Drill string design bha design schlum

IPM DPT DPT Drill String and BHA design Schlumberger Private Drill String and BHA Design References DPT Drill String and BHA design Schlumberger Private • API RP 7G Drill Stem Design and Op Limits • API SPEC Specifications for Rotary Drilling Elements • API SPEC 5D Specifications for Drill Pipe • SLB Drill String Design manual • TH Hill DS-1 Drill String Design Objectives At the end of this lecture YOU will be able to describe: Functions of Drill Pipe , Drill Collars and BHA selection • Grades of Drill Pipe and strength properties • Thread types and tool-joints • Drill collar weight and neutral point • Bending Stress Ratios and Stiffness Ratios • Margin Of Overpull • Basic design calculations based on depth to be drilled • Functions of stabilizers and roller reamers DPT Drill String and BHA design Schlumberger Private • Agenda Introduction to Drill String Design: Overview II Drill String Components • Drill Collars - Drill Pipe - HWDP III Drill String Design • Bottom Hole Assembly Design • Drill Pipe Selection • Buckling and max WOB DPT Drill String and BHA design Schlumberger Private I Functions of the Drill String The drill string is the mechanical linkage connecting the drill bit on bottom to the rotary drive system on the surface D P Transmit and support axial loads - WOB Schlumberger Private The drillstring serves the three main following functions : Transmit and support torsional loads - rpm Transmit hydraulics to clean the hole and cool the bit DC DPT Drill String and BHA design WOB Drill String Components Schlumberger Private The Drill String includes all tubular equipment between the Kelly Swivel and the bit • Kelly • Surface Safety Valves • Drill Pipe • Heavy Walled Drill Pipe • Drill Collar • Jars – Shock Subs – Bumper Subs – Junk Baskets – Accelerators etc… DPT Drill String and BHA design The Kelly/Top Drive Schlumberger Private Strictly speaking, Kelly/ Topdrive are not components of the drill string; however, they provide the essential requirements for drilling a well: 1) Transmit rotation to the drillstring 2) Provide access to the drilling fluid into the drillstring 3) Support the weight of the string DPT Drill String and BHA design The Kelly • Supports the weight of the drillstring • Connects to the swivel and allow circulation thru pipe The Kelly comes in lengths ranging from 40 to 54 ft with cross sections such as hexagonal (most common), square or triangular Connected to a Kelly Saver Sub DPT Drill String and BHA design Schlumberger Private The Kelly is the rotating link between the rotary table and the drill string • Transmits rotation and weight-on-bit to the drillbit Kelly Cock Schlumberger Private The Kelly is usually provided with two safety valves, one at the top and one at the bottom, called Kelly cock The Kelly cock is used to close the inside of the drillstring in the event of a kick The upper & lower Kelly cocks operate manually IBOP / DPSV are not run in the drill string but kept handy on the rig floor DPT Drill String and BHA design Top Drive The top drive is basically a combined rotary table and kelly Advantages over the kelly system: Efficient reaming and back reaming Circulating while running in stands hole or pulling out of hole in The kelly system can only this in singles; ie 30 ft DPT Drill String and BHA design Schlumberger Private It is powered by a separate motor and transmits rotation to the drill string directly without the need for a rotary table Exercise DP11 - Burst Load Case • In the last example assume we are performing a DST test in the well at 9000 ft with BHP 200 psi less than the mud wt What is the burst DF on the top of the Premium Grade E DPT Drill String and BHA design Schlumberger Private • Worst load case happens during DST operations in a gas well Pressure at surface is BHP- gas gradient with no backup DP-11 • From last Example 5” 19.5# E Premium • OD=5, Wall = 0.2896” Yp= 75,000 • Design factor = 8688/4516=1.92 DPT Drill String and BHA design Schlumberger Private • Burst = 8688 psi • BHP= 12*0.052*9,000-200=5,416 psi • P Surf= 5416-900=4516 psi Drill String Design Process-2 DPT Drill String and BHA design Schlumberger Private After the BHA Design is performed: • Slip Crushing forces on DP • Overpull tensile design at surface • Lengths of DP Sections • Burst Design Check • Collapse under tension Design check Drill String Design Factors Tension DFt Governs Max allowable tension on the system SLB DFt is 