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Development of geothermal drilling technology

Release date:2018-11-12  source:东盟  Browse times:153
1. Well structure and casing structure:

In the 70-80s, the well structure was mostly: 153/8′′+81/2′′, and the corresponding casing structure was a combination of 103/4′′ (surface layer) + 51/2′′ (technical sleeve and water collecting casing).

Since the mid-1990s, with the differences in buried depth, lithology, structure, etc. of single wells, and the advanced technology of oil drilling and geothermal drilling, the well structure has changed from single to well, diversified. coexist. Often used are:

A. Well structure: 171/2′′ (surface layer) +121/4′′ (set pump section) +81/2′′ (technical sleeve + water collecting section)

Casing structure: 133/8′′ (set) +103/4′′ (pump tube) +51/2′′ (technical sleeve + water filter)

The typical well was the “Geothermal Well of Shaanxi Post and Telecommunications Administration” completed in 1994.

B. Well structure: 171/2′′ (surface layer) +121/4′′ (set pump section) +95/8′′ (technical sleeve + water collecting section)

Casing structure: 133/8′′ (set) +103/4′′ (pump tube) +7′′ (technical sleeve + water filter)

The typical wells are the geothermal wells of the Second Engineering Bureau of China Communications Construction completed in 1997, and the geothermal wells of the China Ordnance Industry Zero May 1 base in Huayin City, South Anhui Province, completed in 1998. It is worth noting that at the time, the A and B structures in the geothermal market were drilled in sections in the application, and the casing was sectioned. Finally, the technology sleeve and the water filter string were inserted into the pump tube and overlapped for one section. The method of forcibly connecting the overlapping segments and sealing them from top to bottom has the following disadvantages:

1. The water filter pipe needs to be inserted into the bottom of the well, so that the alignment rate is limited by the amount of sand at the bottom of the well, which is difficult to guarantee;

2. When the cement is cemented, the pressure difference of the cement slurry will increase the pollution of the water layer to the water layer;

3. Cementing and condensing prolongs the mud standing time in the water layer and increases the difficulty of washing the well. In view of the above drawbacks, a continuous drilling and opening pump section and all the water collecting sections are used in the construction process, and then the pumping section and the water collecting casing are connected by a self-designed reducing device, and the process of once entering the well after drilling is completed. The above problems have been effectively solved, and a number of high-quality geothermal wells have been drilled, which has also made this process the preferred solution for drilling deep-hole geothermal-deep wells.

C. Well structure: 171/2′′ (surface + pump section) +95/8′′ (technical sleeve + water collection section)

Casing structure: 133/8′′ (table and pump tube integrated) +7′′ (technical sleeve and water filter)

The scheme is based on the geothermal deep well pump body, and the power is continuously increased and modified. During the implementation process, the casing suspension device and the soft metal sealing device are designed by the Sanpu pump between the pump tube and the water layer casing. The problem in the above-mentioned I and H common schemes is avoided, and the scheme has achieved great success in the completed “Shaanxi Provincial Provincial Geothermal Well”.

D. Well structure: 171/2′′ (surface layer) / 121/4′′ (set pump section) +95/8′′ (technical sleeve section) +81/2′′ (water collection section)

Casing structure: 133/8′′ (table)/103/4′′ (pump room) +7′′ (technical cover)+81/2′′ (open hole water collection section)

The scheme is applied to geothermal wells in bedrock water production layers, and is typically used as “Geothermal Wells of Lushan Microelectronics Company” in Lintong District, Xi'an City. A similar scheme was adopted for geothermal wells constructed in Beijing after 2001.

2, drilling process

The advantage of occupying the geothermal market development market is to organically combine advanced and mature processes in oil drilling with related hydrological and geothermal construction. Make full use of existing equipment, preferably drill bit and mechanical parameters, actively promote and adopt near-jet drilling, which greatly improves drilling efficiency and shortens the construction period. In 1994, the geothermal market in Xi'an was mainly occupied by hydrographic drilling rigs. The drilling speed was slow and the risk was high. One well per month, the monthly efficiency was less than 500 meters, and the oil rig created 17 days to complete the test of 2013 meters and 28 days. The monthly efficiency has increased to more than 3,300 meters and the mechanical drilling rate has increased to 8-10m/h. From the quality of the project to the well water temperature and water volume indicators are far beyond the contract indicators.

