Classification of drilling mud treatment agents

Classification of drilling mud treatment agents

1、 Specific gravity of drilling fluid

1. The specific gravity is inversely proportional to the drilling speed. A high specific gravity means that the solid content in the drilling fluid, namely the content of rock cuttings bentonite, is high, the drilling speed will significantly decrease. For every 1% increase in specific gravity, the drilling rate decreases by 10%.

2. Low gravity drilling fluid can reduce bit wear extend bit life, vice versa.

3. Reducing the specific gravity of drilling fluid can reduce eliminate drilling fluid leakage.

4. Low gravity drilling fluid is beneficial for the deposition of rock debris on the ground.

5. Properly adjusting the specific gravity of drilling fluid can balance formation pressure.

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2、 The Relationship between Rheology Drilling

The rheological properties of drilling fluid refer to the characteristics of its activity internal structural deformation under external forces. It includes drilling fluid apparent viscosity, plastic viscosity, static shear force, dynamic shear force, Thixotropy, activity index, consistency coefficient other parameters.

l. The connection with the speed of rock fragmentation by the drill bit:

The drilling speed increases with the decrease of viscosity, vice versa, due to:

a. The power of the mud pump is constant, the viscosity is reduced, the pump pressure is reduced, the displacement is increased, the hydraulic horsepower of the drill bit is added, which enhances the ability to spray;

b. The turbulent viscosity of the nozzle decreases, the cleaning debris removal effects of the drilling fluid are increased; 

c. Low viscosity drilling fluid is prone to entering micro fractures at the bottom of the well, which can reduce the pressure holding force of rock cuttings the drillability strength of rocks.

2. The connection with suspended rock debris carrying rock debris.

        The high flow velocity during turbulent flow causes severe erosion of the wellbore wall. If the mud pump is too small, it is impossible to achieve turbulent flow conditions. Laminar flow causes the rock debris to flip over face the wellbore. Some form a "pseudo mud cake" on the wellbore, while others slide downwards, causing drilling accidents.

        Therefore, improving the dynamic plastic ratio τ／μ p. By transforming the laminar flow into a flat laminar flow, the annular return velocity of 0.5-0.6m/s can be achieved to meet the powder carrying requirements avoid damage to the wellbore caused by turbulence.

3. The connection with the stimulation of fluid column pressure in the well

Pressure agitation is harmful to drilling, which is proportional to the viscosity, shear force Thixotropy of drilling fluid. Pressure stimulation can easily lead to wellbore leakage collapse. Therefore, when drilling in formations prone to leakage collapse, it is necessary to control the rheological properties of the drilling fluid well. It is advisable to operate too aggressively during tripping pumping. Before starting the pump, the drilling tool should be moved to avoid various complex downhole situations caused by pressure stimulation.

3、 Filtration function

Excessive water loss of drilling fluid ≥ 10mL/30min results in thick loose mud skin, which has the following effects on drilling operations.

1. Make water sensitive mudstone, shale other rock layers absorb water, swell, collapse, shrink;

2. Add tripping resistance;

3. Prone to mud gravel accidents;

4. If the mud skin is too thick, the annular space will decrease, the mud will wrap the drill bit, causing an increase in tripping pressure causing collapse leakage;

5. Hazardous production layer;

6. Affects casing installation;

Inorganic treatment agents: refer to compounds with small molecular weight simple molecular structure, such as bentonite, soda ash, caustic soda, calcium chloride, salt, water glass, sodium dichromate, etc.

Bentonite is divided into three types: calcium based bentonite, sodium based bentonite, modified bentonite.

1. Calcium based bentonite: The pulping rate is 8-12 cubic meters per ton. It is necessary to add sodium carbonate to calcium based bentonite in order to use it.

2. Sodium based bentonite: pulping rate 15-18 cubic meters per ton. 3. Modified bentonite: By participating in data such as soda ash, caustic soda, cellulose, low molecular weight polyacrylamide, the pulping rate of bentonite is improved to achieve the functional goal of sodium based bentonite.

The effect of bentonite:

1. Leakage stoppage: Both loess layer leakage bedrock fissure leakage need to be used for slurry preparation cooperation with leakage stoppage agents for leakage stoppage.

2. Wall protection: Collaborating with wall protection agents to form mud cakes on the wellbore, reducing the water content in the drilling fluid soaking it into the wellbore, achieving the effect of protecting the stability of the wellbore.

3. Carrying sand: Produce a certain amount of high specific severe viscosity bentonite mud regularly inject it into the well, to smoothly carry the falling blocks rock cuttings out of the well, to maintain cleanliness inside the well.

4. Manufacturing Slurry: When the wellbore collapses due to long-term immersion, conventional mud still cannot protect the wellbore, bentonite should be added to improve the specific gravity, shear force, viscosity to achieve the intention of stabilizing the wellbore.

5. When encountering water inrush high-pressure oil gas reservoirs, bentonite needs to be added to the mud to balance the formation pressure.

6. Preparation of completion fluid closing slurry: To ensure smooth logging, the drilling fluid needs to be prepared when drilling is completed; Close off slurry is required in the easily collapsed well section, which requires the addition of bentonite.

Sodium carbonate: also known as soda ash soda, pay attention to moisture prevention.

Effect: Depositing exchanging calcium magnesium ions in bentonite, improving hydration function, promoting bentonite dispersion slurry making, reducing mud loss, improving mud viscosity shear force, improving mud cake quality. The dosage is usually 5% of the bentonite content (100 kilograms of soil plus 5 kilograms of soda ash).

Sodium hydroxide: also called caustic soda, caustic soda caustic soda.

Effect: a. Adjust the pH value of the mud. b. Promote the dispersion pulping of bentonite. c. Accelerate the dissolution of organic processors. The dosage is usually 0.1% to 0.5% of the mud.

Sodium metasilicate: also known as sodium silicate foam alkali, the aqueous solution is alkaline. When it is added to the mud, it can add the viscosity of the mud, promote the mud cementation, prevent leakage, have a certain inhibiting effect on shale hydration swelling. It can react with Ammonium nitrate to produce gel slurry for plugging.

Sodium chloride: also known as table salt. Primary effect:

1. Produce saline mud (with an dosage of 8-10%) to prevent rock salt layer corrosion wellbore expansion.

2. Balance the mineralization degree of formation water, reduce the infiltration of filtrate into the formation, achieve the intention of suppressing the hydration infiltration of muddy rock formations.