Water Injection Facilities
Typical Changes in Production Rates During the life time of a 100,000 bopd oil field
Particle size
Particle size
≤ 50 – 150 µm
≤ 10 – 20 µm
Bulk Oil Removal
Produced Water from: FWKO Treaters Test Equipment Etc.
Large Oil droplet removal
Small Oil droplet removal
Primary Treatment
Secondary Treatment
Disposal
Equipment Types
Equipment Types
Equipment Types
Skim Tank Skim Vessel CPI Cross Flow SP Pack HydroCyclone
CPI Cross Flow Flotation SP Pack HydroCyclone
Disposal Pile Skim Pile SP Pile Reinjection Disposal Wells
Plate Coalescers • Parallel Plate Interceptors ( PPI) • Corrugated Plate Interceptors (CPI) • Cross Flow Separators
Metoda diatas bekerja berdasarkan konsep pemisahan secara gravitasi, dimana butir butir minyak bergerak keatas sampai menyentuh plate bagian atas. Minyak yang menempel pada plate kemudian mengalami proses coalescence dan bergerak sepanjang plate dan terpisahkan dengan fasa air.
A
B
Plate
OIL
A
Oil Droplet
h
θ
B
Plate
Water
h
θ
Corrugated Plate Interceptor ( CPI )
How to Clean Produced Water
Gas
Oil + Emulsion Oil + Water
FWKO 1
Skimmer
Flotation
Oil + Emulsion
Oily Water
Well
2
Oily Water
3 Clean Water
Mechanical IGF Gas
Induced Gas Flotation
How to Clean Produced Water
Gas
Oil + Emulsion Oil + Water
FWKO 1
Skimmer
Flotation
Oil + Emulsion
Oily Water
Well
2
Oily Water
3 Clean Water
4
Filter
Hydrocyclone
Gas
Water Injection System
OiLStorage Tank
Gun Barrel
Crude Oil
Sale Point
Surge Tank
O2 , CO2 , H2S
Wells
Deaeration
FWKO GAS FLOTATION
Water Tank
Solid Filter Hydrocyclone
CPI
Min 25% of the water volume to be injected
PUMP
To Injection Wells
Vacuum Deaerator Cold water can be deareated by reducing pressure until the water boils. Vacuum deareation is often used where a maximum axygen content of 0.3 ml/liter is permissible. Removal of Oxygen, CO2 dan H2S dapat meningkatkan PH, yang selanjutnya dapat mempermudah terjadinya carbonate scale formation.
Boiling Point of Water at Reduced Pressure Temperature (F)
Pressure (psig)
40
0.123
60
0.256
80
0.507
100
0.950
120
1.690
140
2.890
160
4.740
180
7.510
200
11.530
212
14.700
Oil Gas Field Surface Facilities System
Prinsip prinsip Gas Flotation OIL
OIL
DROPLET vR
dm
h GAS
Water Water
tR
h
w
2 1.786 x 10 - 6 ( o - w ) dm
Dissolved Gas Flotation Cell SKIMMER
Clean Water
Oily Water
Oily Froth
Full Stream Pressurization Gas
Flotation Cell
GAS
Oily Water
Split - Stream Pressurization Gas
GAS Oily Water
Flotation Cell
Induced Gas Flotation ( IGF )
Modern IGF
Gas Flotation Unit
Mechanical IGF
Mechanical IGF
MECHANICAL EQUIPMENT FOR INDUCTION
Autostable Floating Skimmer with Gas Seal
OIL OUTLET DESIGN
OIL
Over Flow
SCHEMATIC OF A HYDROCYCLONE FOR WATER OIL SEPARATION
(Oil) Liquid Inlet
Ls
Dc > Du > Do
Oil Lu
Du
(Clean Water) Under Flow
WASTE DISPOSAL BY INJECTION IN UNDERGROUND FORMATION • For many years, the petroleum industry has disposed of
oilfield brines by injection into underground formation. • A formation suitable for the injection of waste water obviously must be available. • The formation selected should not allow the waste water to migrate to a fresh water stratum, thereby polluting the water in that stratum. • Generally, if the selected formation contains salt water, it is reasonable to expect no future pollution of any fresh water stratum.