2) Introducing scientific mud technology

In the development of geothermal energy, once entering the “soil + alkali” original dispersed mud that has passed the water well market, the scientific mud formula is adopted for different strata, the concept of near-balance drilling and completion fluid is introduced, and the purpose is to use fine dispersion. Do not disperse low-solid polymer mud and anti-high-temperature mud, and reduce the specific gravity of the mud in the target layer to reach the near-balanced drilling.

In the “Zero-51” geothermal well constructed by Huayin in 1998, the lessons learned from the waste wells caused by formation pollution in the adjacent wells were absorbed. In the process of drilling the target layer and completion, the low-solid phase, low-density non-dispersible polymer drilling and The completion fluid ensures smooth construction and protection of the water layer, making the well the first high-temperature and high-yield geothermal well in the work area.

In 1999, with the deepening of geothermal wells, the temperature at the bottom of the well increased sharply. In the construction of the geothermal wells of the Shaanxi Provincial Committee, the problem of metamorphism and degeneration of the mud at the bottom of the well was observed. The construction of the Chinese weapon industry was followed by the construction of the "2002" In the geothermal well of the institute, the high-temperature mud was replaced in time to the target well section below 3,000 meters, and there was no significant change in performance when the mud well was allowed to stand for more than 4 days after drilling, ensuring a 3400-meter casing. All went well into the well in less than 24 hours.

3. Completion process

In the 1970s and 1980s, due to the non-professional geothermal drilling, the geothermal wells were found to be completed along the wells. The water layer was filled with gravel through the cage filter, and the ancient method of stopping the water by using the mud ball to seal the water was used. .

After 90 years of research on well completion technology, combined with oil completion technology, it is used for different water layers: net-wrapped filter water pipe, non-wire-wrapped filter water pipe completion (most pore geothermal well), naked eye finish Wells (base rock, fissure-karst type heat storage, such as the geothermal well of Lushan Microelectronics Co., Ltd.) Beijing Dolomite fissure-cavity heat storage), water filter + perforation and other completion methods have achieved ideal yields. The water method has perfected the traditional water stop device, and improved the hybrid water stop device with kelp and umbrella rubber and metal tray. The geothermal well is mostly characterized by large-scale mixed mining, and an umbrella-shaped anti-collapse device is added at the top of the single water layer. To ensure the smoothness and longevity of each water layer.

4. Well washing process

The original well washing is repeated pumping. Gradually introduce high-pressure jet flushing in geothermal well washing, piston pumping (such as geothermal well in provincial post and telecommunications bureau), gas lift washing in pressure blower (geothermal well in 185 coalfield geological team in Shaanxi Province), carbon dioxide gas lift, acidification (Beijing geothermal well), high energy Gas fracturing (20 geothermal wells), these methods have produced good results for different well sites.

Geothermal is a clean and environmentally friendly green energy source. China's geothermal resources are abundant. From the national and world perspectives, geothermal energy is expected to become a new force for green energy. Geothermal development in China's economically developed regions, such as Beijing and Tianjin, has been extensively developed and utilized, and has begun to transform resource advantages into industrial advantages. Geothermal drilling technology has been continuously researched and explored, especially in the aspects of safe drilling, water layer protection, completion methods, well washing operations, analysis while drilling, judgment, etc., and gradually improved into a systematic, diversified and adaptable Drilling technology methods and process technologies with different geological conditions, using geotechnical drilling technology to develop geothermal development resources, geothermal drilling will become a pillar industry in the future.

First, the mechanical properties of rock

1. Mechanical properties of rock

(1) Strength of rock: The strength of rock refers to the ability to resist external damage.

(2) Hardness: The hardness of rock refers to the ultimate strength of rock resistance.

(3) Plasticity of rock: Under the action of external force, the property of permanent deformation before rock fracture is called the plasticity of rock.

