AlMansoori’s wholly owned subsidiary Target Energy Group is leading the way in delivering MWD and LWD technologies to the engineer’s steering the sharp end of the business.
Measurement and logging whilst drilling (MWD / LWD) is a system developed to perform drilling related measurements downhole and transmit information to the surface while drilling a well. MWD tools are conveyed downhole as part of bottom hole assembly (BHA). The tools are either contained inside a drill collar or are built into the collars themselves.
MWD systems can take several measurements including gamma ray, directional survey, tool face, borehole pressure, temperature, vibration, shock, torque etc.
Key to the challenges facing the Middle East, MWD are also vital in relaying the telemetry for operating rotary steering tools (RSTs), critical in the directional, or horizontal drilling business.
Target Well Control, a subsidiary of Target Energy Group, is a high technology oil and gas drilling service company specialising in directional drilling, and MWD / LWD operations. “We provide a broad range of well placement technology and is particularly advanced in providing drilling engineering, directional drilling, well planning, rotary steerable tools, MWD and LWD provided on a rental or service basis,” explains John Daniels, MWD operations Manager at Target Well Control.
“In addition to these products, we provide field engineers and office based supervisors who are widely experienced in the management of challenging drilling projects,” he says.
MWD tools are generally capable of taking directional surveys in real time. The tool uses accelerometers and magnetometers to measure the inclination and azimuth of the wellbore at that location, and they then transmit that information to the surface. With a series of surveys at appropriate intervals, the location of the wellbore can be calculated.
“We are specialised in providing directional surveys, which is the azimuth inclination toolface for when operators are steering. We also provide, gamma ray and resistivity steering and pressure while drilling tools,” says Daniels.
On the directional side, MWD or LWD is a fairly established requirement for surveying the well, even if it’s a vertical well the deployment of the right tools means drilling engineers can get a survey in two or three minutes rather than having to run wireline.
“On the logging while drilling side we have developed our own annular pressure while drilling tool which can help prevent things like stuck pipes because you can see when the annular pressure is building up with cuttings and loadings, for example,” explains Daniels.
Data is fed back through mud pulse telemetery. Downhole a valve is operated to restrict the flow of the drilling mud coming back up the annular, according to the digital information to be transmitted.
This creates pressure fluctuations representing the information. The pressure fluctuations propagate within the drilling fluid towards the surface where they are received from pressure sensors. On the surface, the received pressure signals are processed by computers to reconstruct the information.
The technology is available in three varieties – positive pulse, negative pulse, and continuous wave.
“Our tools can transfer that signal encoded as either a negative or a positive pulse, which means either a momentary drop in pressure, or a momentary rise in pressure. The negative pulse tool is probably the more robust, but for shallow holes and low-cost drilling projects the positive pulse has the advantage of being retrievable, which means if you get stuck in hole you can yank out the expensive bits,” says Daniels.
To relay information the tool will start by telling the operator what data it will be sending, typically using a three digit code. One set of numbers, or identifier, will signify a resitivity test, another will signify a gamma ray information feed is to follow.
High temperature lithium batteries provide the power source for Target’s MWD and LWD tool kits.
“Developments in battery technology means we can now run around 500 hours, or around 20 days drilling,” reveals Daniels.
Environmental factors
MWD tools are extremely complex pieces of high- tech electronics, and there’s no question that operating downhole is a harsh environment. “Our tools are rated up to 20,000 psi hydrostatic pressure, and around 150 degrees C, and built to cope with high vibration, and they are built to stand up to a combination of those conditions simultaneously,” says Daniels.
The sensors can ride anything from anything as close as five feet behind the bit, right up to 35 – 40 feet depending on whether a motor is behind run, and depending on which tool it is.
“Vibration can potentially be a problem, but most of there tools out now very robust. In the early 1980s we had a number of sensor failures because they were simply shaken too much. That is very rare now under typical drilling conditions,” he says.
MWD and LWD tools typically now come with a vibration sensor as standard built in, which will send back vibration warnings at certain thresholds.
Flexible Friends
MWD probably came of age around ten years ago, and is very much taken as fairly standard rather than being utterly top-end only, and where any deviation in the well and steering is expected, then MWD is a no-brainer.
Regulatory frameworks in many mature drilling environments actually specify that certain downhole tools are delpyed as standard.
“Often a minimum requirement is to have a gamma ray survey as part of the project. It’s particularly useful for horizontal drilling because you need to become horizontal in the right formation bed. In Abu Dhabi Gamma Ray is often used when whipstocks, which are sometimes used in controlled directional drilling, in straightening crooked boreholes, and in sidetracking to avoid hazards such as unretrieved fish,”
Daniels says that the MWD and LWD technology today is not just better in the sense the tools have improved, but also more processing power is improving the way the data interacts with the operator.
“There are many more sensors available now and there is no doubt LWD has come a long way. It’s not just an improvement in the tools and their capabilities and processing power, but also the computer power on the surface which enhances the information at the user interface, for example graphically so that operators can understand it better.”
The Target Well Control and AlMansoori directional drilling teams have been successful in winning a lot of remote exploration work, says Daniels. We “One of the reasons we’ve excelled in that niche is because all of our pressure while drilling and resistivity tools can be added on to the basic, most commonly deployed directional gamma. We have managed to develop a very flexible system which makes these add-ons simple to implement for the engineer,” he concludes.
