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:
In-situ Cross linking Acid Diverting System (ISCADA).
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.

IN-SITU CROSS LINKING ACID DIVERTING SYSTEM HSCADA)
BACKGROUND OF THE INVENTION
1. Field of the Invention:
Present invention relates to a polymeric Gel that effectively diverts the stimulation fluid to lesser permeable zones by temporarily blocking the high permeable formations. Process involves a Linear Polymer gel of specific concentration to be cross linked with trivalent metal cation to increase the viscosity and subsequently breaking the cross linked gel to water like viscosity after effecting the diversion of treating fluid covering the zones of interest.
2. Description of the Prior Art:
Diversion is the process by which the treating fluid is diverted and allowed to enter the lower permeable zone, thereby making the homogenous distribution of treating fluid in the zone of interest. A critical factor to the success of a matrix-acid treatment is proper placement of acid so that all productive intervals are contacted by sufficient volumes of treating fluids. Effective placement of the treating /stimulation fluids evenly across the zones of interest is important specially when treating long perforated intervals or multiple zones. If there are significant variations in reservoir permeability, the acid will tend to flow primarily into the highest- permeability zones, leaving, lesser permeability zones virtually untreated. Even in relatively homogeneous formations, the damage may not be distributed uniformly without the use of techniques to improve the acid placement; much of the damage may be left untreated. When it is determined that sufficient acid coverage cannot be obtained by allowing the acid to choose its

own path, the acid should be diverted by means of chemical diversion technique.
3. DETAILED DESCRIPTION OF THE INVENTION:
3.1 What is Diversion
Diversion is the process by which the treating fluid is diverted and allowed to enter the lower permeability zone, thereby making the homogeneous distribution of treating fluid in the zone of interest.
3.2 Why diversion
A critical factor to the success of an acidisation treatment is proper placement of acid so that sufficient volumes of treating fluids contact ail productive intervals. Effective placement of the treating /stimulation fluids evenly across the zones of interest is important specially when treating long perforated intervals or multiple zones. If there are significant variations in reservoir permeability, the acid will tend to flow primarily into the highest- permeability zones, leaving lower permeability zones virtually untreated. Even in relatively homogeneous formations, the damage may not be distributed uniformly without the use of techniques to improve the acid placement; much of the damage may be left untreated. Thus the distribution of the acid into the formation is a very important consideration in matrix acidzing, and treatment design should include plans for acid placement.
3.3 Diversion with ISCADA
In-situ cross linked acid diverting agent (ISCADA) essentially contains a gelling agent, a cross linker and a cross-link breaker. ISCADA is a temperature and pH sensitive cross-linked gel. The gelling agent is a cross-linkable polymer and stable in acid at higher temperatures. Cross-linkable polymers were chosen that are stable in all

concentration of HCL up to a temperature of at least 115 'C. The cross linker is active only in the pH range of 4 to 6. Once a cross link has formed.. The breaker breaks the cross-link but not the polymer itself. Thereafter, the viscosity returns to its original low value for easy cleanup. The treatment is performed in alternating stage of gelled acid and ISCADA. The first stage involves weak acid (100/0 HCI) injection that takes the path of least resistance in the interval and enters the regions with the least damage and highest permeability. The acid will clean the perforation, dissolve the rock and create wormhole in the process. An ISCADA injection follows that enters the same regions and flows to the tips of the wormholes. A highly viscous cross-linked gel will develop that effectively blocks the permeability and stops wormhole growth. The subsequent acid injection will then be diverted to other regions in the zone that are more severely damaged and have lower permeability. The ISCADA cross-link gel then breaks and the diverter is quickly cleaned up. During the treatment, the pressure will drop as more and more regions in the zone accept acid and are stimulated. By increasing the rate to keep the pressure at a maximum, zona! coverage can be further improved. This technique of diversion is based on polymers, which exhibit fluid properties that act as a barrier and divert the acid to the next high permeable layer. Acid and polymer diverter are pumped in alternating 'stages. The first stage of acid will go to the most permeable layer and the diverter gel follows which diverts the next stage of acid to the next high permeable layer.
3.4 LABORATRY STUDY
Carried out several lab studies on the combination of chemicals for fine
- tuning the ISCADA formulation suitable to specific reservoir
conditions.
1. Optimization of cross linking agent and breaker