(4) Abrasiveness of rock: While the bit breaks the rock, it is also subject to rock wear. The ability of the rock to wear the drill bit is called the abrasiveness of the rock.

(5) Drillability of rock: refers to the difficulty of drilling into a rock under certain conditions. It can also be understood as the magnitude of the rock crushing strength during drilling.

2. Influence of rock properties on drilling

The main effects are: affecting the drilling speed and the drill footage: making the drilling process have a complicated situation such as lost circulation, blowout, stuck drill, etc.: the drilling fluid is polluted, the performance is deteriorated, the diameter is irregular, and then the logging is affected. , cementing, etc.

(1) Clay rock formations. Mudstone and shale are generally soft and have a fast drilling rate, but are prone to bit mud packs. This formation is very easy to absorb the free water in the drilling fluid and expand, resulting in a reduction in the diameter of the well. As the immersion time is prolonged, the well wall will collapse and the diameter will increase.

(2) Sandstone layer. Sandstone is generally a better permeable layer, and it is easy to form a thick filter cake on the well wall, which is easy to cause the mud cake to adhere to the stuck drill. In addition, filter cakes also have an impact on logging, so high quality drilling fluids must be used.

(3) Conglomerate layer. Drilling in the conglomerate layer is prone to jump drilling, boring and wall collapse.

(4) When the local layer is soft and hard, it is prone to well deviation, and the dip angle of the formation is also prone to well deviation.

(5) When the rock layer contains soluble salts, that is, drilled into the gypsum layer and salt rock layer, attention should be paid to the performance of the drilling fluid.

Second, geological logging work in drilling

1. Logging while drilling

Concept: It is a process of reflecting and recording the time when a specified unit is measured by a timer, which is generally expressed by “minutes/meter”.

(1) Well depth calculation

Well depth = total length of drill + square entry

Total length of drill = length of drill bit + length of joint + length of drill collar + length of drill pipe

(2) Calculation of square entry

In the end, the square entry = well depth - the total length of the drill

The whole rice square = the difference between the depth of the new drill pipe and the depth of the whole well before the previous single root

(3) Recording method

That is, the drilling time, the single root, the stop drilling, the pump stop, the variable pump and the like are recorded in detail on the drilling time record table. Changes in drilling can reflect the hardness or looseness of the formation. The lithology and the stratigraphic contrast can be roughly judged according to the size of the drill. According to the drilling time record, the drilling time curve is drawn, and the relevant geological data is used to comprehensively analyze the formation, lithology and oil and gas.

2, cuttings logging

Concept: During the deepening of the well depth, according to a certain sampling interval and late arrival time, the cuttings are continuously collected for observation, analysis, and various logging data are used to carry out the cutting of the cuttings to restore the underground original profile. process.

3, core logging

Concept: Using the coring tool, the rock in a certain depth of the well is taken in a column form, and the process of obtaining various data is carried out by analyzing and researching it.

4, fluorescent logging concept: oil in oil, asphalt, etc. under the illumination of ultraviolet light, can emit a special kind of light, that is, fluorescence. According to the difference in brightness and color of the fluorescence display, the content and composition of the oil are determined, and the qualitative and quantitative interpretation of the oil and gas layer is the fluorescence logging.

Fluorescence logging method

(1) Dry cuttings.

(2) Drop analysis.

5, gas logging

Concept: The process of determining the oil and gas layer by directly measuring the gas content in the drilling fluid by gas measuring instrument is called gas logging.

Third, geophysical logging

1. Electrical logging

It is a method to study the lithology, oil storage properties and oil-bearing properties of the rock formation by studying the electrical properties of the underground rock formation and the fluids contained therein.

2, sonic logging

It is a logging method that uses the acoustic properties of media such as rock to study the drilling geological section and judge the cementing quality. It is further divided into sonic time difference logging and sonic amplitude logging.

3. Radioactive logging

It is based on the nuclear physical properties of rocks and well media to study drilling profiles, to find useful mineral deposits and to study geophysical logging methods for well quality. It can be divided into methods of detecting gamma rays and detecting neutrons.

4. Other logging methods

(1) Well temperature logging

(2) Formation dip logging

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