(6) Potassium-Based Polymer Drilling Fluids
Potassium-based polymer drilling fluid is a type of anti-collapse drilling fluid that uses potassium (or ammonium, calcium) salts of various polymers and KCl as the main treatment agents. Among various common inorganic salts, KCl has the best effect in inhibiting the hydration and dispersion of clay; and the presence of polymer treatment agents makes this type of drilling fluid possess various excellent properties of polymer drilling fluids. Therefore, when drilling into mud shale formations, it can achieve a more ideal anti-collapse effect.
(7) Oil-Based Drilling Fluids
Drilling fluids that use oil (usually diesel or mineral oil) as the continuous phase are called oil-based drilling fluids. At present, ordinary oil-based drilling fluids with a water content below 5% are rarely used, and water-in-oil emulsion drilling fluids with an oil-water ratio in the range of (50-80): (50-20) are mainly used. Compared with water-based drilling fluids, the main characteristics of oil-based drilling fluids are that they can resist high temperatures, have strong inhibitory properties and the ability to resist salt and calcium pollution, have good lubricity, and can effectively reduce damage to oil and gas layers, etc. . Therefore, the use of this type of drilling fluid has become one of the important means for drilling deep wells, ultra-deep wells, extended reach wells, horizontal wells and various complex formations. But on the other hand, its application is subject to certain restrictions due to its high preparation cost and the fact that it will cause certain pollution to the environment when used.
(8) Synthetic Drilling Fluids
Synthetic-based drilling fluid is a new type of drilling fluid that uses synthetic organic compounds as the continuous phase, brine as the dispersed phase, and contains emulsifiers, fluid loss agents, and flow pattern improvers. Since the diesel oil commonly used in oil-based drilling fluids is replaced by non-toxic and biodegradable non-water-soluble organic matter, this type of drilling fluid not only maintains the various good properties of oil-based drilling fluids, but also greatly reduces the weight of drilling fluids. Adverse effects on the environment when discharged, especially for offshore drilling.
(9) Gas-typed Drilling Fluids
Gas-type drilling fluid is mainly suitable for drilling low-pressure oil and gas layers, formations prone to leakage, and certain heavy oil layers. It is characterized by low density and fast drilling speed, which can effectively protect oil and gas layers and effectively prevent the occurrence of complex situations such as well leakage. Gas drilling fluids are usually divided into the following four types:
1. Air/Natural Gas Drilling Fluids
That is, dry air or natural gas is used as the circulating fluid in drilling. The key to the technology is that the injection pressure must be large enough to ensure that the annular flow rate can be achieved to carry all the drilling cuttings from the bottom of the well to the surface.
2. Mist Gas Drilling Fluids
That is, a mist-like fluid formed by a small amount of liquid dispersed in the air medium. It is a transitional form between air drilling fluid and foam drilling fluid.
3. Foam Drilling Fluids
The foam used in drilling is a dispersion system formed by dispersing a gas medium (usually air) in a liquid and adding an appropriate amount of foaming agent and stabilizer.
4. Aerated Drilling Fluids
Sometimes in order to reduce the density of drilling fluid, gas (usually air) is evenly dispersed in the drilling fluid to form aerated drilling fluid. Obviously, the more gas mixed in, the lower the density of the drilling fluid.
(10) Drill-in Fluids Drilling Fluids for Formation Damage
Control)
This refers to a type of drilling fluid used when drilling into reservoirs. When a well reaches its target layer, the designed drilling fluid should not only meet the requirements of drilling engineering and geology, but also meet the needs of protecting the oil and gas layer. For example, the drilling fluid density and rheological parameters should be adjusted to a reasonable range, the filter loss should be as low as possible, the treatment agent selected should be compatible with the oil and gas layer, and a suitable temporary plugging agent should be selected.