The primary purpose of treating injection water, both waste water and water used in secondary recovery, is to prevent plugging of the disposal wells.
Water Quality
The principal factors which define the water quality are: (i) solids - dissolved or suspended (ii) dispersed oil (iii) dissolved gasses (iv) bacteria
The Common Sources of Water for A water Flood 1. Produced water 2. Brine or fresh water from other subsurface zones (supply wells) 3. Surface water from oceans, lakes, ponds, streams or rivers 4. Alluvial water wells which draw water from shallow aquifers which are connected to a surface water body.
Primary Constituents and Properties
Cations
Anions
Properties
Calcium (Ca)
Chloride (Cl)
pH, Suspended Solid (amount, size, shape, chemical composition)
Magnesium (Mg)
Carbonate (CO3)
Turbidity, Temperature, SG, Dissolved oxygen, Dissolved CO2,
Sodium (Na)
Bicarbonate (HCO3)
Sulfide as H2S, Bacterial Population,
Iron (Fe)
Sulfate (SO4 )
Oil Content
Barium (Ba) Strontium (Sr)
The above constituents and properties are important from the standpoint of plugging or corrosion.
Common Water Analysis Determination for Injection Water • • • • • • • • • • • • •
Alkalinity Calcium Carbonate Chloride Hydrogen Ion (pH) Iron Magnesium Silica Specific Gravity Specific Resistivity Sulfate Total Dissolved Solid (TDS) Suspended Solids
Commonly Handling Problems in Water Floo ding Issue
Effect
Treatment
Suspended solids
Plugging of Injection formation
Filtration
Suspended oil
Plugging of Injection formation / (particularly in presence of solids)
Hydrocyclones / Flotation / Filtration
Dissolved Gases {O2 / CO2 / H2 S}
Corrosion of well and facilities. Plugging of formation by corrosion products Equipment and formation plugging by scale
Degasification Corrosion inhibitor Injection Scale inhibitor Injection
Bacteria {Aerobic / Anaerobic (sulphate reducing)}
Formation plugging by bacterial residues or corrosion products
Biocides
Water incompatible with formation
Loss of permeability of injection formation
- Pre-treat formation (clay stabilizers) - Alter injection water chemistry
Formation of Solids {CaCO3 / Ba SO4 / CaSO4 / FeS}
De-Oxygenation
The presence of Oxygen in concentrations greater than 5 x 10-3 g/m3 (5 ppb) in water flood operations can cause severe corrosion and plugging of the formation by corrosion products.
Gas Stripping (Left) & Vacuum Deaerator to Deoxygenate Water
Ga s Stripp ing
Removal of oxygen by gas stripping is based on lowering of the solubility of oxygen in water by reducing the oxygen partial vapour pressure. Henry’s gas’s solubility Lawto states that pressure is proportional the vapour of the gas
over water. Oxygen from the water may be stripped by passing a (low oxygen content) stripping gas through the water in co-current or counter-current flow.
Vacu u m De -ae ration
The principle of vacuum de-aeration is to reduce the partial pressure of oxygen by boiling the water. At a temperature of 15ºC, water boils at a pressure of about 0.017 atm and the residual water oxygen content is reduced to 150 ppb.
Chemical Treatment With Oxygen Scavengers Oxygen removal to the required 5 ppb level is rarely possible. Oxygen scavengers are used to achieve this very low value. Oxygen scavengers remove oxygen from water by chemical reaction. A large number of chemical
compounds can be used for this purpose.
