The Difference between MWD and LWD

Measurement While Drilling (MWD) is an advanced technology in directional drilling, which can measure some information near the bottom of the drill hole without interruption, and the information is immediately transmitted to the surface.

MWD( Measurement While Drilling), wireless MWD can timely measure in the process of drilling, which kept drilling, downhole mud pulse generator sends the data measured by the detector to the ground, by collecting and processing computer system, get well parameters and formation parameters in real time. The LWD can measure the inclination angle, azimuth, tool face angle and stratum gamma ray intensity during drilling. It can provide well parameters and stratigraphic evaluation data for drilling in large deviated wells and horizontal wells. This instrument is a necessary technical equipment for improving drilling speed and ensuring drilling quality in directional well and horizontal well drilling operation.During drilling, the physical properties of the bottom hole are measured, usually including downhole pressure, temperature, and 3D drilling trajectory. Because of the high cost of offshore drilling platform and the high requirement of drilling reliability and safety, MWD has become the operating standard of offshore directional Wells.

MWD is mainly measured with drills. Well, well, azimuth measurement tools face (magnetic, gravity), guiding drilling. ER-MWD-38 Small Diameter Measurement While Drilling (MWD-Φ38mm) has the characteristics of high precision, high stability and high vibration resistance. According to the conditions of the drilling tool, different diameters (drill collar diameter of 50.8mm, 71.4mm) rubber wings are selected to adapt to different drilling tools. In the small hole construction, the hole of the non-magnetic drill tool can not be reamed (the diameter of the drill collar is 50.8mm), which reduces the erosion of the drill tool and enhances the safety of the downhole drill tool. It is more suitable for second and third development and window sidetracking and other small hole operations. Also suitable for coiled tubing connections while drilling.

LWD(Logging While Drilling) generally refers to the measurement of formation petrophysical parameters in the process of drilling, and the data telemetry system sends the measurement results to the surface in real time for processing. Due to the limitation of data transmission technology, a large amount of data is stored in the memory of downhole instruments and played back after drilling.The first is to measure the resistivity, then the neutron, the density, etc. The difference between the parameters and the parameters obtained is different.

LWD is to add several parameter sensors for formation evaluation on the basis of MWD. Such as compensated bi-lateral resistivity, natural gamma, azimuth neutron density, sound wave, compensated neutron density and so on developed.On the measurement of LWD in wells, and the tool surface inclination, azimuth measuring resistivity, natural gamma, wells, porosity, density and so on, it can replace the cable logging now.

Advantages :

MWD over wireline measurement systems: It can be used for real-time formation evaluation and drilling geological guidance, and it has shown economic and technical advantages in solving formation evaluation problems in horizontal Wells or high-angle Wells and difficult logging environments. The LWD data is measured shortly after the formation is drilled, when the formation is not polluted by drilling fluid or the intrusion is very shallow, the logging response is not affected by drilling fluid intrusion, and can reflect the characteristics of the original formation more accurately.

Characteristics and advantages of measurement while drilling
(1) With the help of MWD, engineering parameters that are difficult to measure on the surface can be accurately obtained underground, such as bottom-hole bit weight, torque, speed, pressure, temperature, etc. The real-time acquisition of these parameters helps to modify various models, optimize drilling parameters, predict, prevent and control downhole accidents in advance.
(2) For special process Wells such as high-inclination Wells and horizontal Wells, wireline logging is difficult to implement, and MWD can save a lot of drilling time and reduce engineering risks.
(3) The surface software system of MWD has data processing, logging interpretation, block reservoir description and other technologies, which can realize real-time structure simulation and interpretation, and complete formation evaluation while drilling; The combination of drilling tools such as guide motor can realize automatic and intelligent drilling and improve drilling efficiency.

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