FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
THE PATENTS RULES, 2003
Provisional/ Complete specification
[See section 10 and rule 13]
1. Title of invention:
"Polymer Doped Scale Inhibitor For Oil Field Produced Brines In Calcium Stressed Environments".
2. Applicant(s):
Name Nationality Address
Oil and Natural Gas India IOGPT, Phase -II, Panvel -
Corporation Ltd. 410221, Navi Mumbai,
Maharashtra, India.
3. Preamble to the description :
The following specification particularly describes the invention and the manner in which it is to be performed.

POLYMER DOPED SCALE INHIBITOR FOR OIL FIELD PRODUCED BRINES IN CALCIUM STRESSED ENVIRONMENTS-BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION:
The present invention is aimed at developing a scale inhibitor for produced brines in highly Calcium stressed liquid environment. Polyphosphonates doped with a suitable polymer enhances the overall efficiency of scale inhibitor in the highly stressed conditions.
2. DESCRIPTION OF THE PRIOR ART:
Scale formation is a burning issue in the petroleum industry. Whenever water production occurs, a potential for scale formation exists. Scaling can occur anywhere between the reservoir and surface facilities, when the conditions are conducive to scale deposition. Scale begins to form when the state of any natural fluid equilibrium is perturbed such that the solubility limit for one or more components is exceeded. Mineral solubility themselves have a complicated dependence on temperature and pressure. Calcium carbonate shows the inverse trend of increasing water solubility with decreasing temperature. An additional complexity is the solubility of the carbonate minerals in the presence of acid gasses such as C02 and H2S. Generally as pressure falls, C02 leaves the water phase causing the pH to rise -leading to calcite (CaC03) scale formation. These scales can hamper the process operation by plugging the fluid flow path thus reducing the efficiency of operating system.

It is suspected that heat transfer from the steam (Shell) to processing crude (tubes) is ineffective due to scale formation in the exchanger tubes. Flow diagram at Fig. 1
The present innovation is aimed at finding out a tangible solution to mitigate the scale problem. The produced water samples from CSU inlet and dehydrator out let were analyzed to determine the brine chemistry. Solid scale samples of dehydrator out let pipe line were analyzed for mineral composition. Saturation index model, developed by OLI, USA known as 'ScaleChem' software is used to obtain insight of causes of scale formation and to predict the thermodynamic scaling tendency of the produced brines at various locations of CSU plant. Brine chemistry and operating parameters of CSU are the input parameters for the software runs. Out put data for the Software reveals that the mineral super saturation of liquid with CaC03 is likely to trigger calcite scale deposition in the flow channels under existing operating condition.
To minimize the scale deposition and to arrest the mineral precipitation, chemical Scale inhibitors were considered to be effective and technically suitable method. A numbers of scale inhibitor samples were evaluated in the laboratory adopting NACE standard TM037401 to find out the most effective one for use in the CSU. Commercial inhibitor samples along with generic chemicals were also screened for optimum efficiencies. HEDP, an organic phosphonate inhibitor under use, was found to have limited tolerance in the present mineral saturation level. However, some of the commercial samples containing phosphonates supplemented with a polymer appear to render enhanced mineral tolerance and improve inhibitor efficiency. Most of the screened commercial samples were acidic in nature and required acid corrosion

inhibitor to prevent material corrosion. The innovated formulation has neutral pH, does not require addition of corrosion inhibitors.
Process Description: As per the flow diagram at Fig.1, Crude
stabilization unit is designed to handle 20 MMTPA of stock tank crude
oil.
There are five trains. Each train consists of:
•Crude pre-heater where incoming oil @ 500-700 m3/hr (Oil with 7-8%
water) is designed to be heated up to 45°c. Actual temperature
achieved is 35 °c.
• HP separator which operates at 3.5 kg/cm2g to separate out oil and
gas.
•Crude-crude exchanger, where the oil coming from HP separator is
heated to 55 °c by crude oil. •Crude heater where the crude oil flowing through tube is heated is
heated to 65 °c by steam on shell side. •Degasser/dehydrator, where oil, water and gas separation takes place
at 2.5 kg/ cm2g under high electrostatic field. •LP separator, where oil and gas separation takes place at 0.1
kg/cm2g. Oil from LP separator goes to intermediate tank and then to
main tank for final dispatch to refineries.
• No scale inhibitor is dosed at the inlet point of pre-heater.
•HEDP, a scale inhibitor is dosed at the out let of dehydrator prior dispatch of water to Minimum Admissible Standard (MINAS) plant.
ONGC Uran has experienced severe scale deposition problem in pre-heater & heat exchanger tubes. Scaling is also observed in degasser to dehydrator down stream, dehydrator distribution header, and produced water line. Scaling in these areas is a major limiting factor in the processing crude. Recently scaling problem agravated due to increased

water cut in the crude oil (7-8% in place of 5%). The extent of scaling can be judged from the fact that in nearly 6 months, 50% of the tubes in crude preheater observed choked. The scale is so hard that it is even impossible to clean the tubes.
Operating parameters:

Sr.No Parameters HP Crude Dehydr LP
Separator Heater ator Sepera tor
1 Operating
Pressure
Kg/cm2 3.5 2.5 2.5 0.1
2 Operating Temp.Deg C 45 65 65 53
Table.1 Ideal Operating parameters of CSU at different points.
Effect of Operating Parameters on CAC03 scale formation:
Calcium carbonate scale is formed by the combination of calcium ion with either carbonate or bicarbonate ions as follows:
Ca+2 + C03- → CaC03 → (1)
Ca+2 + 2(HC03-) → CaC03 ↓+ C02 + H20↑ → (2)
Effect of C02: The presence of C02 increases the solubility of CaC03 in water. When carbon dioxide dissolves in water, it forms carbonic acid, which ionizes according to following series of equations:
C02 + H20 ► H2C03 (3)
H2C03 ► H+ + HC03 (4)
HC03 ► H+ + C03 — (5)

Only a small percentage of the bicarbonate ions dissociate at the pH values found in most formation water to form H+ and C03—ions. At any point in the system where a pressure drop takes place, the partial pressure of C02 in the gas phase decreases, C02 comes out of solution, and the pH of the water rises. This shift reaction (2) to the right and may cause CaC03 precipitation. Pressure drop across a restriction such as a valve can also induce local turbulence, which can in turn aid in initiating scale deposition.
Effect of Temperature: Contrary to the behavior of most materials, calcium carbonate becomes less soluble as temperature increases. The hotter the water gets, the more likely CaC03 scale will form.
In the process system, the pressure decreases as the brine flows from one point to other; a decrease in pressure causes carbon dioxide gas in solution to evolve into the gas phase and the pH of the solution begins to rise. As the pH rises, the tendency to form calcium carbonate scale also begins to rise. The C02 and the Ca++ ions dissolved in the aqueous phase (brine) are the main culprits causing the CaC03 precipitations from the aqueous phase during any fluid production process in the field.
3. DETAILED DESCRIPTION OF THE INVENTION;
To develop a suitable scale inhibitor formulation, necessary inputs required are:
1. Brine chemistry of produced water.
2. Scale composition.
3.1. Produced Brine analysis: Quantum of Scale deposited in a particular location is function of quantity of produced brine flowing through the

section and the concentration of Calcium, Bi-carbonate, Sulphate ions in the brine. The CSU brine samples were collected from exchanger inlet and analyzed for scale forming species by standard chemical methods; results are tabulated below:

Property/Parameter Source of sample


Unil Pre-heater of HP separator (Hut oil*) De-Hydrator out let (mix of Hut & But oil)



Results
Ph 7.9 7.8
Anions
Carbonate, C03^ mg/l 0 0
Bicarbonate,HC03 mg/l 1037 1708
Chloride, CI" mg/l 18815 17750
Sulphate, S04"' mg/l 523 76
Cations
Calcium, Ca" mg/l 762 601
Magnesium, Mg+4 mg/l 194 207
Iron mg/l 1.0 3.0
Strontium, Sr+2 mg/l 90 5.0


Na+ mg/l 11535 11014
TDS mg/l 32957 31521
Salinity as NaCt mg/l 31005 29250

Observation on Results (Table.2): Analysis data indicate that
the produced brine is rich in calcium and Bi-carbonate ions which are potential scale generating species. During the course of fluid flow from well-bottom hole section to surface processing unit, scale deposition may occur in the flow channels. This brine is considered to be highly stressed with respect to Calcium and Bi-Carbonate ions.
3.2. Scale sample Analysis: The scale deposit samples from Crude stabilization unit of ONGC Uran were collected at exit point of the heat exchanger section and analyzed for its mineral composition; results are tabulated below:
Sr.No I Parameter I Unit I Results
1 Physical state : Brown red solid
_2 Chloroform extractable solid %w/w 11.0
_3 Inorganic matter [ %w/w ] 89.0
_4 Analysis of Inorganic Matter •
(A) Solubility in Water
i Water Soluble I %w/w 11.82
ii Water insoluble | %w/w | 87.18
Composition of Water Soluble
i "Calcium Ca++ j %w/w I 0.03
ii Magnesium Mg++ %w/w 0.007
iii Iron ,Fe | %w/w ] Nil
(B) Solubility of Water insoluble 15%HCI
i HCI Soluble l %w/w I 86.58
ii HCI insoluble [ %w/w I 0.6
Composition Acid Soluble
i Calcium Ca++ I %w/w I 28.56
ii Magnesium Mg++ %w/w 1.57
iii Iron ,Fe | %w/w [3.48
Table.3 Mineral composition of scale
Observation on Scale sample results (Table.3): Laboratory analysis data indicate that the scale deposits are basically inorganic in nature and over 90% of the sample is acid soluble. Carbonate scales

