Title of Invention

A SYNERGISTIC CEMENT SLURRY COMPOSITION AND PROCESS THEREOF

Abstract The present disclosure relates to a synergistic cement slurry composition for cementing low temperature wells such as oil and gas wells where the temperature ranges between 55˚C to 75˚C comprising accelerator, fluid loss additive, friction reducer, cement and water where the accelerator offsets the increase in the setting time of said cement slurry composition caused by the addition of ingredients such as fluid loss additive and friction reducer. The present disclosure provides optimum setting time to said cement slurry composition in the range of about 240-260 min. The present disclosure further relates to a process for the preparation of said cement slurry composition and process of cementing of oil and gas wells with said cement slurry composition.
Full Text

FIELD OF INVENTION:
The present disclosure provides a synergistic cement slurry composition which has optimum setting time in the range of about 240-260 min for cementing low temperature wells such as oil and gas wells where the temperature ranges between 55 to 75 and process thereof.
BACKGROUND OF THE INVENTION
Cement compositions are generally used in the oil and gas industry for cementing the annular space in the well bore between the surrounding formation and pipe or casing. Typically, cement slurry is pumped down the inside of the casing and back up the outside of the casing through the annular space. The amount of water used in forming the cement slurry will depend on the type of hydraulic cement selected and the job conditions at hand.
In the low temperature wells, the requisition received from the field have an emphasis on minimum possible water loss content with thickening time around 240 min to 260 min as an operational requirement.
About a decade back there was a commercial product called D160, which was a unique additive, was known as Low Temperature Non-Retarding Fluid Loss Additive. It was a patented product under the United States of Americas under Patent Application No.4, 610,306. This special additive having non-retarding nature was best suited to reduce the fluid loss at higher doses without affecting the increase in thickening time.
Since December 1999, this low temperature non-retarding fluid loss additive was not available commercially in India. Since then well cementing jobs in low temperature wells were performed with the cement slurries designed with conventional cement additives like fluid loss control additive and friction reducer additives and the required thickening time was successfully designed with these conventional additives. However the fluid loss content was quite high in the range of 1400ml to 1800ml which in some cases lead to channeling problems.
In most cases the cementing jobs were satisfactory but some secondary repair jobs were also required to reinforce the poor set cement bond behind the casing pipes of the wells due to performance limitations of conventional cement additives in designing the perfect cement

slurries covering all the parameters like optimal thickening time, proper rheological properties and suitable compressive strength to pump and displace the cement slurry behind the casing with minimum fluid loss.
Due to retarding (increase in thickening time) nature of all conventional fluid loss additives, the required low fluid loss control could not be achieved while maintaining the desired thickening time around 240 - 260 minutes. At higher doses of the fluid loss additives, the control in fluid loss was achieved but the increase in thickening time was undesirable. In such cases the displaced cement slurry in liquid state behind the casing and drilled formation are prone to intrusion of formation fluids into the cement slurry thus forfeiting the object of hydraulic sealing of the well formation by providing communication through channels in the set matrix formed by the cement slurry.
The conventional cement additives, like fluid loss control agents are organic polymers mainly made from partially hydrolyzed poly acrylonitrile, cellulose compounds, latex etc, and friction reducers or turbulence inducers are lignin derivatives, organic acids, synthetic aryl/alkyl sulphonates, naphthalene sulphonates condensates etc. Their main functions are to decrease the fluid loss of the cement slurry by surface adsorptions but this in turn leads to increase in thickening time of the slurry.
Instead of developing synthetic cement additives like non-retarding fluid loss additive, a different approach was adopted. In this new approach, specific dose of conventional fluid loss additive was added to reduce the fluid loss of cement slurry to desirable limit. The quite high increase in thickening time due to high dose of fluid loss additive was compensated to desirable limit by addition of non-conventional moderate accelerator, which also improves the rheological properties of the cement slurry to an appreciable extent. These accelerators are added to cement slurries to offset the delay caused by fluid loss additives.
The examples of inorganic salts used as accelerators of Portland Cement include calcium chloride, sodium chloride and sodium silicates. The examples of other known accelerators include carbonates, aluminates, nitrates, nitrites, sulfates, thio- sulphate and alkaline bases like sodium, potassium and ammonium hydroxide. The examples of other organic acids and amines that have been reported to accelerate the setting time of Portland cement include

