Abstract
This paper presents the significant benefits accomplished from the utilization of robotic, electric-line (e-line) intervention to mill out a malfunctioning flapper valve versus the use of coiled tubing (CT). In addition, it will discuss the flexibility and control features of e-line based, intervention technology towards addressing short lead time and design modifications required to meet dynamic well challenges.
On the West Coast of India a well was completed using a flapper valve as the method of isolating the completion while being installing it into the well. A standard practice in the field, the flapper valve has been utilized successfully for a decade without any failures. Hence, during the current operation, contingencies to overcome a mechanical failure to open the valve were not on board. And unfortunately, in this particular well, the flapper valve failed to open as per SOP.
After multiple days spent on attempting to cycle open, attempts were then made with slickline to determine if debris accumulation was an issue. When this proved false, it was concluded that the flapper valve was mechanically stuck.
After evaluation of solutions incorporating CT and e-line interventions, it was determined that standard milling operations would pose additional challenges for the well due to the design of the completion below the flapper valve which incorporated a 2.56" restriction. If the milled portion of the flapper valve was not retrieved there was consequential risk that the well could become plugged by the coupon.
After an extensive review with the PMT JV (Panna, Mukta and Tapti Joint Venture) plus the Design and Engineering team of a service provider, it was agreed that the probability of retrieving the milled fIapper valve coupon with standard bits was low. However, the service provider suggested a unique, star shaped milling bit that enabled milling a coupon which was small enough to pass through the restriction should it not be captured. E-line milling was selected due to several reasons including the finer control, efficiency of operations and minimum debris generation.
The newly designed ‘star’ bit enabled milling a small coupon and subsequently expanding that hole to the desired OD of 2.7" which would enable access for future interventions as needed. The total time from the identification of the problem to designing, manufacturing, testing the new bit, transporting it to India and executing the solution was less than 45 days. This enabled the well to be intervened upon while the rig was on the platform. The operation itself was carried out within 45 hours vs the 120 hours projected for CT, leading to a cost saving of ~ 750,000 USD. This unique methodology also enabled early onset of production, avoiding a delay of ~ three months.
This was the first time this new mill bit was applied and the first time that this type of flapper valve had been milled out. Existing, standard bit designs were not sufficient to accomplish this solution nor were conventional approaches satisfactory in today's economic climate.
