What Are Drilling Fluids?

Drilling fluid is a general term for various circulating fluids that meet the needs of drilling work with its multiple functions during the drilling process. Drilling fluid is the blood of drilling, also known as drilling flushing fluid. Drilling fluid can be divided into clean water, mud, non-clay phase washing fluid, emulsion, foam and compressed air according to its composition. Qingshui is the earliest drilling fluid to be used without treatment. It is easy to use and suitable for complete rock formations and areas with sufficient water sources. Mud is a widely used drilling fluid, which is mainly suitable for unstable rock formations such as loose walls, fissure development, easy collapse blocks, and expansion and spalling when exposed to water.

Initial formation period: From 1888 to 1928, rotary drilling was started. Initially drilling with clear water.

Period of rapid development: From 1928 to 1948, it was found that mud carrying sand has a higher carrying capacity than water.

better. As a result, finely divided drilling fluids appear and simple treatment agents are used.

High-speed development period: From 1948 to 1965, the deficiency of finely dispersed mud was found: poor anti-aggression ability,

So it developed into a calcium-treated, moderately flocculated, coarsely dispersed drilling fluid.

Period of scientific optimization: From 1965 to now, low-pressure solid phase is required in high-pressure jet drilling.

The polymer does not disperse low solid phase drilling fluids.

From the end of the 1980s to the beginning of the 1990s to the present, drilling fluid systems such as electropositive gel, silicate, formate, polyhydric alcohol, and biodegradable have appeared and have been widely used. But they have not formed the mainstream and cannot completely replace the polymer drilling fluid system.

At the same time, the oil-based drilling fluids that have been used since the 40s of the last century are also constantly developing, from the development of crude oil to diesel to mineral oil; from full oil-based to water-in-oil emulsified drilling fluids; from toxic pollution Oil-based development into a low-toxic, non-toxic oil-based drilling fluid. ^[1-2]

In the early days of rotary drilling, the main function of drilling fluid was to carry cuttings from the bottom of the well to the surface. At present, drilling fluids are recognized to have at least the following ten functions:

(1) Clean the bottom of the well and carry cuttings. Keep the bottom of the well clean, avoid repeated cutting of the drill bit, reduce wear and improve efficiency.

(2) Cooling and lubricating drill bits and drill strings. Reduce drill bit temperature, reduce drill wear and increase drill life.

(3) Balance the rock side pressure of the well wall to form a filter cake on the well wall to close and stabilize the well wall. Prevent pollution to oil and gas layers and collapse of borehole walls.

(4) Balance (control) formation pressure. Prevent blowouts,

Up mud pump high-pressure pipe square drill pipe drill pipe drill bit water jet at high speed

Water

Pond Various solid control equipment Mud pond Annular space Cleaning the bottom of the well to carry rock cuttings

Drilling fluids can be divided into water-based drilling fluids, oil-based drilling fluids, and gas-based drilling fluids based on the dispersion medium (continuous phase).

Drilling fluid is mainly composed of liquid phase, solid phase and chemical treatment agent. The liquid phase can be water (fresh water, brine), oil (crude oil, diesel) or emulsion (oil-mixed emulsion and inverse emulsion). The solid phase includes the useful solid phase (bentonite, weighting material) and the unwanted solid phase (rock). Chemical treatment agents include inorganic, organic and

Drilling fluid is the "blood" of drilling and plays a very important role in drilling operations. Therefore, the drilling fluid is very demanding. There are four main aspects:

Requirements for drilling cycles

The drilling fluid requires drilling fluid with low pump pressure (low viscosity), strong sand carrying capacity (high dynamic shear force), low starting pump pressure (low static shear force), good lubrication performance, low friction, and low wear (less solid particles ).

To keep the wellbore stable

For drilling through the formation, the pressure column of the drilling fluid and the formation pressure must be used to balance the drilling fluid density, and the drilling fluid density must be stable. When drilling the oil and gas layer, the pressure column of the drilling fluid must be used to balance the oil and gas pressure. The drilling fluid is required to have the ability to overcome unstable formations, such as the shrinkage of boreholes caused by mudstone water swelling;

The harsh environment of underground drilling operations has promoted the research and development of drilling fluids, which requires the following key tasks to be completed during drilling: suspension, pressure control, rock formation stability, buoyancy, lubrication and cooling.

According to the API (America Petroleum Instistite) recommended drilling fluid performance test standards, the conventional drilling fluid properties that need to be tested are:

Density, funnel viscosity, plastic viscosity, dynamic shear force, static shear force, API filtration loss, HTHP filtration loss, pH value, sand content, solid content, bentonite content, and various ion concentrations of the filtrate. ^[4]

1. Drilling tool corrosion and anticorrosion (corrosion mechanism research, detection and prevention measures)

Environmental pollution and disposal of waste drilling fluid

1. Environmental impact of abandoned drilling fluids (on soil, plants, underground drinking water, marine life, etc.)

2. Treatment methods (backfilling method, land cultivation method, pumping into the borehole annular space, solid-liquid separation method, chemical solidification method, other methods)

3. Anti-pollution new drilling fluid (glycerin drilling fluid, methyl glucoside drilling fluid, polyacrylamide drilling fluid)

Research on new drilling fluid system Synthetic base drilling fluid, polymerized drilling fluid, silicate drilling fluid, formate drilling fluid

4. Classification of unstable borehole formations and drilling fluid technology for stable boreholes

V. New progress in protecting oil and gas layers ^[2]