Leak-Off Test & Kick Circulation Methods
Arun S Chandel Assistant Professor . . 09997200339
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Leak-Off Test Leak Off Test is conducted in order to find the fracture gradient of maximum equivalent mud weight that should be applied to the well duri during ng dril drilli ling ng oper operat atio ions ns..
roce ure Leak Off Test (LOT) guide line procedures are as follows: 1) Drill out new formation few feet, circulate bottom up and collect sam le to confirm that new formation is drilled to and then ull strin into the casing. 2) Close annular preventer or pipe rams, line up a pump, normally a cemen pump, an c rc rcu a e roug an open c o e ne o ensure a surface line is fully filled with drilling fluid.
Leak-Off Test Leak Off Test is conducted in order to find the fracture gradient of maximum equivalent mud weight that should be applied to the well duri during ng dril drilli ling ng oper operat atio ions ns..
roce ure Leak Off Test (LOT) guide line procedures are as follows: 1) Drill out new formation few feet, circulate bottom up and collect sam le to confirm that new formation is drilled to and then ull strin into the casing. 2) Close annular preventer or pipe rams, line up a pump, normally a cemen pump, an c rc rcu a e roug an open c o e ne o ensure a surface line is fully filled with drilling fluid.
3) Gradually pump small amount of drilling fluid into well with constant pump stroke. Record total pump strokes, drill pipe pressure and casing pressure. Drill pipe pressure and casing pressure will increase continually while pumping mud in hole. When plot a graph , , graph will demonstrate straight line relationship. When pressure exceeds formation strength, formation will be broken and let drilling fluid permeate into formation, therefore a trend of drill pipe/casing pressure will deviate from straight line that mean formation is broken and is injected by drilling fluid. We may call pressure when deviated from straight line as leak off test pressure. 4) Bleed off pressure and open up the well. Then proceed drilling operation.
Leak-Off Test Calculations Leak off test pressure can be calculated into equivalent mud weight in ppg as formula below:
Leak off test in equivalent mud weight (ppg)
= {(Leak off test pressure in psi) ÷ 0.052 ÷ (Casing Shoe TVD in ft)}
+ (current mud weight in ppg)
= (Leak off test pressure in psi) (Casing Shoe TVD in ft)
Leak off test pressure = 1600 psi Casing shoe TVD = 4000 ft Mud weight = 9.2 ppg = 1600 psi ÷0.052 ÷4000 ft + 9.2ppg ppg = 16.9 Pressure gradient = 1600 ÷4000 = 0.4 psi/ft
Question
Solution
Normal Procedure followed when a Kick is Encountered 1) Pick up the kelly and note the position of tool joints n re a on o e r ng spoo s. 2) Stop the pumps. 3) Open the choke line. 4
C ose t e annu ar preventer or ram preventers.
5) Close the choke. 6) Record the pit gain. 7) Record the SIDP and SICP when they stabilize. 9
Circulating out a Kick For a well to be killed successfully, the pressure in the formation must be kept under control during the entire kill operation. The only exce tion is in cases when the maximum allowable annular ressure will be exceeded. The simplest method of doing this is to control the drillpipe pressure by running the kill pump at a constant rate and controlling the pressure by regulating the choke on the choke line.
