1. n. [Drilling] The amount of pressure (or force per unit area) in the wellbore that exceeds the pressure of fluids in the formation. This excess pressure is needed to prevent reservoir fluids (oil, gas, water) from entering the wellbore.
What is the difference between over balance and under balance?
If hydrostatic pressure in a well is higher than the reservoir pressure, the difference is called overbalance pressure, or simply overbalance. Conversely, if reservoir pressure is more than hydrostatic pressure, the difference is called underbalance.
What is the difference between hydrostatic pressure and formation pressure?
Normal. Normal pore pressure or formation pressure is equal to the hydrostatic pressure of formation fluid extending from the surface to the surface formation being considered. Its magnitude varies with the concentration of dissolved salts, type of fluid, gases present and temperature gradient.
What is under balance?
1. n. [Drilling] The amount of pressure (or force per unit area) exerted on a formation exposed in a wellbore below the internal fluid pressure of that formation. If sufficient porosity and permeability exist, formation fluids enter the wellbore.
Why underbalanced drilling is not suitable for directional drilling?
Directional drilling equipment can have limitations on UBD. Hydraulic operated tools cannot be used in underbalanced wells, and if a gasified system is used, the measurement while drilling (MWD) pulse systems may not work.
What is drilling mud density?
1. n. [Drilling Fluids] The mass per unit volume of a drilling fluid, synonymous with mud weight. Weight is reported in. lbm/galUS (also known as ppg)
What is the difference between ECD and EMW?
Equivalent Circulating Density: Definition: ECD is defined as the EMW (hydrostatic) value plus friction pressure. Unlike EMW, ECD calculations can be applied to a single fluid such as drilling mud being pumped through a wellbore.
What is hydrostatic pressure drilling?
The pressure at any point in a column of fluid caused by the weight of fluid above that point. Controlling the hydrostatic pressure of a mud column is a critical part of mud engineering. Mud weight must be monitored and adjusted to always stay within the limits imposed by the drilling situation.
Why is drilling underbalanced?
Flow from any porous and permeable zones is likely to result when drilling underbalanced. This helps to improve productivity of the well and reduce related drilling problems. UBD produces an influx of formation fluids that must be controlled to avoid well-control problems.
What is the difference between oil based mud and water-based mud?
Oil-Based muds can be formulated to withstand high temperatures over long periods of time, however, Water-Based mud can break down and lead to loss of viscosity and fluid loss control. The initial cost of Oil-Based mud is high, especially those formulations based on mineral or synthetic fluids.
What is underbalanced drilling and how does it work?
Underbalanced drilling, or UBD, is a procedure used to drill oil and gas wells where the pressure in the wellbore is kept lower than the fluid pressure in the formation being drilled.
What are the problems associated with overbalanced drilling?
However, there are numerous problems that accompany overbalanced drilling. Such problems are differential pipe sticking, loss of circulation, formation damage and other problems. A relatively new technique was introduced, known as underbalanced drilling, where the well is being drilled with a hydrostatic pressure less than that of the formation.
What is the difference between UBD and overbalanced operations?
In UBD, the fluids from the well are returned to a closed system at surface to control the well. With the well flowing, the blowout preventer (BOP) system is kept closed while drilling, whereas, in conventional overbalanced operations, drilling fluids are returned to an open system with the BOPs open to atmosphere ( Fig. 2 ).
What is the difference between UBD and conventional drilling?
In conventional drilling, pressure control is the main well control principle, while in UBD, flow control is the main well-control principle. In UBD, the fluids from the well are returned to a closed system at surface to control the well.
