WHOC16 - 322 Changes in Annulus Pressure, Increase Oil Production. Carlos Brunings; PDVSA. Gabriel Becerra, PDVSA. Richard Marquez, INPELUZ. Linerbeth Garcia, INPELUZ. Leonardo Mena, ATS. Armando Riviere, ATS. Jose Marcano, PDVSA.. This paper has been selected for presentation and/or publication in the proceedings for the 2015 World Heavy Oil Congress. The authors of this material have been cleared by all interested companies/employers/clients to authorize dmg::events (Canada) inc., the congress producer, to make this material available to the attendees of WHOC2015 and other relevant industry personnel. ABSTRACT The objective of this paper is to show lab test performed and field experiences for improving production in a well , with an equipment which has an expert system and control valve that automatically control the annular fluid level, obtaining an optimal point. Gas pressure variations that occur in annulus are reflected down hole and it’s a mean to evaluate optimization conditions in each well, detecting the optimum pressure point where crude mobility is favored over water or gas, from near wellbore up surface, increasing pumping efficiency too. In order to explain what happens through the porous medium near wellbore, an analysis of laboratory conducted at the Zulia University Petroleum Research Institute determined that the permeability’s behavior in rock-oil-water systems changes due to pressure changes: results obtained from rock samples shown that the effective permeability to water changes from 56 mD to 24 and 0.5 mD, when the pressure drop through the rock changes from 36 Psi to 30 Psi and 24 Psi, respectively. Software incorporated in the valve system at the well allows closing the annulus and detects the pressures increments, choosing the optimal point by means of mathematical calculations to achieve maximum crude production with minimum water yield. Likewise, a new multiphase water cut monitor gives information to a computer controller, in order to modulate automatic openings and closings of annulus gas production. On February 6, 2015 a test began in a 15 API oil 420 bopd well of Petrolera Indovenezolana, daily monitoring by owner and officially 5 well tests in 6 months were performed obtaining an increment of 13% in crude yield and 10% decrease in water cut. Over 70 automatic casing control valves of different types have been installed in Venezuela, with a successful rate of 50% and incremental production over 10 %, since 1998. 1. INTRODUCTION Annulus pressure control in well casings was developed in Venezuela since seventeen years ago. Over 70 of these devices have been installed approximately 50% successful rate on improving production has been obtained, (1,2). Some of the improvements (1/3 of the wells) are due to increasing pump efficiency owing to the reduction of gas entrained into the pump when the pressure of casing is being controlled by an automated pressure control valve set at an optimum value; it causes a variation of the dynamic fluids reducing the amount of free gas in the annular space and pump The other 2/3 of the wells occurred because of water cut reduction; See table 1. In order to demonstrate this process a mathematical model and lab test was developed at Inpeluz. World Heavy Oil Congress 2016 Page | 1
Transcript
WHOC16 - 322
Changes in Annulus Pressure, Increase Oil Production.
Carlos Brunings; PDVSA. Gabriel Becerra, PDVSA. Richard Marquez, INPELUZ. Linerbeth Garcia, INPELUZ. Leonardo Mena, ATS. Armando Riviere, ATS. Jose Marcano, PDVSA..
This paper has been selected for presentation and/or publication in the proceedings for the 2015 World Heavy Oil Congress. The authors of this material have been cleared by all interested companies/employers/clients to authorize dmg::events (Canada) inc., the congress producer, to make this material available to the attendees of WHOC2015 and other relevant industry personnel.