Water Injection System
Chlorination
Chlorination is a widely used, inexpensive, effective biocide. Chlorine hydrolyses to form hydrochloric and hypochlorous acid with water
By contrast, chemical incompatibility between injected sea water and formation water is the cause of the deposition of sulfate mineral scales. This occurs because sea water contains reasonable concentrations of Sulfate anions (up to 2,800 ppm) but is low in divalent cation {420 ppm Calcium (Ca++), trace Ba++ and Strontium (Sr++)}. By contrast, many formation waters
contain significant concentrations of barium – from tens of parts per million to thousands.
The solubility of Barium Sulfate (BaSO4 or Barite) is very low, being only 4% of that of calcium carbonate. Barite is precipitated by the reaction: Ba++ + SO"4
Ba SO4 ¯
BaSO4 is one of the most insoluble of the scaling minerals. A similar problem is encountered with Strontium Sulfate (celestite or SrSO4) in some fields.
A less frequently encountered scale is Calcium Sulphate (CaSO4). This is due to the unusual solubility behaviour of Gypsum (CaSO4. 2H2O), the most commonly encountered form of calcium sulphate. Gypsum has a solubility maximum at 40°C (i.e. it shows reduced solubility at both higher and lower temperatures). The issue is complicated by the fact that the equilibrium form above 40ºC is Anhydrite (Ca SO4); which is even less soluble. A further complication is that this transition temperature is itself dependent on the salinity.
Common Water Analysis Determination for Injection Water in Oil Field • • • • • • • • • • • • •
Alkalinity Calcium Carbonate Chloride Hydrogen Ion (pH) Iron Magnesium Silica Specific Gravity Specific Resistivity Sulfate Total Dissolved Solid (TDS) Suspended Solids
Common Water Analysis Determination for Potable Water • • • • • • • • • • • • •
Alkalinity Calcium Carbonate Chloride Hydrogen Ion (pH) Iron Magnesium Silica Specific Gravity Specific Resistivity Sulfate Total Dissolved Solid (TDS) Suspended Solids
•Arsenic •Bacteriologic •Chromium •Fluoride •Lead •Manganese •Odor •Oxygen •Phenol •Phosphate •Selenium •Turbidity •Zinc
Suspended Solids • Solid concentration • Particle Size Analysis • Particle shapes • Composition of Solids • Turbidity
The main items to be considered in water source selection • Corrosion • Scaling tendency • Water compatibility • Formation Sensitivity • Water quality
Alkalinity and Acidity For waters over pH 4.5, alkalinity may range to 1200 ppm, but it is generally less than 500. Acidity may range from zero to several hundred ppm in mine waters.
Hardness Hardness has usually been referred to as the soap consuming power of water. Most of this effect with soap is caused by magnesium and calcium in the water , but other alkaline earths give the same effect.
Calcium and magnesium hardness
represent values calculated from the concentrations of these two ions.
Turbidity Turbidity simply means that the water is not " clear " and that it contains undissolved matter such as suspended solids, dispersed oil or gas bubbles. It is a measure of the degree of "cloudiness" of the water. Turbidity indicates the possibility of formation plugging. Turbidity measurements are often used to monitor fiIter performance.
Temperature The temperature of the water affects the scaling tendency, the pH and the solubility of gases in water. The specific gravity of water is also a function of temperature.
Chemical Composition of Suspended Solids Determination of the composition of suspended solids is extremely important. It
makes it possible to ascertain their srcin (corrosion products, scale particles formation sand, etc.) so that proper remedial action can be taken. Known edge of their chemical composition is also important from the standpoint of designing a cleanout procedure should plugging occur.
Specific Gravity of Water • The magnitude of the specific gravity is a
direct indicator of the total amount of solids dissolved in the water.
