Monthly Archives: April 2020

Function of the Drilling Mud

4. Cooling and lubrication
When drilling, the drill bit has been rotating and breaking rock strata at high temperature, producing a lot of heat; the drilling tool also continuously friction with the shaft wall to produce heat. Through the circulation of drilling fluid, the heat is taken away in time, which can play the role of cooling bit, drilling tool and prolonging its service life. Because of the existence of drilling fluid, the drill bit and drilling tool are rotated in the liquid, so the friction resistance is greatly reduced, which plays a good lubricating role.
5. Transfer of hydrodynamics
The drilling fluid is ejected at a very high flow rate at the drill nozzle, and the high speed jet produced a strong impact on the bottom of the well, thus improving the drilling speed and rock breaking efficiency. High pressure jet drilling is to use this principle, significantly improve the mechanical drilling speed. When drilling with turbine drilling tools, the drilling fluid flows through the turbine blade at a higher flow rate from the drill pipe, making the turbine rotate and driving the bit to break the rock.
6. Access to underground information
Through the change of rock debris and drilling fluid performance to obtain all kinds of underground information for drilling construction to provide the basis for the formulation of technical measures.
In addition, in order to prevent and minimize damage to oil and gas reservoirs, modern drilling technology also requires that drilling fluid must be compatible with the oil and gas reservoirs encountered by drilling to meet the requirements of protecting Shantou gas reservoirs; in order to meet geological requirements, the drilling fluid used must be conducive to formation testing without affecting formation evaluation; drilling fluid should also be free from injury and pollution to drilling personnel and the environment, small corrosion to downhole tools and surface equipment or minimize corrosion.
Generally, the drilling fluid cost only accounts for 7%~10% of the total drilling cost. However, the advanced drilling fluid technology can often save drilling time twice, thus greatly reducing the drilling cost and bringing considerable economic benefits.

Function of the Drilling Mud(1)

  1. Circulation of drilling fluid
    The circulation of drilling fluid is maintained by drilling pumps (commonly known as mud pumps). High-pressure drilling fluid discharged from the drilling pump passes through the surface high-pressure manifold, riser, hose, faucet, square drill rod, drill pipe, drill collar to the drill bit, ejected from the drill nozzle, then flowing upward along the annular space formed by the drill rod and the shaft wall (or casing), returning to the ground through the discharge line, vibrating screen flow into the mud pool, and then through the treatment of various solid control equipment back to the upper pool, into the recirculation, this is the drilling fluid circulation process and  Circulating system.

II. Function of drilling fluid
1. Carrying and suspended cuttings

The most basic function of drilling fluid is to carry the cuttings of the bottom hole broken by the bit to the ground through circulation, to keep the hole clean, to ensure that the bit always contacts and breaks the new formation at the bottom of the well, not to cause repeated cutting, and to keep safe and fast drilling. The drilling fluid can suspend the drilling debris retained in the well in the annulus, so that the drilling debris will not sink quickly and prevent the sand-sinking drilling.
 2. Solidify wellbore
Well-wall stability and well-hole rules are the basic conditions for safe, high-quality and fast drilling. The drilling fluid with good performance should be able to form a thin and tough mud cake on the shaft wall by means of liquid phase filtration, stabilize the drilled formation, prevent the liquid phase from invading the formation, and reduce the degree of hydration expansion and dispersion of shale.
3. Equilibrium formation pressure and rock lateral pressure
In the process of drilling engineering design and drilling, it is necessary to adjust the drilling fluid density continuously, so that the liquid column pressure can balance the formation pressure and the formation side pressure, so as to prevent the occurrence of downhole complex situations such as blowout and well collapse.

Analysis on Treatment Method of Oil Field Waste Drilling Fluid(3)

Other processing technologies

3.1 Demulsification: demulsification methods are mainly chemical demulsification, membrane demulsification, electric field demulsification, shear demulsification, heating demulsification, centrifugal demulsification, etc. Now more chemical demulsification is used, that is, adding demulsifier to emulsified oily drilling wastewater, through chemical action, supplemented by other separation methods, to achieve the purpose of emulsion de-stability, demulsification and oil-water separation. The chemical demulsification methods adopted at home and abroad mainly include salting-out method, acid-base method, condensation method and mixing method, but although these methods make the treatment effect remarkable, but because of the addition of chemical additives, the cost is increased, and the new impact on the environment is also brought.    

