This paper was prepared for presentation at the SPE Asia Pacific Oil & Gas Conference held in Melbourne, ... pressure drop along horizontal oil-well can be.
Society of Petroleum Engineers
SPE 28801
The Application of Pressure Drop Through a Horizontal Well Correlation to Oil Well Production Performance. by Azmi M. Arshad, Muhammad A. Manan and Abdul R. Ismail Universiti Teknologi Malaysia Copyright 1994, Society of Petroleum Engineers, Inc. This paper was prepared for presentation at the SPE Asia Pacific Oil & Gas Conference held in Melbourne, Australia, 7-10 November 1994. This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presen1ed. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A. Telex 163245 SPEUT.
ABSTRACT
INTRODUCTION
From the petroleum engineering standpoint, pressure drop through a horizontal wellbore is very small and is negligible in predicting the production performance. However, not much research has been done to study this phenomenon and more importantly to prove the above assumption.
Many researchers argued that multiphase flow pressure drop along horizontal oil-well can be ignored when predicting well production performance. Some of these arguments were supported by calculation of pressure drop due to pipe wall friction. This, however is not true. Fluid inflow through the perforation causes flow disturbance and momentum change along the hole, thus creating additional pressure drop (See Fig. 1). This pressure drop may affect the calculation of inflow rate distribution along the hole especially in long low drawdown wells and high permeability reservoirs. The inflow rate distribution calculation is very important when dealing with thin oil rims with underline water or/and overlying gas, where possible coning problems might occur at the highest inflow rate section. Controlling the optimum oil production rate and designing appropriate completion should be done to avoid premature water or gas breakthrough.
This paper discuss the application of published pressure drop through a horizontal well correlation in the prediction of horizontal oil-well production performance. The correlation relates two-phase pressure drop along the hole to the fluid inflow from the reservoir. This correlation together with friction and hydrostatic effects were used to determine the total pressure drop from the wellhead to the well tip. The calculations by iteratively solving pressure drop along pipe equations with reservoir flow equations was done with the aid of computer program. The study proves that pressure drop is very important in predicting the inflow rate distribution along well bores especially when using small perforated rough pipes and dealing with long horizontal wellbores.
References and illustrations at end of the paper
The early study on this subject was made by Dikken 1• He developed simple analytical models for single phase flow in well bores and steady state fluid flow in the reservoirs. These two models were solved simultaneously to give solutions for cases of infinite or fmite well length. The results of the study are quite interesting. It shows that the calculation of pressure drop along the horizontal hole is very
2
AZMI M. ARSHAD, MUHAMMAD A. MANAN & ABDUL R. ISMAIL
important especially in calculating inflow rate and production performance. The study was then followed by several others. 2 -7 Only correlations by Asheim et al. 8 and Arshad et al.9 were found in literatures where simple and direct correlation describing the effect of fluid inflow through the perforation on the pressure drop along the pipe were developed. However, no application of the correlations was introduced. The focus of this study was on the use of these correlations to calculate well performance behavior. The correlations was combined with the two phase frictional effect along the pipe and coupled with the reservoir flows. Pressure drop and flow behavior along the well and the relationship between the pressure drop and the fluid inflow from the reservoir were studied.
PRESSURE DROP BY FLUID INFLOW Conceptually, fluid inflow through the perforations may affect the pressure drop along the wellbore by: (a) Disturbing the boundary layer at the pipe Wall, thus altering the wall friction. 8 (b) Disturbing the pipe flow pattern, thus changing the flow frictional effect, and (c) Consuming pressure energy to accelerate the inflow streams up to the average pipe flow velocity.8
Asheim et ale Correlation Asheim et al. correlation was produced from combined theoretical and experimental studies on single phase wellbore flow with fluid inflow effects due to perforations. They proposed a new flow resistance correlation combining the effect of wall friction and external fluid inflow through perforations. The external fluid inflow pressure drop correlation itself can be described by:
SPE 28801
Arshad et ale Correlation Arshad et al. correlation is the results of two phase experimental studies and mathematical modeling. One inch inside diameter PVC pipe was used to study the effect of single and multiple perforations on pressure drop along the pipe. Eighty-one sets of data points were analyzed from the experiment that was used air and water as two phase fluids. The study proves that the effect of multiple perforations can be neglected to calculate the pressure drop. However, the volume of in situ two phase inflow rates entering the pipe controls the amount of pressure drop. The correlation developed is given by:
where cross-sectional area of the pipe (m2) Ap Vg gas flow velocity in the pipe (mls) gas density (kg/m3) Pg gas inflow rate per length unit (rft3/s/m) qg In horizontal pipe flow, the difference between the velocity of liquid and gas through the pipe is very small. For that reason, the terms liquid and gas velocities can be replaced by single term named average mixture velocity. The equation then can be modified to:
where Vm
average mixture flow velocity of gas and liquid in the pipe (mls)
COMPUTER MODELING Computer programmed model was developed to predict the performance of horizontal oil-well. Only Arshad et al. correlation was used in this model because both correlations by Arshad et al. and Asheim et al. are identical when dealing with liquid flow.