Waterflood Inspection and system Analysis
Dissolved Iron (mg/l)
Waterflood Inspection and system Analysis
Turbidity ( JTU )
Waterflood Inspection and system Analysis
1
Corrosion Rate (mpy)
2
3
4
5
6
7
Waterflood Inspection and System Analysis No 1
Item Iron
Record
Indication
Increase
corrosion
decrease
deposition
2
Calcium
decrease
Possibly scale formation
3
Bicarbonate
decrease
Deposition unless the PH is being changed
4
Carbonate
decrease
Deposition unless the PH is being changed
5
Sulfate
decrease
Deposition as Ca SO4 and or Ba SO4
6
Temperature
7
H2S
8
Suspended Solid
Change in temperature affect scale formation increase
Sulfate reducing bacteria
decrease
The presence of oxidizing agent in the system (air)
increase
Corrosion, scale formation, bacterial activity.
decrease
deposition
No 9
Item Turbidity
Record
Indication
Increase
Increase plugging solid
decrease
deposition
closed
Increase indicate a oxygen entry
10
Water quality
11
Corrosion rate
12
Oxygen
Measurement Should be taken along the system
13
Oil carryover
Check all separation system
14
Filter Operation
Check upstream and downstream point
15
Bacteria Count
Check all the time
16
Visual inspection
Very important , most reliable method
Water Analysis Results
Schematic of Coreflood Apparatus Pressure Gauge
Pressure Gauge Valve 1
Valve 2
OIL
Core Holder
Transfer Vessel
Measuring Cylinder
Constant Rate Pump
Sea Water Source for Water Injection
Water Quality Plot 100 Flow Rate (ml/sec)
Excellent
10
SLOPE
Poorest 1 10
20
30
Liquid Volume Injected
40
The wells can be plugged by : • Entrained solid, • Oil and bottom settlings, • Sulfur, • Bacteria, • Precipitation of salts after treatment.
While a few parts per million of plugging material do not appear to be very great amount , the large volume of water injected in some wells can accumulate parts per million into a a considerable these mass few of material which can plug well. When the water is disposed of by injection into a sand formation, the sand face acts as a filter.
Example
:
If 10,000 barrels of water containing 5 ppm ( parts per million ) of a plugging material are injected daily, 17.4 pounds of solids will collect each day on the surface of the sand, resulting in over 500 pounds per month and probable plugging of the well. Well plugging is not caused by only solids volume, but also due to particle size of the solids.
Injection Rate Decline due to impairment by one of Four Mechanisms
• Well bore narrowing • Invasion • Perforation Plugging • Well bore fill-up
An Injection System for water disposal • Gathering system of water waste, •• Collection center, Water treatment facilities, • Injection well
Evaluating Suitability of Subsurface Disposal Project
Geology
1. The areal extent 2. Thickness 3. Lithological character, Water Composition
Whenever possible, water samples representing all aquifers penetrated should be collected and analyzed. Samples of the disposal brine should also be analyzed. Compatibility tests should be made with waters that are to be mixed in the operation.
Well and Re servo ir Data A study of the performance records of existing production and disposal wells is helpful in predicting future requirements for disposal system. The disposal reservoir and its ability to handle waste water is vital to the success of the project.
Porosity
Porosity is used to determine the storage capacity of the reservoir. It is designated as absolute and effective porosity. Absolute porosity is the percentage of pore volume in the rock, without regard for interconnection of pore spaces. Rock of high porosity may have low permeability, because there is no connection between pores.
Permeability
The ability of reservoir rock to let fluid flow through its interconnected pore volume or its fluid conductivity is termed its permeability (K).
Inject ion Ra te
Darcy equation can be used to calculate the rate of brine or waste disposal into a subsurface formation containing fluid.
Components of a Subsurface Brine Disposal System • Gathering System for Waste Injection Water, • Collection Center, • Water Treatment Plant, • Injection well, • Pumps
Collection Center A collection center is a tank or lined pond used to collect waste water from various heater treaters and separators in the field. From here, the water is pumped or gravity flowed to the treating plant. Injection water containing oil will generally plug the injection formation. Since waste water from heater treater contains a small amount of oil which was not removed, or oil accumulated from leaks, it may be necessary to remove this oil before water is injected.
