PETE 203 DRILLING ENGINEERING CASING DESIGN Objectives Understand

PETE 203 DRILLING ENGINEERING CASING DESIGN

Objectives Ø Understand primary functions of casing Ø Recognize the various types of casing strings used. Ø Understand the procedures used in the design of casing strings.

Types of Strings of Casing 1. Drive pipe or structural pile {Gulf Coast and offshore only} Diameter Example 16”-60” 30” 16”-48” 20” 8 5/8”-20” 13 3/8” 150’-300’ below mud-line. 2. Conductor string. 100’ - 1, 600’ (BML) 3. Surface pipe. 2, 000’ - 4, 000’ (BML)

Types of Strings of Casing Diameter 4. Intermediate String 5. Production String (Csg. ) 6. Liner(s) 7. Tubing String(s) 7 5/8”-13 3/8” 4 1/2”-9 5/8” Example 9 5/8” 7”

Example Hole and String Sizes (in) Hole Size Pipe Size 36” 26” Structural casing Conductor string 30” 20” 17 1/2 Surface pipe 13 3/8 12 1/4 Intermediate. String 9 5/8 8 3/4 Production Liner 7

Example Hole and String Sizes (in) Hole Size Pipe Size 36” 26” Structural casing Conductor string 30” 20” 17 1/2 Surface pipe 13 3/8 12 1/4 Intermediate. String 9 5/8 8 3/4 Production Liner 7

Example Hole and String Sizes (in) Structural casing Conductor string Mudline 250’ 1, 000’ Surface pipe Intermediate String Production Liner 4, 000’

Example Casing Programs

CONDUCTOR (1 or 2) (40’ – 300’) Ø Prevent eroding surface sediments and rig foundation by circulating the drilling fluid to the shale shaker. Ø Protects subsequent casing strings from corrosion. Ø Install director system on it. SURFACE (300' - 5000') Ø Control caving and washing out of poorly consolidated surface beds. Ø Protect fresh water sands from possible contamination by drilling fluid mud, oil or gas and or salt water from lower zone. Ø Install BOP on it.

INTERMEDIATE CSG (1 or 2) It depends on well depth and geology in specific area. Primary Purpose: To seal off troublesome zones which: Ø Contaminate drilling fluid. Ø Jeopardize drilling progress with possible pipe sticking, excessive hole enlargement. Ø Contain abnormal pressure fluids, protect formation below the surface casing from higher pressure credited by mud.

PRODUCTION CSG 1. It is set through productive interval to; 2. Segregate pay zone. 3. Can be used to produce fluid instead of tubing. DRILLING LINER 1. Lower in cost. 2. Functions like intermediate. PRODUCTION LINER 1. Lower in cost 2. Functions like production.

6. 2 Standardization of Casing API: Ø Ø Ø American Petroleum Institute Standards. Range of length Outside diameter Wt/ft. Type of coupling Steel grade

Classification of CSG. 1. Outside diameter of pipe (e. g. 9 5/8”) 2. Wall thickness (e. g. 1/2”) 3. Grade of material (e. g. N-80) 4. Type to threads and couplings (e. g. API LCSG) 5. Length of each joint (RANGE) (e. g. Range 3) 6. Nominal weight (Avg. wt/ft incl. Wt. Coupling) (e. g. 47 lb/ft)

Length of Casing Joints RANGE 1 16 -25 ft RANGE 2 25 -34 ft RANGE 3 > 34 ft.

Ø OUTSIDE DIAMETER v Tolerance (4. 5 -20") 0. 75% v Usually slightly oversized. v Minimum permissible v Wall thickness = 87. 5% of nominal wall thickness. v Nominal = approximate average v Drift diameter : Check ID Ø Minimum mandrel diameter that must pass Ø Unobstructed through the pipe. Ø Insures a bit size less than drift diameter.

Ø WEIGHT PER FOOT Ø Nominal wt/ft : for as an (wt/ft) is not true wt/ft but is useful identification purposes approximate average Ø Plain-end wt/ft: is the wt/ft of the pipe body excluding the threaded portion and coupling wt. Ø Average wt/ft: total wt. of avg. joint of threaded pipe with a coupling attached power tight of one of avg. joint.

6. 3 Type of Coupling ¨ A coupling is a casing connector which is made of casing material. ¨ Most common types of casing. Joints are externally threaded from each end. ¨ API specification the coupling should be of the same grade as the pipe body.

