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 underbalanced and overbalanced drilling?

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.

Why are drills underbalanced?

Increased reservoir knowledge

During an underbalanced drilling operation, reservoir productivity and the produced fluids can be measured and analyzed while drilling. This allows a well to be drilled longer or shorter, depending on production requirements.

Why is underbalanced drilling not suitable for directional drilling?

Factors that negatively affect underbalanced drilling

Spontaneous imbibitions because of incompatibility between the base fluid used in the UBD fluid and the rock or reservoir fluid. ... Wells that require hydrostatic fluid or pressure to kill the well during certain drilling or completion operations.

What is the difference between hydrostatic pressure and formation pressure?

Formation pressure is the pressure acting on the fluids (i.e., formation water, oil, and gas) in the pore space of the formation. Normal formation pressures in any geological setting are equal to the Hydrostatic Head (hydrostatic pressure) of water extending from the surface to the subsurface formation.

What is Overbalanced (OBD) & Underbalanced (UBD) Drilling?

What is hydrostatic pressure drilling?

The force per unit area exerted by a static column of fluid. In US oilfield units, it is calculated using the equation: P (psi) =Density*TVD*0.052, where Density is the fluid density in pounds per gallon (ppg), TVD is the true vertical depth in feet (ft.), and 0.052 is a conversion factor.

What is the difference between a kick and a blowout?

A kick is defined as flow of formation fluids or gas into the welbore, a blowout is the uncontrolled release of the fluid or gas, gained through the kick. A blowout can take place at the surface or into another formation( underground blowout).

What is UBD balance?

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 static pressure of the formation being drilled.

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.

What is directional drilling used for?

Directional drilling is the practice of accessing an underground oil or gas reserve by drilling in a non-vertical direction. Directional drilling is also called directional boring. Directional drilling increases the efficiency of oil and gas extraction, and can also lessen the environmental impact of drilling.

How is a horizontal well drilled?

Most horizontal wells are started by drilling a vertical well. After drilling down to the target rock, the pipe is pulled out of the well and a motor is attached to the drill bit. ... In a horizontal well, the bit and pipe are lowered down into the well and the bit drills a path that curves from vertical to horizontal.

What is differential sticking in drilling?

A condition whereby the drillstring cannot be moved (rotated or reciprocated) along the axis of the wellbore. Differential sticking typically occurs when high-contact forces caused by low reservoir pressures, high wellbore pressures, or both, are exerted over a sufficiently large area of the drillstring.

What is managed pressure drilling?

Managed Pressure Drilling (MPD) is an adaptive drilling process used to precisely control the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly.

What is kelly bushing?

Kelly bushing is that elevated device positioned right on top of the rotary table and used to transmit torque from the rotary table to the kelly. The kelly bushing is designed to be the connection between the rotary table and the kelly. The kelly is a 4 or 6 sided steel pipe.

What are the methods used for well test analysis?

The chapter explains six interpretation methods for well tests: (1) wellbore storage and skin effect, (2) outer boundaries and discontinuities, (3) well-test interpretation, (4) pressure-derivative analysis, (5) interpretation using simultaneously measured pressure and sand-face flow rate, and (6) wellbore storage ...

What is drilling fluid made of?

Drilling muds are traditionally based on water, either fresh water, seawater, naturally occurring brines, or prepared brines. Many muds are oil-based, using direct products of petroleum refining such as diesel oil or mineral oil as the fluid matrix.

What is a UBD lesson plan?

Understanding By Design, or UBD, is a framework and accompanying design process for thinking decisively about unit lesson planning. ... It is not designed to tell teachers what or how to teach; it is a system to help them teach more effectively. In fact, its flexibility is one reason it has gained so much acclaim.

What does UDL stand for?

Universal Design for Learning (UDL) is an approach to teaching and learning that gives all students equal opportunity to succeed.

What are the types of well control equipment?

[1] Understanding of pressure and pressure relationships are very important in well control. Other types of BOP, Pipe Ram, Blind or Shear Ram, Annular Ram, Diverters.

Why do blowouts happen?

Blowouts occur when pressurized gas, oil, and other materials shoot up through the main drilling pipe and cause a violent explosion. Blowouts are usually handled by the rig's blowout preventer, but these components have failed in the past.

How can you tell if a drill is a kick?

1. Flow rate increase.
2. Pit volume increase.
3. Flowing well with pumps off.
4. Pump pressure decrease and pump stroke increase.
5. Improper hole fill-up on trips.
6. String weight change.
7. Drilling break.
8. Cut mud weight.

How does hydrostatic pressure work?

Hydrostatic pressure is the pressure that is exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. ... The more dense the fluid above it, the more pressure is exerted on the object that is submerged, due to the weight of the fluid.

How do you calculate hydrostatic pressure?

The pressure in a liquid at a given depth is called the hydrostatic pressure. This can be calculated using the hydrostatic equation: P = rho * g * d, where P is the pressure, rho is the density of the liquid, g is gravity (9.8 m/s^2) and d is the depth (or height) of the liquid.