Wellbore-reservoir Boundary Conditions where
PI VI
qi Q
liquid density (kg/m3) liquid flow velocity in the pipe (mls) liquid inflow rate per length unit (m3/s/m) liquid pipe flow rate (m3/s)
Fluid inflow between the reservoir and the wellbore relates the pressure drawdown to the horizontal well productivity indices. Several solutions are available in literature to predict the radial steady state flow rate in a horizontal well. For this study, the oil production rate equation from Borisov lO was
THE APPLICATION OF PRESSURE DROP THROUGH A HORIZONTAL WELL CORRELATION TO OIL WELL PRODUCTION PERFORMANCE
SPE 28801
selected to be used. The equation can be expressed by: _ qh -
where qh
kh h
Pr Pwf Ilo Bo reh
L
rw
21tk h h(P r
-
P wf)
~.B.H 4~m )+(~)mC!JJ
horizontal well inflow rate (m3/s) horizontal well permeability (m2) reservoir thickness (m) reservoir pressure (Pa) well flowing pressure (Pa) oil viscosity (kg/rn/s) oil formation volume factor (vol/vol) drainage radius (m) horizontal well length (m) well bore radius (m)
Well bore-reservoir Coupling The final phase of the study was to couple the two phase correlation to the reservoir flows. The methodology used for the study is a sequential algorithm outlined below: (1) All the reservoir, well bore and oil properties
were initialized. Initial predicted of oil production rate has to be estimated (at this time, inflow rates was assumed to be constant in the whole section of horizontal length). (2) Based on the predicted value of production rate, the pressure distributions along the vertical and horizontal hole were calculated using Beggs and Brill correlation 11 and Arshad et al correlation. The pressure drop from the top (fixed wellhead value) to the tip of the well was calculated by dividing the well into several segments. (3) The new value of production rate was calculated based on the drawdown between the new horizontal well bore pressure distribution and reservoir pressure. (4) A comparison is made between the predicted and calculated values of production rates. If the difference was less than a user specified tolerance, this implies that the well bore pressure distribution and production rates were fully coupled. Otherwise, the calculated production rate was used as new predicted value and the procedure repeated from step (2) onwards.
3
RESULTS The computer modeling study was design to investigate the effects of inside pipe diameter size and pipe surface roughness on pressure drop along the well. This pressure drop will be used to determine whether its effects are significant or can be ignored in calculating inflow rate distribution and production performance. The basic datas for well, reservoir and crude oil properties that were used in this study are shown in Table 1. A very high reservoir pressure was introduced so that the well can produce at a very high flow rate.
Well Pressure Drop vs. Constant Well Pressure To study the difference between these two schemes, several runs were been made. Fig. 2 to 5 show the results of the study. It was found that pressure drop along 3000 ft horizontal section is about 53 psia. Friction contributes about 43 psia and another 10 psia comes from fluid inflow pressure drop. This pressure drop causes the inflow distribution along the well ranging from 6.54 B/D/ft at the front end to 4.86 B/D/ft at the tail end of the perforations. However, this difference does not alter significantly the overall production rate compared to when constant well pressure was used. As shown in Fig. 4, the use of constant well pressure is predicted to be only about 1.3% higher than the use of well pressure drop.
