| This paper systematic research and demonstration well construction on PVC-U pipe well completion at home and abroad for the first time, the related main filed contains drilling engineering, mechanics of materials, corrosion, elastic and plastic mechanics.As the rapid development of shallow geothermal develop, emergency (reserve) underground water source, project of rural safety drinking water, industrial water supply, town water supply, people begins to pay more attention on underground water well technology and engineering. The traditional well completion material is mainly contains ordinary steel pipe and cast iron pipe, and the corrosion and scale seriously which reduce the service life greatly is the biggest problem on traditional well completion; another aspect, the resource is dried up with each passing day, iron mine development and steel industrial have the high energy consume, high pollution problems which effect the ecological environment and sustainable development seriously. So under the conflicting situation between source and environment, use new material instead of metal has great significance on low carbon society, energy-saving emission reduction, environment protection and sustainable development.In the1950s, the United States of America began to use plastic pipe instead of steel and iron pipe in water well project. In the1960s, China began to pay more attention on plastic pipe well completion research and test. This period is a climax on plastic pipe well completion research and test. Because of the limited of plastic pipe formula and the well completion technology, the depth of plastic pipe well is from more than ten meters to dozens of meters. From the1970s to the1990s, majority water well use plastic pipes in foreign countries, but the diameter and depth are smaller, and our country steel use the steel or iron pipes. In early twenty-first Century, people found the problems on low service life, corrosion and scale seriously, high cost, frequent repair gradually. A handful of institute and factory begins a new round of research on plastic pipe well completion, but the depth are steel from dozens of meters to hundreds of meters, only some individual well depth more than200meters. Because of the plastic pipe can not sinking easily and burst during the well completion, it very difficult to use plastic pipe well instead of steel pipe in ground water well. This paper aims to the situation and mainly problem, put forward the "The Application and Research on PVC-U Plastic Pipe Well Completion" research topic, according to the large number of literature review and practical investigation, analyzed the problems on steel pipes corrosion and scale, the low depth, pipe sinking difficult, burst easy of PVC-U pipe well, and give the Specific research technique route.This paper aims to a new kind of PVC-U plastic pipe, from the material types, properties, formulation and processing technology aspect to analyzed and research. From the deformation-temperature curve of PVC-U pipe, the PVC-U materials with temperature difference will show a glassy, high elastic state and flow state, and analyzed the processing temperature effect on quality. Under the foundation of PVC-U plastic pipes characteristics summarized, it conduct the test on physical mechanical performance, safety and health, harmful substances(arsenic, cadmium, lead, mercury, antimony, tin, phenol, aluminum, chromium, chloroform, carbon tetrachloride) test. The test conclusion shows this kind of PVC-U plastic has the excellent mechanical and safety index, and does not dissolution in the water.In order to choose the well completion pipe reasonable and observe the corrosion and it speed, ordinary steel, cast iron pipe, bridge galvanized screen pipe, PVC-U pipe, wire ladder screen pipe are use for corrosion and scale problem research and test, the test method conclude the laboratory corrosion test and the actual underground color television dection. According to the test result and the actual engineering test, the metal pipe has the corrosion and scale problems universal, and the pipe strength will be sharp decline because of the corrosion and scale, and the PVC-U pipe do not have the corrosion and scale situation.This paper aim to the PVC-U pipe characters, and reference the stress analysis of oil casing, use the theory of material mechanics, elastic and plastic mechanics, from the point of axial tensile force, axial pressure, external pressure, the pressure in the tube, the transverse shearing force, bending moment, temperature aspects, researched the stress analysis of PVC-U pipe in water well, and use the demonstration well as an example, analyze and calculation the actual stress analysis form the PVC-U pipe sinking, well flushing and gravel throwing, well completion processing, got the following conclusions:(1) The overburden pressure, outside fluid column pressure, inside fluid column pressure will should a linear increase tend with the PVC-U pipe sinking depth, it means the more depth, the more pressure. And under the certain hydrogeological condition, the pressure value can not changed by human.