Drilling fluids, or mud, are used to drill oil and gas wells, and other types of wells. These fluids are utilized to cool the bit, carry cuttings from the bottom of the hole, and to control the formation pressure encountered when drilling a well. Different types of drilling fluids are used depending on the specific loads encountered and what type of formation is being drilled.
Drilling fluids primary purpose is to lubricate the drill bit, allowing it to cut through the formation being drilled. It also carries cuttings from the wellbore back to the surface and reduces friction in the drill string. In addition, drilling fluid suspends the cuttings while they are being lifted to the surface by the returning drilling fluid.
In addition to these primary functions, drilling fluid also serves to:
Keep the face of the formation wet and act as a barrier between the wellbore and the formation.
Provide a weight on the bit in order to keep the drill string on bottom.
Create a hydrostatic pressure in order to control the wellbore pressures and to keep undesirable formation fluids from entering the wellbore.
Inhibit corrosion of metal components.
Stabilize open hole sections.
There are three basic components to a drilling fluid system: fluid, a solid or liquid additive, and a control system. The fluid can be either an oil or water-based fluid, with oil-based fluids being the most prevalent in today’s industry.
The additives are used to modify the characteristics of the drilling fluid. They are typically selected based on the formation being drilled, the operating environment and other conditions. Common types of additives include weighting materials, emulsifiers, corrosion inhibitors, and dispersants.
The control system includes all the components and methods used to monitor and control the drilling fluid parameters and properties. Components of the control system include the vessels, pumps, and gauges used to control and monitor the drilling fluid parameters.
The selection of a drilling fluid system is based on a number of factors, including the formation being drilled, well depth, and the rock type encountered. The most important factor is safety. Safety is determined mainly by the fluid’s ability to control the wellbore pressure, since pressure is the primary hazard when drilling.
A successful drilling fluid program will help ensure that production and operations are uninterrupted by unforeseen pressure conditions, and that resources and time are not wasted due to poor well control. To ensure the desired drilling fluid performance, selection and operation of the proper equipment is essential, careful monitoring of drilling fluid parameters is imperative, and timely adjustment of the drilling fluid system is required.