1.1 Excess BHA Wt Dfbha Amount of BHA in terms of Wt in excess of that used to drill to assure all Compressive and torsional loads are kept in the Collars, SLB Dfbha is 1.15 DPT Drill String and BHA design Schlumberger Private Margin of OverPull MOP Desired excess tensile capacity over an above the hanging weight of the string at Surface SLB MOP 50-100K Drill String Design Factors Collapse DFc Tube is de-rated to account for Biaxial Tensile reduction and a design factor of is used SLB DFc is 1.1-1.15 DPT Drill String and BHA design Schlumberger Private Torsion No Design Factor Required Tool Joints are made up to 60% of Torsional Capacity, and Tool joints are designed to 80% of the tube Torsion Capacity Thus if the design limits to tool joint make-up there is an adequate design factor built into the system Drill String Design Factors Burst DFb Simple burst is used with no allowance for axial effects SLB DFB is 1.0 DPT Drill String and BHA design Schlumberger Private Buckling DFB In Highly deviated wells it is possible to use DP in compression, provided it is not buckled Agenda Introduction to Drill String Design: Overview II Drill String Components • Drill Collars - Drill Pipe - HWDP III Drill String Design • Bottom Hole Assembly Selection • Drill Pipe Selection • Buckling and max WOB DPT Drill String and BHA design Schlumberger Private I Buoyancy Buoyancy is the weight of the displaced fluid • Buoyancy is usually accounted for via BF • Buoyancy is creating a hydrostatic effect: the Pressure-Area Force • The forces acting on a drillstring are the self-weight and the hydrostatic pressure of the drilling fluid • Buoyancy is creating a force acting at the bottom of the drill string and placing the lower portion of the drill string in compression and reducing the hook load by HP x CSA DPT Drill String and BHA design Schlumberger Private • DP12 - Buoyancy • What is the hook load with BF? • What is the hook load with Pressure Area Force? DPT Drill String and BHA design Schlumberger Private • We are running open ended DCs 9” x 3” – 192ppf • The fluid in the well is 14 ppg • The depth is 10000 ft Bending & Buckling A tube subjected to a load will bend • Bent is a condition in which the bending increases proportionally with load • When a little increase in load will result in large displacements, the tube is said to be buckling • The tube may not necessarily be yielded as buckling does not necessarily occurs plastically • The load which produces buckling is called the Critical Buckling Load Schlumberger Private • DPT Drill String and BHA design Neutral Points • Neutral Point of Tension & Compression: The point within a tube where the sum of the axial forces are equal to zero Schlumberger Private • Neutral Point of Bending: The point within a tube where the sum of moments are equal to zero The point within a tube where the average of the radial and tangential stress in the tube equals the axial stress The point within a tube where the buoyed weight of the tube hanging below that point is equal to an applied force at its bottom end DPT Drill String and BHA design Forces in the Drill String Neutral Point of Bending occurs where the effective hydrostatic force equals the compressive force in the drillstring Schlumberger Private DPT Drill String and BHA design Buckling Neutral point of bending is H = WOB / buoyed weight per foot of string In vertical wells, buckling will occur only below the neutral point of bending, hence the necessity to keep the buoyed weight of the BHA exceeding the WOB • In deviated wells, buckling will not only occur below the neutral point of bending but also above the neutral point of bending when the compressive force in the drillstring exceeds a critical load (OD − ID ) * BF * (OD − ID ) * sin(α ) Fcrit = 1617 Dhole − ODtooljt DPT Drill String and BHA design Schlumberger Private • DP13 – Max WOB in inclined holes Schlumberger Private DPT Drill String and BHA design Drillstring Design Now you should be able to describe: Functions of Drill Pipe , Drill Collars and BHA selection • Grades of Drill Pipe and strength properties • Thread types and tool joints • Drill collar weight and neutral point • Bending Stress Ratios and Stiffness Ratios • Margin of overpull – Slip crushing force • Basic design calculations based on depth to be drilled • Functions of stabilizers and roller reamers • Critical Buckling force and Neutral Point of Bending DPT Drill String and BHA design Schlumberger Private •