By Mike Killalea, Editor and Publisher
Petrobras’ first use of MPD aboard a dynamically positioned rig proved successful and kept NPT to less then 3%, according to a paper presented at the 2015 IADC/SPE Managed Pressure Drilling and Underbalanced Operations Conference, held in Dubai during April. In addition to the low NPT, drilling time was cut by seven days. Petrobras elected to try MPD, specifically mud cap drilling, after suffering total losses that could not be remedied otherwise. The choice was a wise one in terms of the drilling window, as well. Although initial geopressure studies predicted a 2-ppg operational window, a subsequent formation integrity test (FIT) indicated the operational window was much narrower, at 0.25 ppg.
“In 2012, we had some drilling issues due to salt creeping, low ROP,” explained co-author Alonso Fernandes, Petroleum Engineer Advisor with the Brazilian national oil company. “Many of these were overcome with different bit technology, new rigs, mud pumps…. (but) we noticed that some development wells … and other exploratory wells were facing more losses due to more fracture zones.”
The Franco Field, located in the presalt Santos Basin, was first drilled in 2006. Field development began in 2009 with parallel exploratory activities. Water depths are some 2,000 m.
Losses were a known risk but became more frequent in 2012, when several wells suffered huge mud losses that led to significant NPT. In some cases, TD could not be reached safely.
During 2013, in preparation for the mud cap drilling project, the Ocean Valor semi was modified, and teams trained in MPD and mud cap drilling procedures.
Both pressurized and floating mud cap drilling (PMCD and FMCD, respectively) were evaluated. PMCD was ultimately chosen because, with PMCD, there is always a closed system on the annular, Mr Fernandes said. Further, with PMCD, annular injection is performed only when needed, reducing the amount of fluid injected through the annular.
IADC/SPE 173825, “MPD/MCD Offshore Application on a Dynamic Positioning Rig,” was co-authored by Mr Fernandes with Danilo Signorini Gozzi, Emmanuel Franco Nogueira, Felipe de Souza Terra, Guilherme Sirqueira Vanni and Rafael Schettini Frazão Filho, all with Petrobras.