This condition compromise a relatively shallow top packer placement. In some cases, abandonment pressure has been reached as characterized by low static liquid level below deepest gas-lift mandrel. Apart from that, tubing integrity is becoming important issue as fields are maturing. Less operational complexity for the installation of siphon string or velocity string to tackle the two challenges above and better economic returns make it a better option compared to recompletion. The applied strings are from 1.75″ QT-900 coiled tubing, installed with various configurations of packer, gas-lift mandrel, and length depending upon wellbore completion, artificial-lift concern and well integrity requirement. Siphon string has been installed in 6 strings; whereby 3 strings with tubing integrity issue (well A, B and C), 3 strings with liquid level below deepest gas-lift injection mandrel (W, Y and Z). After installation, well A and B were flowing for 2 years before they were finally shut-in due to leak below the siphon string assembly. Well C had flowed for another 6 years before it was shut-in. Well X has been flowing since the inception of siphon string in 2006 until this paper is written, well Y has flowed for 8 years and well Z has been flowing for 1 year. An increase of 0.5% – 2% of recovery factors for these wells has created opportunity for other similar wells to continue or increase production. The first part of the paper will describe on the candidate selection and well configuration, the second part of the part will cover the installation procedures, challenges and lessons learnt. Finally, production results comparison from pre and post installation is presented.