FIELD OF THE INVENTION

The present invention relates to a pre-flush chemical and method of manufacturing thereof. The pre-flush chemical is used in a scale inhibitor squeeze treatment to increase the retention time of at least one scale inhibitor within a hydrocarbon producing system such that scale deposition can be prevented and delayed and hydrocarbon production can be maximized.

BACKGROUND OF THE INVENTION

Scale deposition is one of the most common flow assurance problems in operation of hydrocarbon well. Deposition of scale, particularly inorganic scale such as but not limited to calcium carbonate and barium sulfate onto rock formation of hydrocarbon well will hinder the oil and/or gas production by restricting the flow of fluid and/or gas.

Scale inhibitor squeeze (SISQ) treatment is one of the most common and optimal way of preventing scale formation in the hydrocarbon well. Typically, in SISQ treatment, there are three (3) injection slugs involved. Firstly, pre-flush fluid are injected into the hydrocarbon well to condition the rock formation prior to injecting the scale inhibitor into the hydrocarbon well. Then, the main flush fluid having scale inhibitor are injected into the hydrocarbon well. Subsequently, post-flush chemicals will be injected into the hydrocarbon well to further displace the scale inhibitor into the hydrocarbon well. The hydrocarbon well is then shut for a duration between 20 hours to 24 hours before production of oil and/or gas recommences.

Ideally, as the production resumed, the retained scale inhibitor would slowly leach out, but in effective concentration, from the rock formation of the hydrocarbon well to prevent scale deposition. However, the known SISQ treatment to date have a short squeeze lifetime between 6 months to 12 months. According to Freundlich adsorption isotherm, the squeeze lifetime of scale inhibitor refers to the duration of the scale inhibitor return concentration to reach the Minimum Inhibitor Concentration (MIC) level.

Having said the above, it is obvious that existing scale inhibitor squeeze treatment of preventing scale formation in the hydrocarbon well are inept at extending the retention time of the scale inhibitor onto rock formation of hydrocarbon well. As such, there is a need for a pre-flush chemical that would extend the retention time of the scale inhibitor within a hydrocarbon producing system such that scale deposition can be delayed and hydrocarbon production can be maximized.

SUMMARY OF THE INVENTION

The present invention relates to a pre-flush chemical for scale inhibitor squeeze treatment, wherein the pre-flush chemical comprising carbon compound, wherein the carbon compound is used in an amount ranging between 0.01 % to 0.1 % by weight of the pre-flush chemical, surfactant, wherein the surfactant is used in an amount ranging between 0.005% to 0.05% by weight of the pre-flush chemical and solvent, wherein the solvent is used in an amount to achieve 100% of total weight of the pre-flush chemical.

Also, the present invention relates to a method of preparing pre-flush chemical for scale inhibitor squeeze treatment, wherein the method comprises the steps of (i) mixing carbon compound and surfactant in a medium while stirring to produce a mixture for a duration ranging between 45 minutes to 75 minutes at a temperature ranging between 30°C to 40°C, (ii) sonicating the mixture obtained from step (i) to produce surfactant grafted carbon compound for a duration ranging between 1 hour to 3 hours at a temperature ranging between 22°C to 27°C, (iii) centrifuging the surfactant grafted carbon compound obtained from step (ii) at least once, preferably twice to obtain supernatant for a duration ranging between 10 minutes to 20 minutes at a temperature ranging between 22°C to 27°C and wherein the second centrifugation is carried out for a duration ranging between 25 minutes to 45 minutes at a temperature ranging between 22°C to 27°C, (iv) washing the supernatant obtained from step (iii) using a solution to obtain purified surfactant grafted carbon compound, (v) filtering the purified surfactant grafted carbon compound obtained from step (iv) using a mesh, (vi) drying the purified surfactant grafted carbon compound obtained from step (v) for a duration ranging between 20 hours to 30 hours at a temperature ranging between 90°C to 120°C to obtain surfactant grafted carbon compound powder, (vii) mixing the surfactant grafted carbon compound powder obtained from step (vi) into a solvent while stirring to produce a dispersion for a duration ranging between 5 minutes to 10 minutes at a temperature ranging between 22°C to 27°C and (viii) sonicating the dispersion obtained from step (vii) to produce the pre-flush chemical of the present invention for a duration ranging between 30 minutes to 90 minutes at a temperature ranging between 60°C to 80°C.

