Borders & Southern Petroleum PLC will plug and abandon its 61/25-1 Stebbing exploratory well in the South Falkland basin with inconclusive results in shallower formations and leaving the lower targets unevaluated.
Total depth is 3,060 m measured depth, 3,011 m true vertical depth. The well penetrated the upper Tertiary target on prognosis but was unable to reach lower targets due to anomalous pressure conditions.
Stebbing encountered strong C1 to C5 gas shows while drilling the Tertiary section. Petrophysical analysis of the wireline logs suggest an interval of thin-bedded siltstones and claystones at 2,500-2,651 m with a net to gross of 36% and an average porosity of 19%. Due to the thin bedded character of this sequence it was not possible to obtain a clear indication of the fluid type or saturation.
The geophysical anomalies identified on seismic are coincident with this zone containing hydrocarbons. Our initial assessment is that this upper target is unlikely to be commercial although further technical evaluation is required.
Strong gas shows continued below the upper target. However, progress was slow due to lost circulation and well flows that occurred in consecutive hole sections. Several of the flows contained gas. On each occasion the well was successfully controlled, but it became necessary to set additional strings of casing, using the contingency casing considered in the well design.
In the final 6-in. hole section, the fluid pressures continued to rise giving further well flows, and it became impossible to continue drilling while maintaining well integrity. A decision was therefore made to cease drilling.
“It is very disappointing not to have reached all the potential reservoir targets in this well. The geological and engineering data will now be reviewed in detail in order to understand the complexities of this prospect,” Borders and Southern said.
The company will plug the Stebbing well and assign the rig to Falkland Oil & Gas Ltd.
Meanwhile, fluid samples from the Darwin discovery are undergoing lab analysis, and the results are on track to meet the previously reported 10-week timeframe.