ENBD, the proprietary Eni Managed Pressure Drilling with Uninterrupted Mud Circulation: Technical Update after the First Year's Activity
Authors: Calderoni Angelo , Girola Giorgio 
Published: March 2015

Abstract
MPD means an adaptive drilling process used to control precisely the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly. MPD is intended to avoid continuous influx of formation fluids to the surface. - Eni owns its own MPD, called ENBD - Eni Near Balance Drilling. - ENBD is an innovative drilling process used to maintain constant bottom hole annular pressure at all times while circulating and to manage the annular dynamic hydraulic pressure profile accordingly. -ENBD is assisted by a proprietary system for continuous circulation, called E-CD and composed of special subs which are positioned on top of the stands. Only the stands which will be drilled through the section of the well requiring continuous circulation need to have the subs installed. A dedicated Manifold positioned on Rig Floor will divert the mud flow from the Stand Pipe Manifold to the subs. - ENBD through E-CD System assures the continuity of the MPD process, without "transitory" times.
Conventional MPD instead, always need to stop the mud circulation and request to back-up the momentum lack of friction losses in the wellbore by the mean of some "surrogate" systems. Having conceptualized the ENBD back in 2005, several independent test applications were requested before bringing the "whole tool" at work; E-CD tool independently accumulated more than 1500 working days over 9 challenging wells, including one Extended Horizontal at 5650m, two HP/HT's, and one complicated deep sidetrack. The first ENBD application selected to prove the concept and benefits was conducted within the most challenging available environment: mud weight has ranged up to 2.23 SG (18.6 ppg), with fracture gradient of equivalent 2.26 SG and with operational pressures of 5000 psi. This Paper will update the Industry about the achieved results, including some off-shore application from Floaters.

Introduction
Exploratory wells can be challenging due to the inherent uncertainty relative to the downhole pressure limits, pore and fracture pressures, as well as formation uncertainties that are not clearly mapped from seismic. As the exploration frontier moves increasingly towards more difficult environments, many wells are abandoned before reaching target, therefore failing to meet its commercial or technical. Despite many advances in drilling systems, it has been the arrival of a closed-loop Managed Pressure Drilling (MPD) method that has provided a significant step change in drilling performance. For the first time, pore and fracture pressures can be determined very accurately and safely while drilling and as a consequence the mud weight can be properly adjusted and managed, avoiding loss circulation, stuck pipe, and low ROP. The industry loses an enormous amount of time trying to solve these problems, which very often leads to misunderstanding that the well's technical limit has been reached and abandoned unnecessarily.

Definitions
1) - Continuous Circulation: is the ability to maintain uninterrupted flow of drilling fluid to the well whilst all the steps to add (or remove) joints of "drill pipe" to the drilling string are performed within the drilling process, including trips in and out of hole. 2) - Managed Pressure Drilling (MPD) - IADC definition - MPD means an adaptive drilling process used to control precisely the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly. MPD is intended to avoid any continuous influx of formation fluids to the surface.