ABSTRACT
The objective of this paper is to show lab test performed and field experiences for improving production in a well , with an equipment which has an expert system and control valve that automatically control the annular fluid level, obtaining an optimal point. Gas pressure variations that occur in annulus are reflected down hole and it’s a mean to evaluate optimization conditions in each well, detecting the optimum pressure point where crude mobility is favored over water or gas, from near wellbore up surface, increasing pumping efficiency too.In order to explain what happens through the porous medium near wellbore, an analysis of laboratory conducted at the Zulia University Petroleum Research Institute determined that the permeability’s behavior in rock-oil-water systems changes due to pressure changes: results obtained from rock samples shown that the effective permeability to water changes from 56 mD to 24 and 0.5 mD, when the pressure drop through the rock changes from 36 Psi to 30 Psi and 24 Psi, respectively. Software incorporated in the valve system at the well allows closing the annulus and detects the pressures increments, choosing the optimal point by means of mathematical calculations to achieve maximum crude production with minimum water yield. Likewise, a new multiphase water cut monitor gives information to a computer controller, in order to modulate automatic openings and closings of annulus gas production.On February 6, 2015 a test began in a 15 API oil 420 bopd well of Petrolera Indovenezolana, daily monitoring by owner and officially 5 well tests in 6
months were performed obtaining an increment of 13% in crude yield and 10% decrease in water cut.
Over 70 automatic casing control valves of different types have been installed in Venezuela, with a successful rate of 50% and incremental production over 10 %, since 1998.
1. INTRODUCTION
Annulus pressure control in well casings was developed in Venezuela since seventeen years ago. Over 70 of these devices have been installed approximately 50% successful rate on improving production has been obtained, (1,2). Some of the improvements (1/3 of the wells) are due to increasing pump efficiency owing to the reduction of gas entrained into the pump when the pressure of casing is being controlled by an automated pressure control valve set at an optimum value; it causes a variation of the dynamic fluids reducing the amount of free gas in the annular space and pump The other 2/3 of the wells occurred because of water cut reduction; See
table 1. In order to demonstrate this process a mathematical model and lab test was developed at Inpeluz.
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2. THEORETICAL MODEL AND LABORATORY TESTS
Fluid flow of two immiscible fluids trough porous media can be described by Darcy’s law, and a mathematical correlation can be obtained that combines: pressure, permeability and fluid rate. This mathematical expression is developed for a cylindrical core as shown, by which oil and water is injected through it, in order to determine relative permeability and irreducible water saturation.
oeP And
weP represents inlet pressure for oil and
water osP and
wsP defines outlet pressure at the
outlet for both fluids. Fluid rates for water and oil are
represented by oq and wq , respectively. oµ And
wµ represents viscosity of oil and water. Effective
permeability are also represented by ok and wk , respectively.
This mathematical expression differs from the ones used in the lab for determining inlet pressure in cores when using triaxial cells (3):
oe
o
w
o
we P
qP
=
µµ1
556.0
Applying Buckley-Leverett, for oil flow of can be rewritten as follows:
−
−
+
=
oe
os
we
ws
oe
we
w
o
o
w
o
PP
PP
PP
kk
f
1
1
1
1
µµ
Now of depends on inlet and outlet pressure for each phase. If we consider that outlet pressure for
water is cero ( 0=wsP ), then permeability
relationships as a function of pressure can be written as:
o
ooe
os
we
oe
o
w
ro
rw
o
w
f
f
P
P
P
P
k
k
k
k )1(1
−
−
=
=
µµ
This mathematical expression combines permeability
as a function of outlet oil pressure ( 0=osP ) and
water saturation.
Meanwhile the institute of oil research (Inpeluz) of Zulia University in Venezuela has modified its laboratory equipment, in order to obtain from some core samples of different reservoirs, a family of curves of relative permeability as a function of pressure. The determination of effective permeability of water or oil is measured through a triaxial cell which has been transformed in order to control pressure at the outlet, by means of the installation of a control valve, so it can measures different differential pressures (See figure 1 ).Also a hydro pneumatic system was installed in order to guarantee constant pressure for fluid flow displacement though the core sample In addition five rock samples from the same core were carefully selected with similar permeability values . Displacement fluids were treated water and an oil type of fluid called Marcol. See table 2
During the experiment, the water and oil phases were handled at a constant flow rate and injection pressure. It was decided to choke the flow of fluid only for water at different values of Pws/ Pwe = 0%, 16.6%, 33.3%.
It was determined that the effective permeability of water, changes from 56 mD (milidarcies) to 24 and 0.5 mD, when the pressure drop through the rock
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−
−
=
we
ws
oe
os
oe
o
w
ow
ow
we
PP
PP
Pqk
kqP
1
11
µµ
changes from 36 Psi to 30 Psi and 24 Psi, respectively. See table 3 also different curves of permeability relationship krw/kro, as a function of pressure and saturation were obtained. See Figure 2 It can be seen that at higher outlet pressure, the value of effective permeability of water is less thus favoring the mobility of oil.
