Measurement-While-Drilling (MWD) Survey Part1
Downhole measuring system
The downhole telemetry system is a set of equipment for collecting and processing data over the state of the well and optimizing the installation of the submersible pump. The efficiency of application and, so as well, durability of the equipment is mostly dependent on the correct definition of technical specifications and selection criteria. Downhole sensors of Triol Corporation are specially designed to monitor oil well and ESP operation parameters with its further transfer to VFD controller. Telemetry sensors help to optimize oil production and protect ESP installation. Motor temperature sensors are a reliable and secure solution that can easily operate under a wide range of temperatures. Pump monitor sensors helps to optimize and facilitate operation process for Customer convenience. It allows reducing oil wells down time, getting actual information about the well operation and its immediately analyzing. The use of this downhole system provides total control and safe operation of the dual ESP installation.
Progress is speedy and Triol Corporation is trying to be at the helm by applying
technical expertise and fact-based decision for the long-term benefit. We are actively promoting the highest technical and safety standards facing the question of efficient technologies. That is why we want to share our future plans over the future developments included in this technical overview over such a stirring matter as MWD.
What is MWD?
Measurement While Drilling (MWD) systems measure formation properties (e.g. resistivity, natural gamma ray, porosity), wellbore geometry (inclination, azimuth), drilling system orientation (tool face), and mechanical properties of the drilling process.
The term Measurement While Drilling (MWD) includes any tool that can be used while drilling, including wireline steering tools. In practice it means ‘wire-less’ measuring systems, e.g. systems using mud pulse or electromagnetic telemetry.
Measurement While Drilling (MWD) surveys can be used both as orientation surveys with steerable BHAs, or to replace magnetic multi-shot surveys while rotary drilling. MWD surveys are of comparable accuracy as wireline solid state magnetic surveys and can be used as definitive surveys.
The simplest Measurement While Drilling (MWD) system is the Teledrift offered by Scientific Drilling International, which is a mechanical inclination-only mud pulse tool. Most basic MWD systems take surveys of inclination and azimuth at discrete survey stations. More sophisticated systems have the capability to have extra sensors, for drillstring mechanics (e.g. downhole weight on bit, downhole torque, downhole shock, downhole pressure and temperature) or petrophysical evaluation (e.g. gamma ray, resistivity, density and porosity). Most of the systems transmit the data to surface using pressure pulses in the drilling mud inside the drillpipe.
How Does Measurement-While-Drilling (MWD) Work?
As drilling has become more complex, with horizontal and directional drills increasing in numbers, well logging has also had to adapt and improve. Measurement-While-Drilling is a type of well logging that incorporates the measurement tools into the drillstring and provides real-time information to help with steering the drill.
Once a well angle exceeds 60 degrees, the logging tools can no longer be pushed through the well to retrieve information, making conventional logging tools ineffective. Originally designed in the 1980s to overcome well logging challenges of wells being drilled at extreme angles, MWD is a type of Logging-While-Drilling (LWD) where tools are encompassed in a single module in the steering tool of the drillstring, at the end of the drilling apparatus (or the bottom hole assembly).
Providing wellbore position, drillbit information and directional data, as well as real-time drilling information, MWD uses gyroscopes, magnetometers and accelerometers to determine borehole inclination and azimuth during the actual drilling. The data is then transmitted to the surface through pulses through the mud column (mud pulse) and electromagnetic telemetry. Decoded at the surface, the data can also be transmitted to an offsite location immediately.
With such precise wells being drilled, MWD aids drilling engineers with real-time information so that they can make important decisions while drilling. Geosteering is a relatively new concept of positioning wells according to the geological features in the reservoir obtained through MWD. Now, video is even available to help in the process.
MWD provides time-critical survey data and essential logging data to help direct the bit during horizontal, vertical, and deviated drilling. Without accurate and precise survey and gamma ray measurements in real time, drilling operations can be delayed or even stopped.
The main aim of a MWD system is to determine directional survey data (zenith angle and magnetic azimuth values) in real time during drilling and transfer this data to the surface with the purpose of identifying the spatial location of the well path. With that, directional survey data is often supplemented with drilling parameters, BH temperature and gamma logging data. Gamma logging enables operators to measure the natural radioactivity of rock, separating the geological section into clay and non-clay constituents, which works especially well for the terrigenous sections of Western Siberia as well as in other conditions. When various LWD systems are used for more detailed reservoir research, MWD systems, amongst other things, acts as a connecting link by sending data to the surface.