considered to be acid soluble, so the analyzed scale deposits are mostly Calcium carbonate in nature.
3.3. Software runs: Based on the produced water chemistry software runs using 'Scale Chem' software, have been carried out to evaluate the mineral super saturation in the brine. Results are:
Brine Volume Brine composition Result
1729M3/d at Ca = 530 ppm, CI =18680 571 mg/L
Temp;45 deg C Mg=194 ppm HC03 =415 Mineral Super
Na =11469 S04 = 519 saturation as
Sr = 89 CaC03
Table.4 Software results based on produced brine chemistry.
Observation on Software runs: The soft software run results indicate that the liquid is super saturated with CaC03 mineral and change of any of the parameters such as pressure .temperature, may lead to CaC03 scale deposition'
3.4 Selection of Scale inhibitor: Considering the concentrations of scale forming minerals in the produced brine, conventional Organo phosphonates may be ineffective in sequestering the calcium ion. A combination of Polyamino - polyethoxyiate - methyl - phosphonate (PAPEMP), and Acrylic Terpolymer, considered providing required efficiency under present operating conditions of heat exchangers.
3,4.1. Polyamino-polyethoxylate-m,ethyl-hosphonate:(PAPEMP):
The selected Ethoxylated polyphoshonate (PAPEMP) has high chelation and dispersion effects, high value for calcium tolerance, and good scale inhibition effects. PAPEMP has

excellent inhibition ability to calcium carbonate, calcium sulfate and calcium phosphate in oilfield water system exclusively in situations of high hardness and high temperatures. PAPEMP is obtained as 50% solution in water.
3.4.2. Terpolymer: This terpotymer consists three monomers
1. Acrylic acid;
2. Acrylo- methyl-propane-sulphonic acid;
3. Maleic acid.
The Terpolymer prevents nucleation of precipitation, aids in dispersing the calcium carbonate precipitates in case of excess calcium ion concentration in the system. Terpolymer is obtained as 50% solution in water.
3.5 Inhibitor Evaluation: To determine the efficiency and performance of inhibitor in the simulated field condition, the synthetic brine is prepared conforming to NACE method TM037401. This test describes the scale formation by mixing two incompatible synthetic brines of specified composition
Brine Preparation: Composition of brine is similar to the produced brine (with respect to calcium ion concentration); hence data generated is expected to match the performance of inhibitor in actual field conditions.
The exact compositions of calcium and bicarbonate brines are as
under:
1. Calcium containing brine;
CaCI2.2H20 = 12.15 g/l (M.W. of CaCI2.2H20 = 147.02)
MgCI2.6 H20 = 3.68 g/l (M.W. of MgCI2.6 H20 = 203.30)
NaCI =33.0 g/l (M.W. of NaCI = 58.44)

2. Bicarbonate containing brine:
NaHC03 = 7.36 g/l (M.W. of NaHC03 = 84.01)
NaCI = 33.0 g/l
Very small quantities of insoluble materials may remain after the specified reagents have completely dissolved. For consistency of results, the solutions were filtered through a 0.45 urn filter. Both the Calcium & Bicarbonate containing brines were saturated with C02 immediately before using. Saturation was accomplished at room temperature by bubbling C02 through a fritted-glass gas dispersion tube immersed to the bottom of the container. A rate of 250 ml/min of C02 for 30 minutes is considered sufficient to saturate up to 1 L of each brine.
Determination of Calcium ion in the brine: Mixing of brines results in to generation of CaC03 scale precipitates, as a result, the metal ion concentration, i.e Ca+2 gets depleted in the solution. Calcium ion in the resultant solution is determined by EDTA titration and quantified simultaneously. When EDTA (Ethylenediamine tetraacetic acid or its salts) is added to water containing both calcium and magnesium after the pH is made sufficiently high that the magnesium is largely precipitated as the hydroxide and indicator (Calcon) combines with calcium and determined directly, with EDTA. Indicator gives a color change when all of the calcium has been complexed by the EDTA at a PH of 12 to 13.
Jar tests: Glass bottles of capacity 250 ml were selected as test cells to conduct scale inhibition tests To the test cells containing varied ppm of inhibitors is added calcium containing brine, and bicarbonate containing brine, of same volume. A test cell without inhibitor dose (as blank solution) is also evaluated along with inhibitor solutions under the

