How properly used solids control equipment in different types (Natural mud, chemically-treated mud and saltwater mud) Water-Based Mud (WBM).
Natural Mud (sometimes called “native” mud) is usually unweighted water-base mud which contains mostly drilled solids. Some bentonite and small amounts of chemicals may be used to improve filter cake quality and help prevent hole problems. Natural mud is often the next mud type used after spud mud. Often, natural mud is used to drill the first few thousand feet of hole, where only minor hole problems are expected.
Chemically Treated Mud is waterbase mud which contains chemicals to control physical and chemical properties. Bentonite is usually added to help control viscosity and fluid loss. Barite (weight material) may be added to increase density.
This mud is used where more severe hole problems are expected, in order to prevent these problems.
Lightly Treated Chemical Mud is usually unweighted water-base mud. It is used where minor hole problems are expected, such as sloughing or caving of the walls of the hole.
Highly Treated Chemical Mud is usually weighted, water-base mud that contains larger amounts of chemicals, bentonite, additives, and barite to maintain strict control of viscosity, fluid loss, chemical properties，and density. Chemical muds are often treated with lignosulfonates or lignite and are therefore commonly called “lignosulfonate mud” or “lignite” mud.
These muds are used where moderate to severe hole problems are expected or high down-hole pressures occur. Of all the water-base mud types, these are the most expensive to maintain. As mud density is increased and potential hole problems (such as stuck drill pipe) become more of a risk, the removal of drilled solids by mechanical solids control equipment becomes increasingly important.
Low Solids Muds are water-base mud containing less than ten percent (10%) drilled solids; 1–5% is a normal range. Generally speaking, the lower the solids content in the mud, the faster the bit will drill.
Low solids muds are usually expensive to maintain because the solids, chemical, and fluid loss properties have to be kept very close to prescribed levels. It is absolutely essential that all solids removal equipment operate at maximum effectiveness in order to maintain the desired low level of solids at a reasonable cost.
Polymer Muds are special types of low solids mud which contain synthetic materials, polymers, designed to control viscosity and fluid loss. Polymers are very expensive and often difficult to screen when a high viscosity fluid is used.
Calcium Treated Muds are special water-base muds, usually weighted, which have lime or gypsum added. Calcium Treated Muds are normally used to prevent shale type formations from swelling or sloughing – problems which could lead to stuck pipe or a ruined hole.
Saltwater Muds contain a high concentration of salt. They may be weighted or unweighted.
Sea Water Muds contain sea water as the continuous phase and, usually,
only sea water is used for dilution. They may be weighted or unweighted. These muds are used offshore and in bay areas where fresh water is not readily available.
When sea water mud is being used, only sea water should be used to rinse or wash the shaker screens in solids control equipment.
Saturated Salt Muds (sometimes called brine fluids) contain as much salt as can be dissolved in the water phase. This mud type is often used to drill through salt formations so the fluid will not dissolve the salt formation. If fresh water mud is used, greatly enlarged holes would result, usually leading to hole trouble.
It is important to be aware of the use of salt mud because shale shaker screen blinding can occur when salt dries and cakes on the solids control equipment. Fresh water may be used to clean the screens, but it must be used very carefully because too much fresh water can upset the chemical balance of this mud.