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Computer-aided control system design for drilling systems
Mathematics and Computers in Simulation 33 (1991) 165-172 North-Holland
165
Computer-Aided Control System Design for drilling systems W. Wajs and M. Capik University of Mining and Metallurgy, A! Mickiewicza 30, Krakow 30-059, Poland Abstract Wajs, W. and M. Capik, Computer-Aided Control System Design for drilling systems, Mathematics and Computers in Simulative, 33 (1991) 165-172. The paper outlines the application of a Computer-Aided Control System Design for a freeze-hole drilling system. The paper describes the discrete model of the drilling operation based on the constant energy methods of Fullerton, coupled with the hydraulic program and steering program for a solids control system for different drilling situations. It also presents the optimization of drilling operations for the freeze-hole drilling system as a problem of ordering.~obs on machines with simultaneous allocation of the constrained resources represented by the value of function.
1. Introduction
The paper outlines ~he application of a Computer-Aided Control System Design (CACSD) for a freeze-hole, drilling system. Efficiency of drilling performance for the (40-59) series of freeze-holes located on circles 14 to 17 m in diameter is a function of: technology, equipment and coordination of all drilling operations. The particular problems of drilling technology, selecting proper equipment and planning a drilling schedule, were solved, and most mining and drilling engineers are now reasonably familiar with the solution. More prominent was the successful araptat",,on of oil drilling equipment and practices in deep freeze-hole drilling. In spite of the long history of application of the ground freeing method (1883-Europe, 1888-North American continent) many drilling and coordination problems still occur during drilling for freeze-holes. Therefore, this paper proposes the application of System Engineering Technique (SET) for the current planning of drilling operations for the freeze-holes series. Drilling performance for a series of freeze wells is defined as a hierarchical system. In particular, the system elements are identk'2ed on the basis of the data from 391 freeze wells (depth H - 725 to H = 770 m) drilled in a mining region of Polav, d. The paper also describes a discrete model of the drilling operation, based on the constant energy methods of Fullerton coupled with the hydraulic program and steering program for a solids control system, for different drilling situations.
2. Problem statement
CACSD is used as two sep:~rated steps: ...~.r~,"~t,.~;t.~ ,~,~,~.....h,~,,.-.-v...,,,,,realizatiol~ of a SET operation for the design of a freeze hole drilling system; second it is used at the moment of realization of 0378-4754/91/$03.50 © 1991 - Elsevier Science Pub'.ishers B.V. (North-Holland)
166
W. Wajs, M. Capik / Control system design for drilling
the drilling operation. The freezing method is used for sinking shafts through unconsolidated and water-bearing formations which cannot be grouted effectively or economically, and which cannot be enclosed by piling. Under these conditions, it is the only sinking method for which a firm cost and time schedule can be given, znd the results guaranteed. A series of near vertical holes are drilled in a circle around the proposed shaft. These holes are cased and an internal plastic, brine circulation pipe runs inside each of them. Chilled brine is then circulated uniformly through all these freeze holes in order to completely freeze a cylinder of ground to a predetermined level beneath the water-bearing formations. The shaft is excavated inside the frozen cylinder, and the permanent lining placed. The ice wall is designed to assure safety of the shaft sinking operations, while providing the most economic cost for the project. The strength calculation is normally ba~ed only on that part of the ice wall which is between the freeze circle and the excavation. This strength will vary depending on the material to be frozen, the water content, and the circulating brine temperature. The excavation size also affects the required ice wall thickness. After excavation, the frozen material expands or moves slightly inwards to relieve the ice pressure built up. This can reduce the diameter of the excavation from 2 to 5 inches, depending upon the material frozen, and must be provided for in the shaft sinking plans. The process of freeze-hole drilling system design comprises the following steps: (1) (2) (3) (4) (5)
Choice of the design task and criteria (quality coefficients and bounds). Determination of the clrilling system structure. Flow sheeting scheme design, and processing of flow sheeting procedures. Optimization of parameters of the drilling system selected in Step 2. If requirements defined in Step 1 are not fulfilled go to Step 2.
2.1. Choice of the design task and conditions Condition for the task realization: (1) Speed of drilling process (rate of penetration) is given by a function [5]:
o, = l ( z , . , v/D , . ) (2) (3) (4) (5) (6)
Total number of bit rotation K c is defined by statistical method. H(i) - H(i - 1) = const. P and n are const, for the distance H ( i ) - H ( i - 1). If technical conditions for the drill are not fulfilled then the drill is replaced by a new one. If relation P • n / D s ---f(Ns) is not fulfilled, the P and n are changed t~ntil it is true.