calcium formate, oxalic acid and tri ethanolamine. However, their use in Oil Well Cementing is not documented.
Further the known accelerators which are usually added to cement slurries to offset the delay in setting time caused by addition of components such as fluid loss control agents and dispersants or turbulence inducers are unsuitable either due to very fast accelerating or retarding nature of setting time of Oil Well Class "G" High Sulphur Resistant cement.
US Patent No. 4036301 discloses a cementing composition comprising hydraulic cement, water and fluid loss additive. US 4036301 disclose calcium chloride and anhydrous sodium metasilicate as accelerator for retarding the thickening time of the cement slurry composition which is encapsulated in an encapsulating material. The accelerators used in the US 4036301 patent are conventional and known to be used in oil industry such as chloride and anhydrous sodium silicate which are coated with petroleum derived paraffin wax to make it suitable for high temperature condition. Further, the cement slurry composition of US 4036301 patent is used for cementing oil wells at high temperatures of 200 F (93.33°C) to 400 F (204.44°C).
US Patent No. 5336316 discloses phosphonate polymer having phosphonated group pendant to a polymeric backbone as additives which is well known to the oil industry. This synthetic phosphor-polymer itself acts as a fluid loss control additive at low temperature.
US Patent No. 4721160 discloses light weight cement slurries having densities US Patent No. 5850880 discloses composition comprising of cement, fluid loss additive, namely polyvinyl acetate polymers used in conjunction with a surfactant. This composition is then adjusted to individual well conditions by adding chelating agent, cross-linking agent, biocides, antifoams, or combinations thereof. Further, in US 5850880 there is no mention of use of an accelerator to offset the increase in thickening time of the cement composition that is caused due to addition of fluid loss additives.

SUMMARY OF INVENTION
The present disclosure relates to a synergistic cement slurry composition for quality cementing of the annular space in the well bore between the pipe casing and surrounding formation of low temperature wells such as oil, and gas wells where temperature ranges between SS'‘C to 75 ‘C.
The present disclosure also relates to a method of preparation of the synergistic cement slurry composition. The synergistic cement slurry composition of the disclosure makes use of accelerator to offset the setting time caused by addition of the ingredients such as fluid loss additive and friction reducer.
The present disclosure relates to the synergistic cement slurry composition for cementing low temperature oil and gas wells having setting time in the range of 240-260 minutes. The temperature of the oil and gas wells lies between 55’C to 75 ‘C.
The present disclosure relates to the synergistic cement slurry composition for cementing low temperature oil and gas wells that controls fluid loss by addition of Fluid loss additive and also maintains setting time of the cement in the range of 240-260 minutes by addition of accelerator namely, ammonium acetate.
The present disclosure also relates to a method of cementing of low temperature oil and gas wells with the synergistic cement slurry composition.
BRIEF DESCRIPTION OF TABLES
Table 1: Cement slurries with non-retarding fluid loss additive cement Table 2: Slurries designed for cementing with conventional additives Table 3: Field design for casing and plug jobs using conventional additives Table 4: Slurry designing using conventional accelerator Tables: A: Screening of R-Acetate as accelerator
B: Screening of Acetate salts as accelerator Table 6: Laboratory cement slurry design with ammonium acetate as the accelerator Table7: Fixation of optimal dose of accelerator in cement slurries designed at 55°C Table 8: Fixation of the optimal dose of accelerator in cement slurries designed at 65*’C

Table 9: Fixation of optimal dose of ammonium acetate as the accelerator Table 10: Recommended cement slurry designs for field trials Table 11: Recommended cement slurry stability at 55’C Table 12: Recommended cement slurry stability at 65°C Table 13: Recommended cement slurry stability at 75°C
Table 14: Cost comparison of cement slurry composition of the present disclosure vis-a-vis cement slurry with low temperature non retarding fluid loss control additive (NRFLA)
Table 15: Requirements for a cement slurry using conventional additives for application in low temperature well
Table 16: Results achieved using the conventional additives of table 15 BRIEF DESCRIPTION OF FIGURES
Figure 1: Fixation of optimal dose of accelerator in cement slurries designed at 55’C
(Chart 1) Figure 2: Fixation of optimal dose of accelerator in cement slurries designed at 65’C
(Chart 2) Figure 3: Fixation of optimal dose of accelerator in cement slurries designed at 75°C
(Chart 3) Figure 4: Graphical representation of Chart 1 Figure 5: Graphical representation of Chart 2 Figure 6: Graphical representation of Chart 3
DEFINITIONS AND ABBREVIATIONS:
Thickening time and setting time has been used interchangeable hereinafter.
Accelerator: An accelerator is used for optimal setting of the cement slurry/ Shortening the setting time or thickening time
Fluid loss additive has been referred to as FLA hereinafter. FLA is a chemical additive used to control the loss of fluid to the formation through filtration. In cementing operations, loss of the aqueous phase can severely affect the performance of the slurry and set cement. In almost any operation, loss of fluid to the reservoir formation carries a high risk of permeability damage.
Friction Reducer has been referred to as FR hereinafter. FR is a chemical additive that alters fluid Theological properties to reduce friction created within the fluid as it flows through