Today, the use of MWD systems has become an integral part of drilling deviated and horizontal wells. It is nearly impossible to meet the objectives the geologists set to the drilling crews – following the designed well path and hitting geological targets without using MWD systems. As for using MWD to increase drilling efficiency, the purpose here is simple: drilling a well without deviations from the planned well path and without NPTs due to equipment failures. Triol Corporation strives to be a best-in-class independent manufacturer company, offering a wide range of services. We help our customers efficiently manage the operation of their remote assets in critical infrastructure and provide a complete offer of smart and integrated telemetry solutions and services. We see the necessity of such an implementation in our future development.
What is the difference between measurements while drilling (MWD) and logging while drilling (LWD)?
At the most basic, LWD is “logging while drilling” or attempting to make the same or similar measurements as a wireline log. LWD is accomplished by intergrating measurement tools into the drilling assembly as near the bit as possible. These tools measure formation properties – resistivity and natural radioactivity are the most common. Wireline logging is done after the borehole is drilled from a logging truck by lowering the tools on a multi-conductor wireline and then recording the signals as the tool is pulled up the hole.
MWD is much the same except for the measurements made. This measures the deviation of the well bore and the direction the bit is traveling. This application is essential to the horizontal drilling now necessary for gas and oil from shale. There are wireline tools which also track the hole position but, again, that is after the fact and of no help during the drilling procedure.
The key difference between LWD and measurement while drilling (MWD) is that whereas LWD data are recorded in memory and downloaded when the tools reach the surface, MWD data are transmitted up the pipe by means of a pressure wave (mud pulsing) at 3 bits/s and monitored in real time. The term LWD is also used more generically to cover both LWD and MWD.
LWD provides formation measurements, while MWD provides drilling mechanics and survey measurements.
- Inclination, azimuth, tool face
- Rotational speed of the drill string
- Smoothness of that rotation
- Type and severity of any vibration downhole
- Downhole temperature
- Torque and weight on bit
- Mud flow volume
- inclination at the drill bit (NBI)
- magnetic resonance
- formation pressure
An MWD system can improve the drilling efficiencies by ensuring accurate real-time well placement and providing real-time drilling dynamics information to optimize the drilling parameters and improve ROP or longevity in hole. Real-time formation evaluation from Gamma, resistivity and other LWD measurements allow the operator to adjust the wellpath in real-time to ensure the well remains in the sweet spot in the reservoir as well as its position in three-dimensional space.
LWD employs formation evaluation tools that measure pressure, gamma ray, resistivity, sonic, porosity and density properties of a formation, just to name a few. The porosity and density tools induce radiation into the formation from 2 known isotopes(Am241Be and Cs137) to measure their respective properties. There are more specialized services replicating those provided by wireline logging. These include magnetic resonance imaging and formation testing tools which are deployed in a combo string. Recent developments have further advanced petrophysical and geosteering capabilities with higher resolution imaging and forward looking sensors. These tools are programmable as standalone sensors or slaved to a primary control module. They operate on lithium batteries or run off an intergrated turbine power source.
MWD is basically a combo containing a survey tool that measures wellbore trajectory, provides magnetic or gravity tool faces for directional control and a telemetry system that pulses data up through the drill pipe as pressure waves. Surface acquisition systems decode the signals using a various standard or patented detection algorithms. Decoded information is then plotted on a log or displayed. Both systems share this mode of communication to the surface and are combined as one string in a drilling assembly.
Real-time Surveys for Directional Control
As deviated and horizontal drilling has become the norm, so has the industry’s need for cost-effective, reliable measurement-while-drilling (MWD) systems that can deliver accurate directional azimuth, inclination, and toolface data in all types of drilling environments.
- Inclination is the angle between a vertical line and the path of the well bore at that point.
- An inclination of 0° is a vertical hole.
- An inclination of 90° is a horizontal hole.
The Earth’s gravitational force is referred to as “g.” “g” describes the force of attraction exerted by the Earth’s mass onto each particle of matter.
Azimuth is the angle between North reference and a horizontal projection of the current Survey position
To determine the direction, or azimuth, of a survey point, the MWD tool must measure the Magnetic field (this allows us to get the North reference).
Azimuth measurement requires both Magnetometers and Accelerometers.
- Azimuth is the angle between North Reference and a horizontal projection of the current Survey position.
- A hole drilled due North has an azimuth of 0°.
Tool-Face is used by the Directional Driller to steer the motor in the direction he wants to go. It may also be used to set a whip stock in the borehole. We can use either the magnetometers or the accelerometers to orientate with. If we are at an inclination of less than 3° and are clear of magnetic interference we can use the magnetometers – Magnetic Tool Face. At inclinations greater than 3 degrees we can use the accelerometers – Gravity Tool Face.
- ToolFace is the angle which describes where the bend of the motor is pointing.
If you find yourself interested in such an overview stay tuned and keep up with tomorrow`s update, there you`ll find the final part of today`s technical survey.
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