2. Core flow study to confirm formulation and design actual job
3. Sludge and anti-sludge test.
4. Emulsion test.
3.5 Optimization of ISCADA
Innovated diversion system, In-situ cross linked acid diverting agent (ISCADA) which essentially contains a gelling agent, a cross linker and a cross-link breaker. ISCADA is a temperature and pH sensitive cross-linked gel. The gelling agent is a cross-linkable biopolymer and stable in acid at higher temperatures. Cross-linkable biopolymers were chosen that are stable in all concentration of HCL up to a temperature of at least 130 deg 'C. The cross linker is active only in the pH range of 4 to 6. The breaker breaks the cross-link but not the polymer itself. Thereafter, the viscosity returns to its original low value for easy cleanup. Entire optimatton studies were aimed at considering the operational time for an oil well matrix acidization job with diversion, over three hours. XC- Polymer is selected as gallant and the minimum concentration of Gellant is tentatively fixed at 500 ppm. Chromium Acetate and Ammonium persulphate (APS) are selected as Cross-linker and breaker respectively. Cross linker concentration is varied from 1000 ppm to 400 ppm and the breaker concentration varied from 500 to 200 ppm. Temperature is tentatively chosen as 130 deg C as the bottom hole temperature of most of the offshore wells is around 110-130 deg C. Gel formation on mixing gallant with cross linker and breaking mechanism with APS and stability of the emulsion is evaluated as function of time as is shown in Fig 1 and Fig.2.
Observation on Laboratory results:
Optimizing the concentrations of various components of gel formulation with in the operational time frame of three hours (Three

hours), the optimum concentration of Gellant is 5000 ppm, cross linker 1000 ppm, Breaker 500 ppm.
3.6 CORE FLOW STUDIES
After evaluating the chemicals required for the gel preparation, the optimized formulations were flowed through core pack. Two packs of different permeability (K1 & K2) was prepared in API (3 %"x 1 % ") cells for core flow. These two cells were placed in parallel to represent a well of two different permeable layers. Sequences of tests as shown in Fig.3 were as under:
• Initially 2% KCI was flown through the pack individually and measured the differential pressure (DP) across the pack in order to determine the permeability of individual pack.
• 2 % KCI was then flowed through the packs in parallel mode and again verified their permeability.
• One pore volume of diverting fluid consisting of polymer gel mixed with x-linker and breaker was flowed through the pack and the lines flushed with KCI keeping both the API cells in a water bath having a set temperature of 95 'C.
• 40 minutes time was provide for gellation
• 2 % KCI pumped through the packs. But no return from any pack observed and DP rose high.
• However, at a higher pressure low permeable pack started flowing.
• Similar test was carried out keeping the cells at oil bath of 130 'C and found same result.
Observation on core flow
In-site cross-linking acid diverting agent (ISCADA) system is a temperature and pH sensitive chemical, which has indicated encouraging diversion in core flow test at lab. ISCADA essentially contains a viscous

solution of polymer with cross-linker and breaker. Initially when the gel is pumped through the set-up, it traced the path of least resistance and passed through high permeable sand pack cell-H (K2). After 40 minutes of retention time, the polymer mixer in the cell acquired viscosity and resulted in to high viscous gel. In the next stage, when acid is pumped through the set up it again traced the path of least resistance and flowed through less permeable sand pack (k1) which is the result of diversion due to presence of high viscous gel in the cell-L( K2).
3.7 EMULSION TEST:
• Prepared partially spent acid by reaction of two liters of acid (15!/o HCI + corrosion inhibitor any other additives to be used in field)
• Decanted spent acid solution
• Dispersed 2.5 gms. of pulverized formation core (representative carbonate core of well no. BH # 25) in 25 ml spent acid.
• Added 75 ml crude oil of ICP well to this spent acid. Emulsified with stirrer at 4000 RPM for 30 seconds.
• Poured emulsion immediately into 100m1 graduated cylinder and recorded volume broke out at 15 min., 1 Hr. & 24 Hrs.
Results: Emulsion broke out even before 15 minutes.
3.8 ACID SLUDGE TEST:
• Poured acid into a clean bottle.
• Added equal volume of ICP crude oil free of solids and emulsion.
• Shaken vigorously.
• Placed in water bath at temp, of 100 'C (formation temp.) and kept for 24 hrs.
• Poured the mixture through a clean 100 mesh SS wire screen.

• As per procedure, if no solids remain on the screen no sludge formation. However, a few number of small soft lumps remained on the screen, which had to wash by scrapping the screen by solvent like toluene.
Results: There may be minor sludge formation with crude of ICP plot farm but when the acid is treated with anti-sludge agent no sludge resulted.
4. FIELD APPLICABILITY
The innovated gel formulation is applied in a number of oil wells for sor stimulation of multilayered reservoir. The treatment is performed in alternating stage of gelled acid and ISCADA. The first stage involves weak acid (10% HCI) injection that takes the path of least resistance in the interval and enters the regions with the least damage and highest permeability. The acid will clean the perforation, dissolve the rock and create wormhole in the process. An ISCADA injection follows that enters the same regions and flows to the tips of the wormholes. A highly viscous cross-linked gel will develop that effectively blocks the permeability and stops wormhole growth. The subsequent acid injection will then be diverted to other regions in the zone that are more severely damaged and have lower permeability. The ISCADA cross-link gel then breaks and the diverter is quickly cleaned up. During the treatment, the pressure will drop as more and more regions in the zone accept acid and are stimulated. By increasing the rate to keep the pressure at a maximum, zona! coverage can be further improved. This technique of diversion is based on polymers, which exhibit fluid properties that act as a barrier and divert the acid to the next high permeable layer.