Additional aspects, features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:

In the appended drawings:

FIGURE 1a is an illustrative figure showing Transmission Electron Microscopy image of raw GNP.

FIGURE 1 b is an illustrative figure showing Transmission Electron Microscopy image of GA-GNP.

FIGURE 2 is a graph showing the Raman spectra of raw GNP and GA-GNP.

FIGURE 3a is a graph showing predicted scale inhibitor squeeze lifetime without GA-GNP. FIGURE 3b is a graph showing predicted scale inhibitor squeeze lifetime without GA-GNP.

DETAILED DESCRIPTION OF THE INVENTION

Detailed description of preferred embodiments of the present invention is disclosed herein. It should be understood, however, that the embodiments are merely exemplary of the present invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention. The numerical data or ranges used in the specification are not to be construed as limiting.

The present invention relates to a pre-flush chemical and method of manufacturing thereof. The pre-flush chemical is used in a scale inhibitor squeeze treatment to increase the retention time of at least one scale inhibitor within a hydrocarbon producing system such that scale deposition can be prevented and delayed and hydrocarbon production can be maximized.

For the purpose of the present invention and the accompanying claims, the term “hydrocarbon producing system” refers to the subterranean formation (e.g. rock) from which hydrocarbon is extracted as well as the equipment used in the extraction process. Further, it should be understood that the subterranean formation can be gas well or oil well. Also, it should be understood that the equipment used in the hydrocarbon extraction process can be subsurface and surface equipment such as but not limited to tubes, pipes, pumps, valves, nozzles, storage containers and screens.

As used herein, the term “pre-flush chemical” refers to a composition used in a method step of scale inhibitor squeeze treatment in which the subterranean formation is conditioned prior to treatment with at least one scale inhibitor. First aspect of the present invention discusses on a pre-flush chemical, wherein the pre-flush chemical comprises carbon compound, surfactant and solvent, details of which is summarized in the Table 1 .

The carbon compound is selected from the group consisting of graphene, carbon nanotubes and mixtures therefrom, preferably graphene. The graphene is a one- atom-thick planar sheet of sp ² -bonded carbon atoms that are densely packed forming a honeycomb crystal lattice structure. The graphene has a density ranging between 2 g/cm ³ to 2.5 g/cm ³ , wherein the graphene is used in the form of but not limited to nanosheets or nanoplatelets and wherein the nanosheets or nanoplatelets have particle size ranging between 100 nm to 200 nm. The carbon compound is used in an amount ranging between 0.01 % to 0.1 %, preferably ranging between 0.02% to 0.07%, most preferably 0.03% by weight of the pre-flush chemical.

The surfactant is selected from the group consisting of Arabic gum, sodium dodecyl sulphate and cetyltrimethylammonium bromide, preferably Arabic gum. The surfactant is used in an amount ranging between 0.005% to 0.05%, preferably ranging between 0.008% to 0.03%, most preferably 0.017% by weight of the preflush chemical.

The solvent is selected from the group consisting of deionized water, distilled water, brine and mixtures therefrom, preferably deionized water, wherein the solvent is used in an amount to achieve 100% of total weight of the pre-flush chemical.

For the purpose of the present invention, the pre-flush chemical of the present invention is known as Arabic gum-grafted graphene nanoparticles. The pre-flush chemical of the present invention is used in a dispersion form, wherein the pre-flush chemical has total solid content ranging between 0.01 % to 0.05% by weight, pH value ranging between 7.8 to 8.5, viscosity ranging between 1 cP to 1.3 cP and density ranging between 1 g/cm ³ to 1 .05 g/cm ³ .

Table 1 shows the chemical components and compositions of pre-flush chemical of the present invention. Table 1 : Chemical components and compositions of pre-flush chemical of the present invention

