WELL DESIGN AND CONSTRUCTION NM957 COURSEWORK 1

Queson 1a(i) If there are no problems with hole condion I would recommend the use of water based drilling mud. This would contain readily available seawater as a carrier for a range of possible addives like bentonite and barite which are used extensively, polymers e.g. PAC( Poly Anionic Cellulose), etc. These addives help to enhance cung removal and hole cleaning thereby improving the ROP (rate of penetraon) of the drill bit. This presents an inexpensive opon given the availability of sea water oshore and these do

not have adverse environmental impact.

ii) Drilling reacve shales presents a great challenge with water based mud. It is an easy but comparavely very expensive opon to switch to oil based mud (oil is inert and there would be no swelling of the clay). I would rather recommend an inhibive mud system like a silicate mud system that contains Sodium Silicate or Potassium Silicate. These type of mud systems provide enhanced well bore stability and are accepted in most areas as regards environmental issues. The risk of boom hole and bit balling are greatly minimized and the eciency of cung removal is improved. Comparavely they are far cheaper than using oil based mud to drill highly reacve shale.

Queson 1bI would recommend the use of a Tungsten Carbide Insert tricone bit for drilling the lower Terary, Ekofisk and upper Tor with possible Chert. These bits have deep intermeshed cuer row which help to prevent bit balling when drilling formaons that are scky. Moreso their cung structure gives high rate of penetraon in low compressive strength and so formaons as in this case.

((Question2))

Data;

Water depth Dw ; Dw 325 ft

Depth of mudline Dm ; Dm 405 ft

Tail Height Dt ; Dt 500 ft

Casing Shoe Depth Ds ; Ds 3733 ft

Tail Density tail ; tail 16 lb

gal

Lead Density lead ; lead 13.2 lb

gal

Mud Density mud ; mud 11.4 lb

gal

Density of seawater w ; w 1025 kg

m3

=w 8.554 lb

gal

From slide 14 of the second lecture, the casing dimensions and collapse rating are obtained:Wall thicknes ((t)) ; t 0.5141 in

Outside Diameter Do ; Do 13.375 in

Collapse Resistance Pc ; Pc 2671 psi

The collapse safety factor is given as; SC Pc

Pe Pi1 2 t

Do

Pi is the internal pressure calculated by; Pi mud Ds 0.05195

Pi 11.4 3733 0.05195

Pi 2210.8 psi

Pe is the external pressure which is the summation of the lead

pressure Plead ; tail pressure Ptail ; and the hydrostatic pressure Ph

Ptail tail Dt 0.05195

Ptail 16 500 0.05195

Ptail 415.6 psi

Lead Height hlead ; hlead =Ds Dt Dm 2.828 10

3 ft

Plead lead hlead 0.05195

Plead 13.2 2828 0.05195

Plead 1939.27 psi

Ph =w g Dw 144.419 psi

Pe =++Ptail Plead Ph 2.499 10

3 psi

SC =Pc

Pe Pi1 2 t

Do

5.826

QUESTION3

Data

Fracture density frac ; frac =13.2 lb

gal

1.582 103

kg

m3

Depth of Mud line Dm ; Dm 405 ft =Dm 123.444 m

Depth of shoe Ds ; Ds 3733 ft =Ds 1.138 10

3 m

Depth of 12.25 inches drilled hole Dt ; Dt =10912 ft 3.326 10

3 m

compressed gas density g ; g =0.1 psi

ft

2.262 103

N

m3

seawater 1025 kg

m3

The minimum safety factor ((SF)) is calculated by; SF Pb

Pi Pe

From the casing sizes table the burst pressure is obtained; Pb 5380 psi

The internal pressure Pi is Pi Pfrac Pif

The pressure of the internal fluid Pif ; Pif =g Ds Dm 332.8 psi

The fracture pressure Pfrac ; Pfrac frac 0.05195 Ds

Pfrac 13.2 0.05195 3733

Pfrac 2559.87 psi

Pi =Pfrac Pif 2.227 10

3 psi

The external pressure Pe Pe =seawater Dm g 179.968 psi

The minimum SF for the casing full of gas load is;

SF =Pb

Pi Pe2.628