3.    Wireless MWD major progress and  status about technology

With the directional wells, horizontal wells, branch wells and horizontal wells, such as large displacement special process of the rapid development of drilling technology, wireless MWD technology of the world's major oil companies is becoming more and more well developed and its equipment  has been serialized and further promoted at the scene , wireless technology as the basic platform of MWD special process technology and downhole drilling parameters to expand , exert their advantage gradually.

(1) Schlumberger company solved two major problems facing about high temperature and high pressure in deep horizontal well with its new SlimPulse waste-to-MWD system. At Italian Villafor2tuna - Trecate oilfield they succeed in drilling the deepest horizontal well in the world  using SlimPulse MWD technology. Tatsu finally depth is 6421 m, deviation angle is 89. 6 °. It has set up a world record drilling 184m deep underground horizontally at the condition of vertical depth at 6062 m, deviation angle 85 ° ~ 90 °.

(2) Precision Drilling Computalog's harsh environment MWD (HEL MWD) system can work stably at 180 ℃, 172MPa under well. HEL includes directional detectors, high temperature bearings gamma device, measurement for harsh environment and boreholes / annulus pressure detector. HEL system have been tested in Mexico and the United States on an extensive field, succeed in working at the condition of the mud density as high as 1.87g/cm3, downhole temperature exceeded 170 ℃in the wells. 

(3) Russian directional drilling are primarily used in electromagnetic measurement-while-drilling, the research is earlier, and technology is more sophisticated. By arrangements of the Ministry of Science and Technology of China Petrochemical Corporation , ZTS-172M wireless electromagnetic MWD system of the Russian horizon company was tested at Sin 110 - Ramp 8 wells of Shengli Oilfield. Sin 110 - Ramp 8 wells in Shengli Oil Field is located in Dongying depression central fault anticline belt, Formation Resistivity is 2 ~ 4Ω m. After ZTS electromagnetic MWD apparatus went down, above 1600m the test shows that the system is working well, at a relatively low resistivity formation it can effectively sent and received data, with measurement data of high reliability, repeatability, and faster transmission speed. But at 2250m , the signal is abnormal, site analysis reported the reason was probably insufficient displacement. ZTS MWD system uses turbine ,the speed of the generator to 800 ~ 3000 r / min, the scope of the rated pump displacement  to 30 ~ 75L / s, while the actual pump displacement calculated for the 26.8L / s, less than the rated capacity request, should not the normal turbo-generator power supply, leading to not work correctly. Through this experimental situation, the system can lower the resistivity of formation use, must be able to guarantee the transmission distance. ZTS system has a larger transmission power can be set to launch a lower frequency, at low-resistivity formation must be able to guarantee the transmission distance, I believe, after further improvement can be at most of oil use.

(4) Weatherford has developed electromagnetic MWD system (EM / MWD) TrendSET, and put into commercial application in the first season of 2004. TrendSET can fit the under-balanced drilling under conditions of poor balance requirements or have applied some basic requirements. TrendSET is able to provide than conventional MWD tools more reliable and faster data transmission speed, data transmission speed can reach 12 bps, the system may be at high resistance layer, anhydrous salt layer or layers of regional work, ground-based measurement system to identify and filter more weak signal, has a strong ability to work deep well. TrendSET the various components through more than 500 hours of field test without damage, transmission achieved the depth of 10800ft (3292m).

(5) The United States PathFinder Energy Services has recently developed a new MWD measurement method, which adopts the two sets of accelerometers - sensors group rather than fluxgate to measure position,  use  the intrinsic bend of drilling tool at bottom between two accelerometers  100ft away from each other to measure the  relative changes in position. And based on this way, we develop Gravity MWD system called Gravity which is free from magnetic interference,  The system is a longitudinal anti-jamming measurement system, not very sensitive to the underground movement  and should not permit the normal measurement environment for the top job . The system is designed for casing drilling,  drilling casing shoes, re-entry operations,  geothermal wells, drilling recovery wells with magnetic interference , drilling wells of anti-collision cases ,and the branch Well . The system uses a high-speed mud - pulse telemetry to transmit data and can be used to wells in the depth of 28000ft.

(6) On March 15, 2005, American Scientific Drilling Company puts a high-precision directional gyro systerm to the MWD . the system abandons the cable design, developing gMWD systems, greatly improving the safety performance, at one of the  land-based drill machine in Texas gMWD system is used to create the first measurement of the total footage to achieve the 1000000ft gyro measurement-while-drilling record. 

(7) At present, MWD apparatus of HALLIBURTON company is mainly HDS1 (High-Speed Directional Survey) system, that is, "Pathfinder" MWD system of a new generation, it uses positive pulse transmission, can be applied to well hole which is more than φ149.23mm . Combination schemes of pulse coding is used to reduce the number of pulses fired, to maximize data transfer rate, double  battery tube apparatus can work a longer period of time, the largest measuring depth is up to  8500m.

4 Development Trend

There are Halliburton Company (including the NL SPERRY-SUN Corporation), SCHLUMBERGER companies (including Anadrill) and BAKER-HUGHES INTEQ company which are still exists and influence the world oil situation on the development . In the fierce competition that the three companies  continuously developed and improved  their own brands,  jointly promote prosperity and development of wireless  MWD technology. From the introduction of foreign companies, abroad has been committed to develop MWD apparatus adapting to harsh environments (high temperature, high pressure, intense vibration, magnetic interference, etc.) , there is no domestic using report of such devices. Only a few domestic companies, research institutes are in initial stage for the research and development apparatus of MWD. compared with foreign countries, our technically still has  gap.

With the growing of drilling engineering technology development, vigorously developing the MWD wireless technology is a major current direction . At present ,MWD wireless technology in solving the reliability of equipment, at data transmission technology ,will develop towards the following aspects: 

(1) need to develop MWD apparatus to meet the different conditions and various sizes to adapt to the practical borehole of drilling engineering;

(2) design of measurements near the bit . The more MWD close to drilling bit more around, the more measurement results is in favor of trajectory measurements, enhance layer target rate; 

(3) MWD equipment to enhance reliability. With the massive amount of memory chips and anti-high temperature and high pressure emergence of electronic components, will be able to create a better environment to adapt to the MWD apparatus of drilling strong vibration, high temperature and high pressure , in order to adapt to Drilling MWD construction under different environments ; 

(4)  Data transfer rate is further improved. To improve data transmission rates are  the demand for underground increasing information. Mud pulse transmission, acoustic transmission, electromagnetic transmission, fiber optic transmission technology improvements and  lot of technically difficult to break.

(5)The complexity of purpose layer for measurement accuracy of the instruments have become increasingly demanding, it is only committed to develop high-precision measurement sensors , in order to meet the requirements of drilling engineering.

5 Conclusions and recommendations

(1) the domestic need to learn from foreign advanced wireless MWD technology, follow the path of introducing, digesting, absorbing of the industrialization , at the same time to increase investment in research and development, vigorously develop their own intellectual property rights of MWD / LWD equipment, continuously shortened with the international advanced levels, which enhance the overall level of technical services and core competitiveness, to meet  technical services of the domestic market, resulting in further open up foreign oilfield technical services market, it has great strategic significance.

(2) Although the wireless drilling apparatus is a series of drilling, machinery, automation, materials, and so many disciplines into a high-tech products. R & D investment, and risks are also high. However, at present in case of our country's overall industrial manufacturing and technological level, we are fully capable of self-study and further success.

(3) In order to take full advantage of wireless MWD technology and equipment R & D capability existing ,  competition should be carried out in cooperation, joint research, joint development, based on summing up experiences and lessons , so that the current study job has a higher starting and  develop by leaps.