similar conditions. Test cells were capped immediately and agitated for mixing of the contents thoroughly and solution is aged for 24 hours at 71 deg C in hot air oven. Cells were removed after the 24-hour exposure and were allowed to cool to 25 ±5°C) for a time not to exceed two hours. Titrated with 0.02 N EDTA solutions and the efficiency of inhibitor is calculated by finding Calcium in the solution with and without inhibitor as per NACE standard.
% Inhibition =
Ca - Cb x 100
Cc-Cb Where:
Ca = Ca2+ concentration in the treated sample after precipitation Cb = Ca2+ concentration in the blank after precipitation Cc = Ca2+ concentration in the blank before precipitation
Ratio of PAPEMP to Terpolymer Ratio of phoshonoethoxylate to
polymer is varied from 1:3, 1:2, 1:1 and dosed in to test solution with
1, 2, 3 ppm of Polyphosphono ethoxylate { 50% active content) and
corresponding quantity of Terpolymer ( 50% active content). Efficiency
observed is as under:
EFFICIENCY OBTAINED USING INHIBITOR RATIO 1:3
~Sr.No l Inhibitors ~ Dose I Efficiency%
PAPEMP I TER POLY.
1 0 0 BLANK 50
2 2 ppm 6 ppm 2,6 ppm 95
3 3ppm 9ppm 3,9 ppm 92 Table.5 Test results of 1:3 ratio, PAPEMP to Terpolymer

Observation on 1:3 ratio results: Performance data listed in the table.5 indicate that 2ppm of PAPEMP ( 50% act.cont) and 6 ppm of Terpolymer ( 50% act.cont) appear to impart maximum inhibition efficiency over 94 %.

EFFICIENCY OBTAINED BY USING INHIBITOR RATIO OF
1:2'
Sr. No. Inhibitors Dose Efficiency
PAPEMP TER POLY.
1 0 ppm Oppm BLANK 50
2 2 ppm 4 ppm 2,4ppm 81
3 3 ppm 6 ppm 3,6 ppm 83
Table.6 Test results of 1:2 ratio, PAPEMP to Terpolymer.
Observation on 1:2 ratio results: Performance data listed in the table.6 indicate that 2ppm of PAPEMP (50% actcont) and 4 ppm of Terpolymer (50% act.cont) appear to impart inhibition efficiency over 80%. Higher dose has insignificant effect.

EFFICIENCY OBTAINED USING INHIBITOR RATIO 1:1
Sr.
No. Inhibitors Dosage Efficiency
PAPEMP TER POLYMER %
1 O ppm O ppm Oppm 50
2 2 ppm 2 ppm 2,2ppm 79
3 3 ppm 3 ppm 3,3ppm 79

Observation on 1:1 ratio results: Performance data listed in the table.7 indicate that 2ppm of PAPEMP (50% act.cont) and 2 ppm of Terpolymer (50% act. cont) appear to impart inhibition near 80 %efficiency.
4. SUMMARY OF THE INVENTION:
Oil field produced brines with calcium and bi-carbonate stressed environment require an efficient scale inhibitor to prevent scale deposition in heat exchanger tubes. Polyamino-polyethoxylate-methyl-phosphonate (PAPEMP) in combination with Terpolymer (consisting of three monomers- (i) Acrylic acid, (ii) Acrylo- methyi-propane-suiphonic acid, (iii) Maleic acid) inhibits scale deposition with over 94 % efficiency. Combined optimum inhibitor dose of Polyamino-polyethoxylate-methyl-phosphonate (50% active content), and Terpolymer (50% active content) is 2, 6 ppm respectively.

BRIEF DESCRIPTION OF DRAWINGS
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
1) Fig-1 is an illustration showing the Process flow diagram of CSU.

We claim:
1. Oil field produced brines with high Calcium and Bi-carbonate stressed conditions can be effectively inhibited for scale deposition in heat exchanger tubes with Polyamino-polyethoxylate-methyl-phosphonate doped with Terpolymer (consisting of three monomers- (i)Acrylic acid, (ii)Acrylo- methyl-propane-sulphonic acid, (iii)Maleic acid);
2. Optimum dose of Polyamino-polyethoxylate-methyl-phosphonate (50% Act cont) doped with Terpolymer (50 % Act cont) is 2, 6 ppm respectively to achieve over 94 % efficiency.
3. An Inhibitor dose of 2 ppm of Polyamino-polyethoxylate-methyl-phosphonate and 2ppm of Terpolymer will provide near 80% inhibition efficiency.