The Bakken formation, mostly in North Dakota, is turning out to be one of the most prolific oil plays in the history of the United States. It was named after Henry Bakken of Tioga, N.D., in 1953. It was his farm on which the discovery well was drilled. It didn't produce too much oil per day but, remarkably, the well is still in production! In 2007, the United States Geological Survey (USGS) estimated that there might be as much as 3.65 billion barrels of oil in the Bakken. In 2012, estimates revised that up that to a mean of 18 billion barrels, with recoverable oil around 7.4 billion barrels. That is, recoverable with today’s technology. Drillers are an inventive bunch and, if history is any guide, much more oil will be recoverable.
|Columnist Wayne Nash worked the Bakken for two years, and has seen firsthand the production boom there. Source: iStock|
Part of the problem with the Bakken, in the early days, was the formation itself. These shale plays are called “unconventional” because they are source rock and reservoir, all in one. Conventional oil wells tap reservoirs almost exclusively, the source rock being deeper and harder to get at. The Bakken is also not very thick. It ranges from 30 or 40 feet thick in some areas to 300-plus feet thick in others. Since most drilling “back in the day” was vertical, it didn't open much formation to the well-bore. The other problem was permeability (measured in milidarcys). The porosity is fair, thus trapping a fair amount of oil, but with low permeability, the oil would not flow to the well-bore.
The solution was two-step, and it took the combined engineering skills of the entire industry to pull it off. First was directional drilling. We’ve all grown up in the industry trying to make “straight hole,” so it was kinda strange to kick one off in a new direction. Kicking off is no big deal, heck, I've seen me do it. But kicking off in a particular direction, at a particular depth is another matter. This required navigation in an extreme environment. The best minds in the field worked on this for years before they got it right. With proper navigation, the driller can put the bit in the Bakken and keep it there for 5000 or more feet. That is a lot of producing formation in one well. In order to do this, rigs had to be modified. Gone is the venerable kelly, replaced by a huge, powerful, sophisticated tophead-drive system on a track in the derrick. Us old timers call these, “blocks with training wheels.” It can rotate the pipe in either direction, drill up or down, and makes and breaks the tool joints.
Along with navigation came mud motors and bent subs. This allows the DD (directional driller) to aim the bit in the direction he wants to go. Once the bit is properly oriented (aimed), the tophead is locked and the pump started. This causes the mud motor to turn the bit. As the driller slacks off, the bit follows the orientation of the bent sub, and the hole is “kicked off.” This is called “sliding” because the drill pipe does not turn, just slides down the hole. Orientation and angle are read at the surface in near real time, so the DD knows where the bit is at all times.
Usually, the goal is to turn 90 degrees in 1,000 feet. This makes a nice, gentle bend. When the bit is headed in the right direction at the right depth, the driller will start rotation of the tophead. This cancels out the bend in the bent sub and causes the bit to drill straight in whatever direction it is pointed. Monitoring the direction and azimuth of the bit is critical during this time to stay in the producing formation. If the bit wanders too far, rotation is stopped, the tophead is re-oriented and sliding is done to correct the direction.
With the extended reach of these, it was discovered (the hard way), that conventional drill pipe was not up to the extreme torque loads of a mile of pipe laying on the bottom of the hole being rotated. New tool joints were developed. Instead of having the torque face only on the root of the pin and the face of the box, they added another torque face to the end of the pin and the root of the box. This nearly doubled the usable torque capacity of the tool joint.
These new tools have more than kept up with the navigation technology. At present, the navigation signals are sent to the surface in the form of mud pulses, which are read and interpreted. The limiting factor is noise. At extreme depths, the rotating drill pipe and natural bit noises overcome what the DD can hear. We are now routinely working at over 20,000 feet from the rig to the bit. This is constantly improving with each generation of DD tools. Nowadays, most drillers drill until they can’t navigate, and then drill a couple hundred feet further, hoping to stay “in the zone.”
The wells drilled in this manner will produce quite a bit of oil for a long time, but there is another step to realizing the full potential of a tight shale with very little porosity. The oil must be released to flow into the well. Sixty or so years ago, “Big Red” developed a method of breaking open the rock, called hydraulic fracturing. It opens the formations and introduces sand to hold the fractures open, allowing much more oil to flow into the well. It was originally done in vertical wells, and it took a learning curve to successfully adapt to 5,000 or so feet of horizontal formation, but it is being done every day. It is hilarious to all of us in the industry that, although we have been fracking for 60 years without problems, the general public just learned a new word a couple years ago. It is human nature to distrust anything one doesn't understand, and the amount the general public doesn't understand about fracking would fill an encyclopedia, so they don't trust it and fight against it. This is very short sighted, since we have been doing it safely for longer than most people have been alive, but some people just will not be confused by the facts.
In the two years I've worked in the Bakken, I've learned a lot of things, made some lifelong friends and seen some big changes. I feel these changes are only the beginning of the technology to come in the drilling industry. Earth first, I say. We'll drill the other planets later!