Back-Out Analysis

iProdTech were requested by a UK based operator to conduct an integrated asset modelling (IAM) study to analyse the back-out effects on one of their offshore gas fields due to the tie-in of a new field planned to be developed by a third party. The idea is to make use of the client’s existing platform facilities and the export pipeline for the new field. The study included GAP network modelling of the two fields and evaluation of the impact of third party field’s production on the production of the client’s gas field for various scenarios. Since the client’s producing gas field is a mature field with depleted reservoir pressures, some of the wells have already reached unstable flow and they are being produced in a cyclic manner.

The key finding from the analysis of the tie-in of the third party field was that the back-out effects on the producing gas wells primarily depend on whether the unstable wells could continue to be cycled against higher back pressure. There is a significant risk that the increase in back pressure would lead to severe liquid loading issues. This issue was evaluated through sensitivities in minimum stable rate in the IAM analysis.

It is recognised that well cycling is expected to get more and more difficult with increase in third party field rates. It has therefore been strongly recommended that a liquid loading mitigation strategy is planned for the client’s gas field to cater for third party production through their facilities. Further work (e.g. transient modelling) has been recommended to analyse the liquid loading effects at higher back pressure.