Comparison of theoretical and actual decline profiles in Eromanga oil wells.
Engineering Honours Degree 2008
University of Adelaide
The Eromanga Basin is one of Santos’ most important oil producing assets. In recent years, the Birkhead and Murta Formations of the Eromanga Basin have been primary targets for field development, however disappointing production results have routinely been encountered with many wells experiencing rapid decline in oil production rate relative to pre-drill predictions. The aim of this report is to investigate the rapid production decline affecting many Eromanga oil wells and attempt to identify some of the potential factors responsible.
To investigate possible causes for why pre-drill production estimates were not reflected in actual production data, four wells were selected and analysed from each of the Birkhead and Murta Formations. At a high level, the mechanisms responsible were separated into reserves overestimation, pressure depletion, time dependent skin effects and high watercut. A simple methodology for analysing selected wells to determine which mechanism was most likely to have
affected the production profile of the well was developed and applied.
The methodology utilised in this report provides a means of determining some of the key factors causing oil well production profiles to deviate from the pre-drill forecast production profiles. While all four mechanisms were found to be responsible for rapid production decline at least once, of the small sample analysed, reserves overestimation and high watercut were seen to be major factors causing substantial difference between pre-drill predicted production profiles and actual production profiles.
Additionally, sensitivity analysis was performed on the inputs of the pre-drill decline curve equation to investigate which parameters in the hyperbolic decline equation are the most sensitive.