small-diameter tubular or similar restrictions. Generally polymers, or similar friction reducing agents, add viscosity to the fluid, which reduces the turbulence induced as the fluid flows.
American Petroleum Institute is abbreviated as APL
Bottom hole static temperature is abbreviated as BHST. It is the undisturbed temperature at the bottom of a well. After circulation and after the well is shut in, the temperature approaches the BHST after about 24 to 36 hours which depending on the well conditions. The BHST is the temperature used in most tests in which the cement slurry is required to set or is set.
BHT it is measured as the temperature in a borehole at total depth at an instant of time. In log interpretation, the bottom hole temperature (BHT) is taken as the maximum recorded temperature during a logging run, or preferably the last of series of runs during the same operation. BHT is the temperature used for the interpretation of logs at total depth. Farther up the hole, the correct temperature is calculated by assuming a certain temperature gradient. The BHT lies between the bottomhole circulating temperature (BHCT) and the bottomhole static temperature (BHST).
BHP is abbreviated form for bottom hole pressure. It is the down hole pressure, measured or calculated at a point of interest, generally the top of the perforated interval.
BWOC is abbreviated form of by weight of cement. It refers to the amount (in percent) of a material added to cement. BWOC is the method used to describe the amount of most additives in the dry form.
DETAILED DESCRIPTION OF THE INVENTION:
The present disclosure provides a synergistic cement slurry composition that has optimal setting time in the range of 240 to 260 minutes for cementing the annular space in the well bore between the pipe casing and surrounding formation of low temperature wells such as oil and gas wells where the temperature ranges between SS'‘C to TS'‘C. Further, the synergistic cement slurry composition minimizes the fluid loss as a result of addition of Fluid Loss Additive (FLA) and maintains consistent density without producing zones in said cement

sheet. The said cement slurry composition comprises accelerator, fluid loss additive, friction reducer, cement and water where the accelerator offsets the increase in the setting time of said cement slurry composition that is caused by the addition of ingredients such as fluid loss additive (FLA) and friction reducer (FR).
The present disclosure also relates to a method of cementing of low temperature oil and gas wells with the synergistic cement slurry composition.
An embodiment of the present disclosure provides synergistic cement slurry composition which comprises FLA (0.40 to 0.70 Wt% of cement), Friction reducer (0.10 to 0.20 Wt% of cement), ammonium acetate as accelerator (0.025 to 0.05 Wt% of cement) and water (43.0 to 5L0Wt% of cement).
Another embodiment of the present disclosure relates to a synergistic cement slurry composition that uses cement oil well class "G" High Sulphur Resistant cement.
Another embodiment of the present disclosure provides a synergistic cement slurry composition that uses FLA selected from a group comprising compounds such as partially hydrolyzed poly acrylonitrile cellulose compounds and latex.
An embodiment of the present disclosure relates to a synergistic cement slurry composition that uses FR selected from a group comprising of lignin derivatives, organic acids, synthetic aryl/alkyl sulphonates, condensates and naphthalene sulphonates.
Another embodiment of the present disclosure provides a synergistic cement slurry composition where the accelerator used is ammonium acetate.
Another embodiment of the present disclosure provides a synergistic cement slurry composition having desirable low thickening time and low fluid loss.
Still another embodiment of the present disclosure provides a synergistic composition where at 55'‘C the retarding effect of 0.45 FLA and 0.2% FR is offset by adding 0,02-0.025% accelerator to achieve setting time of 240-260 minutes.

An embodiment of the present disclosure provides a synergistic composition wherein at 65°C the retarding effect of 0.5 FLA and 0.2% FR is offset by adding 0.025% accelerator to achieve setting time of 240-260 minutes.
Another embodiment of the present disclosure provides a synergistic composition wherein at 75"C the retarding effect of 0.6 FLA and 0.2% FR is offset by adding 0.4% accelerator to achieve setting time of 240-260 minutes.
Yet another embodiment of the present disclosure provides a synergistic slurry composition that improves the rheological properties and compression strength of said cement slurry composition.
Yet another embodiment of the present disclosure provides a method of preparing said cement slurry for cementing of low temperature oil and gas well, said method comprising of obtaining a mixture by blending FLA, FR and cement followed by addition of an aqueous solution of accelerator namely ammonium acetate to said mixture to obtain said synergistic cement slurry composition.
Still another embodiment of the present disclosure provides a method of preparing the synergistic cement slurry composition, wherein the said accelerator used has minimum secondary and moderate acceleration which makes it suitable for designing the cement slurries for primary cementing.
Another embodiment of the present disclosure provides a synergistic cement slurry composition which is economical vis-a-vis cement slurry compositions that uses low temperature non-retarding fluid loss control additive (NRFLA). The details of the cost comparison of said cement slurry composition of the present disclosure vis-a-vis cement slurry with low temperature non-retarding fluid loss control additive (NRFLA) is provided in Table 14.
Another embodiment of the present disclosure relates to a process of preparing the synergistic cement slurry composition where an accelerator is used that offsets the increase in the setting time caused due to the addition of fluid loss and other cement additives.

