## Directional Drilling Calculation Example for J-Profile Well

This article demonstrates how to design the well trajectory in J-shape from the surface location to the required target depth (TD).

Information Given

• The surface location coordinate of Well-A is 6,543,065.00N 416,695.00E and the target is located at 6,542,213.00N 415,456.00E and the UTM zone is 31N.
• Kick off depth = 4,200’MD/4,200’TVD
• Planned build up rate = 2 degree/100 ft
• Well profile = J-profile (build and hold)

The surface location coordinate of Well-A is 6,543,065.00N 416,695.00E and the target is located at 6,542,213.00N 415,456.00E and the UTM zone is 31N. Therefore, the surface and the target for Well-A can be illustrated is Figure 1. Continue reading

## Suction Anchor Calculation

Suction anchor or suction caisson is an offshore foundation which is quite popular for offshore installation. It utilizes a negative pressure concept to drive the suction anchors down. This article will demonstrate some simple calculations used for the suction anchor.

Example:

A suction anchor, 40” OD x36” ID, is deployed as part of a mooring anchor for a floating production platform in 900 ft of water. The initial penetration due to its weight is 5 feet into the sea.  Soil resistance is 450 lb/ft2 by average.  Based on the given information, determine values from these two questions below;

• What is the volume evacuated for each foot of penetration?
• How long of a suction anchor will be needed so that the top of the suction anchor is 5 ft above the seabed at the end of the operation?

Figure 2 – Suction Anchor Submerse by Its Weight

Important Information

The sea water density = 64.0 lb/cu-ft (8.6 ppg)

Steel specific gravity = 785

What is the volume evacuated for each foot of penetration?

Assumption: Impermeable formation

Volume (ft3) = 7.07

How long of a suction anchor will be needed so that the top of the suction anchor is 5 ft above the seabed at the end of the operation?

Figure 3 – Suction Anchor Diagram (Before and After)

The initial penetration support weight of the suction anchor therefore is only the frictional force between soil at the seabed and the hydrostatic pressure from the water column will be taken into account.

L = the length of the suction anchor resisting the force from hydrostatic pressure applied at the top of the suction anchor.

This is assumed that the friction generated by initial penetration continues to oppose and equal the buoyed weight of the suction anchor.

Based on the assumption, the force from soil resistance is equal to force from the hydrostatic pressure acting against the top of the suction anchor.

450 × surface area = Hydrostatic pressure × area of top of the suction anchor

L = 56.2 ft

Total length of the suction anchor = 5+ 56.2 + 5 = 66.2 ft

Figure 4 demonstrate the final condition compared to the initial condition.

Final Diagram

References

James G. Speight, 2014. Handbook of Offshore Oil and Gas Operations. 1 Edition. Gulf Professional Publishing.

Trond Bendiksen, 2015. Commissioning of Offshore Oil and Gas Projects: The manager’s handbook. Edition. AuthorHouse.

Joseph A. Pratt, 1997. Offshore Pioneers: Brown & Root and the History of Offshore Oil and Gas. Edition. Gulf Professional Publishing.

SEMAR AS, (2013), Shelley Field [ONLINE]. Available at: http://www.semar.no/semar/bilder/Shelley-field.jpg [Accessed 29 July 2016].

## Formation Temperature Calculation

Formation temperature is one of the most critical parameters in drilling and workover operation and it varies by true vertical depth of wellbore.

The following formula shows relationship between formation temperature and true vertical depth of well.

Formation temperature = (ambient surface temperature ) + (temperature gradient x  Well TVD)

Where:

Formation temperature in F (Fahrenheit)

ambient surface temperature in F (Fahrenheit)

temperature gradient in F/ft (Fahrenheit / ft)

Well TVD in ft

Example: The temperature gradient in a specific area is 0.015 °F/ft of depth and the ambient surface temperature is 90 °F.

Determine the estimated formation temperature at a TVD of 12,000 ft:

Formation Temperature, °F = 90 °F + (0.015 °F/ft x 12,000 ft)

Formation Temperature, °F = 90 °F + 180 °F

Formation Temperature = 270 °F (estimated formation temperature)

Please find the Excel sheet used for estimating formation temperature.

Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.