Milling on Electric Line-Conveyed Technology in West Africa

Abstract A new application of electric wireline (e-line) tractors in combination with well milling technology has been successfully proven in two wells in West Africa. In July of 2011 on an offshore platform, a downhole tractor in conjunction with a milling tool were conveyed on e-line to remove an obstruction created by Lost in Hole (LIH) electric wireline cable at 9,500ft (2,896m). In total, 13 successful milling runs were made. During this unique operation most of the milled wireline material was recovered, and the challenges of controlling rate and milling penetration were overcome. In between milling runs, slickline fishing attempts were made to recover the remaining LIH wireline. After the last milling run, a major breakthrough was made as fishing operations were successful in retrieving sufficient wireline to reach the target depth. In another case, this time in a subsea well, a flapper valve used to set a production packer needed to be opened, but despite multiple pressure cycles down the tubing, the valve remained closed. The operator had the option to pump in acid to disintegrate the valve, but due to the estimated volume of acid required, the operator wanted a different solution. The milling tool was fitted with a tungsten carbide milling bit specially designed to mill the aluminum flapper valve. The milling bit was designed with a spring-loaded skirt that kept the valve closed while the bit was exposed. This prevented the flapper valve from opening when pulling the bit backwards. After approximately 20 minutes of milling time, the valve was milled out. The operator saved at least one day of operation. Additionally, due to their lightweight nature, e-line tools offer HSE benefits and logistical advantages. This paper describes the process from decision-making to completion of these milling operations.