Another embodiment of the present disclosure relates to a process of preparing the synergistic cement slurry composition where said accelerator used is ammonium acetate.
Another embodiment of the present disclosure relates to a process of preparing the synergistic cement slurry composition where fluid loss control additives such as organic polymers such as partially hydrolyzed poly acrylonitrile, cellulose compounds and latex are used.
Another embodiment of the present disclosure relates to a process of preparing said cement slurry composition where friction reducers or turbulence inducers such as lignin derivatives, organic acids, synthetic aryl/alkyl sulphonates, naphthalene sulphonates condensates are used.
Another embodiment of the present disclosure relates to a process of preparing said cement slurry composition where said accelerator is used that has minimum secondary and moderate acceleration which makes it suitable for designing the cement slurries for primary cementing.
Another embodiment of the present disclosure provides cement slurry composition for cementing low temperatures wells such as oil and gas wells under deep water at in the range of about 55’C to 75°C which is as herein described in the specification and with illustrative examples.
Another embodiment of the present disclosure provides cement slurry composition for cementing low temperatures wells such as oil and gas wells wherein a setting time of the cement slurry composition of 240-260 min is maintained on addition of the R-acetate, namely, ammonium acetate and fluid loss is curtailed as against cement slurry compositions where non retarding FLA or conventional additives are used. The cement slurry compositions where non retarding FLA or conventional additives are used, in order to maintain the setting time the fluid loss minimization is not possible. The detail of the delayed high fluid loss in case of cement slurry composition where known non retarding FLA is used is provided in Table 1.
Another embodiment of the present disclosure provides cement slurry composition for cementing low temperatures wells such as oil and gas wells where sodium acetate is used as the accelerator, details of which are provided in Table 4. Sodium acetate cannot be used as the accelerator as the optimum setting time of 240-260 minutes cannot be achieved. Further, sodium acetate is found to be carcinogenic in nature.

Another embodiment of the present disclosure provides cement slurry composition for cementing low temperatures wells such as oil and gas wells wherein a setting time of the cement slurry composition of 240-260 min is maintained on addition of the R-acetate, namely, ammonium acetate and fluid loss is curtailed as against cement slurry compositions where non retarding FLA or conventional additives were used. The cement slurry compositions where non retarding FLA or conventional additives were used, in order to maintain the setting time the fluid loss minimization is not possible. The detail of the delayed high fluid loss in case of cement slurry composition where known non retarding FLA is used is provided in Table 1.
Another embodiment of the present disclosure provides cement slurry composition for cementing low temperatures wells such as oil and gas wells wherein a setting time of the cement slurry composition of 240-260 min is maintained on addition of the R-acetate, namely, ammonium acetate and fluid loss is curtailed as against cement slurry compositions where non retarding FLA or conventional additives were used. The cement slurry compositions where non retarding FLA or conventional additives were used, in order to maintain the setting time the fluid loss minimization is not possible. The detail of the delayed high fluid loss in case of cement slurry composition where known non retarding FLA is used is provided in Table 1.
Another embodiment of the present disclosure provides a process of preparing said cement slurry composition for cementing low temperatures wells such as oil and gas wells under deep water at in the range of about 55°C to 75’C as herein described in the specification and with illustrative examples.
Another embodiment of the present disclosure provides a process of preparing said cement slurry composition where said accelerator used was dry blended with powdered fluid loss additive as indicated in Table 6 in the ratio of 2:8 by weight in Serial no. 1-4, 4:6 in serial no 5, 3:7 in serial nos 6 & 7, 0.35:0.65 in serial nos. 8-12 and made the FLA + accelerator as one additive. Thickening time of the 15.8 ppg cement slurries dry blended with different ratio of FLA- Accelerator and friction reducer at 75’C were determined and reported in table 6 to select the optimum combination with accelerator. The response of 0.35 + 0.65 ratio wise combination of FL-19 and ammonium acetate from 1 to 0.6% BWOC were found to be accelerating the thickening time in the range of 225 - 250 minutes.