Remark: % refers to percentage by weight of the pre-flush chemical

Second aspect of the present invention discusses on a method of preparing the preflush chemical as described above, wherein the method comprises the steps of: i. mixing carbon compound (as described in the first aspect) and surfactant (as described in the first aspect) in a medium in the ratio ranging between 0.7:0.2:98.1 to 1.2:0.7:99.1 by weight/weight/volume respectively while stirring to produce a mixture, wherein the medium is but not limited to deionized water, wherein the mixture is continuously stirred at a speed ranging between 300 rpm to 400 rpm for a duration ranging between 45 minutes to 75 minutes at a temperature ranging between 30°C to 40°C, preferably 35°C; ii. sonicating the mixture obtained from step (i) to produce surfactant grafted carbon compound, wherein the mixture is sonicated at an amplitude ranging between 50% to 70%, preferably 60%, pulser ranging between 40:5 to 60:15, preferably 50:10 for a duration ranging between 1 hour to 3 hours, preferably 2 hours at a temperature ranging between 22°C to 27°C; iii. centrifuging the surfactant grafted carbon compound obtained from step (ii) at least once, preferably twice to obtain supernatant, wherein the first centrifugation is carried out at a speed ranging between 2500 rpm to 3500 rpm, preferably 3000 rpm for a duration ranging between 10 minutes to 20 minutes, preferably 15 minutes at a temperature ranging between 22°C to 27°C and wherein the second centrifugation is carried out at a speed of 6000 rpm to 8000 rpm, preferably 7500 rpm for a duration ranging between 25 minutes to 45 minutes, preferably 30 minutes at a temperature ranging between 22°C to 27°C; iv. washing the supernatant obtained from step (iii) using a solution to obtain purified surfactant grafted carbon compound, wherein the solution comprises water and ethanol in a ratio of 1 :1 by volume respectively; v. filtering the purified surfactant grafted carbon compound obtained from step

(iv) using a mesh with size ranging between 0.3 pm to 0.5 pm, preferably 0.45 pm; vi. drying the purified surfactant grafted carbon compound obtained from step

(v) using but not limited to drying oven to obtain surfactant grafted carbon compound powder, wherein the drying is carried out for a duration ranging between 20 hours to 30 hours, preferably 24 hours at a temperature ranging between 90°C to 120°C, preferably 100°C; vii. mixing the surfactant grafted carbon compound powder obtained from step

(vi) into a solvent (as described in the first aspect) in the ratio ranging between 0.02:99.95 to 0.05:99.98 by weight/volume respectively while stirring to produce a dispersion, wherein the dispersion is continuously stirred at a speed ranging between 200 rpm to 300 rpm for 5 minutes to 10 minutes at a temperature ranging between 22°C to 27°C; and viii. sonicating the dispersion obtained from step (vii) to produce the pre-flush chemical of the present invention, wherein the dispersion is sonicated at an amplitude ranging between 50% to 70%, preferably 60%, pulser ranging between 40:5 second to 60:15 second, preferably 50:10 second for a duration ranging between 30 minutes to 90 minutes, preferably 60 minutes at a temperature ranging between 60°C to 80°C.

Third aspect of the present invention discusses on the SISQ treatment, wherein the treatment comprising the steps of: i. injecting the pre-flush chemical (as described in the first aspect and second aspect) into the hydrocarbon producing system such as but not limited to oil and/or gas well, wherein the pre-flush chemical is injected in a concentration ranging between 200 ppm to 500 ppm; ii. injecting a scale inhibitor into the hydrocarbon producing system, wherein the scale inhibitor is preferably phosphonate-based scale inhibitor such as but not limited to diethylenetriamine penta (methylene phosphonic acid); iii. injecting a post-flush solution into the hydrocarbon producing system, wherein the post-flush solution is but not limited to brine for further displacement of the scale inhibitor into the hydrocarbon producing system; iv. shutting the hydrocarbon producing system for a time period ranging between 12 hours to 24 hours for soaking, preferably 24 hours; and v. allowing the hydrocarbon producing system to stabilize with constant thermal hydrolysis process to prepare for the next hydrocarbon production cycle.

The following example is constructed to illustrate the present invention in a nonlimiting sense.

The pre-flush chemical of the present invention is prepared using the composition as disclosed in the first aspect of the present invention adopting the method as disclosed in the second aspect of the present invention, wherein the pre-flush chemical comprising graphene nanoplatelets, Arabic gum and brine.

Test results for the pre-flush chemical the present invention

Raw graphene nanoplatelets (hereinafter referred as raw GNP) and pre-flush chemical of the present invention (hereinafter referred as GA-GNP) are tested to evaluate their stability in brine under reservoir condition at a high temperature up to 120°C. Further, the raw GNP and GA-GNP are analyzed using Transmission Electron Microscopy (TEM) and Raman spectroscopy. Lastly, the raw GNP and GA- GNP are analyzed to study their effect on scale inhibitor adsorption and retention on the rock formation of hydrocarbon producing system.

