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 I 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.

ENZYME APPLICATION FOR WELLBORE CLEANING TO REMOVE MUD CAKE IN OIL / GAS WELLS - TO ENHANCE
THE PRODUCTIVITY
BACKGROUND OF THE INVENTION
1. Field of the Invention:
Present invention relates to a chemical system which can be used to effectively degrade the mud polymer cake formed in the wells during drilling by the application of polymer breakers.
2. Description of the Prior Art:
Oil and gas wells are drilled with polymer mud, in which fluid loss additives and bridging materials are added to control the losses. These materials foam a cake at the formation face to prevent the loss of fluid during drilling. The polymer cake will induce damage to the formation and affect the productivity of the formation. In low pressure wells, the reservoir pressure goes down and the well which is expected to come on self may not be able to overcome the barrier of filter cake. Drilling mud-induced damage is more and requires cleaning of mud cake during activation. Cleaning of mud cake is effective and economical if done during drilling phase.
Well cleaning can be done with suitable polymer breakers such as Acid, Oxydiser, Enzyme etc. during the drilling phase itself, through drill' string. Acid and oxidizers react fast and are difficult to be placed throughout the open hole. The acid will wormhole, result in losses of treating fluid and drilling mud. The enzyme can be placed at the end of drilling to remove the polymer damage as its reactivity is very slow

(need 12-24 hrs soaking time). Enzymes are polymers of amino acids with a high molecular weight. Their role is as catalysts, which speed up the chemical reactions, required for life, under relatively mild conditions of ph and temperature. Since the enzyme is a catalyst only small quantities of enzyme are required compared to other breakers.
The Coil Tubing intervention in open hole horizontal and multilateral wells are difficult task as the limited availability of conveyance tools. Moreover additional rig days required for Coil Tubing cleaning in addition to coil tubing operational cost.
3. OBJECT OF INVENTION:
The mud cake deposited by drilling fluid is left un-cleaned during activation. In sub hydrostatic wells the cake will create barrier for hydrocarbon flow. Hence cleaning of the polymer cake is required at the time of activation. The object of this invention is therefore to develop a chemical system to degrade the polymer cake effectively by the application of polymer breakers.
Permeability reduction that occurs because of the interaction between the rock and incompatible mud filtrate that penetrates into the vicinity of the well bore. These factors, often combined with the heterogeneity of the pay zone, decrease the productivity in horizontal wells. Normally in horizontal wells, the water base polymer type systems are when polymer come-in contact with formation, adsorption of polymer molecules to the formation grains results in a local build up off polymer concentration at formation pore throats, which in turn causes a reduction in permeability. This damage is very difficult to remove with ordinary cleaning methods.

The drilling induced formation damage is more pronounced for horizontal wells than the vertical wells. During horizontal well drilling, the main factors governing the selection and preparation of ideal drilling fluid with respect to formation damage control include the following areas:
► The types of formation to be drilled
► The compatibility of drilling mud with reservoir rocks and fluids,
► The performance of drilling mud, particularly the low fluid loss and thin filter cake, as well as well bore stability, lubricity, and acceptable suspension and transport capacities, etc.
► The drilling mud composition that yields lowest drilling cost.
• Mud damage, which adversely effects productivity, occurs as a result of several factors. First, in open hole, the filter cake can be formed both as external and uniform at the face and internal, inside the porous medium around the well bore. The action of different chemicals on filter cake is shown in Fig-1. Another problem is that, the polymer contained in the filter cake are tough and not easy degradable.
Internal filter cake: Solid particle invasion takes place when the filter cake is in contact with formation. The flow initiation pressure is the measure of the pressure needed to remove particle bridges from the pore throats, i.e, pressure required to remove the internal filter cake. The flow initiation pressure is controlled by solid invasion, i.e., the internal filter cake rather than external filter cake. Larger pore size decreases the flow initiation pressure, but causing more solid invasion and thus increases the flow initiation pressure. Higher overbalance pressure also increases the internal formation damage and thereby flow initiation pressure. The cake deposited external to the formation is called external cake. The drawdown given to the well for well activation

can lift off the external cake as shown in Fig -1. But in some cases external cake also required cleaning because of low well pressure.
4. DETAILED DESCRIPTION OF THE INVENTION:
Enzymes are polymers of amino acids with a high molecular weight All living organisms produce them. Their role is as catalysts, which speed up the chemical reactions, required for life, under relatively mild conditions of ph and temperature. Many of the reactions they catalyze can only be performed chemically under extreme conditions. Many hundreds of different enzymes exist with hundreds of different catalytic activities. These activities are often extremely specific i.e. a certain enzyme can only catalyze the breakdown or synthesis of certain compounds. Since the enzyme is a catalyst only small quantities of enzyme are required. The enzyme is regenerated in the course of the reaction and the catalytic cycle is repeated. Enzymes are normally highly soluble in water and pose no significant environmental problem. Enzyme-based process may provide an alternative to conventional chemical technology used in oil and gas production operations. In order to displace the chemical alternatives the biotechnology processes need to be technically superior or offer cost advantages. Biopolymers such as starch, xantan, guar, and cellulose are widely used in the oil industry.
The modern biotechnology industry can provide robust enzymes capable of tolerating oil reservoir environments. Enzyme-based process may provide an alternative to conventional chemical technology used in oil and gas production operations. In order to displace the chemical alternatives, the biotechnology processes need to be technically superior or offer cost advantages. Biopolymers such as starch, xantan, guar, lignin and cellulose are widely used in the oil industry. In order to

