Drilling mud plays an imperative job when boring an oil well, where it produces adequate hydrostatic weight that could prevent the influx of formation liquids into the well bore, Barium sulphate, which is more commonly known as barite in the petroleum industry, is the principle weighting material used to increase mud weight. With the expected increase in drilling activities and dwindling reserves, quality barite supply may fall short in the foreseeable future. The study involved of laboratory experiments, and amongst the parameters studied were mud weight/density, rheological properties of drilling mud with all the weighting materials, and the abrasiveness effect.
Drilling fluid density or mud weight must be measured at regular intervals of the drilling process because as different formations are encountered during the drilling process, different fluids and substances are released by those formations into the drilling fluids which alter the density of the mud. The most convenient method of determining the mud weight is through the use of the mud balance set of equipment. In using this method, the drilling fluid whose weight needed to be measured was prepared through a number of procedures.
The chemical samples to be used were measured in the right proportion and kept using the weighing balance. The appropriate amount of water to be used was also determined and kept. All the components were then mixed up in one container to form the drilling mud. The cup of the mud weighing balance was then filled with the drilling fluid whose weight or density was determined and the cup was then closed with the lid. The mud weight of the various samples was determined to be 8.6ppg, 8.8ppg and 8.6ppg, and the hydrostatic pressures were 450 psi/1000ft, 455 psi/1000ft and 451 psi/1000ft.
The drilling fluid is commonly a suspension of clay and other materials in water and called drilling mud. The objective of a drilling operation is to drill, evaluate and complete a well that will produce oil and/or gas efficiently. Drilling fluids performs a lot of functions that help make this possible. The most common drilling fluid functions are; Remove cutting from the well, Control formation pressure, Suspend and release cuttings, Seal permeable formation by forming mud cake, maintain well bore stability, minimize reservoir damage, Cool, lubricate and support the bit and drilling assembly.
Drilling liquids can be arranged based on its essential component; Water base mud, Oil base mud, Air mud. The water-base mud consists of a mixture of solids, liquids, chemicals and water (continues phase).
Weighting agents; a material added to a drilling fluid to perform some specific functions, such as a weighting agent, viscosifier or lubricant. The most important weighting additive in drilling fluids is barium sulfate (BaSO4). Barite is a dense mineral comprising barium sulfate. The specific gravity of barite is at least 4.20 g/cm3 to meet API specifications for producing mud densities from 9 to 19 lbm/gal. However, a variety of materials have been used as weighting agents for drilling fluids including siderite (3.08 g/cm3), calcium carbonate (2.7–2.8 g/cm3), hematite (5.05 g/cm3), ilmetite (4.6 g/cm3), and galena (7.5 g/cm3).
The density or weight of a given volume of mud is determined by using a mud balance. The balance is constructed so that the fixed volume cup at one end of the beam is balanced by a fixed counterweight at the opposite end, with a sliding weight rider.
- Laboratory equipments used in carrying out this experiment includes;
- Mud balance;
- Measuring cylinders;
- Electrical Mud mixer;
- Mud mixer cups.
A mud balance, also known as a mud scale is a device used to measure the density (weight) of drilling fluid, cement or any type of liquid or slurry.
It consists of a graduated beam with a bubble level and a weight slider along its length and a cup with a lid on one end. The cup is used to hold the fluid so it can be weighed. A slider-weight can be moved along the beam, and a bubble indicates when the beam is level. Density is read at the point where the slider-weight sits on the beam at level.
Calibration is carried out using a liquid of known density (often fresh water) by adjusting the counter weight. Typical balances are not pressurized, but a pressurized mud balance operates in the same manner.
- Place the mud balance base on a flat level surface;
- Fill the clean, dry cup to the top with the test drilling fluid;
- Put the lid on the cup and set it with a delicate contorting movement. Make sure that some mud is ousted through the opening in the glass as this will guarantee the container is full and furthermore will free any caught air or gas;
- Cover the lid hole with a finger and wash all mud from the outside of the cup and arm. Then thoroughly dry the entire balance;
- Place the balance on the knife edge and move the rider along the outside of the arm until the cup and arm are balanced as indicated by the bubble;
- Read the mud weight at the edge of the rider towards the mud cup.
We need to clean our apparatus before we start the experiment so as to avoid error in our measurement.
If the water used to create the bentonite mixture isn’t clean, there will be an error in the equilibrium of the mud balance.
In this experiment we want to re-calculate the density of the mud, first we weigh 20 grams of the bentonite on the weighing balance and mixed it with 350ml of water, then we stired the mixture with the mixing tool. After mixing the first sample, we add 5 grams of Barite and put in the mixture of the bentonite and water(mud) in the mixture tool, we then create a third sample by adding 50ml of water to the first mixture. We find the density of the samples by the mud balance, from the measurements we know the difference between the densities of the samples.
After measuring it is discovered the density of the second sample (bentonite-barite mixture) to be higher than the bentonite mixture. Adding the weighting material(barite) increases the density of the mud, this procedure is carried out to control the hydrostatic pressure in order to prevent influx of the formation fluids. To avoid the risk of a blowout, the hydrostatic pressure should be greater than formation (reservoir) pressure.
The experiment carried out makes us understand the use in the addition of weighting materials like Barite, as used in the experiment. Adding the weighting material (Barite) increases the density of the mud mixture, in order for us to control the hydrostatic pressure so as to avoid the risk of blowout during drilling operations for the safety of rig equipments and lives of those involved in the drilling process on the field.
- Chilingar, George V.; Paul Vorabutr (1983). Drilling and drilling fluids. Elsevier. pp. 121;
- Henn, Raymond W. (2003). AUA guidelines for backfilling and contact grouting of tunnels and shafts. ASCE Publications. pp. 214–215;
- Schlumberger’s oil field glossary;
- Oil Field Team. Drilling Fluid additives
- Heriot-Watt Institute of Petroleum Engineering (2005). Drilling Engineering