Inside Pipe Diameter Size Fig. 6 to 8 show the results of sensitivity analysis the effects of three different sizes of inside pipe diameter. The values of the diameter used were 4.276", 5.920" and 8.535". It is known that the use of bigger diameter will decrease the velocity inside the pipe, thus reducing the pressure drop along the pipe. As an example, for 8.535" ID pipe size, the inflow distribution along the pipe is almost constant due to small pressure difference along the pipe. However, low pressure drop and the increase in well productivity index for bigger ID pipe size do not increase the total production rate significantly. The use of 8.535" ID instead of 4.276" ID for 3000 ft horizontal length only contributes about 1.34% additional production.
4
AZMI M. ARSHAD, MUHAMMAD A. MANAN & ABDUL R. ISMAil..
SPE 28801
Pipe Surface Roughness
CONCLUSIONS
Three values of pipe surface roughness was used in this study. The values range from 0.00006 ft. for a quite smooth pipe to 0.006 ft. for a very rough pipe. To overcome the convergence problems, horizontal well length was extended only to 2,000 ft. Fig. 9 and Fig. 10 show the results of the study. From the figure, one can see that the use of three different values of surface roughness do not significantly affect the overall production performance. The difference in total production rates when using 0.00006 ft and 0.006 surface roughness is only 170 BID (1.1 % different). However, the use of the later surface roughness causes the inflow distribution to vary significantly along the hole, with the value at the front end about 25% higher compared to the value at the tail end of the perforations.
1.
A computer model that coupled frictional and inflow pressure drop with reservoir flows was developed. The model could be used to study the effect of well pressure drop on horizontal well production performance.
2.
Study on pressure drop along horizontal well bore must be incorporated with tubing performance relationship. Ignoring it will leads to underprediction of production rate.
DISCUSSIONS All the above results show that pressure drop in horizontal wellbore does not alter significantly the overall production rate compared to constant pressure drop. Of course one can understand that an increase in pressure drop along the horizontal hole causes the inflow rates to decrease towards the tail end, thus decreasing the overall production. However, one has to remember that the decrease in oil production rate will change the pressure distribution along the tubing, and at the same time increase the draw down at the front end of the perforation that contributes additional inflow at this section. These 'gain and loss' processes do not cause the total production rate to change significantly. It proves that some of the previous study that do not include tubing performance relationship will only can see the 'loss' process and of cause it will lead to underprediction of production rates. Although this pressure drop does not alter significantly the production rate, it could be very important in the reservoir point of view. The variation of inflow rate distribution along a horizontal hole could be used to predict the behavior of water/gas coning. Possible water/gas coning might occur at the front end of the perforations where the inflow rate are highest. Furthermore, the use of injection well nearby might causes an early breakthrough at this section and resulting in poor oil recovery and sweep efficiency. Further study must be made in this area such as to incorporate this pressure drop correlation to a reservoir simulator, so that long term effect of both production and reservoir behavior can be studied.
3. The effect of pressure drop along horizontal wellbore, whether by frictional or by fluid inflow do not alter significantly the overall production rate compared to the used of constant well pressure. 4.
Pressure drop along horizontal hole might be very important in the reservoir point of view. Higher inflow rate at the front end of the perforation might cause water/gas coning occur at this section. In the case where a nearby injection well is present, early breakthrough might occur at this section resulting on very poor recovery and sweep efficiency.
NOMENCLATURE Ap
Bo h kh L p Pr Pwf Qg
qh Q qI reh rw £
110 Vg VI Vrn Pg PI
cross-sectional area of the pipe (m2) oil formation volume factor (vol/vol) reservoir thickness (m) horizontal well permeability (m2) horizontal well length (m) pressure (Pa) reservoir pressure (Pa) well flowing pressure (Pa) gas inflow rate per length unit (m3/s/m) horizontal well inflow rate (m3/s) liquid pipe flow rate (m3/s) liquid inflow rate per length unit (m3/s/m) drainage radius (m) well bore radius (m) pipe surface roughness (m) oil viscosity (kglrn/s) gas flow velocity in the pipe (rn/s) liquid flow velocity in the pipe (rn/s) average mixture flow velocity of gas and liquid in the pipe (rn/s) gas density (kg/m3) liquid density (kglm3)
SPE 28801
THE APPLICATION OF PRESSURE DROP THROUGH A HORIZONTAL WELL CORRELATION TO On.. WELL PRODUCTION PERFORMANCE
5
Drop Along the Wellbore on Horizontal Well Productivity", SPE 25502, presented at the Production Operations Symposium, Oklahoma City, OK, USA, March 21-23, 1993.
