Drilling mud or chemicals are widely used in geo- technical engineering to aid the boreholes into the earth. These chemicals are used in drilling process of oil and natural gas as an additive with bentonite and other chemicals. Drilling mud chemicals are mainly used to create hydrostatic pressure and avoid the formation of fluids from entering into the well bore. This pressure keep the drill bit cool and to limit the corrosion. Because of the mud chemical additives and weighting materials, the drilling chemicals always increased and the fraction of total solid in drilling mud is the solid content. When it comes to solid content of drilling mud system, it includes both soluble and insoluble content.
Three major types of solid content found in drilling mud are salt as soluble material and HGS (high gravity solid) as insoluble weighting agents such as barite, hematite and calcium carbonate etc. and LGS (low gravity solid) as insoluble particles from cuttings. Drill solids gradually deteriorate the mud properties and that's why considered as a worst content in the drilling fluid. Furthermore, it can be removed by mechanical method if the particle size is less than 5 microns, however normally it takes 7 percent of the total volume of mud. Therefore the solid content in drilling mud is very essential and should be checked on regular basis.
In order to make drilling practices good, it should be tested twice a day by reporting. The approximate limit of the drill solid fraction is around 55- 60 pound per barrels and upper limit should be around 6 to 7% of the volume. This value is according to the general thumb rule, not the exact value. However, you can operate drilling operation practically with more solid content but remember the overall performance will be constantly down. Apart from the HGS and LGS, the average density of solid is another value that you must consider in the drilling mud system.
Calcium carbonate, barite and other weighting materials have specific gravity value around 4.2 whereas the solid drill such as clay and slit have less gravity value around 2.6. The relative concentration of both the weighting agent and drilled solid is the average density of it. Generally about 3.8 or above is the acceptable value of the average solid density. In case you are using less than 3.8 then it shows that there may be too much low gravity solid in the mud system.
These solid contents have different operational impacts such as penetration rate, swab pressure, ECD (Equivalent Circulating Density) and differential sticking. If solid content has high concentration then it will affect the overall penetration rate. So in order to manage rate of penetration, you need to control the drilled solid amount in the mud system.