As the mixture of FLA + Accelerator could not be stored for long because of ammonia and change in its physical appearance as fluffy powder instead of free flowing one and difficult to blend with cement, efforts for dry blending were substituted with the addition of water to the mix and it was found that at 75’C the optimum dose of Ammonium Acetate should be around 0.3% - 0,4% by weight of the cement. This accelerator was then added in the aforementioned proportion and mixed with water and the thickening time was measured of the 15.8 ppg cement slurries at 55°C, 65T and 75’C with respective 3,500, 4,500 and 5,000 psi pressures to select the optimum dose of the accelerator. The temperatures were raised from ambient to final in 30 minutes In preparation of cement slurries, it is common practice to dissolve the accelerators or readers in mixing measured quantity of water and cement is dry blended with powdered FLA and FR and in stirred condition it is mixed with water to prepare cement slurry Secondary effects means the side undesirable effects such as to reduce the fluid loss, addition of extra dose of FLA will work but it will increase the thickening time which can be termed as secondary effect because primary function of FLA is to reduce fluid loss.
The present invention involves method of cementing oil and gas well with the synergistic cement slurry composition where the method comprises of:
a.) blending fluid loss additive, friction reducer and cement;
b.) adding an aqueous solution of the ammonium acetate to the above to obtain cement slurry composition;
c.) pumping the above obtained cement slurry composition to desired location in said well and allowing the cement slurry composition to solidify.
Having described the present disclosure, a further understanding can be obtained by reference to the specific preferred embodiments which are provided herein for the purpose of illustration only and not to limit the scope of the appended claims.
The synergistic cement slurry for cementing of low temperature oil and gas well was prepared by blending fluid loss additive, friction reducer and cement (oil well class 'G" High Sulphur Resistant cement) followed by addition of an aqueous solution of said accelerator to the above. The cement composition of 15.8 ppg is obtained by standard test procedure laid

down in American Petroleum Institute (API) specifications. 10, API - ten (10) different specifications for slurry preparations are enclosed in the following examples.
EXAMPLES
It should be understood that the following examples described herein are for illustrative purposes only and that various modifications or changes in light will be suggested to a person ordinarily skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims.
EXAMPLE 1
Selection and Mechanism of action of Accelerator:
The mechanism by which the accelerator of the present disclosure operates is complex. The use such an accelerator has never taken place in cementing of low temperature wells, especially oil well and gas wells before. While screening different accelerators, R-Acetate was found to retard the designed cement slurries. The R-Acetate such as sodium acetate as shown in Table-5A and ammonium acetate as shown in Table - 5B was used to retard the setting time of the cement slurry compositions on addition of FLA and FR. It was found tat ammonium acetate had encouraging accelerating tendency. The acceleration tendency of ammonium acetate as the accelerator may be due to the formation of ammonium hydroxide in the cement slurry. The portable chemical reaction is given below:
Temperature & Pressure
1. CH3COO-R (Accelerator) + HOH >CH3COOH + ROH
(Closed system in cement slurry)
Temperature & Pressure
2. CH3COONH4 (Accelerator) + HOH >NH40H -f CH3COOH
(Closed system in cement slurry)
As shown in the above reaction, the formation of ROH and acetic acid is common in case of all the accelerators, here in this case sodium acetate and ammonium acetate. It therefore appears that ROH and acetic acid do not act as accelerator when R-acetate breaks by reacting with the water of cement slurry in closed system.

Hence it was confirmed that NH4OH formed when ammonium acetate was used as the accelerator was responsible for imparting moderate acceleration in setting time of the cement slurry compositions on addition of FLA and FR.
EXAMPLE 2 Specification Criteria:
Table 15 (in API lOB, 22"‘ Edition, December 1997) provides the parameters for cement slurry designing such as adequate thickening time, low fluid loss values, permissible or zero free water separation, good early compressive strength, compactness of the set cement matrix and slurry stability test at down hole condition for settling to be the various criteria and inputs for the specifications while using conventional additives. Further, table 16 provides the thickening time achieved by using conventional additives.
In the absence of low temperature non retarding fluid loss additive, the dose of the conventional FLA was used with added addition of accelerator to reduce the API fluid loss from 1400 to 1600 ml to half its level (600 to 800) without compromising the thickening time of around 240 to 260 minutes. To reduce the fluid loss to its half level by increasing the dose of additives and its retarding effect on thickening time was
compensated by addition of accelerator to get the desired thickening time. This was just adequate to complete the slurry pumping, displacement and final wash out to prevent any possible channeling in the cement matrix during hydration of cement on setting.
High free water can allow the communication between cemented zones because free water separation from the cement slurry can migrate vertically in flow upward through the cement slurry. This flow can create a channel in the cement column in set cement because the channel consists of water rather than cement. The free water separation was measured as per API specification 10 to ensure that it is under permissible limit.
The cement slurry composition must develop sufficient strength, a minimum of 2000psi to support the pipe and provide the permanent hydraulic seal for zonal isolation. The pressure