Step-wise treatment of ISCADA:
1. The first stage involves weak acid (10% HCI) injection that takes the path of least resistance in the interval and enters the regions with the least damage and highest permeability.
2. Pump ISCADA, which enters the same regions and flows to the tips of the perforations and wormholes.
3. Behind the slug of diverting fluid tubing volume of spacer fluid would be pumped to occupy the tubing volume. This spacer fluid consists of organic acid (100/0 HAc) and mutual solvent (EGMBE).
4. The subsequent acid injection will then be diverted to other regions in the zone that are more severely damaged and have lower permeability.
5. The ISCADA cross-link gel then breaks and the diverter are quickly deaned up,
6. Stages can be determined based on level of damage or skin value and the number of zones to be treated.
7. Back flush with a solution of 10%0 EDTA, EGMBE, Dodecyl Benzene sulphonic acid.
8. Well is desired to be flowed back as quick as possible after the treatment.
Job Design: Based on the experimental evaluation of breaker and cross liker of the ISCADA formulation job design as set out in Figures 4A and 4B are made for well #NW 66 for job execution.
ISCADA Stages
Flush Vol = 48 bbl (T/S = 1729m; Top of N4 = 1932.5m)
Chemicals for ISCADA:
N2-1 = 1846.5-1852 5.5 m
N2-2 = 1878.5-1896.5 18 m

N3 = 1910.5-1922.5 12 m
N4 = 1932.5-1939.0 6.5 m
Total: Acid = 24 m3
ISCADA = 3 m3 Spacer (EGMBE) = 6 m3 Flush (2% Kcl) = 8.8 m3 (56 bbl).
Post Job Evaluation:
Post job analysis was carried out on the basis of injection pressure, Pressure difference 'Dp' and production analysis (i.e.BLPD)
Pressure analysis:
• In the first stage, acid was injected at an initial injection pressure of 1650-1700. It is expected to enter the high permeable zone N2-1, N2-2. Subsequently pressure dropped to 1100 psi and stabilized. ISCADA was injected to block the stimulated N2-1, N2-2 zone to divert the acid to N3 layer. Acid was injected to stimulate N3 layer and expected to cover entire N3 layer due diversion effect. Injection pressure rose to 1350 psi indicating a 'DP' rise of '250 psi due diversion effect of ISCADA .
• In the second stage ISCADA was pumped to block the N3 layer and injected acid to enter N4 layer. Pressure rose to 1500 indicating a 'Dp' of 150 psi.
• Well was flown back and observed for stabilization overnight.
Production analysis:
Post job production figure as shown in Fig 5A reveals that gain from the job is appreciable from the well NW#66 after acid diversion job using Insttu cross linked gel ISCADA. There is appreciable gain of oil in the well NW#66 on application of ISCADA as is clear from Fig. 5B.

SUMMARY OF THE INVENTION:
Stimulation of heterogeneous reservoir with permeability contrast requires Effective diversion of reactive fluid to lesser permeable layers in presence of high permeable zones. The invented gel formulation with 500 ppm of XC-polymer gallant, 1000 ppm of Chromium Acetate Cross-linker, 500 ppm of Ammonium persulphate breaker from 95 deg C to 130 deg C can divert the reactive fluid to lower permeable zones and achieve complete zonal coverage all the potential layers.

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 a table showing optimization gellant, cross-linker and breaker.
2) Fig -2 is an illustration of the variation of Viscosity of ISCADA, as a function of time and Temperature.
3) Fig.3 is an illustration of the Core flow set up for in-situ acid diversion test.
A) Fig.4A is a table showing chemical requirement for well NW#66 perforation Interval.
5) Fig.4Bis a table showing job design for well NW#66.
6) Fig.5 A is a diagram of real-time pressure Data of well NW# 66.
7) Fig 5B is a table showing post job evaluation results.

We claim:
1. In-situ Cross-linked Acid Diverting agent (ISCADA ), consisting of 5000 ppm of XC-Polymer as gellant, 1000 ppm of Chromium Acetate as cross-linker, 500 ppm of Ammonium Persulphate as breaker at 130 deg C, effectively diverts the stimulation fluid to lesser permeable layers by temporarily blocking the high permeable layer.
2. The invented gel formulation is effective in the temperature range of 95 deg C to 130 deg C.
3. The invented gel formulation does not form emulsion with produced crude or spent acids.
4. The invented gel formulation does not generate sludge with crude or spent acids.