Overview of Bentonite Slurry Proportioning Knowledge

1、Classification and performance of mud
1.1 Classification
China's bentonite ore resources are very rich, both calcium-based bentonite, sodium-based bentonite, in addition to hydrogen-based, aluminum-based, sodium-calcium-based and unclassified bentonite. Bentonite (Bentonite), also known as bentonite, etc., is to montmorillonite (also known as microcrystalline kaolinite, gabbro) as the main component of the clay rock - montmorillonite clay rock, often containing a small amount of ilmenite, kaolinite and zeolites, feldspars, calcite, etc.. Montmorillonite is a small amount of alkali and alkaline earth metal hydrous alumino-silicate mineral, and its chemical formula is Nax(H2O)4{(Al2~xMg0.)[Si4O10](OH)2}.
Due to the presence of montmorillonite interlayer water and interlayer exchangeable cations, according to the montmorillonite exchangeable cations contained in the type, content and crystallization chemistry, etc., can be divided into sodium-based bentonite (alkaline soil), calcium-based bentonite (alkaline soil) and natural bleaching soil (acidic soil) three. Calcium-based bentonite including calcium sodium-based, calcium magnesium-based bentonite. The main exchange cation of alkaline soil is Na+ (and K+), the alkaline coefficient is greater than or equal to 1, the main exchange cation of alkaline soil is Ca2+, Na+ or Ca2+, Mg2+, etc., and the alkaline coefficient is less than 1. The main exchange cation of acidic soil is H+ (Al3+).
1.2 Properties
1) Physical properties
Bentonite is generally white, yellowish, because of its iron content is different and light gray, light green pink, brown, black and other colors. Bentonite has some loose as earth, there are also dense and hard.
2) Chemical composition
The main chemical components of bentonite is silica (SiO2), aluminum oxide (Al2O3) and water (H2O). Iron oxide and magnesium oxide content is sometimes higher, calcium, sodium, potassium, etc., often with different content in the bentonite. Bentonite in the Na2O and CaO content of the physical and chemical properties of bentonite and technical performance of the process has a great impact.
3) physical and chemical properties
Bentonite has a strong hygroscopicity, swelling after absorbing water, the number of expansion up to 30 times. In the water medium can be dispersed as a colloidal suspension, this suspension has a certain viscosity, thixotropy and lubricity. It has plasticity and adhesion with water, mud or sand and other fine debris material admixture. It has strong cation exchange ability. A variety of gases, liquids, organic substances have a certain degree of adsorption capacity, the maximum adsorption amount can be up to 5 times its weight, with surface activity of acidic bleaching soil can adsorb colored substances.
The physical and chemical properties of bentonite clay depends mainly on the type and content of montmorillonite it contains. General sodium-based bentonite compared to calcium- or magnesium-based bentonite physical and chemical properties and process technology performance is superior. Mainly in: slow water absorption, but the water absorption rate and expansion times; high cation exchange; good dispersion in water media, high gel price; its colloidal suspension thixotropy, viscosity, lubrication, PH value; good thermal stability; high plasticity and strong adhesion; hot and wet tensile strength and high dry compressive strength. So the use of sodium bentonite and high economic value.
2、The mud test method
Measurement of mud density of the instrument is currently the most used density scale. Measurement, the mud will be filled in the mud cup, cover the excess mud from the cup cover center hole overflow. After drying the surface of the mud cup, place the lever on the stand (the main cutter mouth sits on the main cutter pad). Move the vernier so that the lever is horizontal (the horizontal bubble is in the center). Read the scale on the left side of the traveler code, which is the density value of the mud. Before measuring the mud density, calibrate the instrument with water. If the reading is not at 1.0, it can be adjusted by adding or subtracting metal particles mounted in the locket at the right end of the lever.
The density of slurry is the ratio of the weight of the slurry to the weight of a specified volume of water. The size of the mud density measured on site during construction depends mainly on the sum of the weight of slurry clay and the weight of drill cuttings in the mud. When there are additives and other substances added, the weight of additives and so on must also be counted.