used in the different examples of cement slurry composition is designated by Bottom Hole Temperature (BHP) which is maintained above 2000 psi as is shown in Table 7 to 12,
EXAMPLE 3
Preparation of Cement Slurry Composition:
The cement slurry of 15.8 ppg was prepared by dry blending cement and conventional additives and then adding accelerator solution namely ammonium acetate solution to the above mentioned dry blended powder by following the standard procedure laid down in API specs. 10.
Testing Conditions:
Stable non-retarding cement slurries with good compressive strength and minimum fluid loss was designed for different temperatures and pressures suitable for cementing the annular space in the well bore between the pipe casing and surrounding formation of low temperature wells such as oil and gas wells where the temperature ranges between 55’C to IS’C is given in Tables 11,12 & 13.
Stability Test:
The stability test of the designed slurry is of prime importance because temperature and pressure of the unstable slurries at the annular space in the well bore due to excessive setting may increase the risk of annular communication and gas migration. With good displacement practices the risk of inter zonal communication during primary cementing behind the casing was minimized. But channeling can also be formed during hydration of cement from fluid to set state if the slurry is unstable. In unstable cement slurries, especially under static conditions due to sedimentation and excessive settling high free water it generated. This leads to zonal isolation problems in wells.
If the air permeability of the set cement, designed and recommended for field use is less than .Im Darcy, which is within the permissible limit, the set cement quality is supposed to be good. Air permeability of the recommended designs cured for 24 hours was measured using Rusk Air Permeameter. The limit of air permeability of cement stone has been fixed at 0.1m

Darcy, which is an internationally accepted value. Approximate 25mm width and 1" long set cement core from the Sedimentation tube after the stability test was cut and used to measure the compactness of set cement matrix.
Testing of stability of cement slurry at simulated conditions of the well bore, invented by BP and recommended in API-specs the cement slurry composition was allowed to set hard to permit the measurement of both free fluid and density variation along the length of the set cement column. The 'Sedimentation Tube" used to measure the stability of the designed and recommended slurry for field trial was fabricated indigenously.
The recommended cement slurry stability at 55’C is provided in Table 11. The density profile of the cement in the annular space in the well bore between the pipe casing and surrounding formation the temperature is 55’C is found to be consistent. The sample density in the top portion of the set cement in the well is 1.91, followed by 1.92 in the middle portion, followed by 1.94 in the bottom portion of the set cement in the well bore.
The recommended cement slurry stability at 65°C is provided in Table 12. The density profile of the cement in the annular space in the well bore between the pipe casing and surrounding formation the temperature is 65*’C is found to be consistent. The sample density in the top portion of the set cement in the well is 1.91, followed by 1.92 in the middle portion, followed by 1.93 in the bottom portion of the set cement in the well bore.
The recommended cement slurry stability at 75’C is provided in Table 13. The density profile of the cement in the annular space in the well bore between the pipe casing and surrounding formation the temperature is 75’*0 is found to be consistent. The sample density in the top portion of the set cement in the well is 1.92, followed by 1.93 in the middle portion, followed by 1.94 in the bottom portion of the set cement in the well bore.
EXAMPLE 3
Optimal dose of Accelerator for cement slurry designing at 55 :
The accelerator was added in mixing water from 0.6 to 0.025% by weight of cement. It was observed that at higher dose of 0.6%, 15.8 ppg cement slurry blended with 0.6% DO-60 &

0.1% DU-5’ gives the thickening time to 300 +minutes. Ihr 0.025% addition to accelerator by weight of cement in 15.8 ppg cement slurry can offset the retarding effect of the 0.4% fluid loss control additive and 0.2% Friction reducer to get 240 to 260 minutes of setting time are provided in Table 7and Chart 1 (Figure 1). The graphical representation of the results of chart 1 is provided in Figure 4. It was concluded that at lower temperature 0.025%) dose of the accelerator is optimal.
EXAMPLE 4
Optimal dose of Accelerator for cement slurry designing at 65 ‘C:
The optimal dose of the accelerator at 65 ‘'C well temperature was determined by using cement slurries that have varying dose of additives. The details of fixation of optimal dose of accelerator used in the cement slurry composition of the present disclosure at well temperature of 65’C to obtain setting time in the range of 240-260 minutes are provided in Table 8 and Chart 2 (Figure 2). The graphical representation of the results of chart 2 is provided in Figure 5. It was found that ammonium acetate (accelerator) dose of 0.025%) was required to offset the retarding effect of 0.5% Fluid loss control additive (FLA) and 0.2% Friction reducer (FR) to achieve the thickening time to suit field conditions.
EXAMPLE 5
Optimal dose of Accelerator for cement slurry designing at 75'‘C:
The optimal dose of the accelerator at 75 ‘C well temperature was determined by using ten cement slurries that have varying dose of additives. A maximum accelerator dose of 0.8% and minimum accelerator dose of 0.05% was used to design 15 cement slurries as shown in Table 9. The details of the above mentioned fixation of optimal dose of accelerator used in the cement slurry composition at well temperature of 75’C is also provided in Chart 3 (Figure 3). The graphical representation of the results of chart 3 is provided in Figure 6. It was found that the optimal dose of 0.4% of the ammonium acetate (accelerator) offsets the retarding effect of 0.6% fluid loss control additive and 0.2% of friction reducer. The optimal setting (thickening) time for the cement slurry composition of 245 minutes was obtained which is well suited for field cementing requirements.







