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Diverting Acid Fracturingfor Carbonate Reservoirs
www.cnpc.com.cn9 Dongzhimen North Street, Dongcheng District, Beijing 100007, P. R. China
Case Study
High-yield gas flow obtained from Well Dabei 302 in Tarim Basin by diverting acid fracturing stimulation.
Treatment: 1) Large amount of slickwater injecting to expand natural fractures; 2) HCI-based acidizing fluid to communicate natural fracture system; 3) Fiber assisted inner-fracture diversion to intensify the creating of fracture network and the distributing of acidizing fluid.
Central Asia
Middle East
Aktobe Oilfield 128
Tarim Oilfield, PetroChina 282
Northwest Oilfield company,Sinopec 190
Changqing Oilfield,Petrochina 2
Qinghai Oilfield,Petrochina 21 Shengli Oilfield,
Sinopec 11
Southwest Oil & Gas Field,PetroChina 9
Jidong Oilfield,PetroChina 9
IranYadavaran Oilfield 5South Adegan Oilfield 8Syria
Tishrine Oilfield 3
Ahdeb Oilfield 55
Industrial Application
Diverting acid fracturing has been applied 677 well-times for carbonate reservoirs in 10 oil and gas fields in China, including Tarim, Changqing, Huabei, Jidong, Dagang, Southwest, Qinghai, Northwest, Southwest, and Shengli. This technology has also been applied for 244 well-times in 7 overseas oil and gas fields, namely Aktobe in Kazakhstan, Amu Darya in Turkmenistan, Ahdab and Halfaya in Iraq, Yadavaran and South Adegan in Iran, and Tishrine in Syria. Field application has been proved fruitful, as evidenced by a cumulative oil production increment of 2.842 million tons and gas output increment of 1.49 billion cubic meters over the past three years.
4. Design optimization software and matching equipment and tools for diverting acid fracturing: ensure safe operation at high temperature and under high pressure
Fib
er c
once
ntra
tion,
%
Flow rate, m/s
Parameter optimizing plate for fracture blocking Diversion pressure optimization plate
Before stimulation: 5mm nozzle with daily gas output of 210,000 cubic meters and flow pressure at 61MPa, but unstable.
After stimulation: 8mm nozzle with daily gas output of 780,000 cubic meters and flow pressure at 87.7MPa; 10mm nozzle with daily gas output of 1,167,000 cubic meters and flow pressure at 78.6MPa.
Diverting Acid Fracturing for Carbonate Reservoirs
Conventional acid fracturing generally creates fractures only along the direction of maximum horizontal stress, resulting in partial connection among fissures and vugs, small swept volume by acid fluid, and limited yield increase. Diverting acid fracturing is proved to be an effective solution to create multiple fractures, increase connectivity of fissures and vugs, enlarge swept volume, and hence substantially improve stimulation efficiency.
By temporarily block exited fracture to increase inside pressure, more fractures are induced in new places and new directions, which link up more storage space of fissures and vugs. Meanwhile, by increasing the viscosity of acidizing fluid inside the fracture, the fluid will divert from high permeability zone to low permeability zone, creating an acid etching network and enlarging the swept volume, to maximize the oil and gas flow channels.
Diverting acid fracturing treatment combining fluid diversion and fracture reorientation
Blocking up the existing fracture temporarily with high strength can force it to divert and create new fractures. The minimum blocking strength required for fracture diversion, under different horizontal differential stresses and included angles between horizontal principle stress and natural fracture azimuth, has been worked out.
Diversion by blocking the fracture temporarily
1. Technical principle and simulated experiment apparatus & method
Temporaryblocking
Main fracture by acid fracturing
Wellbore
New fractures created by fracture reorientation
Acid etching network createdby fluid diversion
Core CT Scanning after acid flooding(conventional acid)
Core CT Scanning after acid flooding(self-viscosifying acid)
Floating screening material: It can force the fracture to extend downward to link up the reservoir below acid fractured interval, or avoid penetrating the above aquifer. The material is made mainly from silicate powder, aluminum powder and nano calcium carbonate through melting, spraying and cooling, with a density of only 0.37g/cm3 and pressure-bearing up to 124MPa.
Temporary plugging material of degradable fiber: Used to block existing fracture temporarily to force it to divert and create multiple new fractures. The fiber can be degraded automatically after the treatment, restoring all the oil and gas channels formed by acid fracturing. It has a shut-off capacity of over 20MPa, degradation rate of over 99%, and is suitable for reservoirs at temperature of 60oC-160oC.
Acid flooding test on parallel cores has proved that, after self-viscosifying, the acidizing fluid may divert its flow from high permeability core to medium-low permeability core, resulting in enlarged swept volume.
