Horizontal directional drilling has been widely used in municipal and communication pipeline crossing. The size of the hole is getting bigger and bigger, the length of the crossing is getting longer and longer, and more and more geological conditions are being drilled. Drilling hole formation rate and hole stability on the quality of mud configuration requirements are getting higher and higher. The adaptability of mud configuration in horizontal drilling is analyzed in detail in this paper.
Mud classification and performance
1.1 classification
China is rich in bentonite mineral resources, including calcium bentonite, sodium bentonite, hydrogen bentonite, aluminum bentonite, sodium calcium bentonite and unclassified bentonite. Bentonite, also known as Bentonite rock, is a clay rock with montmorillonite (also known as microcrystalline kaolinite and jiaolinite) as the main component -- montmorillonite clay rock, which often contains a small amount of illite, kaolinite and zeolite, feldspar and calcite. Montmorillonite is an aqueous aluminosilicate mineral containing a small amount of alkali and alkaline earth metals. Its chemical formula is Nax(H2O)4{(Al2 ~ xMg0.)[Si4O10](OH)2}. Due to the existence of interlayer water and interlayer exchangeable cation in montmorillonite, bentonite can be divided into sodium bentonite (alkaline soil), calcium bentonite (alkaline soil) and natural bleached soil (acidic soil) according to the types, content and crystalline chemical properties of exchangeable cation contained in montmorillonite. The calcium bentonite includes calcium sodium bentonite, calcium magnesium bentonite and so on. The main exchange cation of alkaline soil is Na+(and K+), the basic coefficient is greater than or equal to 1, the main exchange cation of alkaline soil is Ca2+, Na+ or Ca2+, Mg2+, etc., the basic coefficient is less than 1, the main exchange cation of acidic soil is H+(Al3+).
1.2 performance
1) physical properties
Bentonite is generally white, light yellow, because its iron content is different and light gray, light green pink, brown red, black miscellaneous color. Bentonite is either loose as soil or dense and hard.
2) chemical composition
The main chemical components of bentonite are silica (SiO2), alumina (Al2O3) and water (H2O). Iron oxide and magnesium oxide content is sometimes higher, calcium, sodium, potassium and so on often exist in different content in bentonite. The content of Na2O and CaO in bentonite has great influence on the physical and chemical properties and technological properties of bentonite.
3) physical and chemical properties
Bentonite has a strong hygroscopicity, after water absorption expansion, expansion number can reach 30 times. Colloidal suspension can be dispersed in water medium, which has certain viscosity, thixotropy and lubricity. It has plasticity and adhesion with admixtures of water, mud or sand and other fine clastic materials. It has strong cationic exchange capacity. It has a certain adsorption capacity for various gases, liquids and organic substances, with the maximum adsorption capacity up to 5 times its weight. Acid bleaching soil with surface activity can absorb colored substances.
The physical and chemical properties of bentonite mainly depend on the type and content of montmorillonite. The physical and chemical properties and technical properties of sodium bentonite are superior to those of calcium or magnesium bentonite. The main performance is: the water absorption speed is slow, but the water absorption rate and expansion multiple are large; High cation exchange capacity; Good dispersion and high gelatinous value in water medium; Its colloidal suspension thixotropy, viscosity, lubricity, high PH value; Good thermal stability; It has high plasticity and strong adhesion. High thermal and wet tensile strength and dry compression strength. Therefore, the application value and economic value of sodium bentonite are relatively high.
Inspection method of mud
Density scale is the most commonly used instrument for mud density measurement. When measuring, fill the mud cup with mud, and make the excess mud overflow from the center hole of the lid after capping. After drying the surface of the mud-cup, place the lever on the bracket (the main blade is seated on the main blade cushion). Move the game code so that the lever is horizontal (the horizontal bubble is in the center). Read the scale on the left side of the travel code, that is, the mud density value. Calibrate the instrument with clean water before measuring mud density. If the reading is not at 1.0, the metal particles in the small box at the right end of the lever can be added or decreased to adjust.
Mud density is the ratio of the weight of mud to the weight of the specified volume of water. The size of mud density measured in the construction site mainly depends on the sum of the weight of slurry clay and drilling cuttings. When there are admixtures and other substances to add, admixtures and other weight must be accounted for.
