For this specially extended edition of his monthly OE column, Professor Michael Economides invited famed horizontal drilling pioneer Jacques Bosio to collaborate on a piece discussing the provenance of this breakthrough technology and its continuing influence on oil & gas well design today. These are their thoughts.
About 30 years ago, a bona fide revolution took place in the oil & gas industry. Drilling of horizontal wells, eventually in massive numbers, took off – and the industry has never wavered since then. Arguably, horizontal wells along with 3D seismic measurements and hydraulic fracturing, are the three most effective technologies to emerge in the petroleum industry, the ones that have made by far the biggest difference since the advent of rotary drilling.
After making a huge initial impact on the industry in the 1990s, horizontal wells came back in the last several years with yet another coup. Exploitation of shale gas, without question the current big push in the industry, can only be done with long horizontal wells, drilled perpendicular to the expected fracture plane and, then hydraulically fractured with a very large number of treatments.
As always happens with ideas, the notion of drilling horizontal wells goes much further back in history, as far as 1914. Quite a few wells have been drilled using rather complicated, specially designed drilling assemblies: HJ Eastman and JH Zublin in the US, in the 1940s; A Grigorian in the former Soviet Union, who drilled 43 wells including multilaterals; Chinese engineers, stopped in the 1960s by the Cultural Revolution.
Most of these endeavors concluded that horizontal wells were technically feasible but uneconomical. They were put more or less to sleep until the end of the 1970s during which time drilling engineers believed that the maximum possible inclination for a well could not exceed 70° to 72°.
At that time Elf-Aquitaine was about to shut down its operations in Italy. Attempts to develop its biggest asset, the large Rospo Mare field in the Adriatic Sea, had failed. The reservoir is a karstic formation with a small matrix permeability and most of its heavy oil contained in large vertical fractures. It became clear to me that the only way to produce the field was to intersect the vertical fractures with horizontal wells.
Obviously a ridiculous idea.
When we talked to our drillers about disregarding the past dogma of 72° well inclination, first they laughed and then turned real angry at us 'crazy R&D people'. 'Even if you could drill it, a horizontal well makes no economic sense,' they said. ‘It will cost at least 10 times as much as a nearby vertical well but will never produce 10 times more. Besides, no coring, logging or testing will be possible and it will collapse on you before a liner can be run.'
And then the clincher: 'Jacques, you have been away from a rig floor for too long, go back to your playground and let us work on the serious matters.'
It proved far more difficult to change by 90° people's minds than to do it with the trajectories of the wells themselves.
Because the drilling division refused to participate, the R&D division decided to take over. We put together a common research project with the French Petroleum Institute (IFP) and in May 1980, after two years of hard preparation we were ready to drill our first test well. Where? In Lacq Superior, an old and shallow (600m) reservoir, in the south of France, completely at the end of its life 'and where we could not do any harm'. We even had to swear that 'we would be able to plug the well if it happened to disturb the drainage of the reservoir so that production could go back to normal,' ie nearly zero. The well was Lacq 90, a pure coincidence that this was our first well drilled at a 90° inclination from the vertical.
The well went 275m (900ft) into the reservoir and 100m (320ft) purely horizontal, at a cost of 3.2 times the cost of a vertical nearby well. Since the reservoir was 90% watered out, our well did produce much more water than its vertical neighbors, enough for our detractors to claim that 'horizontal wells are only good at producing water'. Funny as it may sound today this is an honestly true statement at the time, one that eventually horizontal wells made a shambles of in exactly the opposite way. Horizontal wells often remedy water production prevalent in vertical wells. Crests are a lot harder than cones for water to enter the well.
But it was not just the drillers that were the doubting Thomases. Reservoir engineers could not accept the idea that a horizontal well could increase the Productivity Index (PI) of a well enough to compensate for the extra cost.
Nevertheless we went ahead and drilled a second test well, Lacq 91, 472m (1500ft) into the reservoir, 300m (980ft) horizontal, now three times the cost of a vertical well.
Having acquired what we considered a sufficient proficiency in drilling and completion of horizontal wells we managed to convince the management of Elf-Aquitaine to take a risk and apply the technology to the Rospo Mare field (water depth 60m, reservoir depth 1300m). A pilot project that included a drilling and production platform was deemed necessary, an expensive risk.
In January 1982, we drilled Rospo Mare 6, 370m (1200ft) horizontally, with a cost 2.1 times that of a vertical well. But the well became an instant success. It produced 3000bopd, over 20 times more oil than a neighboring vertical well, boosting the recoverable reserves from nearly zero to 450 million barrels, enough to save the Elf- Aquitaine subsidiary in Italy.
Rospo Mare became the first oil field to systematically produce thru horizontal wells. Amazing results kept coming. While it took 85 days to drill RSM, by 1986 the third well was completed in 45 days, including coring and logging .In 1987 the sixth well only took 38 days, with a PI of 660bopd/psi (vs 3-30bopd/psi for a vertical or deviated well), and an initial natural flow rate of 7100bopd.
At that time we thought the Rospo Mare success story would have the industry jumping onto the horizontal well bandwagon. Not so in an eminently conservative industry, set in its ways. I remember the first paper I presented on horizontal wells at the World Petroleum Congress in London in 1983 .When I went to the podium, more than half of the room, which was full for the previous paper, got up and left. Simply not interested.
It took several WPCs for horizontal wells to make a dent. By the 1991 WPC in Buenos Aires, we had a full session devoted to horizontal wells. Since then horizontal wells have become indispensable to reservoir exploitation strategies in a number of fields and geologic structures. They are the obvious way to drain relatively thin layers and naturally fractured formations. They are a powerful means to control and reduce influx from underlain water and they have ushered in an era of multilateral wells and complex well architecture.
For me and my colleagues in Elf-Aquitaine's R&D division, horizontal wells became the most interesting technical adventure of our life. And we had lots of fun. Like the time in 1984 when a few of us Frenchies were invited to Houston to tell Texans how to drill a horizontal well. OE
About the Author
Michael J Economides is a professor at the Cullen College of Engineering, University of Houston, and editor-in-chief of the Energy Tribune.
The views expressed in this column do not necessarily reflect OE's position.