According to the characteristics of waste drilling fluid as water-based and oil-based mixture, an efficient and economical treatment process was adopted. The results show that the treatment technology can effectively separate the three phases of oil, mud and water in the waste drilling fluid, reduce the amount of sludge, improve the content of pollutants in the effluent, and basically meet the national solid waste discharge standard after treatment, which basically solves the problem of disposal and discharge of waste drilling fluid in oil fields.

 3.2 Mechanical Dehydration: This method is to separate the solid-liquid two phases from the waste drilling fluid by means of enhanced measures such as chemical flocculant deposition and mechanical separation. However, because of the different characteristics of drilling fluid produced by each oil field, a single flocculant can not make the drilling fluid of various properties carry out effective solid-liquid separation, and different flocculants should be used for different waste drilling fluids.  

3.3 MTC (Mud To Cement) technology: the conversion of waste drilling fluid into cement slurry technology, referred to as MTC technology, which mixes waste drilling fluid with slag and uses activator to activate the solidified components in slag. With other additives to obtain various uses of cementing fluid. This technique has been studied extensively at home and abroad, and has been widely used. There are many advantages to cementing with it: low turbulent displacement, good compatibility with mud, short thickening transition time and static gel strength transition time.   

With the continuous development of oil fields, drilling waste treatment has higher requirements, China’s drilling waste treatment work can not be compared with developed countries, because of its late start, research and application is still in a relatively basic stage, the control and prevention of drilling waste liquid is still not in place, and there is still a big gap with the world’s advanced level, so we should increase the research on drilling waste liquid treatment and application, and strive to prevent drilling waste liquid as the focus of drilling pollution control.

Analysis on Treatment Method of Oil Field Waste Drilling Fluid (2)

2. Curing Method

Curing method is to add curing agent to waste water-based drilling mud or drilling mud sediment, so that it can be converted into soil-like solid (pseudo soil) landfill in place or used as building material, etc. This method can greatly reduce the erosion of soil by metal ions and organic matter in waste drilling mud, thus reducing the environmental impact and harm of waste drilling mud, and at the same time can ensure that waste drilling mud pool can be ploughed back at the end of drilling process.

 2.1 Cement curing technology: Cement curing is a treatment of cement as curing agent to solidify the waste slurry. Cement is an artificial inorganic cement material, the main components are SiO2、CaO、Al2O3 and Fe2O3.. There are many kinds of cement which can be used as curing treatment, the most common application is ordinary Portland cement. The curing principle is to form calcium silicate hydrate glue through silicate and water, and to form an object containing silicate fiber and hydroxide after solidification, to contain harmful substances, and gradually harden to form cement solidified body.

2.2 Lime curing technology: Lime curing is a method of curing waste slurry containing sulfate or sulfite with lime as main curing agent and active silicate as additive. The principle of lime curing is that in the presence of moisture, lime and silica-aluminate roots in additives react with the above type of waste mud, gradually coagulate, harden, and finally achieve curing.

2.3 Curing technology of fly ash: fly ash is a mixture of pozzolanic materials, mainly composed of potentially active impurities such as SiO2、Al2O3. The curing principle of fly ash is that, in the presence of water, silica and alumina are excited by alkaline substances in the mud to produce hydration hardening, stable hydration products (CSH and CAH,CAH) are generated by excitation, which will accelerate the reaction to form ettringite, further improve the gel composition and hardening quality of drilling waste mud system, and finally reach the curing target.

2.4 Water glass curing technology: Water glass is a soluble alkali metal silicate material made of alkali metal oxide and silica, which is a colorless and transparent viscous liquid. Water glass has hardening, binding, containment and other properties, can be used as cementitious materials. Water glass curing method is to use water glass as the main curing substrate, supplemented by inorganic acid substances (such as sulfuric acid, nitric acid and phosphoric acid), and then mixed with waste mud according to a certain proportion of ingredients, neutralization and condensation dehydration reaction, so that the harmful substances automatically dehydration, after condensation hardening, finally achieve curing.