Two basic techniques are • The Driller’s method - 2 circulations; • The Engineer’s or Wait and Weight method - 1 circulation; ’
pressure, particularly at the shoe. • One more techni ue called as Concurrent method is also used. 10
Driller’s Method (2 Circulations) The Driller’s Method requires two circulations. Th e Fir st Cir cu la t i o n e rs c rcu a on o e r er s e o s per orme us ng e original mud. Co n s t a n t B H P i s m a i n t a i n e d b y h o l d i n g c i r c u l a t i n g d r i l l p i p e p r e s s u r e c o n s t a n t t h r o u g h t h e f i r s t c i r c u l a t i o n . The choke is o ened sli htl at the same time the um s are started u to the kill rate. When the pumps have reached kill rate, the choke is manipulated to maintain the Initial Circulating Pressure (ICP) on the drillpipe. , drastically if the kick is gas. If the kick is saltwater the annular pressure will drop slightly. When the influx has been circulated out, the pumps are stopped and the choke closed. At this time, the two surface pressures (SIDP & SICP) should be the same. During the first circulation, the influx is circulated out with the original . formation pressure, the well is killed by circulating a heavier mud (kill mud) in a second circulation. 11
Th e Se co n d Cir cu la t io n
Step 1: The Kill mud is pumped in the drillpipe. As with the irst circulation, the choke is opened and the pump speed increased to the kill rate (with the annulus pressure kept constant). until the kill mud has reached the bit. As kill mud begins to fill the system, the drillpipe pressure will decrease from the initial circulating pressure to the final circulating pressure. Step 2: When kill mud reaches the bit, it is good practice to shutin the well. The drillpipe pressure should fall to zero; if it doesn't, a few more barrels should be um ed to ensure that the kill mud has reached the bit. If the drillpipe pressure is still greater than zero when the pump is stopped and the choke closed, the kick control figures should be rechecked. When satisfied, pumping is restarted, displaces the mud in the annulus. When the kick fluids and original mud have been displaced, the choke should be wide open. The pump should be shut down and both SIDP & SICP should read zero. If so, the well should then be observed for flow. 12
T o h o l d c o n s t a n t B H P d u r i n g t h e s e c o n d c i r c u l a t i o n , o n e o f w o p r o ce u r e s s em p oye . as n g p r essu r e s e co n st an t w h ile p u m p in g k ill m u d fr o m su r fa ce t o b it , an d d r il l p ip e p r e ss u r e is h e ld co n st a n t t h e r e a f t e r u n t il k il l m u d is o b se r v e d r e t u r n in t o t h e su r f a ce . A lt e r n a t e ly , d u r in g se co n d ci r cu la t io n , a d r il l p ip e p r e ss u r e sch ed u le ca n b e ca lcu la t e d an d f o llo w ed w h ile p u m p in g k ill u u , u co n st a n t t h e r e a f t e r . T h e k i ck i s n o w k i l le d a n d m u d s h o u l d b e c ir c u l a t e d t o co n d it io n t h e h o le , an d at t h e sa m e t im e t h e t r ip m a r g in ( if an y ) sh o u ld b e ad d ed .
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Engineer’s or Wait and Weight Method This is usually a more effective method of killing a kick than the driller's method, if time is not a prime concern. Kill mud is pumped into the drillpipe as soon as it is ready, which tends to reduce the high annular pressures assoc a e w gas c s. e same s u - n proce ures are used as outlined in the previous section. Ste 1:When all the calculations have been erformed the mud density is raised immediately to the calculated kill mud density. When the kill mud volume is ready, the pumps are started and the choke slowly opened, while keeping the annular pressure constant until the . as to decrease the drillpipe pressure until the kill mud reaches the bit, at which point the final circulating pressure is reached. Step 2: Pumping is continued, holding the drillpipe pressure constant by adjusting the choke. When the kick fluids have been displaced, and further volume has been displaced equal to the pipe volume, the SIDP . . Th e k ick is n o w k ill ed a n d fu r t h er cir cu la t io n s ca n b e p er f o r m ed t o co n d it io n t h e h o l e a n d t o a d d a n y t r i p m a r g i n . 15
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Figure shows diagrammatically the displacement of the , , using the engineers method. 17
Driller’s Method Vs W&W Method 1. Drillers method is preferred in wells where hole stability is a problem–N o n - c i r c u l a t i n g w e l l i s m in im ized .
2. Driller’s method is preferred for Old rigs which have limited fluid mixing capability -c o n t i n u o u s m i x i n g t o m ak e k ill m u d m ay re su lt in ex cessiv e su r face a n d s h o e p r e ss u r e s d u e t o g a s e x p a n si o n .
. well kill operation if using Driller’s method – b i t n o z z l e p l u g g i n g . . method if kill mud is prepared at a faster rate. 5. W&W method results in lower annular pressure, particularly at shoe- d e p e n d s o n l o c a t i o n o f g a s b u b b l e a n d d r i l l s t r i n g v o l u m e. 18
Dynamic Kick Control we
on
e
y
For use in controlling shallow gas kicks
• No competent casing seat conductor ’ • Do not shut well in! 19
Dynamic Kick Control
(higher ECD) 2. Increase mud densit 0.3 #/gal per circulation complete circulation 4. If still flowin
re eat 2-4.
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Conventional Kick Control
Shut in well for pressure readings. (a) Remove kick fluid from wellbore; ep ace o
mu
w
we g
mu .
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Driller’s Method - Constant Geometry
Well Data: Depth = 10,000 ft. Hole size = 12.415 in. (constant) Dri Pipe = 4 1 2 O.D., 16.60 t Surface Csg.: 4,000 ft. of 13 3/8” O.D. 68 lb/ft . . .
