Petroleum Development Oman LLC (PDO) production activities rely significantly upon artificial-lift technology due to the nature of the reservoir fluids and properties. Currently, about 90% of the wells require some method of artificial-lift in PDO. Many existing and future wells will eventually produce with more challenging or high GOR conditions which results in technical and economic challenges to select the appropriate artificial-lift method, as well as, the well completion configuration.
Conventional ESP applications are ideal for high production rate wells with moderate gas rates. Gas lift applications often target medium to low production rate wells and can easily tolerate high gas volumes. Within PDO, gas lift conversions to ESP are growing more common due to reasons related to facilities constraints (e.g. gas compression / injection gas volume, aging compressors, gas flow-lines integrity, etc), declining reservoir pressures due to ineffective water injection or increasing water cut. As a result, some new ESP wells are now producing at higher GOR.
For field developments, artificial-lift concept selection is often one of the key decisions to be assured at the concept selection milestone. In marginally-economic fields, the choice of artificial-lift method can easily erode the project value, especially owed to significant uncertainties with regards to potentially high producing GOR risks. In fact, this was demonstrated during the development planning process for a high GOR field which is generically referenced in this paper as field T in North of Oman with an initial solution GOR of 216 Sm3/m3. In this particular case, artificial-lift selection was based not only on economical terms but also on technical and operational feasibility aspects.
Based on current PDO's experience to date operating high GOR wells, the ESP method was identified during the study as the preferred artificial-lift method for field T. An ESP feasibility evaluation was completed and included a detailed assessment of the expected range of free gas at the well pump intake depth for the entire field production life-cycle. This evaluation considered the completion configuration, as well as, gas-handling and separation equipment limitations. By adjusting the well and reservoir field management plan for field T and incorporating the latest PDO experience and learning's to date, the study provided the technical basis to assure feasibility of the proposed development plan for the expected high GOR producing environment. Further economic assessment of the artificial-lift selection decision, which is not detailed in this paper, supported a significant impact to the project on the order of 1/3 of its expected value.
This paper summarizes the range of PDO operating experience to date with ESPs installed in high GOR conditions. Additional details are shared regarding the feasibility study for field T including supporting rational for the artificial-lift selection for the project concept selection, proposed well completion concept design and the artificial-lift economic evaluation. Finally, established best practices for high GOR fields and key challenges going forward will be discussed.