(7) Prnin < Ppwi < IOrnax"
Model of drilling processes t:=t+ if(H(i)-H(i-1))/(z,p(i), P/D~,)>K~ then Tw(i) + Tp,,3(i) eise (H(i)-H(i-1))/(Zsp(i), P • n / D s ) + Tak + Tp,v2(i)
W. Wajs, M. Capik / Controlsystem designfor drilling
167
K := if (H(i) - H(i - 1))/( Zsp (i) • P / D s ) > K c then K¢ else K+(H(i)H ( i - 1))/(Zsp(i ) • P / D s ) 2.2. Determination of the drilling system structure
Drilling system structure contains of ',hree parts: 2.2.1. Investigation research Identification and evaluation of geological and drilling conditions (identification environmental drilling subsystem). Identification and evaluation of the technical condition of drilling equipment. 2. 2. 2. Technical project Work organization drilling subsystem design. Well performance models for a single frozen hole design (variant 1, variant 2 .... , variant n). Coordination of the drilling operation models (coordination of drilling operation being done on
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L- I
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N
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,, _
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,,
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168
W. Wajs, M. Capik / Control system design for drilling
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users
h
~,~1 WEIGHT ON BIT PREDICTION
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ii
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ii
MUD SELECTION
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ilI~-~.
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Data by DAILY II REPORTING SYSTEM Input data by u s e r s
{ Fig. 3. Drilling technology.
_
m
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~----
Fig. 4. Rig equipment evaluation.
tll
ANALYSIS AND CONTROL OF DRILLING HUD
I
INPUT
~m
"l ANAL'sIs°FII HYDRAULICS
THI
[
DRILLING TIME PREDICTION
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REPORTING SYSTEM Input data by users
ii"
it
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"11
CONTROL OF MUD]~ EQUIPMENT
ANALYSIS ~I ANALYSIS OF MECHANICAL i1 FACTURS
L____-.f.._.....J Fig. 5 Time and cost evaluation.
Fig. 6. Drilling technology analysis.
II'
169
W. Wajs, M. Capik /Control system design ~or drilling
i
NPUT
~m PROCEDURES
INPUT (from integrated data ~ I ] STUCK PIPE system) Company achieve PROCEDURES Bibliography data Data by DAILY REPORTING
SYSTEM
I n p u t d a t a by users
OUTPUT
LOST CIRCULATION PROCEDURES
]i+'
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It
-t__. . . . . . . . . . . . . . . . . . . . . . . .
i
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iEXPLOI+A+'O " t
OUTPUT
I
+!! DRILLING ROPE II,
Fig. 7. Drilling problems.
l
,
I
Fig. 8. Exploitation.
n-rigs). Well performance models analysis. Selection of well performance model-work time schedule. 2.2.3. Research real system
Identification of well performance disturbance. Verification of well performance model-work time schedule.
INPUT EFFICIENT OF . . . . . . ' DRILLING INPUT (form integrated data /| system) ~ 1 BREAKEVEN COST Company a c h i e v e /1 CALCULATION Bibliography data Data by DAILY REPORTING SYSTEM 1[ MUD SYSTEM Input
data by
~I
[i+,
HAINTENANCE
users
[] CALCULATION OF I[ ~ [ PRESENT COST IF1 | l OF THE HOLE l/ I
Fig. 9. Economy.
14". Wajs, M. Capik / Control system design for drilling
170
2.3. Flow sheeting schemes design and processing of flow sheeting procedures See Figs. 1-9.
3. Proposal of the solution We propose to build the CACSD system using a combination method. Dae to the proposed method of calculating the time of the drilling operation, it i~ possible to determine the prognosis of the completion time for a given time interval. Each drilling operation is described by two parameters: P and n. As an introduction to the description of the optimization method, we formulate the basic optimization task. The purpose of optimization is to find a combination (a combination is an arrangement of elements { P, n }) for which the minimal value of the performance index is obtained.
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, ~
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.52
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78
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\
Q
240
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Ns, kW
"-Q, m~/s,4O2 Vm, rn/h
---T, h
~50__~.~___.~@pwi, kg/rn r~
------z:L • -Ns
.......