3、Application of mud under different geological conditions and its influence
Drilling in sand, gravel, pebble and broken zone strata, due to the lack of cementation between the particles, the hole wall is easy to collapse when drilling, so it is very difficult to form a hole. The key to solving the problem is to increase the cementation force between the particles of the hole wall by using mud to protect the wall in this kind of stratum. Viscous mud properly penetrated into the hole wall stratum, can significantly enhance the sand, gravel cementation, so that the stability of the hole wall to enhance. Improve the viscosity of mud, mainly through the use of high dispersion mud (fine dispersion mud), increase the clay content in the mud, add organic or inorganic viscosity enhancers and other measures to achieve. Fine dispersed mud is a dispersed mud containing less than 1% salt, less than 120 ppm calcium, and no inhibitory polymer. Its composition in addition to clay, Na2CO3 and water, in order to meet the needs of drilling, often with viscosity promoter, water loss reduction agent and anti-flocculation agent (diluent). According to the different treatment agents added, there are different types, such as sodium carboxymethyl cellulose slurry, iron and chromium salt slurry, lignosulfonate slurry and humic acid slurry. There are many successful projects of drilling in sand and gravel layers with higher viscosity finely dispersed mud, including drilling in fluvial sand formations.
3.1 Influence of mud on drilling speed
With the increase of mud density, the drilling speed decreases, especially when the mud density is more than 1.06~1.10 g/cm3, the drilling speed decreases especially obviously. Mud density is the same, the higher the viscosity, the lower the drilling speed.
3.2 Influence of sand content in mud on drilling
The content of rock debris in the mud will cause great harm to the drilling. Make the hole purification is not good and cause down drilling blocking, and may cause suction, pressure agitation, etc., resulting in leakage or well collapse. High sand content and thick sedimentation in the hole. Causes the hole wall hydration collapse, and easy to cause the mud skin off to cause accidents in the hole. Meanwhile, the high content of mud and sand is abrasive to the pipe, drill bit, pump cylinder sleeve, piston tie rod, and the service life is short. Therefore, under the premise of ensuring the formation pressure balance, mud density and sand content should be reduced as much as possible.
3.3 Density of mud in soft soil layer
In soft soil layer, mud density is too small or drilling speed is too fast, which will lead to hole collapse phenomenon. Usually it is better to keep the mud density up to 1.25g/cm3 in this soil layer.
4、Common mud formula examples
There are many kinds of mud in the project, but according to its chemical composition can be categorized as the following, and its proportioning method is as follows:
4.1 Na-CMC (sodium carboxymethyl cellulose) slurry
The mud is the most common viscous mud, Na-CMC play a further viscous and reduce water loss. The formula is as follows: 150-200g of high quality slurry clay, 1000ml of water, 5-10Kg of soda ash and 6kg of Na-CMC. Slurry performance: density 1.07 ~ 1.1 g/cm3, viscosity 25 ~ 35s, water loss less than 12ml/30min, pH value of about 9.5.
4.2 Iron-chromium salt-Na-CMC slurry
The mud to improve viscosity and stability, iron and chromium salt to prevent flocculation (dilution). The formula is: clay 200g, water 1000ml, soda ash 50% concentration addition of about 20%, iron chromium salt solution concentration of 20% addition of 0.5%, Na-CMC 0.1%. The mud properties were: density 1.10 g/cm3, viscosity 25s, water loss 12ml/30min, pH 9.
4.3 Lignosulfonate slurry
Lignosulfonate is taken from sulfite pulp waste liquid, generally used in conjunction with coal alkali agent, in the viscosity on the basis of solving the anti-flocculation of mud and reduce water loss. The formula is 100-200kg of clay for 1m3 mud, 30-40kg of sulfite pulp waste liquid, 10-20kg of coal alkali agent, 5-10kg of NaOH, 5-10kg of antifoam agent, and 900-1000L of water.The performance of mud is as follows: density of 1.06-1.20 g/cm3, hopper viscosity of 18-40s, and water loss of 5-10ml/30min, and it is used to further reduce water loss during drilling. In the process of drilling, 0.1～0.3kg Na-CMC can be added in order to further reduce the water loss.
4.4 Humic acid mud
Humic acid slurry is made of coal alkali agent or sodium humate as stabilizer, it can be used in conjunction with other treatment agents such as Na-CMC, etc. The formula for the preparation of humic acid slurry is to add 150-200kg coal alkali agent (dry amount), 3-5kg Na2CO3, 900-1000L of water to 1m3 of slurry. Mud performance: density 1.03～1.20 g/cm3, water loss 4～10ml/30min, pH 9.