Amerisur Resources said it was very encouraged by results from Platanillo-25 which supported the view that there was significant further upside in the field.
In an operational update on its activities in Colombia, Amerisur said that Platanillo-25 was drilled to a planned total depth of 8,699ft, logged using logging-while-drilling tools which indicated 10ft of pay in the U sand.
It added: 'Although the reservoir levels were encountered close to prognosis, overall pay thickness was reduced by increased shale content within the upper part of the U sands.
'This result will help increase our understanding of the location and make-up of the inferred permeability barrier.'
The company said it was now side tracking Platanillo-25 to locate a production well further up dip and nearer to Platanillo-21 where better reservoir quality and additional pay thickness was expected and which had the potential to deliver more sustainable production.
It said the side track was expected to be completed before the end of October.
It added: 'In addition to the discovery of the U sands the well also intersected 3ft of pay in the N sands, a more positive result than expected for the planned drilling campaign in the north/central part of the field targeting 18.8 MMBOE.
'Once the side track is complete, Platanillo-27, a planned well to the north of Pad 2N will be drilled in place of Platanillo-23 while analysis of the data from Platanillo-25 continues.
'Platanillo-27 is targeting a bottom hole location to the north of Platanillo-22 in a structural position similar to Platanillo-21.'
Amerisur also said it had been informed by the operator of the Mariposa discovery in the CPO-5 block that the equipment to initiate the Long Term Test (LTT) of the Mariposa-1 well was 95% mobilised to location and 80% installed.
It said the LTT would commence after the inspection visit by the National Hydrocarbons Agency (ANH) to approve the facilities and begin the LTT.
Chief executive John Wardle said: 'We are very encouraged by the results of Platanillo-25 which supports the view that there is significant further upside in the Platanillo field, both in the separate northern structure targeting 7.82 MMBO of recoverable reserves and in the N Sand Anomaly in the north/central part of the field targeting 18.8 MMBOE.
'The net pay observed in the U sands of Platanillo-25 may well be associated with the inferred permeability barrier which we believe has resulted in the deeper oil-water contact we discovered at Pad 2N.
'These subtle changes in lithology are usually not possible to detect in seismic data.
'To manage risk, we will focus on drilling to the north of Pad 2N with Platanillo-27 post the Platanillo-25 side track and meanwhile continue to analyse the data we have obtained.
'We are pleased to report that the LTT off Mariposa-1 is on track to begin at the end of October, which will not only diversify Amerisur's production base from one to two fields, but also adds further material production to Amerisur in the near term.'
At 9:50am: (LON:AMER) Amerisur Resources PLC share price was +0.5p at 20.75p