Diversion of self-viscosifying acidizing fluid
2. Fracture diverting materials: communicate reservoir vertically and create multiple fractures horizontally by temporarily blocking existing fractures
Low-permeability
Cores Cores
Medium-permeability High-permeability Low-permeability Medium-permeability High-permeability
Aci
d flo
odin
g di
rect
ion
Wel
lbor
e
Aquifer
Injecting at higher rate can force the fracture to grow and extend downward
Temporary pluggingwith fiber
Main fracture formed bydiverting acid fracturing New fractures formed by fracture diversion
Wellbore
Temperature control diverting system: It enables flow diversion by self-viscosifying. With a viscosity of less than 30mPa·s and the friction resistance of 30% of water at ambient temperature, it is easy to be injected. Its viscosity can reach over 220mPa·s due to polymerization reaction in the reservoir, enabling diversion in depth. The viscosity of degraded acidizing fluid is below 10mPa·s, making it easy to flowback.
3. Self-viscosifying acidizing fluid diverting systems: allow in-depth fluid diversion and intelligent diversion to form acid etching network and expand swept volume
Single fracture created byconventional acid fracturing
Multi-fractures created by diverting acid fracturing
Wellbore
Wellbore
Acidity control diverting system: Special viscoelasticity prevents the surfactant from forming reticular micelle under acidic condition. It can work at a temperature of 150oC, and enlarge the acid etching network volume by 3.1-7.2 times than by conventional acid. During acid fracturing, the acidizing fluid will first enter high permeable layer where the acid-rock reaction causes fluid viscosity increase, forcing the follow-up acidizing fluid to enter medium to low permeable layers, thus realizing intelligent diversion of plugging high permeable layer and acidizing low permeable layer. Schematic diagram of intelligent diversion
Low
per
mea
ble
laye
rM
ediu
mp
erm
eab
le la
yer
Hig
hp
erm
eab
le la
yer
Enter low permeable layer,realizing even acidizing
Enter medium permeablelayer, increasing theviscosity and flow resistance
High viscosity Low viscosity
Enter high permeable layer,increasing the viscosity andflow resistance
Diverting Acid Fracturing for Carbonate Reservoirs
Low viscosity when theacidizing fluid is pumped
High viscosity after theacidizing fluid enters the formation
Low viscosityduring flowback
Vis
cosi
ty (m
Pa.
s)
Temperature (oC)
300
270
240
210
180
150
120
90
60
30
020 40 60 80 100 120 140 160 180
Conventional acid fracturing generally creates fractures only along the direction of maximum horizontal stress, resulting in partial connection among fissures and vugs, small swept volume by acid fluid, and limited yield increase. Diverting acid fracturing is proved to be an effective solution to create multiple fractures, increase connectivity of fissures and vugs, enlarge swept volume, and hence substantially improve stimulation efficiency.
By temporarily block exited fracture to increase inside pressure, more fractures are induced in new places and new directions, which link up more storage space of fissures and vugs. Meanwhile, by increasing the viscosity of acidizing fluid inside the fracture, the fluid will divert from high permeability zone to low permeability zone, creating an acid etching network and enlarging the swept volume, to maximize the oil and gas flow channels.
Diverting acid fracturing treatment combining fluid diversion and fracture reorientation
Blocking up the existing fracture temporarily with high strength can force it to divert and create new fractures. The minimum blocking strength required for fracture diversion, under different horizontal differential stresses and included angles between horizontal principle stress and natural fracture azimuth, has been worked out.
Diversion by blocking the fracture temporarily
1. Technical principle and simulated experiment apparatus & method
Temporaryblocking
Main fracture by acid fracturing
Wellbore
New fractures created by fracture reorientation
Acid etching network createdby fluid diversion
Core CT Scanning after acid flooding(conventional acid)
Core CT Scanning after acid flooding(self-viscosifying acid)
Floating screening material: It can force the fracture to extend downward to link up the reservoir below acid fractured interval, or avoid penetrating the above aquifer. The material is made mainly from silicate powder, aluminum powder and nano calcium carbonate through melting, spraying and cooling, with a density of only 0.37g/cm3 and pressure-bearing up to 124MPa.
Temporary plugging material of degradable fiber: Used to block existing fracture temporarily to force it to divert and create multiple new fractures. The fiber can be degraded automatically after the treatment, restoring all the oil and gas channels formed by acid fracturing. It has a shut-off capacity of over 20MPa, degradation rate of over 99%, and is suitable for reservoirs at temperature of 60oC-160oC.
Acid flooding test on parallel cores has proved that, after self-viscosifying, the acidizing fluid may divert its flow from high permeability core to medium-low permeability core, resulting in enlarged swept volume.