(2) When the mud density in well equal to the density of PVC-U tube, the PVC-U pipe equal to the buoyancy, then appear the PVC-U pipe descending difficult.(3) After the PVC-U pipe well completion, during the pumping test or normal pump water period, because of the pipe bear the different types of pressure, the PVC-U pipe has the different pressure value between inside and outside.(4) Under low quality of well completion, well washing not enough, underground water had large deep down distance, the pressure different between inside and outside will be larger, it will effect the safety of PVC-U pipe. If the PVC-U pipe have quality problem, it is easily cause the burst accident.(5) Use the theory of oil drilling and Lame equation analyzed the dynamic load and collapsing pressure, the calculation result shows:when the pressure difference value between pipe inside and outside is bigger than4.53MPa, and formation collapse, throwing gravel "bridge" sinking speed bigger than0.73m/s, the pressure form outside and the collapsing pressure will be over the PVC-U pipe strength, it means these value is the critical value of PVC-U pipe burst.(6) In order to make sure the PVC-U pipe safe in well, it should be reduce the pressure difference between pipe inside and outside as possible.(7) During the well completion, gravel throwing, well washing and pumping processing, the PVC-U pipe will bear the different stress. The well completion and the use processing, PVC-U pipe are safer, and the well flush and gravel throwing processing are the danger period, the safe index is lowest. It means, after well completion, the difference between pipe inside and outside and the collasping pressure are the two main reasons which cause the pipe burst. So in the real project, the key point to make sure the PVC-U pipe safey is reduce the difference pressure between inside and outside, reduce the mud density as far as possible, and avoids the collapsing pressure. Using the theory research result, two PVC-U pipe large diameter demonstration wells were constructed, the depth are400m and437m, according to the science and technology novelty search (from Ministry of Land and Resources of the People’s Republic of China), those two demonstration wells has the largest diameter and depth in the world at that time, the research level belongs to advanced at home and abroad, In order to compare with the traditional well completion technology, the demonstration wells designed two different well structure, in the same geology condition, the result as following:(1) Test1well structure is the distance between PVC-U pipe and well wall is67.5mm, the PVC-U pipe joint part and drilling caliber distance is50mm, this kind of structure has the fast well drilling speed, but because of this less distance, the gravel found the "bridge" situation and increse the collapses pressure, cause the PVC-U pipe burst in well finally.(2) From the accident of Testl well, Test2well use a more reasonable well structure(the distance between pipe and well wall is more than100mm), make sure the gravel throwing smooth. From the experience of Test2well, this well structure design and well completion technology are successful use in Henan, Shanxi area in China, the well amount are15, the total drilling amount is9377m. Those successful project shows the technology of Test2well are reasonable and safety.(3) There are obvious different in water quantity and sand contains, the water amount in unit of Test2is3.1times than Testl, and the sand contains is one in tenth. The main reason is the Test1well has the pipe burst accident, the accident treatment cost long time, and use amount of mud, lead to the water plugging and the gravel thickness can not make sure.(4) From the theory analyze and calculation, explain the reason of the PVC-U pipe sinking difficult and burst, put forward the mud characters adjustment,"pressure balance", well structure design, and gravel throwing speed control measure to solved those problems during the PVC-U pipe well completion, and successfully use in the real projects.