Ns: ~!.5 kW'
/
Q= 2.~ !g~ "~','sI
p=
'
Ti..", = 27,4.4 n TG: ~.~:',-,6 n
d:oO, O08 m I dcO.O08 m J
Tog-- 2,5.~ n
~78,o, 3o. . . . . .
To = 29,g2 n T.pD =45,55 h T(L) =204,78 h
~b,O, 40.
'------------
5~8,0, 50.
..v~ 6g5,0, 6O. i
rG Fig. 10. Example of optimum drilling parameters, and results of the optimization procedure, e.g. rate of penetration and cumulative time of drilling operations.
W. Wajs, M. Capik / Control system design for drilling
171
We formulate a partial optimization task as: To find a combination ( e l , 111). (P2. 112). . . . . (Pk, Elk) for which the minimal value of the performance index t(1) + / ( 2 ) . . . . . t ( k ) satisfying constraints [5] Pp < Ppwi < Pmax
Ns( P * n/D~) < Ns < Ns(Qsz) Kc=K,, is obtained. The total computational effort needed for determining the sequence of drilling operations are not greater than
( H m a x / A H - k + 1) k.
4. R e s u l t s
Results of simulation for i = 60, A H ( i ) = 9 and k = 5 are shown in Fig. 10.
Appendix. Nomenclat
re
® t: total time of drilling operations.
• Tw: drilling time as a function of depth. o Tdk: drill string elements time condition. • Tpw2: time of auxiliary drilling operations the hole before tripping in. • n: rotary speed of bit. o Ns: bit hydraulic horsepower. o Ppwi: density of drilling mud with cuttings. • Ta: cumulative time of drilling operation = total time of drilling operation. e
TG=t.
® To: time of casing and cementing operation.
ej Tpws: time of auxiliary drilling operations the hole before tripping out. o zsp(i): apparent formation drill ability factor. o Ds: bit diameter. o P: weight on bit. o K: current number of bit rotations. o K,.: total number of bit rotations. o Q: mud pump flow rate.
172
W. Wajs, M. Capik /Controlsystem design for drilling
e Qs-: mud pump flow rate for fracturing of wall of the boreho!e. e H(i)" depth of i th hole inte~wa!. 0 Vt'. " " * * of . . , ~ . . o t r ~ t ; , . . e pp: m,ad density. e H: depth of hole. o Thg: time of well testing. ® TM.,D: time of moving the rig. ® Pp: mud pump pressure. o t , - drilling rate.
References
J.E. Encarnacao and E.G. Schlechtendahl, Computer Aided Design (Springer, Berlin, 1983). W. Wajs, Sequencing control of physice-chemical processes, Kybernetes (15) (1986) 157-164. M. Jamshidi and C.J. Herget, Computcr-Aided Control System Engineering (North-Holland, Amsterdam, 1985). M. Capik, Optimizing drilling system for frozen wells, PhD thesis, Univ. Mining and Metallurgy, Krakow, Poland, 1987. [5] H.B. Fullerton and H.B. Fullerton Jr, Constant energy drilling system for well programing, Sii Smith Tools, Irvine, CA, 1973, unpublished.
[1] [2] [3] [4]
165
Computer-Aided Control System Design for drilling systems W. Wajs and M. Capik University of Mining and Metallurgy, A! Mickiewicza 30, Krakow 30-059, Poland Abstract Wajs, W. and M. Capik, Computer-Aided Control System Design for drilling systems, Mathematics and Computers in Simulative, 33 (1991) 165-172. The paper outlines the application of a Computer-Aided Control System Design for a freeze-hole drilling system. The paper describes the discrete model of the drilling operation based on the constant energy methods of Fullerton, coupled with the hydraulic program and steering program for a solids control system for different drilling situations. It also presents the optimization of drilling operations for the freeze-hole drilling system as a problem of ordering.~obs on machines with simultaneous allocation of the constrained resources represented by the value of function.