REFERENCES 1. Dikken, B.J., "Pressure Drop in Horizontal Wells and Its Effect on Production Performance", JPT, November, 1990, p. 14261433.
7.
2. Folefac, A.N., Archer, J.S., Issa, R.I. & Arshad, A.M., "Effect of Pressure Drop Along Horizontal Wellbores on Well Performance", SPE 23094, presented at Offshore Europe Conference, Aberdeen, UK, September 3-6, 1991.
Le Gallo, Y.L.& LatH, M.J., "Modeling Thermal and Pressure Drops for Multiphase Flow in Thermal Horizontal Wells", SPE 26077, presented at the Western Regional Meeting of the SPE, Anchorage, Alaska, May 26-28,1993.
8.
Asheim, H., Kolnes, J. & Oudeman, P., "A Flow Resistance Correlation for Completed Wellbore", Journal of Petroleum Science and Engineering, vol.8, no.2, 1992, p. 97-104.
9.
Arshad, A.M., Othman, A., Abdul, M.R. & Bakar, M.A., "Aliran Dua Fasa di Bahagian Mendatar Telaga", presented at the Faculty of Chemical and Natural Resources Engineering Research Seminar, Universiti Teknologi Malaysia, Kuala Lumpur, June 23-24, 1993.
3.
4.
5.
6.
Ihara, M., Furukawa, H., Takao, S. & Yanal, K., "Experimental Investigation on the Interaction between the Fluid Influx from the Reservoir and the Pressure Distribution Along a Horizontal Well Configuration", presented at 9th Conference & Exhibition of Offshore South East Asia, Singapore, December 1-4, 1992. Islam, M.R. & Chakma, A., "Comprehensive Physical and Numerical Modeling of a Horizontal Well", SPE 20627, presented at 65th Annual Technical Conference and Exhibition of the SPE, September 23-26, 1990. Novy, R.A., "Pressure Drops in Horizontal Wells: When can They be Ignored?", SPE 24941, presented at 67th Annual Technical Conference and Exhibition of the SPE, 1992. Ozkan, E., Sarica, C., Haciislamoglu, M. & Raghawan, R., "The Inference of Pressure
10. Borisov, J u.P.," Oil Production Using Horizontal and Multiple Deviation Wells", Nedra, Moscow, 1964. Translated by J. Strauss, S.D. Joshi (ed.), Phillips Petroleum Co., the R&D Library Translation, Bartlesville, Oklahoma, 1984. 11. Beggs, H.D. & Brill, J.P., "A Study of TwoPhase Flow in Inclined Pipes", JPT, May, 1973, p. 607-617.
SPE 28801
AZMI M. ARSHAD, MUHAMMAD A MANAN & ABDUL R. ISMAil.
6
Fluid Inflow
--'-~
~
~
APFriction
Distance Fig.l: Schematic Diagram of Pressure Drop due to Friction and Fluid Inflow.
Absolute roughness of pipe/liner Absolute roughness of tubing Average reservoir pressure Gas Specific gravity Inside diameter of pipe/J.iner Inside diameter of tubing Length of horizontal well section Length of vertical tubing Oil gravity Producing gas-oil ratio Radius of reservoir boundary Reservoir penneability Reservoir temperature Reservoir thickness Separator pressure Seperator temperature Wellhead pressure
7~
6.5
......
E
.
~
~ e
.:! '" 2750 -9>0 !:!
;
j
2700
~
Well pressure drop (16,110 BID) Constant well pressure (16,330 BID)
2800
o
50 fL 200 psia 1200F 2S0psia
______________________________
--0--
2850
Po.
I6()Op
Table I: Basic Datas for Well, Reservoir and Crudes •
2900
!:!