The collection center may also serve as an oil brine separator. The incoming water passes through a baffle system system which separates the oil by gravity, then a skimmer removes it.
Water Treatment Plant There are two general type of disposal system: the open and the closed type. •Since surface Temperature and Pressure are different from those in the reservoir, the chemical equilibrium of the water may be changed. •Dissolved carbon dioxide, hydrogen sulfide, methane, and other gas will probably escape from the water. •The gases above certainly will be removed on aeration, and oxygen will be dissolved in the water. •Slightly soluble carbonate will precipitate due to the loss of carbon dioxide. These solids are removed by coagulation, sedimentation, and filtration.
•The dissolved oxygen may cause the water to be
very corrosive. However, oxygen corrosion can be minimized by using a de-aerator to remove the oxygen or using corrosion resistant flow line and injection tubing.
Closed System • Designed to exclude oxygen (trouble
maker). • Contains very small amount of oxygen. • Requires very little chemical treatment. • More difficult to exclude oxygen from the system (not economical to remove oxygen)
Open System • No attempt is made to exclude oxygen
from the system. • Oxygen-saturated surface water is used as a source water.
• A water is intentionally aerated to remove
H2S and or CO2. • Open system makes internal coating, lining or plastic pipe a necessity is most system to control corrosion, economically.
SURFACE WATERS
OPEN SYSTEM Solid removal
Source
Water Storage
Injection Pump
Wells
CLOSED SYSTEM Source
Solid removal
Skimmer, Gas Flotation Unit, Filter, Membrane
Oxygen Removal
Heater, Vacuum, Sulfite Ion, Hydrazine
Water Storage
Injection Pump
Wells
SUBSURFACE WATERS OPEN SYSTEM Solid removal
Source
Storage
Injection Pump
Wells
AERATION CLOSED SYSTEM Source
Solid removal
Oxygen Removal
Storage
Injection Pump
Wells
1.5 micron – 10 micron
Typical Disposable Filter Cartridges
Skimmer Tank
Water outlet Oily Water
Oil Outlet
To Remove Oil from Water
Untuk memisahkan padatan yang halus dan butiran minyak yang sangat kecil dari air
Clean Water
4 Stages Gas Flotation Cell
Oil
Sea water (1)
Saturated with oxygen - very corrosive
(2)
Contains suspended solids and marine organisms. Amount varies with location and depth. Normally must be filtered.
(3)
Contains aerobic bacteria and sul fate reducing bacteria.
(4)
Fouling must be prevented in the intake system.
(5)
Calcium carbonate scale is likely to form in the injection wells and heat exchange equipment.
Produced Water
( a ) Usually contains dissolved H2S and/or C02, Corrosivity varies. ( b ) May contain suspended solids. ( c ) 0il carryover is a frequent problem. ( d ) Sulfate reducing bacteria are often present. ( e ) Scale formation is possible.
Subsurface Source Water (a ) May or may not be corrosive, depending on composition. 0xygen Leakage into source well annulus i s a frequent problem. ( b ) May be scale forming. Normally scaling water would not be used unless absolutely necessary. ( c ) If sufficiently fresh, formation sensitivity must be considered. ( d ) Sulfate reducing bacteria can be a problem. ( e ) May contain suspended solids . Normally this is not a serious problem, and many source waters do not require filtration . ( f ) Watch for incompatibility with formation water. Possible scale problems introducing wells after breakthrough.
Necessary to examine in detail the possibility of: 1. 2. 3. 4. 5. 6. 7.
Corrosion Scale formation Water compatibility Formation sensitivity Removal of suspended solid Bacterial activity Oil carryover
Concerns in designing An Injection System Possible water sources Open or close system Material selection, coating and lining Chemical addition, Possibility of dissolved gas removal Need for filtration Need for oil skimming tanks or flotation cells The use of split injection systems to avoid mixing incompatible waters • Sampling points • Monitoring devices • • • • • • • •