The importance of this investigation deals on the fact that permeability can be represented as a function of the pressure variable , especially at the outlet of the core sample which represents in the reservoir Pwf or flowing bottom hole pressure.
3. EQUIPMENT DESCRIPTION
This equipment installed in the well is self-contained (hardware/software) and diagnoses the behavior of the parameters of the artificial lift system and determines the optimal parameters of operation of the lifting system (speed, casing pressure, etc.) to obtain the maximum production of the well. See Figure 3
The software consists of expert systems and diagnostic patterns that control favorably irruption of water or gas and improve oil production, this is performed trough: analysis of electrical parameters coming from the variable frequency drive (vfd), interpretation of down hole well pressure, surface temperature of the fluid and wellhead pressure, in order to obtain the optimal casing pressure.
The equipment monitors the operational conditions of the wells and the software decides if it has to actuate over the control valve installed at the casing or over the speed of the motor. See Figure 4.
COMPONENTS
A. Field computer. The Remote Control Unit (RCU) receives information from: vfd, motor, torque, frequency, velocity of pump, and can control the frequency and speed of the surface drive.
The RCU is programmed to gather information from the drive and operate the artificial lift system based on the analysis of the Expert System. It records and sends operational and historical data to a SCADA, DCS, etc. It communicates with automation devices trough 4-20 mA (miliampere), 1-5 Volts and Modbus
RTU protocol, interfaces with RS-232, RS-485 or Ethernet.
B. Software It is programmed in Language C/CC+; the software was developed using Artificial Intelligent techniques, such as: Expert Systems, neural network, and diffusive logic (4). The expert system tries to increase the input pump pressure by closing the annular control valve, and releasing the casing pressure when it is needed, in order to maintain an optimal point. Maintaining this optimal point is essential for optimizing the well production. The software also analyzes and process information gathered from: the instrumentation installed at the wellhead, VFD parameters, different pattern recognition of pump cards, at the same time, the program must avoid a significant decrease of the dynamic fluid level to avoid down hole pump damage
C. Surface Instruments (Figures 5, 6)
• Fluid temperature device
• Pressure sensor at the tubing
• Control valve at the casing
• Water cut monitor in the flow line, the brand is Sentech WCM, patented Secap technology, based on an electronic oscillator that is influenced by the dielectric constant of the media surrounding it. (Figure 7).
• Batteries to provide energy for valve actuation and avoid harmonics and noise from vfd
4. RESULTS FOR WELL NZZ-196
A well completed in the H sand of the mixed company (ONGC and PDVSA) Indo Venezolana is located in eastern Venezuela (Figure 8), was selected for evaluation because it had a stable production of 730 BFPD (barrels fluids per day) and a water cut that varied between 24-36% in 2014, (method of collecting is by one sampling of water cut at the wellhead), °API of the oil is 15 , a GOR (gas oil ratio) around 200, a progressive cavity pump was installed on July 2012 (Figure 9) . On February 5 2015, a well test was performed with a portable well test unit consisting of a separator and tank, water cut
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measurements were taken, and to get an average, several well samples were collected and the result was 32%, with a total fluid of 623 BFPD and net oil of 440 BOPD (barrels oil per day) at 200 RPM, this velocity remained the same through the whole evaluation till October 2015. This well test was taken as the initial well test to compare against the following tests with the equipment. After that the well was pressurized manually with the equipment, without the use of the water cut monitor, which was not available at the time, and the calibration of the expert system was based on electrical and fluid level parameters as can be seen in table 4. A well test was performed on February 7 at a casing pressure of 250 psi (pound per square inch) and tested 690 BFPD, 490 BOPD with an average water cut of 33%.
Also from this table 4, it can be concluded that fluid level over the pump increased from 502 feet to 723 feet, improving pump efficiency, since less gas is liberated, about 88 psi additional of Pump intake pressure, from 208 psi to 288 psi approximately (Figure 10).