1. Introduction
The paper outlines ~he application of a Computer-Aided Control System Design (CACSD) for a freeze-hole, drilling system. Efficiency of drilling performance for the (40-59) series of freeze-holes located on circles 14 to 17 m in diameter is a function of: technology, equipment and coordination of all drilling operations. The particular problems of drilling technology, selecting proper equipment and planning a drilling schedule, were solved, and most mining and drilling engineers are now reasonably familiar with the solution. More prominent was the successful araptat",,on of oil drilling equipment and practices in deep freeze-hole drilling. In spite of the long history of application of the ground freeing method (1883-Europe, 1888-North American continent) many drilling and coordination problems still occur during drilling for freeze-holes. Therefore, this paper proposes the application of System Engineering Technique (SET) for the current planning of drilling operations for the freeze-holes series. Drilling performance for a series of freeze wells is defined as a hierarchical system. In particular, the system elements are identk'2ed on the basis of the data from 391 freeze wells (depth H - 725 to H = 770 m) drilled in a mining region of Polav, d. The paper also describes a discrete model of the drilling operation, based on the constant energy methods of Fullerton coupled with the hydraulic program and steering program for a solids control system, for different drilling situations.
2. Problem statement
CACSD is used as two sep:~rated steps: ...~.r~,"~t,.~;t.~ ,~,~,~.....h,~,,.-.-v...,,,,,realizatiol~ of a SET operation for the design of a freeze hole drilling system; second it is used at the moment of realization of 0378-4754/91/$03.50 © 1991 - Elsevier Science Pub'.ishers B.V. (North-Holland)
166
W. Wajs, M. Capik / Control system design for drilling
the drilling operation. The freezing method is used for sinking shafts through unconsolidated and water-bearing formations which cannot be grouted effectively or economically, and which cannot be enclosed by piling. Under these conditions, it is the only sinking method for which a firm cost and time schedule can be given, znd the results guaranteed. A series of near vertical holes are drilled in a circle around the proposed shaft. These holes are cased and an internal plastic, brine circulation pipe runs inside each of them. Chilled brine is then circulated uniformly through all these freeze holes in order to completely freeze a cylinder of ground to a predetermined level beneath the water-bearing formations. The shaft is excavated inside the frozen cylinder, and the permanent lining placed. The ice wall is designed to assure safety of the shaft sinking operations, while providing the most economic cost for the project. The strength calculation is normally ba~ed only on that part of the ice wall which is between the freeze circle and the excavation. This strength will vary depending on the material to be frozen, the water content, and the circulating brine temperature. The excavation size also affects the required ice wall thickness. After excavation, the frozen material expands or moves slightly inwards to relieve the ice pressure built up. This can reduce the diameter of the excavation from 2 to 5 inches, depending upon the material frozen, and must be provided for in the shaft sinking plans. The process of freeze-hole drilling system design comprises the following steps: (1) (2) (3) (4) (5)
Choice of the design task and criteria (quality coefficients and bounds). Determination of the clrilling system structure. Flow sheeting scheme design, and processing of flow sheeting procedures. Optimization of parameters of the drilling system selected in Step 2. If requirements defined in Step 1 are not fulfilled go to Step 2.
2.1. Choice of the design task and conditions Condition for the task realization: (1) Speed of drilling process (rate of penetration) is given by a function [5]:
o, = l ( z , . , v/D , . ) (2) (3) (4) (5) (6)
Total number of bit rotation K c is defined by statistical method. H(i) - H(i - 1) = const. P and n are const, for the distance H ( i ) - H ( i - 1). If technical conditions for the drill are not fulfilled then the drill is replaced by a new one. If relation P • n / D s ---f(Ns) is not fulfilled, the P and n are changed t~ntil it is true.
(7) Prnin < Ppwi < IOrnax"
Model of drilling processes t:=t+ if(H(i)-H(i-1))/(z,p(i), P/D~,)>K~ then Tw(i) + Tp,,3(i) eise (H(i)-H(i-1))/(Zsp(i), P • n / D s ) + Tak + Tp,v2(i)
W. Wajs, M. Capik / Controlsystem designfor drilling
167
K := if (H(i) - H(i - 1))/( Zsp (i) • P / D s ) > K c then K¢ else K+(H(i)H ( i - 1))/(Zsp(i ) • P / D s ) 2.2. Determination of the drilling system structure
Drilling system structure contains of ',hree parts: 2.2.1. Investigation research Identification and evaluation of geological and drilling conditions (identification environmental drilling subsystem). Identification and evaluation of the technical condition of drilling equipment. 2. 2. 2. Technical project Work organization drilling subsystem design. Well performance models for a single frozen hole design (variant 1, variant 2 .... , variant n). Coordination of the drilling operation models (coordination of drilling operation being done on
ii SELECTION CASING OF II SETTINGS • DEPTHS l ~ESIGN STRING]i-~.
