Chapter5 Drill String Teahcher Lecturer Rong Institute of

Chapter-5 Drill String Teahcher: Lecturer Rong Institute of Petroleum Engineering

Function of Drill String important (1)Providing the channel of drill fluid from wellhead to the well bottom and convey hydraulic energy to the drill bit. (2)Proving WOB (Weight On Bit) and let the tooth of bit press-in the rock continually. (3)Transmit torque to the bit and let the bit rotate and crush down the rock. (4)Trip the bit. (5)Calculating the depth of well.

Over View of Drill String Many pipes between swivel and the Bit Faucet

Over View of Drill String important swivel

Over View of Drill String Drill string mainly consist of Kelly, Drill Pipe, Drill Collar and some additional component. Rotary Table Kelly Drill Pipe Drill Collar Bit

Main Content o I. The Construction of Drill String o II. Work Status and Force Analysis of Drill String o III. Failure of Drill String

1. Drill Pipe Drill pipe is the basic component in drill string and is processed by seamless steel pipe with wall thickness of 9~11 mm. Drill pipe consists of pipe body and tool joint. le a M nt i jo le a m Fe int jo y d o b pe i P

1. Drill Pipe important How to connect pipe body to tool joint? 2 methods: thread and friction welding Old New y d o b pe i P Old

1. Drill Pipe Upset part on the pipe body To avoid Stress Concentration. Internal Upset External Upset Internal External Upset IU EU IEU

1. Drill Pipe Length and Diameter According to the rules of API The length of drill pipe (DP) divided into 3 types. ① 5. 848~6. 706 m（18~22 ft）; ② 8. 230~9. 144 m（27~30 ft）; ③ 11. 582~13. 716 m（38~45 ft） In the field in China, we use DP with 127 mm(5 in) diameter most commonly.

1. Drill Pipe Steel Grade The material of DP is steel, but with different steel grade. In API rules, there are 5 steel grades D Low E X G S High With the steel grade increased, the strength of steel will be increaese.

1. Drill Pipe in Factory

2. Drill Collar important Drill collar (DC), the part at the bottom of the drill string, connect the drill bit directly. Compare with DP, DC have bigger wall thickness, about 38 -53 mm thickness. Function of DC: (1) Providing WOB to bit. (2) Keep a certain strength of the drill string. (3) Making the bit stable and avoid jumping and vibration. (4) Preventing inclination.

2. Drill Collar Type of DC: Roundness DC Spiral DC

3. Kelly is the component on the top of the drill string, whose function is to transmit the torque. Shape of Kelly: Rectangle Hexagon

4. Heavy Weight Drill Pipe(HWDP) To avoid the stress-concentration between DP string and DC string, HWDP are always add into the drill string between DP string and DC string.

5. XO Cross-over（XO sub） When the DP, DC, HWDP connect with each other directly, they must have the same size, same type of joint and thread. If they are not, then we need XO cross-over.

6. Down-hole Four Apparatus (1)Stabilizer (2)Jar (3)Shock Absorber (4)Suspending Device The most commonly used are Stabilizer and Jar.

6. Down-hole Four Apparatus (1)Stabilizer The mainly function of stabilizer is to ensure the drill string in the middle of the wellbore. The diameter of support part of stabilizer (Ds) approach to the diameter of the wellbore (Dw).

6. Down-hole Four Apparatus (2)Jar is used to deal with the a drilling accident call Pipe-Sticking. When the pipe-sticking happened, the Jar will generate a strong vibration and let the drill string free. This process we called Unfreezing. Pipe-sticking unfreezing terminology

6. Down-hole Four Apparatus important terminology TRIP Run In Hole & Put Of Hole Bit Balling Horizontal Well Kelly Directional Well Swivel Vertical Well WOB ND Bit RPM Borehole Wall EOR

Main Content o I. The Construction of Drill String o II. Work Status and Force Analysis of Drill String o III. Failure of Drill String

1. Working Status Of Drill string a. In TRIP working condition: In Vertical Well: Stretch and Slide In Directional Well: Bending and Slide b. In Drilling working condition: Upper part feels tension, lower part feels pressure.

1. Working Status Of Drill string c. Revolution and Rotation The drill string normally rotate around its own center, that is rotation. But some times it also rotate around the center of the well, that is revolution. In the rotation process, the drill sting have a average abrasion.

1. Working Status Of Drill string tire Ground wear tire. Rock wear bit. abrasiveness

2. Force Analysis Of Drill string a. Axial Tension and Pressure Radial Direction Axial Direction

2. Force Analysis Of Drill string a. Axial Tension and Pressure The maximum tension exist on the top of drill string. The minimum tension exist on the bottom of drill string and the value is 0. The tension at any cross-section on the drill string is shown as follows: q linear density, k. N/m L length

2. Force Analysis Of Drill string a. Axial Tension and Pressure g/cm 3 But there is buoyancy exist in the well filled with mud, so we have consider the influence of buoyancy. Buoyancy Factor Density of mud Density of steel

2. Force Analysis Of Drill string a. Axial Tension and Pressure In the process of drilling, there is WOB exist on the bit. So we also need to consider the influence of WOB.