improve their handling characteristics, in particular the ease with which they form solutions, pre-treatment with enzymes has been widely used.
Enzyme based systems have now been devised for additional oil industry applications in the areas of water shut-off and same consolidation. Significant opportunities exist to use enzyme based processes to generate either minerals, gels or resigns in-situ. The hydrolases offer the most immediate potential for new oil field applications and are the class of enzyme already being used for the earlier oilfield application of enzyme.
Some hydrolytic enzymes, in combination with suitable substrates (chemical compounds which can be broken down by the enzyme) can produce either acidic or alkaline conditions. Enzyme can also be used to generate a specific chemical in-situ which then becomes available as a reactant in a second stage reaction.
A. The working principle of Amylase enzyme:
Amylose is a flexible linear polymer of glucose residues joined by a α-1,4 glycosisdic bond. Branch points occurs every 20-25 glucose units. Amylopectin may also contain several thousands glucose residues. The proportion of the two polymers, amylose and amylopectin, present in a particular batch of starch depends upon the source of starch. Starch from wheat, for examble, contains approximately 25% amylose and 75% amylopectin as shown in Fig- 2.
The enzyme amylase hydrolyse starch in an endo fashion, leave at random internal a -1, 4 glycosidic bonds in both amylose and amylopectin, showing little or no activity on the a -1,6 bonds. These enzymes degrade starch to shorter polymeric fragments, known as dextrins and maltose, a disaccharide, which contain two glucose

residues, a-amylase and α-1, 4- D- glucan-4-glucanohydrolase, are found in microorganisms, plants and animals. The amino acid sequence and the three dimensional structure of α - amylases from strains of Bacillus is known, α- Amylases are relatively small proteins, of molecular weight between 50 - 60 kdaltons.
B. Ecodrillase- P
Ecodrillase contains Amylase, Manmanese and an activator. This enzyme system has capacity to degrade complete polymer filter cake. Ecodrillase -P is a concentrated thermos table bacterial enzyme whose strong amylolytic power allows rapid conversion of the starch size into dextrins, which are easily removed by rinsing following impregnation with enzyme. The enzymes are capable of breaking starch sizes completely. This enzyme is soluble in water and having a Ph of 6 -8.5. This can be operated at 80 -120 degree centigrade with a dosage of 5-8%. This enzyme was tested for mud polymer damage removal test and it was found this chemical is removing the drilling mud induced damage under the operating environmental conditions.
C. Enzyme system (Ecodrillase-P) used for testing:
1. Amylase
2. Manmanese
3. KOH
4. Surfactant (non-ionic)
5. 2% Kcl water
6. Viscosity : 5 Cp
7. Gravity : 1.04
D. Specifications:
Description Thermostable enzyme breaker;

Physical state Material received shall be liquid free from
visible impurities;
Color of product : Brownish colored liquid;
Activity : Not less than 90,000 BAA u / g;
Ph 5,5-8.5;
Sp.gravity 1.00-1.25.
E. Testing of Enzyme for mud cake removal:
The indigenous enzyme was tested at IOGPT lab and the details of test
report given follows:
Core length :31.5 cm.
Core diameter : 4.3 cm.
Area : 14.51 cm2.
Pore volume : 123.47 cc.
Total volume : 443 cc.
Porosity : 27%.
F, Procedure:
1) CaCo3 (Limestone) core pack was prepared and cleaned with HSD.
2) Placed the core pack in flow loop core permeability testing apparatus as shown in Fig 3.
3) Tested the permeability at 500 psi @ 5cc/min. Total volume pumped 162 cc.
4) Pumped drilling polymer (volume 200 cc, as per the composition given in table-1) mud through the pack and kept for 4 hrs to form the filter cake.
5) Tested permeability with 2% Kcl solution (pumped 152 cc). Observed
cake at the core phase on opening the core holder).
6) Pumped 6% enzyme (ph 7-8, volume 145 cc) in 2% Kcl with 0.3%
non-ionic surfactant to remove the damage. Heated up to 120
degree centigrade for 4Hrs in oil bath heater and kept for soaking
for 12 hrs.