0.00006 ft. 0.00006 fL 3,000 psia 0.76 4.276 in. 2.75 in. 3,000 ft 4,000 ft. 3()OAPI 2,000 scf/STB 1,000 ft. lOOmd.
6
5.5
Well pressure drop
5
2650
'--'·0··--·
Constant well pressure
4.5~--~~---r----r----r----r----r~
2600
4000
5000
6000
7000
Measured Depth (ft)
Fig. 2: Wellbore Pressure Distribution with Well Pressure Drop and Constant Well Pressure.
o
SOD
1000
1500
2000
2SOO
3000
Length of horizontal section (ft)
Fig. 3: Inflow Rate Distribution with Well Pressure Drop and Constant Well Pressure.
THE APPLICATION OF PRESSURE DROP THROUGH A HORIZONTAL WELL CORRELATION TO On.. WELL PRODUCTION PERFORMANCE
SPE 28801
ro
17000 - , - - - - - - - - - - - - - - - - - . ,
50 16000
e:e.
40
~
30
e
Total pressure drop
-~--.
Inflow pressure drop
Q
.§
e
14000
"
£"
£ -0--
13000
o
600
1000
1400
Well pressure drop
Constant well pressure
1800
20
2200
2600
3000
10
O~~-----~-------_r-----_r~ o 1000 3000
Horizontal well length (ft)
Fig. 4: Well Production Rate with Well Pressure Drop and Constant Well Pressme.
28ro~-----------------~
Horizontal well length (ft)
Fig. 5: Frictional and Inflow Pressure Drop in Horizontal Well Section.
7-,----------______
2850
2840 ';;j'
].
-0--
.;;
£
ts
. ,a. .......
15000
7
2830
--------~-
---~
••
o~~'
~
-0--
ID = 4.276" (16,110 BID)
--0-
ID = 5.920" (16, 280 BID)
----'0----
ID = 8.535" (16,330 BID)
",...0
e
a E!
2820
J:I"
2810
-0--
ID = 4.276"
-·--0'-'
ID = 5.920"
•••• ~----
ID =8.535"
·~-··--~---·-----o
--O~--O---O~
5
2800
2790 -I---..-----.---r---..---~---r-...J 1000 1500 2000 2500 3000 o 500
4.5 -+----,r---~--__:r_--_r----r__--_.._....J o 500 1000 1500 2000 2500 3000
Length of horizontal section (ft)
Length of horizontal section (tt)
Fig. 6: Wellbore Pressure Distribution with Different Size of Inside Pipe Diameter.
Fig. 7: Inflow Rate Distribution with Different Size of Inside Pipe Diameter.
SPE 28801
AZMI M. ARSHAD, MUHAMMAD A. MANAN & ABDUL R. ISMAil...
8
ee
17~~--------------------------------,
'Il2!J ~-----------------------------,
16000
'IlOO
...... 2680
15000
• e
.;;
E
.&
g
'e:s
~
ill
14000
ID
-----0----
ID
2640
=8.S3S"
262!J
1~_r---~--~----,_--~r_--_r----r_~
600
1~
1400
2660
ID =S.92!J"
0
13000
£
=4.276"
1800
2200
2600
£
= 0.00006 ft
.--~--.
£
= 0.0006 ft
-----0----
£
=0.006 ft
~----__._----__.-----._----..._----.........._I
o
3000
--0-
800
400
Fig. 8: Well Production Rate with Different Size of Inside Pipe Diameter.
-0--
= 0.00006 ft (1S170 BID)
£
8.5 £= 0.0006 ft
0
(1S,13O BID)
...... £
8
= O.OO6ft
(IS,ooo BID)
£ f!
~ 0
7.5
.s 7
o
~
Fig. 9: Wellbore Pressure Distribution with Different Pipe Surface Roughness for 2000 ft horizontal well length.
9
I::
1600
Length of horizontal seaion (ft)
Horizontal we1l1ength (ft)
~ e
1200
400
800
1200
1600
2000
Length of horizontal section (ft)
Fig. 10: Inflow Rate Distribution with Different Pipe Surface Roughness for 2000 ft Horizontal Well Length.