Diversion of self-viscosifying acidizing fluid
2. Fracture diverting materials: communicate reservoir vertically and create multiple fractures horizontally by temporarily blocking existing fractures
Low-permeability
Cores Cores
Medium-permeability High-permeability Low-permeability Medium-permeability High-permeability
Aci
d flo
odin
g di
rect
ion
Wel
lbor
e
Aquifer
Injecting at higher rate can force the fracture to grow and extend downward
Temporary pluggingwith fiber
Main fracture formed bydiverting acid fracturing New fractures formed by fracture diversion
Wellbore
Temperature control diverting system: It enables flow diversion by self-viscosifying. With a viscosity of less than 30mPa·s and the friction resistance of 30% of water at ambient temperature, it is easy to be injected. Its viscosity can reach over 220mPa·s due to polymerization reaction in the reservoir, enabling diversion in depth. The viscosity of degraded acidizing fluid is below 10mPa·s, making it easy to flowback.
3. Self-viscosifying acidizing fluid diverting systems: allow in-depth fluid diversion and intelligent diversion to form acid etching network and expand swept volume
Single fracture created byconventional acid fracturing
Multi-fractures created by diverting acid fracturing
Wellbore
Wellbore
Acidity control diverting system: Special viscoelasticity prevents the surfactant from forming reticular micelle under acidic condition. It can work at a temperature of 150oC, and enlarge the acid etching network volume by 3.1-7.2 times than by conventional acid. During acid fracturing, the acidizing fluid will first enter high permeable layer where the acid-rock reaction causes fluid viscosity increase, forcing the follow-up acidizing fluid to enter medium to low permeable layers, thus realizing intelligent diversion of plugging high permeable layer and acidizing low permeable layer. Schematic diagram of intelligent diversion
Low
per
mea
ble
laye
rM
ediu
mp
erm
eab
le la
yer
Hig
hp
erm
eab
le la
yer
Enter low permeable layer,realizing even acidizing
Enter medium permeablelayer, increasing theviscosity and flow resistance
High viscosity Low viscosity
Enter high permeable layer,increasing the viscosity andflow resistance
Diverting Acid Fracturing for Carbonate Reservoirs
Low viscosity when theacidizing fluid is pumped
High viscosity after theacidizing fluid enters the formation
Low viscosityduring flowback
Vis
cosi
ty (m
Pa.
s)
Temperature (oC)
300
270
240
210
180
150
120
90
60
30
020 40 60 80 100 120 140 160 180
Diverting Acid Fracturingfor Carbonate Reservoirs
www.cnpc.com.cn9 Dongzhimen North Street, Dongcheng District, Beijing 100007, P. R. China
Case Study
High-yield gas flow obtained from Well Dabei 302 in Tarim Basin by diverting acid fracturing stimulation.
Treatment: 1) Large amount of slickwater injecting to expand natural fractures; 2) HCI-based acidizing fluid to communicate natural fracture system; 3) Fiber assisted inner-fracture diversion to intensify the creating of fracture network and the distributing of acidizing fluid.
Central Asia
Middle East
Aktobe Oilfield 128
Tarim Oilfield, PetroChina 282
Northwest Oilfield company,Sinopec 190
Changqing Oilfield,Petrochina 2
Qinghai Oilfield,Petrochina 21 Shengli Oilfield,
Sinopec 11
Southwest Oil & Gas Field,PetroChina 9
Jidong Oilfield,PetroChina 9
IranYadavaran Oilfield 5South Adegan Oilfield 8Syria
Tishrine Oilfield 3
Ahdeb Oilfield 55
Industrial Application
Diverting acid fracturing has been applied 677 well-times for carbonate reservoirs in 10 oil and gas fields in China, including Tarim, Changqing, Huabei, Jidong, Dagang, Southwest, Qinghai, Northwest, Southwest, and Shengli. This technology has also been applied for 244 well-times in 7 overseas oil and gas fields, namely Aktobe in Kazakhstan, Amu Darya in Turkmenistan, Ahdab and Halfaya in Iraq, Yadavaran and South Adegan in Iran, and Tishrine in Syria. Field application has been proved fruitful, as evidenced by a cumulative oil production increment of 2.842 million tons and gas output increment of 1.49 billion cubic meters over the past three years.
4. Design optimization software and matching equipment and tools for diverting acid fracturing: ensure safe operation at high temperature and under high pressure
Fib
er c
once
ntra
tion,
%
Flow rate, m/s
Parameter optimizing plate for fracture blocking Diversion pressure optimization plate
Before stimulation: 5mm nozzle with daily gas output of 210,000 cubic meters and flow pressure at 61MPa, but unstable.
After stimulation: 8mm nozzle with daily gas output of 780,000 cubic meters and flow pressure at 87.7MPa; 10mm nozzle with daily gas output of 1,167,000 cubic meters and flow pressure at 78.6MPa.
Diverting Acid Fracturing for Carbonate Reservoirs
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