7) Tested the permeability (at 110,115 and 120 C) with 2% Kcl by pumping 150 cc volume.
8) Opened the core pack and observed cake degradation
Fig-3 shows the arrangement for core pack study test. The accumulators can be filled with the pumping fluid and can be displaced to core pack by pumping HSD / Kerosene through the pump. A backpressure vaive can create the differential pressure and the return can be measured with measuring cylinder. The permeability's are calculated with Darcy's equation. The result of core pack test is given in table 2, 3 and 4.
G. Permeability:
The permeability can be calculated by the following formula: K= 245QμL
A∆p
Where
K: permeability in md Q: Flow rate cc/min U: Viscosity of fluid in cp L: length of core Ap: Pressure in psi A: Area in cm2.
The enzyme was tested for performance in laboratory under the field operating conditions through a dynamic core flow apparatus. The enzyme mixture was tested at different temperatures for removing the filter cake of polymer drilling mud.

H. Composition of Drilling Fluid:
Composition of drilling polymer mud for test is given in table-1. The polymer mud sample was prepared for lab test.
Table-1

SI No. Chemical Unit
1 XC Polymer 2.5 ppb
2 Starch(PGS) 8ppb
3 CaCo3 12 ppb
4 Soda Ash 0.5 ppb
5 Caustic soda 0.4 ppb
6 Biocide 0.2ppb
/, Testing Results:
Three samples of enzyme system were tested in core flow apparatus. The system tested at 110 C and the regain permeability's are calculated after enzyme cleaning (table-2).
Table-2

Core pack test at IOGPT
lab Original
permeability
md Damaged
permeability
md Regained Permeabilit y md Soakin g time % Re gai n
5%
enzyme 110 °C 23 5 12 5 51
5%
enzyme
110°C 23 5 12 12 80
6%
enzyme
110°C 23 5 20 12 88
The enzyme system tested at 115 C and the regain permeability's are calculated after enzyme cleaning, the results are given in table-3.

Table-3
Core pack test at IOGPT lab Original
permeability
md Damaged
permeability
md Regained Permeabilit y md Soakin g time %
Rega
in
5% enzyme 115°C 23 5 12 12 75
6% enzyme 115°C 23 5 20 12 86
7% enzyme 115 °C 23 5 20 12 86
The enzyme system tested at 120 C and the regain permeability's are calculated after enzyme cleaning, the results are given in table-4.
Table-4

Core pack test at IOGPT lab Original
permeability
md Damaged
permeability
md Regained Permeabilit y md Soaking time %
Regai
n
5% enzyme 120 °C 23 5 12 12 70
6% enzyme 120 °C 23 5 20 12 85
7% enzyme 120 °C 23 5 20 12 85
It was observed that 6% enzyme is optimum and soaking time minimum 12 hrs can achieve a permeability of 86 % at 12 C. The stability test was conducted in saline water also. The enzyme mixture was stable and it can give more than 74% activity (BAA u/g) in saline water environment.
4. FIELD APPLICABILITY
1. Successfully implemented in three wells belonging to ONGC oil fields situated at NE#7H Mumbai high offshore oil field North side, NK#5H

Mumbai offshore oil field North side and NK#2YH Mumbai offshore oil field North side.
2. The wells produced more than expected production from horizontal drain holes.
3. Placement done through drill string at the end of drilling.
4. The acid and oxidizers will react fast and are difficult to place throughout the open hole in horizontal / multilateral wells. The acid will wormhole, result in losses of treating fluid and drilling mud. Hence enzyme has advantage of slow reactivity and less quantity required compared torn acid.
5. SUMMARY OF THE INVENTION:
Oil / gas production from a well will be reduced, if polymer mud invasion take place to oil formation rock down hole. Polymers are being used for drilling mud during oil well drilling. In horizontal / multilateral wells wellbore cleaning can be done during drilling with drill string. In this case the rig days for coil tubing operation can be saved for cleaning. The enzyme system can degrade polymer filter cake upto 120°C very effectively as per lab test with a cleanup efficiency of 86%. The enzyme can be uniformly placed, with minimum fluid loss, at the end of drilling; to remove the polymer damage as its reactivity is very slow (need 12-24 hrs soaking time). Field tested in 3 wells and achieved remarKable oil gain, proved that the enzyme is very effective in removing polymer mud damage. The placement can also be done through Coil tubing after completion.

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 shows the deposition of internal and external filter mud cake.
2) Fig -2 structure of amylase and amylopten.
3) Fig.3 Core flow set to test the enzyme in lab for removing drilling fluid mud cake.
4) Fig.4 is a diagram of the oil /gas well where enzyme application done to remove drilling fluid damage.

We claim:
A 5-8% dosage of an enzyme solution comprising Amylase and Manmanese enzymes mixed with a non-ionic surfactant and with a ph value of 7-8 in a carrier brine of 2% Kcl water degrades starch and xantan polymer filter cake deposited at the formation face of oil and gas wells, thereby increasing production of oil or gas.