EXAMPLE 6
Cost benefit Comparison
The synergistic cement slurry composition is economical vis-a-vis cement slurry compositions that uses low temperature non-retarding fluid loss control additive (NRFLA). The details of the cost benefit analysis is provided in Table 14 by drawing a comparison of the cost of said cement slurry composition when used at 55’C, 65°C and 75’C of the present disclosure vis-a-vis cost of cement slurry that uses low temperature non retarding fluid loss control additive (NRFLA) at 60’C and VS’'C.































FRICTION REDUCER- FR (CONVENTIONAL): 200 / Kg (Old Rate)
LOW TEMPERATURE NON-RETARDING FLUID LOSS CONTROL ADDITIVE- NRFLA: 1500 / Kg (Based on old rate)
1. Only additive cost is calculated for making 1 / M’ cement slurry using oil well class 'G' cement and tap water/ technical water.
2. NRFLA was not available since 1999 at Cauvery Asset, its current cost per Kg. is based on the old procurement, hence may not be exact.
TABLE 15
REQUISITION REQUIRED FOR CEMENT SLURRY DESIGN
Field : Cauvery Onshore
Type of Job : SVi" CASING CEMENTATION JOB
1. Well No. & Depth : FN # 4, 1900 m
2. Hole Size : 8'A"
3. Casing Size & Depth : 5 ‘2", 1900 m
4. Bottom Hole Static Temp (BHST) : 172' FN 78°C
5. Bottom Hole Circulating Temp. (BHCT) : SO’'C
and bottom hole pressure : 1.20 MWI
6. Time to reach bottom hole temp, and :
pressure : 21 Min
7. Density of Cmt Slurry to be designed : 1.9
8. Thickening Time desired (Min) : 180 mints.
9. Type of Cement & Trade Name : 1) DALMIA ‘a'
10. Additives to be used : 2) DO .... 60
: 3) DO ....65, DEFOAMER
11. Flow regime : TURBULENT
12. Break in pumping, e.g. release of plug : 15 minuts after 60 minutes during primary cementation of for :
pulling out before reverse circulation : during plug job.
13. Fluid loss desired : As minimum as possible
14. Compressive strength desired : Minimum 2000 psi after 24
15. Indicate other parameters which needs n', k', Vc and consistency special attention and reason

TABLE 16
FROM: CEMENT LAB, ONGC, CHENNAl
TO: INCHARGE CEMENTING, CAUVERY PROJECT, ONGC, KARAIKAL
RPT
PGM (CHEM), DBG, CAUVERY PROJECT, ONGC, KARAIKAL
REQUISITION NO. & DATE SRBC/CMTG/CAUV/TEST REQ/WELL
: NO.PN=4
RECEIVED ON 02.10.2001
SLURRY DESIGN FOR 5 "A" Csg, at 1900 M.
CEMENT USED : RECEIVED WITH REQ
BLENDING DRY
DRILL SITE WATER, % BWOC : 44
ADDITIVES, % BWOC
l.DO-60 : 0.1
2. DO-65 0.1
3.2-ETHYLHEXANOL : 0.05
SPECIFIC GRAVITY 1.90
TEMPERATURE (oC) : 50
PRESSURE (PSI) : 3500
TIME TO RAISE (MIN) : 21
THICKENING TIME (MIN) : 175
WATER LOSS (CC) : 1667
INITIAL CONSISTENCY (BC) : 5
10 MIN CONSISTENCY (BC) 5
30 MIN CONSISTENCY (BC) : 5
20 BOAT (MIN) 155
FLOW BEHAVIOUS INDEX (n') : 0.40
CONSISTENCY INDEX (k'), : 0.11
(LBS/100 SQ.FT)
CRITICAL VELOCITY Vc (FPS): 11.8
COMP.STRENGTH (Psi), 24 HRS : -
15' BREAK WAS GIVEN AFTER 60'. OBSERVED NO CHANGE IN BC AFTER BREAK.

