Understanding Solid Content in Drilling Mud

Drilling fluids play a prominent role in the extraction of oil and gas. To ensure efficiency and prevent damage to equipment and the production zone, specific properties of the drilling fluids should be kept in check. These properties include solid concentration and particle size.

What is solid content?

Soluble and insoluble solids in the drilling fluid system are referred to as solid content. They include chemical additives, weighting agents and drilling cuttings. The concentration of these solids increases while drilling. There are three types of solid content:

• Soluble solids—These are mainly salts that are added to the drilling mud to stabilize the well and stimulate the formation of the filter cake.
• Insoluble high-gravity solids (HGS)—These include weighting agents such as calcium carbonate and barite that are added to adjust the density of the mud.
• Insoluble low-gravity solids (LGS)—These are also known as drilled solids. Rock cuttings are examples of drilled solids.

Impacts of solids in drilling mud on operations

• Rate of penetration—The rate of penetration will reduce if there is a high concentration of solids in the drilling muds. It will be ill-advised to reduce the level of chemical additives and weighting agents because they maintain mud properties. However, drilling solids should be continuously removed from the mud.
• Equivalent circulating density (ECD)—This is the effective density exerted by the circulating mud against the formation. It takes into account the mud density and the annular pressure loss. Solids increase the equivalent circulation density. Excessive ECD leads to lost circulation and fracture of the formation.
• Surge/swab pressure—High concentration of solids in the mud can lead to excessive surge/swab pressure. In turn, excessive surge/swab pressure leads to lost circulation, partial mud loss and formation fracture.
• Differential sticking—High concentration of low gravity solids in the mud will make the filter cake thick and sticky. Such filter cakes will differentially stick across permeable formations.

Controlling drilling solids in drilling fluids

Insoluble low-gravity solids pose the greatest danger to the drilling fluid; they slowly depreciate the mud properties. Furthermore, removal of some drilling solids from the mud is difficult. For example, if the solid particles are less than five microns in size, they cannot be isolated from the mud by mechanical means.

Typically, the optimum density for drilling fluids is 3.8 or higher. The presence of excess low-gravity solids in the mud can make the density drop below 3.8.

Due to the great danger posed by drilled solids, it is a good practice to test the level of drilled solids in the mud at least twice daily. The concentration of drilled solids in the mud should not exceed 6-7 percent.

Aerion can help you control the properties of drilling mud

Our specialists analyze the properties of your drilling fluids and adjust them to the optimum levels. We do this through particle size and distribution analysis, and by regulating the concentration of solids in drilling muds. For more information on working with Aerion and the services we offer, please contact us here.