Research On Application Of Pressuring Foam With Pump Drilling Technology Of Geothermal Well In Beijing

The technique of foam drilling is kind of drilling methods that use the foam as circular media. The engineering college of Jilin University has successfully drilled a 700-meters deep caliber-rock water well in Ningxia province, and they also developed an pressure increasing device on the base of these studies, whose highest design value is 130kg/cm2. According to the characteristics of the foam drilling, we believe that the foam pressurized drilling technology suits the special circumstance in Beijing. The main performances are following: 1. The foam belongs to the low-density media. Its static pressure is very small in the bore, and it is more stronger to take out the rock powder. The bottom of bore is clean, which is very useful to promote the drilling speed. 2. The foam liquid has the function of washing well, strong ability of cleaning and the small specific weight. The bore bottom pressure is low so that the pieces of rock scraps can hardly enter into the geologic strata. Small grain in the geologic strata will enter into the bore with the groundwater pressure, thus the well can be cleaned by itself. In addition, as a special circular media, the foam will not form the formation mire skin on bore wall of the water layer to block water passage, which makes sure the quantity of the water purpose layer and is good to clean well. 3. Usually liquid leak to the layers during drilling in the purpose layer, sometimes the leakage is very serious and the slurry doesn't return to the ground. Mixing foam and high pressure air can make their volume expand greatly, which can be effectively used to keep static pressure in the bore and fill the large space. These are advantageous to keep the stability of bore wall. 4. Water scattering the geologic strata, inflating, the mud dense increasing, embracing auger often cause auger blocking etc. Because of the anti-water characteristic and containing little amount of water, this technology can make sure the stability of bore wall and avoid many problems during drilling. Besides, it can form a layer of protection film in the rock scraps and grain surface, which can keep the rock scraps from gluing anddecrease auger mire wrapping and adsorbing phenomena. 5. During the application of foam technology, the dosage of foam and water are according to the experiences, often 3-8 ‰. The highest drainage amount of BWZ-1200/130 is 40L/min. For some regions that are shot of water, the foam drilling method is quite applicable. On November 1st 2002, num 2002-1# well's cleaning experiment is done in the southeast of Shijingshan district in Beijing. Description of the experiment: 10 minutes after the foam pressurized system starts, the pressure inside the bore gets 30 kg/cm2. Keep this pressure for 40 minutes, and the water does not yet return. Then speed the air compressor's accelerate. After 1 minute, the foam quickly returns to the ground, and the 18-meter spray appears immediately, which shows good status. The reason of long time of keeping pressure steadily: the static water level is very deep inside bore and air machine has not arrived the standard value. Later, this technique is applied on the JingRe-Geng 34 well.The hole structure in the experiment: 0~260m, the bore diameter is 444.5mm, surface thimble diameter is 339.7mm, slurry solid, the slurry starching to the ground; 260~612 m, the bore diameter is 311 mm, thimble diameter is 244.5mm; 612~985m, the bore diameter is 216mm, thimble diameter is 177.8mm. 985m~end, the bore diameter is 152mm, no thimble. During application of foam pressurized drilling technology, the φ177.8mm thimble has been put into, cement solid, and the surface of crest to face is at 881.09m from the ground. Sweep the crest from the 881.09m to the 985m, then drill to the 1001.08m where the rock is ash segment. Work time is 112h, drill time is 55h purely, and the assistance time is 57h. The highest speed in ash rock is 1.8 m/h. During the sweeping of crest, the returned foam is normal, the bore bottom is clean, the speed is fast, and the eliminating device work normally. When drilling into ash rock segment, large quantity of water flows out and seriously breaks the ratio of media so that the powder carrying ability is decreased, andthe auger is broken up seriously. The foam presented the by fits and starts to spray to flow out, spraying time is 20~30s, the partition time is 3~5 minutes. At this time, the mud pump work pressure is between 2~55 kg/cm2(when the first experiment, the auger was blocked, so the pressure was attained to 86 kg/ cm2, the safe valve opened at that time), the powder elimination device can't work normally, the foam spread all around, so affecting the surrounding machine and equipments. Conclusion and advice: ⑴The foam pressurized drilling technology can be applied in holes that are over 1000 meters in depth and the foam pressurized drilling equipment can work normally. ⑵This technique can be used for large well-clean work, and the foam pressurized drilling equipment can take the place of big air compressor. ⑶The foam pressurized drilling technology can effectively overcome inside leak, and realize to work normally. ⑷Foam pressurized drilling equipment is superior and effective.