REFERENCES:
1. Reese, D.W., Pace, R.S. and McKenzie, L.F. " Non retarding Fluid Loss Additives for Well Cementing Compositions" U.S. Patent No. 4.610.306, 1986.
2. Cook, C.E. and Cunningham, W.C."Filtrate Control-A Key in Successful Cementing Practices" J. Pet. Tech. pp 951-56, Aug. 1977.
3. Older, I., Duck stein, U. and Becker, T. "On The Combined Effect of Water Soluble Ligno-sulfonate and Carbonates on Portland Cement and Clinker Pastes" Cement and Concrete Res., pp 469-479, 1978.
4. Bensted, J. "Effect of Accelerator Additive on the Early Hydration of Portland Cement" Cemento, pp 13-20, 1978.
5. Edwards, G.C. and Angstadt, R.L. "The Effect of Some Soluble Inorganic Admixtures on the Early Hydration of Portland Cement" J. Appl. Chem., pp 166-168, 1966.
6. API Recommended Practices lOB, December 1997, Recommended Practices for Testing Well Cements (twenty second edition) Addendum 1 & Addendum 2, Oct. 1999 & Nov.2000.
7. Matson, R.P., Rogers, M.J., Go Boncan, V.C. and Gandy, R.G. "The Effects of Temperature, Pressure and Angle of Deviation on Free Water and Cement Slurry Stability" SPE, Paper 22551, Oct. 6-9, 1991.
8. Tinsley, John M., Miller, Erik C, Sabin, Fred L. and Sutton, Dave L. "Study of Factors Causing Annular Gas Flow Following Primary Cementing" SPE, paper 8257, Sept. 1979.
9. Gouda, V.K., Mourad, W.E. and Mikhail, R.S. "Additives to Cement Pastes: Simultaneous Effects on Pore Structure and Corrosion of Steel Reinforcement" J. Colloid and Interface Sci., pp 293-302, 1973.



lAVe Claim:
1. A synergistic cement slurry composition for cementing annular space between pipe casing
and surrounding formation of oil and/or gas well, said composition comprising;
a.) Fluid loss additive (FLA) in the range of about 0.4% to 0.7% weight percent of cement;
b.) Friction reducer additive (FR) in the range of about 0.1% to 0.2% weight percent of cement;
c.) Ammonium acetate in the range of about 0.025% to 0.05% weight percent of cement; and
d.) Water in the range of about 43%) to 51 % weight percent of cement.
2. The composition as claimed in claim 1, wherein the cement is oil well class "G" High Sulphur Resistant cement.
3. The composition as claimed in claim 1, wherein the FLA is partially hydrolyzed poly acrylonitrile cellulose compounds or latex.
4. The composition as claimed in claim 1, wherein the FR is selected from a group consisting of lignin derivatives, organic acids, synthetic aryl/alkyl sulphonates and condensates.
5. The composition as claimed in claim 1, wherein the temperature of the well is in the range of55' C-75 .
6. A method of preparing said cement slurry composition as claimed in claim 1, wherein said method comprising;
a.) blending fluid loss additive, friction reducer and cement;
b.) adding an aqueous solution of the ammonium acetate to the above to obtain said cement slurry composition.

7. A method of cementing oil and gas well with the synergistic cement slurry composition as
claimed in claim 1, wherein said method comprising;
a.) blending fluid loss additive, friction reducer and cement;
b.) adding an aqueous solution of the ammonium acetate to the above to obtain cement slurry composition;
c.) pumping the above obtained cement slurry composition to desired location in said well and allowing the cement slurry composition to solidify.
8. The method as claimed in claim 6 or 7, wherein said cement is oil well class "G" High
Sulphur Resistant cement.
9. The method as claimed in claim 6 or 7, wherein said FLA is partially hydrolyzed poly
acrylonitrile cellulose compounds or latex.
10. The method as claimed in claim 6 or 7, wherein said FR is selected from a group
consisting of lignin derivatives, organic acids, synthetic aryl/alkyl sulphonates, naphthalene
sulphonates and condensates.


Documents:

872-che-2004-abstract.pdf

872-che-2004-claims filed.pdf

872-che-2004-claims granted.pdf

872-che-2004-correspondnece-others.pdf

872-che-2004-correspondnece-po.pdf

872-che-2004-description(complete)filed.pdf

872-che-2004-description(complete)granted.pdf

872-che-2004-drawings.pdf

872-che-2004-form 1.pdf

872-che-2004-form 19.pdf

872-che-2004-form 26.pdf

872-che-2004-form 5.pdf


Patent Number 209597
Indian Patent Application Number 872/CHE/2004
PG Journal Number 50/2007
Publication Date 14-Dec-2007
Grant Date 05-Sep-2007
Date of Filing 30-Aug-2004
Name of Patentee M/S. OIL & NATURAL GAS CORPORATION LIMITED
Applicant Address JEEVAN BHARATI, TOWER II, 124, INDIRA CHOWK, NEW DELHI 110 011,
Inventors:
# Inventor's Name Inventor's Address
1 SINGH DR. CHARAN JEET ONGC, REGIONAL LABORATORY, GOWRI BUILDING, NO.3 1ST LANE, N.H. ROAD, CHENNAI 600 034,
2 MOINUDDIN, DR. GHULAM ONGC, REGIONAL LABORATORY, GOWRI BUILDING, NO.3 1ST LANE, N.H. ROAD, CHENNAI 600 034,
3 DAS, SANTOSH KUMAR ONGC, REGIONAL LABORATORY, GOWRI BUILDING, NO.3 1ST LANE, N.H. ROAD, CHENNAI 600 034,
PCT International Classification Number C 04 B 28/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA