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Sun 3 Feb 2008 04:00 AM

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Drilling technology

New technology can provide more effective access to hydrocarbon reserves.

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%.
Offshore drilling technology has also advanced dramatically with new applications including improved offshore rigs, dynamic positioning devices and sophisticated navigation systems. When working offshore, drilling operators face high temperatures and pressures, which can place limits on existing drilling and completion technology.

According to the Society of Petroleum Engineers (SPE), several new solutions are being developed that could potentially improve drilling technology in the High Pressure/High Temperature (HP/HT) sector.

Another technology that offers the prospect of more accurate and cost-efficient drilling (although not on a widespread level) is the use of lasers.

This has been heavily promoted thanks to research carried out by the Colorado School of Mines using technology made available to it from US aerospace company Boeing.

The technology actually has its origins in the 1980s' US government's Strategic Defense Initiative (SDI) also known as Star Wars.

Although the lasers do not actually drill but rather burn holes in the rock, they are highly controllable meaning that downhole activity becomes more predictable.

One of the main stumbling blocks to lasers' use has been the amount of energy required to operate them at the surface, but research carried out in recent years and resultant applications means these costs are not as prohibitively high as first feared.

While it is not thought at present that use of lasers for oil and gas drilling will become widespread, they are expected to have certain niche applications particularly in environmentally sensitive areas - because, in common with horizontal drilling they require less surface infrastructure.

The Colorado School of Mines has also suggested that lasers ability to work well with MWD applications means they would be particularly relevant for fields or areas that have encountered high levels of dry wells.

Another new technology arousing interest is Managed Pressure Drilling (MPD) which also has the potential to help operators drill wells that were previously economically or technically unviable.

The UK's Impact Solutions Group has devised the first ever closed-loop MPD system called the Secure Drilling system. This is based on a micro-flux control method, which uses a high precision mass flow meter to detect kicks and losses from available drilling data.

The system also reportedly manages backpressure at the surface in order to control influxes or losses. The use of the high precision mass flow meter allows the system to do this with very small fluid volumes, reportedly keeping fluid losses to less than 0.5 a barrel.

The system has an automated manifold, which contains two drilling chokes and the mass flow meter.

The manifold reportedly has a small footprint, allowing it to be installed on virtually any rig, and it can be operated automatically or controlled remotely by the driller.

Impact Solutions claims the system keeps the driller and other rig personnel (either at the rig or at a remote location) constantly up to speed on the drilling operation, by providing relevant information on computer monitors.

When the system detects a potential influx (noted when the flow out trend line begins to deviate from the flow in), the system first confirms it and then controls it.

When run automatically, Secure Drilling can close the choke to increase the back-pressure at the surface, thus quickly stopping the influx and restricting kick volumes to less than 1 bbl. The technology was awarded the Spotlight on New Technology Award for 2007 at the Offshore Technology Conference.
In the US, the Department of Energy (DOE) has been carrying out a research programme into microhole drilling technology.

Managed by the Office of Fossil Energy's National Energy Technology Laboratory, the initiative seeks to develop the tools and techniques for drilling ultra-small boreholes (generally, 1-3/4 to 4-1/2 inches in diameter) and related downhole micro-instrumentation, using coiled tubing drilling rigs that are small and easily transportable.

In 2007 a specially designed hybrid microhole coiled tubing rig concluded the drilling of 25 test wells to penetrate a particularly intractable natural gas formation called the Niobrara in western Kansas and eastern Colorado.

The effort delivered cost savings of 25-35% per well drilled compared with conventional drilling equipment. As a result, about 1 trillion ft3 of shallow gas that had been bypassed by conventional drilling has now been made economic.

The DOE says the specific advantages of microhole drilling are: equipment is smaller and weighs less one tenth of conventional systems; it requires less materials for drilling and well completion; time and money are saved because it requires fewer trips in and out of the wellbore than conventional drilling techniques; volumes of drilling fluids and cuttings can be reduced; and the drill rigs and associated equipment have smaller footprints.

Meanwhile in December 2007 the University of Aberdeen, Scotland said it expected to see reduced drilling costs and reduced environmental footprint for the drilling industry as the result of a new multi-million pound research and development programme.

The University's School of Engineering agreed a major research contract with ITI Energy for the first phase of a programme to study Resonance Enhanced Drilling (RED) which could significantly reduce wellbore creation time in hard formations and deliver the capability to drill with one bit through differing formation conditions, reducing or removing the need to trip for bit changes.

The University says market testing has estimated that the application of any successful new technology could result in an annual savings of over US $1 billion for operators and the rise of a new market in Rate of Penetration-improving technologies.

According to principal investigator for the project Professor Marian Wiercigroch, "the oil and gas industry has many challenging problems and the downhole drilling belongs to the most complex ones".

But it's not all good news.

The European Drilling Engineering Association (EDEA) says it has seen a shortage of high-quality technology development project proposals and a drop in the amount of projects that are presented and subsequently sponsored by member oil companies.

It says this is due to a decrease in R&D budgets and the changing dynamics within the industry, whereby innovative companies are sidelined as far as technology development is concerned, by the tendency of oil companies to outsource a range of functions to ‘one-stop shop' providers.

The EDEA says there is a need to stimulate innovation within the industry supply base. Both operators and service companies need to be proactive in this respect.

To do nothing within the context of the current industry dynamics between the operators, service companies, contractors and SME suppliers would be to allow innovative talent to be stifled.

R&D effort should be focused on the key requirements of the industry, rather than allowing suppliers to commit resources to ideas for which there may be no market," it said.
It adds that operators and service companies need to directly fund high-priority development projects and schemes and develop strategic partnerships with key, highly innovative suppliers and collaborate with other companies.

It is likely that market dynamics will trigger greater investment in drilling technology with high oil and gas prices meaning more R&D cash should be available and the continued focus on challenging reservoirs meaning companies will be looking at improving drilling processes to increase efficiency and reduce costs.

At the same time they are under a considerable amount of pressure to reduce their environmental impact and some of the smart drilling technology outlined above when combinedco with the overall ncept of a smart or digital/virtual oilfield means that techniques for actually drilling for the oil are unlikely to remain as basic as they have been for many years.

Managed Pressure DrillingIn times when the oil industry is looking for drilling technologies to optimise the development of its fields, Managed Pressure Drilling has become an attractive technology, offering tangible benefits.

Managed Pressure Drilling (MPD) is an optimised drilling process used to more precisely control the annular pressure profile throughout the well bore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly

From a simplistic view it means that the annular pressure profile is controlled in such a way that the well is balanced at all times and is intended to avoid continuous influx of formation fluids to the surface.

The MPD uses tools and techniques that may mitigate the risks and costs associated with drilling wells that have narrow downhole environmental limits. MPD may also allow for faster corrective action to deal with observed pressure variations. The ability to dynamically control annular pressures facilitates drilling of what might otherwise be economically unattainable prospects.

The two main subdivisions of MPD are 'reactive' and ‘proactive'. Reactive (or contingency) MPD uses a closed and pressurisable returns system. The technique is used as an enhanced form of well control to manage unexpected pressures.

Drilling is carried out using conventional casing and fluids programmes and backpressure is applied to control kicks. In proactive MPD, a fluids programme is designed around the ability to apply back pressure, (nearer-balanced than conventional). The casing programme is designed with deeper set points, and it may be possible to eliminate a casing size.

There are other proactive MPD variants. Pressurised mud-cap MPD mitigates extreme losses and reduces associated NPT when drilling highly depleted zones, avoiding well control issues resulting from the inability to maintain a full column of mud in the annulus.

Constant bottomhole pressure MPD reduces NPT and enables fewer and deeper casing strings when pore-to-fracture pressure gradient windows are narrow. Dual gradient MPD enables total well depth in the right hole size in deep-wells and deepwater drilling. Returns-flow-control (or HSE) MPD reduces risk to personnel and the environment from drilling fluids and well-control incidents.

Today numerous onshore drilling programmes and a rapidly growing number of offshore programmes have proved that drilling with a closed and pressurisable mud returns enables more precise wellbore pressure management.

As wells became deeper, hotter, higher pressured or more depleted, many will require some form of proactive MPD to ensure that they are being drilled at an economically viable cost. The following figure identifies the potential impact of applying MPD for the reduction of NPT associated to kicks, lost circulation, wellbore stability and stuck pipe issues.

MPD Constant Bottom Hole Pressure (CBHP) is one variation of MPD that is used to mitigate NPT with interest growing among operators. This technology enables ‘walking the line' between pore and fracture pressure gradients.

The objective is to drill with a fluid, maintaining bottomhole pressure (BHP) constant, whether the fluid column is static or circulating. The loss of the annulus flowing pressure when not circulating is counteracted by applied surface backpressure.

The basics of CBHP methodology is to accurately determine the change in bottom hole pressure caused by dynamic effects and compensate with an equal change in annular wellhead pressure. For example, if the annular friction pressure loss while pumping is 500 psi, the wellhead pressure is increased 500 psi to compensate for this when the pumps are turned off. Once the drill-string connection is made, the wellhead pressure is reduced and the rig pumps are turned on.

Each increase or decrease in dynamic effects within the wellbore is counteracted with a change in applied annular well head pressure. The precise manipulation of annular wellhead pressure with MPD equipment is used to compensate for changing fluid dynamic frictional and surge/swab effects while making drill-string connections and tripping. Other advantages by using this variation of MPD is it allows the operator to solve drilling problems by increasing or decreasing the resulting bottom hole pressure without changing the drilling fluid properties.

The evolution and demand for this technology across the MENA region continues to go from strength to strength and the results being seen are testament to the fact that this technology is here to stay.

Paco Vieira & Shokuh Ziaian of Weatherford

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