This image illustrates the drillers “traction control,” the means through which the driller keeps within the operational limit of the well. The added benefit of applying this approach is that it keeps the drilling process running as effectively and efficiently as possible.

Automated safeguarding and systems that aid in increased process efficiency have been used for a long time in a variety of industrial areas and applications. One of the more obvious examples is the automotive industry, where anti-lock brakes and electronic traction control have been used for a long time. In fact, it would be hard to find a modern car today that does not have advanced electronically controlled support functions installed.

Other industries, like the chemical industry, the metallurgic industry, and medicine, also have used automation for many years to better control different facets in their respective business processes with the common aim of avoiding errors and improving efficiency through eliminating human intervention in certain parts of the process.
Now, the drilling industry is moving toward this technology to achieve similar improvements. Although quite complex in layout and system architecture, modern drilling control systems have not closed the loop between what is physically possible to do from a well tolerance perspective and what the machine is “told” to do through the drilling controls.

How it works

An example illustrates how applying automated safeguarding and systems might work.

When running a long casing string into the hole, the well is subjected to a certain surge effect. The effect is similar to that created by a perforated piston pushing fluid ahead and through itself inside a cylinder, creating hydraulic pressure on the cylinder walls.

Transferring this analogy to the drilling rig and the casing operation, if the hydraulic pressure exceeds a certain limit, one runs the risk of loosing drilling fluid into the formation because the well can only hold a certain maximum hydraulic pressure before it “gives in.” When this stage is reached, the pressured fluid passes through the microscopic cracks in the walls of the well. These cracks create further cracks, a condition that exacerbates the problems and can lead ultimately to the risk of losing the entire well, an eventuality that brings with it dramatic cost consequences.

Of course, this surge effect can be calculated, measured, and controlled. There are several models available for carrying out this function. In practical life, drilling engineers calculate a maximum running speed using accepted sets of formulas and instruct the driller not to exceed this speed. As the casing is lowered into the well, the maximum speed gradually has to decrease. The deeper the casing is in the well, the more fluid passes through a tight area of the annulus, creating a higher pressure if the same running speed is maintained throughout, which eventually will break the formation.

To compensate for this, the drilling engineer typically provides instruction for incremental steps where the driller gradually reduces the running speed per batch of casing joints. However, there normally are not very many steps defined, and they are rarely calculated per joint. A common result is that the driller is given one speed limit for the lined (cased) hole, and another speed for the open hole.

Since much of this is actually calculated through guesswork, the limits by no means reflect the operational envelope the well can actually withstand. In fact, they may only be correct for as few as two points in the well — at the lower part of the two calculated sections.

This illustrates two things. The first is that with access to a dynamic update on hole conditions, the driller could optimize the running speed of each casing joint, resulting in a more effective casing/running operation. The second is that real-time data would prevent the driller from accidentally exceeding the safe operating limits, which would dramatically reduce the likelihood of damaging the well by creating an excessively high surge effect as a result of high running speeds.

Finding solutions

Since 2003, National Oilwell Varco, in conjunction with operators StatoilHydro and ENI and the Norwegian research institute IRIS, has been involved in a project called “Drilltronics,” where this and other safeguarding and operational efficiency principles have been tested.

The ultimate aim of this project is to monitor and map the operation envelope and feed the results dynamically back to the drilling controls via continuously updated algorithms that use real-time and pre-planned values such as well profiles, sting geometry, and mud properties. By exercising this sort of control, drilling operations can be kept within safe limits. The added benefit of applying this approach is that it keeps the drilling process running as effectively and efficiently as possible.

Successful full-scale tests were carried out on the StatoilHydro-operated drilling and production platform Statfjord C in the North Sea in 2007, where the concept and technology were proven and valuable experience was gained.

Several full-scale and simulated tests were performed prior to the offshore test, mainly at the IRIS facility in Stavanger, Norway, and on the test facility rig Ullrig. The system (which can be installed as a retrofit or newbuild) and the project have attracted significant interest from rig operators as well as drilling contractors.

Additional modules to the above mentioned have also been tested — starting the pumps in a controlled manner to avoid excessive pressures caused by mud gel, machine controlled and repetitive friction tests to better manage hole cleaning, automatic and repetitive connections, etc.

The system will be made commercially available with the above modules in Q3 2008. Further modules will be available in coming releases as part of an ongoing development and rollout plan that extends into 2010.