Fluctuating water cut measurements were reported during the months between March, April and May since the optimal casing pressure point was not obtained as the water cut monitor was damaged during installation and was under repair, the calculation for optimal point was still manual (around 420 psi). A well test performed 12 of April by a multiphase test meter (Agar) with an electronic water cut measurement system, which is the most reliable, since it calculate water cut every 10 minutes during the test, Agar utilize a microwave transmitter (2.45 Giga hertz) to measure bulk dielectric properties of the flow stream, regardless of salinity, density or viscosity and the high frequency signal will maintain accuracy in the presence of process coatings.
Results obtained were 692 BFPD, 398 BOPD, 43%water cut, 238 GOR, Figure 11 represents this period
Finally during late May and early June 2015, the new water cut monitor arrived and was installed, also automatically the software was getting the optimal point due to changes in the program; this water cut was calibrated against continuous water cut sampling collected in two hours at different days in June and analyzed in the laboratory of San Tome District, and also was compared against a well test performed by the electronic system on 14 June 2016 , following
are the results in table 5, in which there is less than 2% difference between AGAR and SOE´s water cut monitor.
The result in Figure 12 shows that the equipment records the water cut in real time and continuously
As mentioned a well test performed by Agar, June 13th yielded: 756 BFPD, 518 BOPD, 386 GOR, 30% water cut at 332 psi casing pressure as the optimal point finally was found for controlling water production and improving pump efficiency (5). .
Further well test were performed at the same casing pressure, resulting for August 12 th, Total fluid per day 712 (BFPD), and 491 (BOPD) barrels of oil with a water cut of 30.5% recorded from the SOE equipment, By September 13 th, 708 BPD and 488 BOPD with the same water cut as August. Finally a well test on 13 of October, with 740 BFPD, 460 BOPD, and 35.3% water cut from the Sentech monitor installed at the wellhead. See table 6.
In early November 2015 the evaluation of the equipment finished, and was disconnected from the well, all equipment were returned to the owner ATS.
5. CONCLUSIONS
1.-Preliminary lab tests have shown that the effective permeability to water decreases as a differential pressure is applied, so an oil phase moves preferentially over a water phase in a core sample at a constant value of saturation
2.-Best water cut accuracy measurement is obtained through electronic monitoring, , if these equipment are not available, then a fair water cut measurement can be calculated by sampling continuously or getting an average, and lastly through a one sample collection at the wellhead.
3.-After automatic control of casing pressure has been established at its optimal point, the equipment has controlled in well NZZ-196 water cut, and improved pump efficiency, increasing oil well production by a 13% average.
6. REFERENCES
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1. – Castillo V. 2012 internal report on evaluation of Maxiprod. Marcano J. Awpa presentation of Petrolera Indovenezolana, 2014.
2. - Brunings C. et al. Oil Production Increase through an Automated Annulus Pressure Control System applied Extra-heavy Oil wells in PDVSA, San Tome District; World Heavy Oil Congress, 2009-128.
3.- Richard Marquez, Linerbeth Garcia, Design of Relative Permeability Curves as a function of
Pressure, Technical Presentation Inpeluz, Maracaibo, March 2016.
4. - Ramirez M, Brunings C. Automated Surface GasHandling Through Expert Systems for Optimizationof Artificial Lift Systems, Spe 13lAAl,2013.
5. – Leonardo M, Pereira A., Marcano J., Technical Report Evaluation of SOE, Expert Optimization System, NZZ-196, August 2015.
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Table 1. Well Evaluation
Table 2. Core Sample Information.
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Air Permeability, md 318
Pore Volume cc 10.1000
Water Viscocity, cp 0.919
Oil Viscocity, cp 1.236
Length over area cm / cm 2 0.33
Differential Pressure, psi 36
Length, cm 3.76
Area, cm2 11.34
Porosity, % 24
SUCCESSFUL AUTOMATIC CASING GAS PRESSURIZATION EVALUATION
# WELL EQUIPMENT YEAR BOPD (BEFORE) BOPD (AFTER) ORIGIN