Casing Threads and Couplings API round threads - short { CSG } API round thread - long { LCSG } Buttress { BCSG } Extreme line { XCSG } Other …

Ø CSG & LCSG These connectors have the same basic design: ý Threads are round shaped and are spaced to give eight threads/inch. ý Sometimes they are called API 8 -round threads. ý Threads are cut with a taper of 3/4 in/ft. ý These are commonly used connectors because of their proven reliability, ease of manufacture and low cost. ý Cut with a 60 angle, and has round peaks and roots. ý Thread compound must be used to fill the voids and obtain a seal. Tensile strength of the joint

API BCSG CONNECTOR ý Joint efficiency is 100% in most cases. ý It is tapered but longer thread run out ¾ inch/ft. for upto 75/8 inch. ý Thread shape is square to reduce unzipping tendency. ý 5 threads cut to the inch. ý 1 inch/ft for 16 inch csg.

Ø API XCSG CONNECTOR ý It is integral joint. ý Pipe thicker near the wall. ý OD is less than other API couplings ý Sealing mechanism is metal to metal seal between the metal and the box. ý Much more expensive.

API Connectors

Ø STRENGTH ¨ Strength is designated by casing GRADE ¨ Grade code : Letter and number H-40, J-55, C -75, L-80 ¨ Letter is arbitrary. ¨ Number designates the minimum yield strength of steel in thousands of psi. ¨ Yield strength : tensile stress required to produce a total elongation per unit length of 0. 005 on a standard test specimen. ¨ Minimum yield strength = 80% of average yield strength observed.

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Grades of Casing Recognized by the API

API Connectors

Tensile force balance on pipe body Example 7. 1: Compute the body-yield strength for 20 -in. , K 55 casing with a nominal wall thickness of 0. 635 in. and a nominal weight per foot of 133 lbf/ft.

Tensile force balance on pipe body K 55 Solution: This pipe has a minimum yield strength of 55, 000 psi and an ID of:

Tensile force balance on pipe body Thus, the cross-sectional area of steel is and a minimum pipe-body yield is predicted by Eq. 7. 1 at an axial force of:

Pipe Body Yield Strength where

Pipe Body Yield Strength Example What is yield strength of body of 7”, 26 #/ft, P-110 casing? (to the nearest 1, 000 lbf). …agrees with Tables

Internal Yield Pressure for Pipe (Burst) FT FP where FP = DLP FT = 2 t. LYP DLP = 2 t. LYP

Example For 7”, 26 #/ft P-110 pipe (to the nearest 10 psi) …agrees with Tables.

TABLE 7. 8 –COMMONLY USED BIT SIZES THAT WILL PASS THROUGH API CASING Casing Size (O. D. , in) Weight Per Foot (lbm/ft) Internal Diameter (in. ) Drift Diameter (in. ) Commonly Used Bit Sizes (in. ) 4 9. 5 10. 5 11. 6 13. 5 4. 09 4. 052 4. 000 3. 920 3. 965 3. 927 3. 875 3. 795 3 7/8 3¾ 5 11. 5 13. 0 15. 0 18. 0 4. 560 4. 494 4. 408 4. 276 4. 435 4. 369 4. 283 4. 151 4¾ 3 7/8

Casing Design - Collapse

Casing Design - Tension

Casing Design - Burst (from internal pressure) 4 Internal Yield Pressure for pipe 4 Internal Yield Pressure for couplings 4 Internal pressure leak resistance p Internal Pressure p

Casing Design - Burst Example 1 Design a 7” Csg. String to 10, 000 ft. Pore pressure gradient = 0. 5 psi/ft Design factor, Ni=1. 1 Design for burst only.

Burst Example 1. Calculate probable reservoir pressure. 2. Calculate required pipe internal yield pressure rating

23 lb/ft 26 lb/ft N-80

Example 3. Select the appropriate csg. grade and wt. from the Casing tables: Burst Pressure required = 5, 500 psi 7”, J-55, 26 lb/ft has BURST Rating of 4, 980 psi 7”, N-80, 23 lb/ft has BURST Rating of 6, 340 psi 7”, N-80, 26 lb/ft has BURST Rating of 7, 249 psi Use N-80 CSG, 23 lb/ft

API Design Factors (typical) Required Design 10, 000 psi 11, 250 psi 100, 000 lbf 10, 000 psi Collapse Tension Burst 1. 125 1. 8 1. 1 180, 000 lbf 11, 000 psi

Table 3 Grade D/t Ratio H 40 16. 44 and less J & K 55 14. 8 and less C 75 13. 67 and N 80 13. 38 and less C 95 12. 83 and less P 105 12. 56 and less P 110 12. 42 and less (4)