Table 2 displays the stability of raw GNP and GA-GNP in brine under reservoir condition (i.e. phase separation and dispersibility in brine).

Table 2: Stability of raw GNP and GA-GNP in brine under reservoir condition Based on Table 2, it is noticeable that the raw GNP undergoes phase separation when mixed with brine, meanwhile GA-GNP does not undergo phase separation and appears as single phase when mixed with brine. Further, it is noticeable that the GA-GNP is able to disperse in brine meanwhile raw GNP is unable to disperse in brine, indicating that the GA-GNP has enhanced stability in brine under reservoir condition at a high temperature up to 120°C. Further, this indicates that the GA-GNP has more active surface areas that are available for the scale inhibitor to adsorb which subsequently prolongs the retention time of scale inhibitor in the hydrocarbon producing system.

Figure 1a displays the TEM image of raw GNP and Figure 1 b displays the TEM image of GA-GNP.

Based on Figure 1a, it is noticeable that the raw GNP has multilayers of large graphene nanosheets with relatively clear and smooth surface as well as flat and undamaged edges. Meanwhile, based on Figure 1 b, it is noticeable that the GA- GNP has bilayers and few layers of graphene sheets with disordered orientation due to ultrasonication and centrifugation. Further, the black dots on the monolayer surface of the GA-GNP can be ascribed to the presence of non-covalent groups resulted from the Arabic gum grafting on the graphene nanoplatelets. Furthermore, the transparency and wrinkles of GA-GNP indicates the success of the non-covalent functionalization of graphene nanoplatelets with Arabic gum.

Figure 2 displays the Raman spectra of raw GNP and GA-GNP.

Based on Figure 2, it is noticeable that the ratio of the intensity of D-Raman peak and G-Raman peak ( ID/IG) of the GA-GNP is 32% higher than the ID/IG ratio of raw GNP. The reason for the increment in the ID/IG ratio of the GA-GNP is due to the change of hybridized carbon sp2 to sp3 with the existence of functionalized groups of Arabic gum as additional layer covering the basal plane of the graphene nanoplatelets. This is also an evidence on successful grafting process of Arabic gum onto the graphene nanoplatelets surface. Table 3 displays the outcome of static adsorption test for scale inhibitor without GA- GNP and scale inhibitor with GA-GNP.

Table 3: Static adsorption test for scale inhibitor without GA-GNP and scale inhibitor with GA-GNP

Based on the results obtained in Table 3, it is noticeable that the GA-GNP in the concentration of 200 ppm and 500 ppm has enhanced the adsorption of scale inhibitor on the rock formation by 2.4 times and 3.2 times respectively as compared to adsorption of scale inhibitor onto rock formation without GA-GNP. The enhanced adsorption of scale inhibitor on the rock formation subsequently prolongs the retention time of the scale inhibitor in the hydrocarbon producing system.

Figure 3a displays the predicted scale inhibitor squeeze lifetime (without GA-GNP) and Figure 3b displays the predicted scale inhibitor squeeze lifetime (with GA- GNP), whereby both follows the Freundlich adsorption isotherm. According to Freundlich adsorption isotherm, the squeeze lifetime of scale inhibitor refers to the duration of the scale inhibitor return concentration to reach the Minimum Inhibitor Concentration (MIC) level, which as per the present invention it is of 5 ppm. Based on Figure 3a and Figure 3b, it is noticeable that the squeeze lifetime of scale inhibitor with GA-GNP is longer as compared to scale inhibitor without GA-GNP. This proves that the GA-GNP as pre-flush chemical of the present invention improves the retention of scale inhibitor in the hydrocarbon producing system.

As a whole, the Arabic gum-grafted graphene nanoplatelets as preflush chemical manufactured in accordance with the present invention is able to overcome the conventional shortcomings since the pre-flush chemical of the present invention has extended the retention time of the scale inhibitor within a hydrocarbon producing system such that scale deposition is delayed and hydrocarbon production is maximized.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", “including” and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups therefrom.

The method steps, processes and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. The use of the expression “at least” or “at least one” suggests the use of one or more elements, as the use may be in one of the embodiments to achieve one or more of the desired objects or results.