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Driller’s Method - Constant Geometry
Additional Information re uired: Kick Data: Original mud weight = 10.0 #/gal Shut-in annulus press. = 600 psi Shut-in drill pipe press. = 500 psi Kick size
= 30 bbl
(pit gain)
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Constant
SIDPP = 500 psi SICP = 600 psi
Geometry. n a conditions: Kick has ust entered the wellbore
DP OD = 4.5 in Hole dia = 12.415 in
4,000 ft
Annular Ca acit = 0.13006 bbl/ft
have stabilized
231 ft , BHP = 5,700 psig 24
Successful Well Control 1. At no time durin the rocess of removing the kick fluid from the wellbore will the pressure exceed the
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the casing the wellhead equipment
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Successful Well Control 2. When the process is complete the wellbore is comp e e y e w a u o sufficient density (kill mud) to control the formation ressure. Under these conditions the well will not flow when the ’ . .
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Calculations -
• Casing seat pressure • eg to c • Density of kick fluid
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Calculate New Bottom Hole Pressure PB = SIDPP + Hydrostatic Pressure in DP
= + 0.052 * 10.0 * 10,000 = , PB = 5,700 psig
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Calculate Pressure at Casing Seat P
,
=P +ΔP
.
. - ,
=SICP +0.052 * 10 * 4,000 =600 +2,080
P 4,000 = 2,680 psig
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Calculate EMW at Casing Seat This corresponds to a pressure gradient of
2,680 psi = 0.670 psi/ft ,
Equivalent Mud Weight (EMW) =
0.670 psi/ ft 0.052 (psi/ ft)(lb/ gal)
.
( ρmud = 10.0 lb/gal ) 30
Calculate Initial Height of Kick
Annular capacity per ft of hole: vx = =
2
4 π
2
(D H − D P )L 2
2
3
(12 .415 − 4.5 ) * 12 in *
gal
bbl 3
= 0.13006 bbls/ft 31
Calculate Height of Kick
eg
B
o
c a
o om o
VB 30 bbl = = = vx 0.13006 bbl/ft hB
o e,
.
= 231 ft 32
Calculate Density of Kick Fluid The bottom hole pressure is the pressure at the surface plus the total hydrostatic pressure between the surface and the bottom: Annulus Drill String
PB = SICP + ΔPMA + ΔPKB = SIDPP + ΔPMD
600 + 0052 . *10 *(10,000-231) + ΔPKB = 500 + (0.052*10*10,000)
+ ,
+
KB
=
+ , 33
Density of Kick Fluid
∴ ΔPKB =
KB
=
20 0 .052 * 231
ps
.
(must be primarily gas!) 34
Circulate Kick Out of Hole NOTE: The bottom hole pressure is kept constant while the the hole! In t is case BHP = 5,700 psig
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Annular Geometry Driller’s Method. Conditions When Top of Kick Fluid Reaches the Surface
BHP = const.
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Top of Kick at Surface As t e ic ui moves up t e annu us, it expan s. I the expansion follows the gas law, then
P V P V = Z 0n0RT 0 Z B nB RT B
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Top of Kick at Surface I norin chan es due to com ressibilit factor Z and temperature, we get:
0
0
P v h i.e .
=
B
B
= P v h
P 0h 0 = P B h B
Since cross-sectional area = constant
(v
0
= v B = const .) 39
Top of Kick at Surface We are now dealing two unknowns, P0 and h0. We have one equation, and need a second one.
BHP =Surface Pressure +Hydrostatic Head ,
=
o
KO
MA
5,700 =P +20 +0.052 * 10 * (10,000 - h ) ,
-
- ,
=
o
- .
PB hB * Po 40
Top of Kick at Surface 480 P 0 = P 0 2 0
−
∴ P0 =
0
=
2
0
480 ±
− 0 . 52 * 5700
−
* 231
=
480
= ,
2
+ 4 * 684 ,684
ps 41
y,
r
r
• A kick is NOT a blowout. • Most blowouts are due to human error in handling a kick. • The fundamental principle in well control is CONSTANT BOTTOM HOLE PRESSURE • u e we n us ng e or SHUT IN using the annular BOP.
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Im ortant Princi les continued
• Control a kick with the bit on bottom. pressures. • Use Measured Depth (MD) for volumes and sp acemen s. • Establish pore pressure by recording the shut in drill pipe pressure.
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Im ortant Princi les continued
• Maintain constant bottom hole pressure by us the casing pressure. • Assume and desi n for a as kick unless the reservoir fluid is known. • Gas is more difficult to handle - primarily due to large expansion during circulating out a kick. (Boyle’s Law: P1V1 = P2V2) 44