Application and influence of mud in different geological conditions
Drilling in sand layer, gravel, pebble and broken zone formation is very difficult because of the lack of cementation between particles and the hole wall is easy to collapse during drilling. For this kind of stratum, the key to solve the problem is to increase the cementing force between the pore wall particles. The cementing force between sand and gravel can be obviously enhanced by proper infiltration of viscous mud into the stratum of pore wall, so as to enhance the stability of pore wall. Improving the viscosity of mud is mainly achieved by using highly dispersive mud (fine dispersive mud), increasing the clay content in mud, adding organic or inorganic viscosifier and other measures. Fine dispersible mud is a dispersible mud with salinity less than 1%, calcium content less than 120ppm and no inhibitory polymer. In addition to clay, Na2CO3 and water, in order to meet the needs of drilling, it is often added with viscosity lifter, water loss reducer and anti-flocculant (diluent). According to the addition of different treatment agents, there may be different types, such as sodium carboxymethyl cellulose mud, iron chromium salt mud, lignin sulfonate mud and humic acid mud. There are many successful projects of drilling in sand and gravel layers with high viscosity fine dispersible mud, including drilling in flowing sand strata.
3.1 influence of mud on drilling speed
With the increase of mud density, the drilling rate decreases, especially when the mud density is greater than 1.06 ~ 1.10 g/cm3. Mud has the same density and the higher the viscosity, the lower the drilling speed.
3.2 influence of sand content in mud on drilling
The content of cuttings in mud will cause great harm to drilling. Make the hole inside the purification is not good and cause drilling resistance card, and may cause suction, pressure exciting, causing leakage or well collapse. The content of sand is high and the precipitation inside the hole is thick. It is easy to cause the mud skin to fall off and cause the accident inside the hole. At the same time, high sediment content, pipe, drill bit, water pump jacket, piston rod wear, short service life. Therefore, on the premise of ensuring the formation pressure balance, mud density and sand content should be reduced as far as possible.
3.3 mud density in soft soil layer
In soft soil layer, mud density is too small or drilling speed is too fast, will lead to hole collapse phenomenon. Mud density is usually better maintained at 1.25g/cm3 in this layer.
4. Common mud formulation examples
There are many types of mud in the project, but according to its chemical composition, it can be classified into the following categories. The ratio method is as follows:
4.1 Na-CMC(sodium carboxymethyl cellulose) mud
The mud is the most common viscosity-lifting mud, and na-cmc plays a role in further viscosity-lifting and water-losing. The formula is: 150 ~ 200g high-quality pulping clay, 1000ml water, 5 ~ 10Kg soda, about 6kg na-cmcs. Mud properties: density 1.07 ~ 1.1g /cm3, viscosity 25 ~ 35s, water loss less than 12ml/30min, pH value about 9.5.
4.2 ferrochrome salt -Na-CMC mud
The mud has strong adhesion and stability. Ferrochrome salt has the function of preventing flocculation (dilution). The formula is: clay 200g, water 1000ml, alkali solution 50% concentration about 20%, ferrochrome salt solution 20% concentration 0.5%, na-cmc 0.1%. Mud properties: density 1.10g /cm3, viscosity 25s, water loss 12ml/30min, pH value 9.
4.3 lignosulfonate mud
Lignin sulfonate is extracted from waste liquor of sulfite paper pulp. It is usually used in combination with coal-alkali agent to prevent flocculation and reduce water loss of slurry on the basis of viscosification. The formula is 100 ~ 200kg clay for 1m3 mud, 30 ~ 40kg sulfite pulp waste liquid, 10 ~ 20kg coal alkali agent, NaOH5 ~ 10kg defoaming agent, 5 ~ 10kg water 900 ~ 1000L. Mud properties: density 1.06 ~ 1.20g /cm3, funnel viscosity 18 ~ 40s, water loss 5 ~ 10ml/30min, in the drilling process to further reduce water loss can be increased by 0.1 ~ 0.3kg na-cmc.
4.4 humic acid mud
Humic acid slurry is made of coal-base agent or sodium humate as stabilizer, which can be used in combination with other treatment agents such as na-cmc. The formulation of humic acid slurry is to add 150-200kg coal-base agent (dry amount), 3-5kgna2co3, 900-1000l water to 1m3 slurry. Mud properties: density 1.03 ~ 1.20g /cm3, water loss 4 ~ 10ml/30min, pH value 9.
5 conclusion
In the process of horizontal drilling construction, proper mud allocation plays a decisive role in crossing. The choice of different densities of mud depends on the specific geological conditions.
