Abstract
Deepwater well control with a subsea BOP is often difficult and in many circumstances impossible with the usual methods and procedures. This is mainly due to the difficulty to maintain the circulating pressure below the low formation fracture pressure, because of high friction losses in kill and choke lines. Such a situation often leads to losing the drilled section. To cope with this situation, a new method was developed and presented in a previous paper. It consists in lightening the mud column inside the choke line by injecting base oil or water at the BOP level. Simulations using a dedicated software demonstrated the possibility to compensate lines friction losses.(essai labo ?) To validate simulations and to confirm the operational feasibility of this method, a field test was conducted on a Deepwater well in Angola. Pressures were recorded at surface, at the BOP level and downhole, and confirmed predicted values. The test was performed without any modification of the drilling rig, and no operational problems were encountered. The test fully confirmed that the method allows the physical removal of friction losses in the choke lines. The obtained downhole pressure during a well control is then lowered compared to a conventional method in all cases where the choke line friction losses cannot be removed artificially at the choke. (such as swak kick in an horizontal section). Test procedure, simulated pressures and field measurements, are detailed in this paper, and complemented by their analysis and resulting operational guide lines.
