Drilling technology

New technology can provide more effective access to hydrocarbon reserves.

Drilling and completions can account for over 50% of costs in some field developments but drilling environments are becoming increasingly more challenging.

Although the sector is achieving tasks in exploration and production (E&P) that would have been unthinkable 20 years ago, finding and producing oil and gas is becoming more difficult technically, economically and environmentally, meaning risks and costs are rising and so the need for new drilling technologies has become acute.

There are essentially two forms of drilling - the traditional method, vertical, i.e. straight down - and horizontal which has become more popular over the last two decades. Despite the fact that most oil deposits are wider than they are thick, for more than a century, vertical drilling has been the preferred method. A horizontal well is more costly, but it has a much greater surface area.

Around 10 years ago horizontal drilling became more popular thanks to its ability to access reserves contained in narrow, fractured formations. Horizontal wells generally increase productivity to at least two to three times that of vertical wells.

As the International Association of Drilling Contractors (IADC) notes, when a vertical well is drilled through a narrow formation, its exposure is limited but if the well is turned and follows the formation for a distance, then the well bore to formation surface is greatly increased. This increase allows for easier retrieval of oil or gas.

This makes horizontal drilling ideal for reservoirs that are shallow, spread out, or in sensitive environments. The use of vertical boreholes in these locations requires more wells and thus more surface infrastructure and raises the potential for damage. Horizontal wells drain a larger area but require fewer wells. Horizontal drilling has helped enhance and increase oil and gas recovery at many fields and also permitted access to reservoirs previously deemed untouchable.

It is also possible to drill multiple wells off the same vertical borehole in a technique, called multilateral drilling, where two or three horizontal boreholes, each a few hundred to a few thousand feet long, can be drilled off the same main stem. Multilateral drilling creates a drainage network in reservoirs with many isolated pockets of oil.

As well as the two forms of drilling, other applications have emerged in recent years. One is Measurement While Drilling (MWD) which has become a viable technology thanks in part to the use of steerable motors.

In MWD instruments monitor variables in the borehole, like position, temperature, pressure and porosity, and communicate these, along with other data, back to the surface via pressure changes in the drilling fluid. This provides immediate data on the rocks being penetrated and eliminates the need to pull the drill string out of the borehole before logging.

Advances in smart wells and digital oilfields means this data can now be analysed quickly and accurately from remote locations enabling immediate action to be taken by engineers during the drilling process.

Steerable motors mean that a rigid drill string is no longer necessary. Also, the invention of flexible coiled tubing continuously unreeled from a giant spool allows uninterrupted drilling and also decreases the equipment footprint at the drill site. Another recent development is slimhole drilling which as its name suggests involves drilling a slimmer hole in the ground to reach oil and gas deposits.

Because of its low cost and reduced environmental impact, slimhole drilling provides a method of economically drilling exploratory wells in new areas, drilling deeper wells in existing fields, and providing an efficient means for extracting more natural gas and oil from undepleted fields.

In order to be considered slimhole drilling, at least 90% of a well must be drilled with a drill bit less than six inches in diameter (conventional wells typically use drill bits as large as 12.25 inches).

Slimhole drilling can significantly improve the efficiency of drilling operations, as well as decrease its environmental impact. The IADC estimates that shorter drilling times and smaller drilling crews can lead to a 50% reduction in drilling costs and reduce the drilling footprint by as much as 75%.