Drilling Mud Decanter Centrifuge

Functions of Drilling Fluids

A drilling fluid, or mud, is any fluid that is used in a drilling operation in which that fluid is circulated or pumped from the surface, down the drill string, through the bit, and back to the surface via the annulus.

Drilling fluids satisfy many needs in their capacity to do the following:

①     Suspend cuttings (drilled solids), remove them from the bottom of the hole and the well bore, and release them at the surface

②     Control formation pressure and maintain well-bore stability

③     Seal permeable formations

④     Cool, lubricate, and support the drilling assembly

⑤     Transmit hydraulic energy to tools and bit

⑥     Minimize reservoir damage

⑦     Permit adequate formation evaluation & Control corrosion

⑧     Facilitate cementing and completion

⑨     Minimize impact on the environment

⑩     Inhibit gas hydrate formation

The most critical function that a drilling fluid performs is to minimize the concentration of cuttings around the drill bit and throughout the well bore. Of course, in so doing, the fluid itself assumes this cuttings burden, and if the cuttings are not removed from the fluid, it very quickly loses its ability to clean the hole and creates thick filter cakes. To enable on-site recycling and reuse of the drilling fluid, cuttings must be continually and efficiently removed.

Types of Drilling Fluids

Drilling fluids are classified according to the type of base fluid and other primary ingredients:

①   Gaseous: Air, nitrogen

②   Aqueous: Gasified—foam, energized (including aphrons) Clay, polymer, emulsion

③   Nonaqueous: Oil or synthetic—all oil, invert emulsion

Figure1: Types of Water-Based Muds

True foams contain at least 70% gas (usually N2, CO2, or air) at the surface of the hole, while energized fluids, including aphrons, contain lesser amounts of gas. Aphrons are specially stabilized bubbles that function as a bridging or lost circulation material (LCM) to reduce mud losses to permeable and microfractured formations. Aqueous drilling fluids are generally dubbed water-based muds (WBMs), while nonaqueous drilling fluids (NAFs) are often referred to as oil-based muds (OBMs) or synthetic-based muds (SBMs). OBMs are based on NAFs that are distilled from crude oil; they include diesel, mineral oils, and refined linear paraffins (LPs). SBMs, which are also known as pseudo– oil-based muds, are based on chemical reaction products of common feedstock materials like ethylene; they include olefins, esters, and synthetic LPs.

Detailed classification schemes for liquid drilling fluids are employed that describe the composition of the fluids more precisely. One such classification scheme is shown in Figures 1 and 2.

Figure 2: Types of Invert-Emulsion Muds



Related posts:

1. Drilling Waste Management System

written by GN Decanter Centrifuge