(5) According to the demonstration well construction and test, the low PVC-U pipe quality, wrong method of transport and keep the pipe, fast gravel throwing speed, large quantities gravel throw, water level drop too fast during the well washing and pumping are the main factors lead to the PVC-U pipe in the unsafe situation.This paper summarize the common PVC-U pipe well type and treatment, put forward the well completion and water pumping, the PVC-U pipe burst or creep deformation. And the burst is the main problem; the creep deformation is only an special case. Combined with the real project, give the specific measure of PVC-U pipe accident treatment.PVC material is very cheap, and the PVC-U pipe make do not need very high temperature. According to the calculation from the environment effect, well completion speed, social benefits, the PVC-U pipe well completion, the pipe cost reduced￥59.65yuan/m, the well completion speed increase13.86times. From the compare, the PVC-U pipe can solve the traditional metal pipe corrosion and scale problems, and PVC-U pipe is the best well pipe for water well, it has the board develop space, has great significance on low carbon society, energy-saving emission reduction, environment protection and sustainable development.This paper has theory analyze and amount of projects and tests, from the PVC-U pipe material and analysis the mechanical properties, describe the pipe requirement, well structure and quanty, mud, well completion and accident treatment separately, and it can support the PVC-U pipe use in water well.The main conclusions are as follows:(1) The metal pipe are generally has the characteristics of fast scale and corrosion speed, maintenance frequent, short service lift time (3-10years), water quality polluted, those are the basic reasons which effect the water supply well quantity and running effect.(2) The main problems which effect the processing of PVC-U pipe well completion are PVC-U pipe descending difficult and pipe burst. Among them, the mud density is the main factor; the dynamic load (impact load) in well and the pressure difference is the main reasons which lead to the PVC-U pipe burst, and also related with the PVC-U pipe quantity and the transport and keep method.(3) Before the well completion, when the mud density larger than1300kg/m3, or similar to the density of PVC-U pipe, the PVC-U pipe may descending difficult or can not descending. According to the theory calculation and the demonstration well test:adjust the mud density before the well completion, and keep the mud density in1050-1200kg/m3, and make some holes on the bottom of the pipe, can resolve the PVC-U pipe descending difficult and pressure difference.(4) The biggest threats for PVC-U pipe safe in the well are dynamic load (impact load) and the large pressure difference, during the gravel throwing, well washing, pumping processing, it is easy happened the "gravel bridge" descending suddenly, collapse, and the large water level drop pumping water may lead the dynamic load and the pressure difference. When the gravel throwing speed bigger than0.73m/s and the pressure difference larger than4.53MPa, the dynamic load and the pressure difference may cause the PVC-U pipe burst accident. (5) In general loose formation, the key to PVC-U pipe well completion is the well structure, the distance between well and pipe should be larger than100mm.(6) During the use period of PVC-U well or well completion processing, if there has the problems of burst or peristalsis deformation, the treat measure is easier than metal pipe well.(7) PVC-U pipes are not allowed use in the environment which temperature above60℃.In a word, PVC material has the characteristics of low cost, light weight, excellent comprehensive physical and mechanical performance, no corrosion and scale, long service life (50years), fast well completion speed, no polluted water quantity, no harmful material dissolve in water. It may realize the purpose of "use plastic instead of metal" in water well and shallow geothermal development field. So, to popularization and application the PVC-U pipe can not only reduce the cost and labor intensity, and have important significance in environment protect, energy saving and emission reduction, save the metal resource, it have significant economic, social and environment benefits. According to the novelty search, this paper technology innovation concludes:(1) Two demonstration well (400m,437m) use PVC-U pipe, has the largest diameter and depth in the world at that time, the research level belongs to advanced at home and abroad, fill the gaps in the field, and has played an exemplary role. The PVC-U pipe wells completion and the accident treatment realize the innovation; it is helpful for the water well drilling and well completion development.(2) It is the first time to analyze the PVC-U material character, conduct the corrosion and scale test, analysis the pressure and calculation, real project aspects to research. From the amount wild test and practice to conclude the technology of PVC-U pipes well completion, combined with the theory analyze and project, it formed the support for the plastic pipe industry development and application in larger field, it also provides the scientific basis for the future of China’s well pipe choose.(3) The theory calculation and demonstration well explained the PVC-U pipe sinking difficult and burst problem, the theory calculate and the real situation almost equal, it shows the calculation formula choose is reasonable. |
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