This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 133127, ’The 'Extreme Lean Profile' Concept as a Crucial Technology for Multilateral, Long, Extended-Reach Wells: The Case History of Cerro Falcone 4 OR,’ by A. Burini, SPE, R. Poloni, P. Valente, G. Cavallaro, and L. Mattioli, Eni E&P, prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed.
Following many successful applications of the “lean profile” (LP) technique, a further step toward production maximization with a simultaneous increase in operational safety and a decrease in overall drilling cost has been achieved with the “extreme lean profile” (XLP). Compared with a conventional profile, the LP allowed running an additional casing between the 185/8- and 133/8-in. strings. The XLP introduces an additional casing between the 133/8- and 95/8-in. strings.
A focus in the industry is achieving operational efficiency and production optimization while, simultaneously, safeguarding the environment. Hydrocarbon resources often are found in highly sensitive areas, and the capability of minimizing the effect on the natural environment could make the difference between obtaining permits and having such areas restricted.
Excellent examples of technologies that enable these objectives are extended-reach drilling (ERD), multilateral drilling (MLD), and their combination, as in the case of Eni’s Cerro Falcone 4 Or well in the Val d’Agri field in Italy.
Reservoirs that benefit most from MLD and/or ERD technologies include the following.
Low-permeability and thin reservoirs
Reservoirs prone to coning of undesired fluids
However, drilling and completing extended-reach and multilateral wells pose operational challenges that must be overcome. The main challenges of ERD are the capability of
Reaching the target and ensuring proper hole positioning relative to the reservoir, in consideration of the long distances involved.
Providing a straight smooth borehole to drill the horizontal section to the maximum reach, and to reduce the risk inherent in casing-running operations.
Ensuring a high drilling performance to prevent possible hole instability, which may be caused by the extended openhole drilling times, and to not compromise hole cleaning.
For MLD, additional challenges include
Exiting the main bore safely and efficiently with the required borehole size.
Achieving the right degree of junction isolation.
“Roadmap” to the XLP
An accepted custom of conventional drilling is to run the surface and intermediate casings in holes that are up to 6 to 7 in. larger than the casing outside diameter (OD). This method is based on the difficulty of drilling a straight smooth borehole with conventional technologies and the stiffness of large-diameter casing strings hindering reaching the planned setting depths. The clearance between casing and open hole is reduced to approximately 1 in. for the deeper sections with more-flexible strings.