2. Force Analysis Of Drill string a. Axial Tension and Pressure Neutral Point: We knew that upper part feel tension and lower part feel pressure, so there must be a point doesn’t feel both tension and pressure on the drill string. That point we call it Neutral Point.

2. Force Analysis Of Drill string a. Axial Tension and Pressure The distance between neutral point and bit can be calculated by the follow formula.

2. Force Analysis Of Drill string Significance Of Neutral Point Neutral point is the boundary point between tension and pressure on the drill string. So there is a alternating stress near the point. It is harmful to the strength of drill string. It is better to let the neutral point locate in the DC part. important

2. Force Analysis Of Drill string b. Drill String Design (a little difficult) ① Design Principles l. Meet the requirements of strength, ensure the drilling work on the rails. l. Lighten the weight of the whole drill string to drill more deeper well.

2. Force Analysis Of Drill string important b. Drill String Design (a little difficult) ② Calculating the length of drill collar m is Safety Factor, 1. 15~1. 25 is WOB, k. N is hole deviation angle is linear density, k. N/m Buoyancy Factor Density of mud Density of steel

2. Force Analysis Of Drill string important b. Drill String Design (a little difficult) ② Calculating the length of drill collar Example WOB=300 k. N, SN=1. 2, qc=1. 35 k. N/m, =8 g/cm 3, =1. 2 g/cm 3 =30 o Please figure out the length of drill collar use in this well. LC=?

2. Force Analysis Of Drill string important b. Drill String Design (a little difficult) ③ Calculating the length of drill pipe is stretching resistance, k. N When you design the drill string, Fy is know condition. What we need to do is calculate the Fa. (The maximum safety tension)

2. Force Analysis Of Drill string important b. Drill String Design (a little difficult) ③ Calculating the length of drill pipe l. Safety Factor Method is safety factor. This St different from that of drill collar’s safety factor SN, but they have the same function.

2. Force Analysis Of Drill string important b. Drill String Design (a little difficult) ③ Calculating the length of drill pipe l. Design Factor Method is design factor

2. Force Analysis Of Drill string important b. Drill String Design (a little difficult) ③ Calculating the length of drill pipe l. MOP Method is margin of pull We choose the minimum Fa calculated by the above 3 methods as the real Fa.

2. Force Analysis Of Drill string important b. Drill String Design (a little difficult) ③ Calculating the length of drill pipe Example WOB=300 k. N, SN=1. 2, qc=1. 35 k. N/m, =8 g/cm 3, =1. 2 g/cm 3 =30 o Fy=1796 k. N, qp=0. 284 k. N/m, St=1. 3 =1. 42, MOP=200 k. N Please figure out the length of drill pipe use in this well. Lp=?

The Procedure of Drill String Design important 1. Calculate buoyancy factor 2. Calculate the length of drill collar 3. Calculate the length of drill pipe

The Procedure of Drill String Design important 3. Calculate the length of drill pipe 4. Total length of drill string is Lc+Lp=? m

Main Content o I. The Construction of Drill String o II. Work Status and Force Analysis of Drill String o III. Failure of Drill String

Failure of Drill String Most of the application in the drilling field tell us the root reason of failure of drill string are alternating load and erosion in H 2 S and CO 2 acid environment.

Failure of Drill String Failure Situation 1. Failure always happened in the process of TRIP, but not the process of unfreezing. 2. The failure part always locate at the place within 1. 2 m to the end of the joint. 3. Failure of drill string related to the etch pit & surface scar. 4. Failure of DC happened at the thread part.

Failure of Drill String ①Leakage ②Twist Off

Failure of Drill String 3 kinds of reasons of failure of drill string: ①Pure Fatigue Failure The drill string suddenly broken without any forecast. ②Scar Fatigue Failure This kind of failure always happened along the scar on the surface of the drill string. ③Corrosion Fatigue Failure Happened in acid conditions.

①Pure Fatigue Failure Fatigue Limit Break Off alternating load Iron wire When the load exceed the fatigue limit of the material, the pure fatigue failure will be happen. ① ② ③ repeat ①and②

①Pure Fatigue Failure Microgroove Pressure Tension

②Scar Fatigue Failure Resource of scar l. Scar of tong

②Scar Fatigue Failure Resource of scar hydraulic tong

②Scar Fatigue Failure Resource of scar l. Scar of slip

②Scar Fatigue Failure Resource of scar slip

②Scar Fatigue Failure elevator

③Corrosion Fatigue Failure Corrosion fatigue failure mainly related to the acid environment in the well bore. Acid material in the mud include: O 2, CO 2, H 2 S O 2 oxidation CO 2 carbonic acid H 2 S hydrosulphuric acid hydrogen embrittlement

③Corrosion Fatigue Failure Corrosion outside the pipe

③Corrosion Fatigue Failure Corrosion inside the pipe

③Corrosion Fatigue Failure pit

③Corrosion Fatigue Failure pit