]!
Fit
" ~ DRILLING ,
II 1[ ....
,'
...... II .ii
INPUT ( f r o m integrated data system) Company a c h i e v e Bib1 i o g r a p h y d a t a D a t a by DAILY REPORTING SYSTEM
Inputdataby
NEASURE '~~~
DESIGN DESIGN
users
L- I
II
-CEMENT ,
N
?[
MOVING Fig. i. Drilling system structure.
,, _
WELL ~ A D
,,
[--ou;Pu; ........... Fig. 2. Hole construction.
I/
168
W. Wajs, M. Capik / Control system design for drilling
"11
SELECTION
i
.... F~
NPUT
INPUT (form integrated data system) Company achieve Bibliography data Data by DAILY REPORTING SYSTEM Input data by
users
h
~,~1 WEIGHT ON BIT PREDICTION
/I
i,I"
li'
~4"IT .YD~.AULICS
IIPREOICTIO.
'4i
ii
DRILLING
ii
MUD SELECTION
iH!
ii i ii i
I
INPUT
I
~
_ Ti. ~ i - ~i DRILLING ~ - RIG
INPUT (form int g r a t e d data system) Company achieve
ilI~-~.
l iI.SELECTION [] |/' :~ "-=--~---='---~" t,.,,.~.] SOLID CONTROL I] h EQUIPMENT IL,
Data by DAILY II REPORTING SYSTEM Input data by u s e r s
{ Fig. 3. Drilling technology.
_
m
OUTPUT
~----
Fig. 4. Rig equipment evaluation.
tll
ANALYSIS AND CONTROL OF DRILLING HUD
I
INPUT
~m
"l ANAL'sIs°FII HYDRAULICS
THI
[
DRILLING TIME PREDICTION
INPUT i form |l| i n t e g r a t e d data ~ { . system) L , ~ I DRILLING Company achieve /1 COST ~i~r~ydata /I PREDICTION
REPORTING SYSTEM Input data by users
ii"
it
INPUT (form i n t e g r a t e d data ~ystem) Company achieve Bibliography data Data by DAILY REPORTING SYSTEM Input d a t a by users
"11
CONTROL OF MUD]~ EQUIPMENT
ANALYSIS ~I ANALYSIS OF MECHANICAL i1 FACTURS
L____-.f.._.....J Fig. 5 Time and cost evaluation.
Fig. 6. Drilling technology analysis.
II'
169
W. Wajs, M. Capik /Control system design ~or drilling
i
NPUT
~m PROCEDURES
INPUT (from integrated data ~ I ] STUCK PIPE system) Company achieve PROCEDURES Bibliography data Data by DAILY REPORTING
SYSTEM
I n p u t d a t a by users
OUTPUT
LOST CIRCULATION PROCEDURES
]i+'
]I+
It
-t__. . . . . . . . . . . . . . . . . . . . . . . .
i
EXPLOITATION INPUT (form integrated data system) ~1! RIG RE ABILITYII Company a c h i e v e FORECAST Bibliography data Data by DAILY REPORTING SYSTEM I n p u t d e t a by users
iEXPLOI+A+'O " t
OUTPUT
I
+!! DRILLING ROPE II,
Fig. 7. Drilling problems.
l
,
I
Fig. 8. Exploitation.
n-rigs). Well performance models analysis. Selection of well performance model-work time schedule. 2.2.3. Research real system
Identification of well performance disturbance. Verification of well performance model-work time schedule.
INPUT EFFICIENT OF . . . . . . ' DRILLING INPUT (form integrated data /| system) ~ 1 BREAKEVEN COST Company a c h i e v e /1 CALCULATION Bibliography data Data by DAILY REPORTING SYSTEM 1[ MUD SYSTEM Input
data by
~I
[i+,
HAINTENANCE
users
[] CALCULATION OF I[ ~ [ PRESENT COST IF1 | l OF THE HOLE l/ I
Fig. 9. Economy.
