Petr 311 Wellbore pressures and Kick Control

Transcription

1 etr 311 Wellbore pressures and Kic Control Reeber b. 05D Consider the wellbore static hydraulic syste The pressures in the drill string and the annulus can be represented as a U-tube. The su of the pressures in the drill string and the annulus ust be equal. dp hdp a ha bh When not puping ud the pressure at the surface should be zero if the syste is balanced. When reservoir pressure exceeds the pressure in the wellbore, reservoir fluids will be produced into the wellbore. The first indication of this the level in the ud pits will raise. This is referred to as a KICK. You are losing control of the well! WHAT TO DO??? Step one, stop the pups Step two, close the O Step three, allow the well to stabilize and record the dp & a Step four, record the increase in the pits Step five, calculate the bh using dp and the density of the ud Step six, calculate the size and density of the ic fro the pit data Step seven, plan how to get it out For step five we now that the ud in the drill pipe is constant because the foration fluid cannot flow up into the drill pipe, so just use the ud density to calculate the dp. For step six we have to assue the hole diaeter and that it is constant. The diaeter of the drill string will change in any cases because you have drill collars above the bit and then drill pipe.

2 y calculating the length of the ic we can deterine the density of the ic, which tells what the fluid that entered the well is, liquid or gas. This is needed when we draw up a plan to get the ic out. c c V Cdp C c Using the pressure balance of the static syste the density can be calculated a.05 dp If the density of the ic is less than 4#/gal it is gas, greater than 8 it is liquid. A ic with gas in it we have to tae in to account the expansion of the ic as it coes up the hole. Exaple A ic of 10 bbls is encountered at a depth of The O is closed and a drill pipe pressure of 500 psi and an annular pressure of 700 psi. The hole has 9.6# ud with 500 of 8 collars drilling a 10 hole. bh x psi C c 8.6 ft/bbl 15bbl x So ic just across the collars 434 a dp ic is gas.05.05* 434

3 If ic is 5 bbls C dp 1.9 ft/bbl for 4 ½ drill pipe c 500 c V Cdp ft C c 8.9 This assues no ixing of the ud and the ic fluid. For a ore accurate lic length and density of the ic ixing of the ic fluids and ud should be taen into account. The ud and ic ix as the ud is puped across the zone giving up the fluid. This is the tie between the start of the ic and the closing of the O. The volue of the ud in the ic is the pup rate of the ud during the ic tie. V qt d So the ic volue is the volue of the ud plus the pit gain V G qt d Now use this volue to calculate the length of the ic and its density. The annular pressure profile for a gas ic is coplicated by the expanding gas as the pressure is lowered as the ic coes up the hole. The length of the ic at different pressures is calculated by So the pressure in the annulus is a a ( D ). f for no change in ud density 05 ( D D1 ). 05 D1 f ud weight increase 1

4 The solution to give the pressure at any point in the annulus For no ud change.05 et A ( D X ). 05 f Increasing the ud weight 1.05 * et A ( D X ) 05 D ( ) f 1 Exaple Well depth 10,000 Hole size 7 7/8 Drill pipe 4 ½ Surface 000 Mud Weight 9.6# it gain 10 bls dp 00 psi a 300 psi up rate of 6 M First calculate 10000() psi New ud weight to aintain a pressure 50 psi above. 550/(.05*10,000)10.1# ength of the ic Annular volue is.04 bpf 3.8*10 38 ft Calculate f f (D- ).05 - a 500 ( ) 300 f 19 psi With a teperature gradient of 1.F/ 100ft, tep at surface 70F. Find the pressure at the casing seat when the ic gets there. Also when the ic reaches the surface.

5 First without a change in the ud A ( D X ) ( ) f psi z T a 550-( ) psi Kic at surface ( D X ) ( ) A 1 f sur psi z T ' ( ) psi With the new ud The internal volue of the drill pipe is.014 bbl/ft The total volue at 10,000 is 141 bbls * D 141/ ' * A ( D X ). 05 f D ( 1 ). 05 A 550 ( ) ( ). 1138

6 psi 650 z T ' a () 505 psi Kic at surface ( ) ( ). 98 A psi 650 z T ' (3357) ( ) psi The length of the ic if ixing is considered, 5 inutes fro when the ic started till pup is shut down. V G qtd bbls 3.8*40 95 ft f (D- ).05 - a 500 ( ) 300 f 376 psi The drill pipe pressure during the ill operation can be calculated. During regular drilling operations ill rate drill pressures are recorded. This will include the friction and bit pressure drops at this rate.