Amerisur Resources, the oil and gas producer and explorer focused on South America, said tests on a Colombian well had been interrupted by equipment failure.The problems have come at the Platanillo-4 well n the Platanillo Field, Colombia, the second of a planned eight well drilling campaign."A 30ft section of the logged 75ft gross oil column was perforated in the U formation in order to perform flow and pressure tests," the firm said."A number of tool failures prevented the test from continuing and the company has had to source alternative equipment and reconfigure the well."The firm now expects to perform the tests over the next seven days and results will be announced once they have been analysed.Amerisur's shares were off 1.3% following the announcement.