14". Wajs, M. Capik / Control system design for drilling
170
2.3. Flow sheeting schemes design and processing of flow sheeting procedures See Figs. 1-9.
3. Proposal of the solution We propose to build the CACSD system using a combination method. Dae to the proposed method of calculating the time of the drilling operation, it i~ possible to determine the prognosis of the completion time for a given time interval. Each drilling operation is described by two parameters: P and n. As an introduction to the description of the optimization method, we formulate the basic optimization task. The purpose of optimization is to find a combination (a combination is an arrangement of elements { P, n }) for which the minimal value of the performance index is obtained.
0
~0
20
f
0 F 0 0 [ ~090 6~,0 ~ .
.
50 0:5 ,t26
60 ~i0 2.52
go 4;5 .5,78
'1~
26
.~g
.(060 . .
4070
'10RO
t
, ~
420 z~o 5L04
~0 z;5 6.~0
480 &o 7t~6
2'10 &--:, 8,82
4:o
4:5
5.0
~0.,38
44,54
42,G0
.52
65
78
g4
J.O4
447
'1]::43
~'10
4.120
4450
'M4U
40£0 - - - - - 4400 . - ~
\
Q
240
27U
,~00
Ns, kW
"-Q, m~/s,4O2 Vm, rn/h
---T, h
~50__~.~___.~@pwi, kg/rn r~
------z:L • -Ns
.......
Ns: ~!.5 kW'
/
Q= 2.~ !g~ "~','sI
p=
'
Ti..", = 27,4.4 n TG: ~.~:',-,6 n
d:oO, O08 m I dcO.O08 m J
Tog-- 2,5.~ n
~78,o, 3o. . . . . .
To = 29,g2 n T.pD =45,55 h T(L) =204,78 h
~b,O, 40.
'------------
5~8,0, 50.
..v~ 6g5,0, 6O. i
rG Fig. 10. Example of optimum drilling parameters, and results of the optimization procedure, e.g. rate of penetration and cumulative time of drilling operations.
W. Wajs, M. Capik / Control system design for drilling
171
We formulate a partial optimization task as: To find a combination ( e l , 111). (P2. 112). . . . . (Pk, Elk) for which the minimal value of the performance index t(1) + / ( 2 ) . . . . . t ( k ) satisfying constraints [5] Pp < Ppwi < Pmax
Ns( P * n/D~) < Ns < Ns(Qsz) Kc=K,, is obtained. The total computational effort needed for determining the sequence of drilling operations are not greater than
( H m a x / A H - k + 1) k.
4. R e s u l t s
Results of simulation for i = 60, A H ( i ) = 9 and k = 5 are shown in Fig. 10.
Appendix. Nomenclat
re
® t: total time of drilling operations.
• Tw: drilling time as a function of depth. o Tdk: drill string elements time condition. • Tpw2: time of auxiliary drilling operations the hole before tripping in. • n: rotary speed of bit. o Ns: bit hydraulic horsepower. o Ppwi: density of drilling mud with cuttings. • Ta: cumulative time of drilling operation = total time of drilling operation. e
TG=t.
® To: time of casing and cementing operation.
ej Tpws: time of auxiliary drilling operations the hole before tripping out. o zsp(i): apparent formation drill ability factor. o Ds: bit diameter. o P: weight on bit. o K: current number of bit rotations. o K,.: total number of bit rotations. o Q: mud pump flow rate.
172
W. Wajs, M. Capik /Controlsystem design for drilling
e Qs-: mud pump flow rate for fracturing of wall of the boreho!e. e H(i)" depth of i th hole inte~wa!. 0 Vt'. " " * * of . . , ~ . . o t r ~ t ; , . . e pp: m,ad density. e H: depth of hole. o Thg: time of well testing. ® TM.,D: time of moving the rig. ® Pp: mud pump pressure. o t , - drilling rate.
References
J.E. Encarnacao and E.G. Schlechtendahl, Computer Aided Design (Springer, Berlin, 1983). W. Wajs, Sequencing control of physice-chemical processes, Kybernetes (15) (1986) 157-164. M. Jamshidi and C.J. Herget, Computcr-Aided Control System Engineering (North-Holland, Amsterdam, 1985). M. Capik, Optimizing drilling system for frozen wells, PhD thesis, Univ. Mining and Metallurgy, Krakow, Poland, 1987. [5] H.B. Fullerton and H.B. Fullerton Jr, Constant energy drilling system for well programing, Sii Smith Tools, Irvine, CA, 1973, unpublished.
[1] [2] [3] [4]