Drilling fluids

Directional

Data given:

Water depth = 430 ft MSL

Rig floor elevation = 70 ft MSL

Hydrogen Sulphide = 0 mol%

Carbon Dioxide = 0 mol%

	N ft	E ft	TVD ft brt
Surface location of rig	0.00	0.00	0.00
Target location	5320.00	0.00	9500.00
TD	5320.00	0.00	10250.00

KOP (immediately below surface) = 2.00 deg/100 ft

DOP (where needed to be) = 4.00 deg/100 ft

Calculation of the radius of curvature:

V₁ = 1000 ft TVD brt

V₄ = 9500 ft TVD brt

D₃ = 5320 ft

V₅ = 10250 ft

Manual profile has to be chosen:

R₁ + R₂ = 2865+1432 = 4297 ft, which is less than 5320 ft, i.e. R₁ + R₂ < total target distance.

Line X = D3 – (R1 + R2) = 5320 – 4297 = 1023 ft

= = 7406 ft

Angle = Angle FOG + = 30.1 + 6.9 = 37⁰

End of build

Measured depth = V₁ + = 1000 + = 2850 ft

Vertical depth (V₂) = V₁ + R₁ = 1000 + 2865*sin(37⁰) = 2724 ft

Displacement (D₁) = R₁ (1-cos ) = 2865*(1-0.798) = 577 ft

Start of drop

Measured depth = V₁ + + OG = 2850 + 7406 = 10256 ft

Vertical depth (V₃) = V₂ + OG*cos = 2724 + 7406*cos37⁰ = 8639 ft

Displacement (D₂) = D₁ + OG*sin = 577 + 7406*sin37⁰ = 5034 ft

End of drop

Measured depth = V₁ + + OG + = 1000 + + 7406 + = 11181 ft

V₄ = 9500 ft

D₃ = 5320 ft

“S” profile design

“S” profile	MD ft	Inc ^0	Azi ^0	TVD ft	N ft	E ft	DLS ^0/100ft
Tie-in
KOP
End of build
Start of drop
End of drop
TD

Casing

Data given:

Rig floor elevation (RFE) = 430 ft

Water depth (WD) = 70 ft

Density of sea water (ρ_sw) = 0.45 psi/ft

where:

ρ_r: density of return fluid

ρ_f: density formation

The value of ρ_r is obtained by adding density of cuttings to seawater density, so it is 9.1 ppg, or 0.476 psi/ft. Convergent factor of 0.052 was used. From the information of fracture gradient at certain depth, ρ_f is calculated:

In order to find the depth of conductor, the following equation is used:

Casing	Conductor	Surface	Intermediate	Production	Production Liner
ft TVD brt
ft TVD brt

Measured Depth from directional plan

Conductor’s MD remains the same as TVD. Adding rig floor elevation and water depth, afterwards subtracting the result from TVDbrt surface casing, the measured depth of surface casing is obtained. 1000 – (430+70) = 500 ft SS.

In order to calculate the Measured Depth for intermediate casing, subsea length of the end of build was obtained, it is 2850 – 500 = 2350 ft MDSS. The difference in TVD subsea from final point of intermediate casing to the TVD point end of build and angle were used to get second part of intermediate casing: (4200-2224)/cos37⁰ = 2474 ft. For the purpose of calculating the Measured Depth of intermediate casing we add these values together:

2350 + 2474 = 4824 ft MD ft subsea.

Measured Depth of production casing is taken from question 1 (i.e. “S” design profile), and the rig floor elevation and water depth values were subtracted: 11181 – 500 = 10681 MD ft subsea.

Measured Depth of production liner is calculated using the same way: 11931 – 500 = 11431 MDftSS.

API 5C2 was examined and wt/ft of J-55 with 20̋ outer diameter and wt/ft of P-110 were used to select the nominal weights. Drift diameter (D_D) is considered as minimum allowable assured diameter, therefore attention needs to be paid for that. In order to reduce uncertainties, the inner diameters should be close to next diameter.

Casing	Grade	Nominal weight, lb/ft	Di (inside diameter), inch	Do (outer diameter), inch	DD (drift diameter) inch	Collapse resistance, psi	Pipe body yield, 1000 lb	DB, (diameter of bit), inch
Surface	J-55		18.73		18.542			17.5
Intermediate	P-110		12.415	13.375	12.259			12.25
Production	P-110		8.681	9.625	8.525			8.5
Production liner	P-110		6.184		6.059

Cementing

Data given:

	Top Lead	Height of tail	Shoe track length	Outer diameter	Inner diameter
Conductor	n/a	seabed	40 ft
Surface casing	seabed	500 ft	40 ft		API 5C2
Intermediate casing		500 ft	80 ft	13 3/8	API 5C2
Production casing	n/a	500 ft	80 ft	9 5/8	API 5C2
Production liner	n/a	entire length	160 ft		API 5C2

TVDSS conductor = 186 ft

Tail yield = 1.15 cuft/sack

Lead yield = 1.5 cuft/sack

In order to calculate conductor tail cement volume we have to use:

1. Annulus volume between diameter of drill bit and outer diameter of conductor casing;

2. Volume of shoe track.

Drill bit diameter is not given; however, initial diameter of borehole is usually 36 inches.

Volume of conductor tail cement = annulus volume + volume of shoe track =

Except conductor, cementation volume is generally taken from iHandbook software. For surface cementing, annulus volume is 472.65 ft³ and shoe track volume is 76.53 ft³.

Volume of surface tail cement = annulus volume + volume of shoe track + height of conductor

So, volume = 472.65 + 76.53 + 333.74 = 882.92 ft³

Volume of intermediate tail cement = 414.55 ft³, volume of intermediate lead cement = 3125 ft³.

Volume of production tail cement = 189.46 ft³, volume of production lead cement = 3268.67.5 ft³.

Volume of production liner tail cement = 128.47 ft³.

Number of sacks is calculated by dividing the volume to the yield.

Casing	Volume of tail, ft^3	Volume of lead, ft^3	Sack number of tail	Sack number of lead
Conductor	560.77
Surface	882.92
Intermediate	414.55
Production	189.46	3268.67
Production liner	128.47
Total

Drilling fluids

Since there is no problems were reported, drilling fluid for conductor is chosen as water based. It is economically valuable.

Flow of the mud to the aquifer should be prevented by controlling loss of drilling mud. For the surface borehole, water based mud is chosen as well. However, it is not pure water, with different additives (e.g. viscosifiers, fluid loss control).

Reactive shales are present in production borehole. To drill intermediate borehole, main issues could be selected as instability of the borehole and shale reactiveness. Silicate based mud is chosen for this borehole. It is economically valuable as well.

Natural fractured layers are evident in production borehole drilling which arise some problems. Again, water based mud type is essential here.

Production liner indicates good reservoir quality, because of high poroperm values. The drilling fluid flows to formation and cuttings, that’s why it is very important not to damage somehow permeability during the drilling processes. Mud is likely to be oil based.

Mud density values are read from Chart 1.

Borehole	Mud density (ppg)	Mud type
Conductor	8.9	Water based
Surface	8.9	Water based
Intermediate	10.2	Silicate based
Production	15.5	Water based
Production liner	13.9	Oil based

Shale shakers are used as equipment that removes drilled cuttings from the mud. When the used drilling mud comes to the surface it is directed to the shale shakers where the process begins. Consequently, drilling mud is moved to the mud tanks where the further solids control facilities remove finer solid. These finer solids are eliminated by desander and desilter.

Дата добавления: 2015-11-14