Directional Drilling Fluids
During and following a directional drilling operation, drilling fluids play a critical role in ensuring that the hole remains stable. Water, bentonite, soda ash, and chemical additives are common ingredients in drilling fluids. The geological conditions and the qualities of the water and other fluids used in the boring process must be considered when selecting the drilling fluid.
The geological features of the area determine the drilling fluid. To stabilize the bore and remove cuttings, drill fluid is utilized in coarse-grained soils like sand and gravel. As in sandy soils, drilling fluid serves the same purpose in clay, but it must also keep the soil from expanding. In addition to bentonite, the drilling fluid must now contain additional chemical additives.
Drilling mud is typically made by combining water and bentonite in a 1:1 ratio for sandy soils. Due to their reactivity to water, clayey soils are more of a worry than other types of soils. Approaching the clay problem in two ways is an option. The clay can be prevented from reacting with water, or the clay's qualities can be altered to decrease the water's effect on the finished product.
Coarse or sandy soils necessitate water management and material sloughing prevention. Using a water/filtrate control additive like poly-anionic-cellulose can achieve this goal. [*] (PACs). PAC binds to bentonite to seal the wall cake and reduce water leakage. It is frequently more cost-effective to remediate the clay than completely seal off the water and soil. For example, the clay can be coated to prevent it from adhering to a steel drill, or it can be flocculated so that the clay can be drained from the borehole quickly.
Here is the overview of the various additives employed to remediate the clay.
- Surfactants (drilling detergents)
- Include using a drill bit to cut the clay and then applying a coating on the cut surfaces.
- Hydrolyzed poly acrylamide-partially (PHPA).
- Preclude the formation of clay lumps (also known as inhibition).
- It's safe to use with drilling detergents, as well.
- Create a flowable slurry of clay particles.
- Find a solution to the difficulty of not reattaching the clay to the borehole's sides when removed.
- Distributors or deflocculates, as the case may be.
- Reduce viscosity by neutralizing clay particle charges.
Numerous providers carry these familiar ingredients. Using bentonite in conjunction with these additions is recommended to improve borehole structure. The "gel strength" of additives, i.e. the ability to maintain particle suspension, is nonexistent. To flush out the borehole, cuttings need to be suspended. Just 10-15 pounds of bentonite per 100 gallons of water is required for rest. Drilling mud requirements are typically 4–5 times as large as the volume of soil to be cut for each hole.
Drilling mud is essential for removing cuttings, lubricating the bore, permitting flow, and cooling down the drill. As a result, careful consideration must be paid to the selection process. Since most of the drilling fluid is composed of water, its qualities will have a significant impact on the drilling fluid's performance. The water's pH is a crucial property to keep in mind. Using simple pH strips, one may perform this task. The amount of soda ash (sodium carbonate) required to raise the pH is determined by the water's pH. A pH of between 8.5 and 9.5 is the most common target.
How much weight each gallon holds in terms of density. The sand concentration should be less than 1%. The stability of a borehole can be determined by the fluid and the cake surrounding the hole's walls being filtered. The water phase that passes through the filter cake is the filtrate. In most cases, the maximum permitted volume is 10-14 cubic centimeters of filtrate. About a sixteenth of an inch is considered a reasonable thickness for a filter cake.
For solids to be suspended appropriately, mud must have a specific viscosity. Figure 11 shows a Marsh Funnel with a graded container and a timer for measuring thickness. To use a Marsh Funnel, these are the steps:
- Using a finger, block the smaller outlet of the funnel.
- If necessary, repeat Step 2 until all drilling fluid has been poured through the screen and down to the mark.
- Remove the finger from the outlet and time how long it takes to fill the graduated container to the 1-quart line marked on the side of the container.
|Soil Type||Marsh Funnel Viscosity|
|Water (with no swelling clay)|
|Natural Swelling Clay||32 - 37 seconds|
|Normal Conditions (with fine sand and non-swelling clay)||40 - 45 seconds|
|Medium Sand||45 - 55 seconds|
|Coarse Sand||55 - 65 seconds|
|Gravel||65 - 75 seconds|
|Coarse Gravel||75 - 85 seconds|
The recommended viscosity is affected by several variables, including the soil conditions. It is possible that there could be a scarcity of fluid or that the wrong type will be used if fluid properties are not carefully considered. Back-ups and spills of drilling fluid to the surface could occur if the discharge is reduced.