CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

61/992,078 filed on May 12, 2014, which is hereby incorporated by reference in its entirety.

BACKGROUND

[0002] Ensuring uninterrupted flow of hydrocarbons from reservoirs is important to the economies of many countries around the world. Scale deposition, both inorganic and organic, is detrimental to this flow assurance. Inorganic scale is a problem in wells with water cut. Organic scale, particularly asphaltenes, may occur in any well and at any stage in the process. Scale may form in the reservoir itself, at the surface facilities of the well, or at any point in between.

[0003] Asphaltenes are a class of compounds defined by their insolubility in light n- alkanes. Being the most polar component of crude, they may be solubilized by aromatics and resins or through polar interactions with their own partial charges or polar resins. While asphaltenes are always present in hydrocarbon reservoirs, they may become problematic once they are destabilized in solution, leading to asphaltene scale deposition. Asphaltenes may be destabilized in solution by changes in some or all of the following parameters of the solution: temperature, pressure and/or chemical composition. Changes in the temperature and pressure of the solution may occur during normal production. The chemical composition of the solution may be changed as a result of strategies employed for enhanced oil recovery (EOR), such as hydrocarbon or C0 ₂ gas injection. As C0 ₂ gas injection for EOR increases, the potential for greater asphaltene scale deposition may also increase.

[0004] Mitigation of asphaltene scale deposition typically involves periodic clean-up operations. The clean-up operations may include washing away the asphaltene scale deposits with a solvent that contains low concentrations of dispersants. However, this method of mitigation is time, labor, and cost intensive. For example, wells that produce severe asphaltene scale deposition may require 3 or 4 clean-up operations per year, with each clean-up operation having a cost of about $200,000.

SUMMARY

[0005] An asphaltene scale deposition squeeze treatment inhibitors exhibiting a lifetime of at least about 6 months is provided.

[0006] A method of reducing asphaltene scale deposition including adding an asphaltene scale deposition squeeze treatment inhibitor to a hydrocarbon reservoir is provided. The asphaltene scale deposition squeeze treatment inhibitor may be added to the hydrocarbon reservoir by a squeeze treatment process.

[0007] It is to be understood that both the foregoing general description and the following detailed descriptions are exemplary and explanatory only, and not restrictive of the inventions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features, aspects and advantages of the present invention will become apparent from the following description and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.

[0009] FIG. 1 depicts a variety of chemical stabilizers that stabilize asphaltene precipitation.

DETAILED DESCRIPTION

[0010] Inhibition of asphaltene scale deposition is an alternative approach directed at reducing or preventing asphaltene scale deposition. Inhibition may include restricting the initial flocculation of asphaltene, thereby reducing or preventing asphaltene scale deposition. An inhibition approach may include employing asphaltene scale deposition inhibitors, such as by downhole continuous injection (DO) or squeeze treatment. [0011] DCI employs a capillary string inserted in a well. DCI may be conducted using a rig or riglessly utilizing chemical injection skids arranged for continuous injection. A capillary string can only be inserted so far down the well. The portions of the well that extend beyond the end of the capillary string are therefore unprotected. Horizontal wells may include large portions of the wellbore that extend beyond the end of the capillary string and that are thus unprotected by DCI. In addition, the DCI process requires monitoring the injection skids, such as on a daily basis, and regular maintenance of the injection skids to maintain efficient operation.

[0012] Squeeze treatment adds asphaltene scale inhibitors directly to the hydrocarbon reservoir. The inhibitors in a squeeze treatment process adsorb to the rock forming the hydrocarbon reservoir and then release from the rocks maintaining the desired inhibitor concentration over time. The rock forming the hydrocarbon reservoir may be a carbonate. This process may reduce or eliminate manpower involvement after the time of inhibitor addition to the hydrocarbon reservoir and does not require modifications of existing wells or allows simplified future well design by not requiring a capillary string. Thus, squeeze treatment asphaltene scale deposition processes may be less time, labor and cost intensive than other asphaltene scale mitigation and inhibition processes. Pre-existing squeeze treatment asphaltene scale inhibitors are not as long-lasting as commonly employed squeeze treatment inorganic scale inhibitors, and thus must be added to the hydrocarbon reservoir more frequently. The pre-existing market leading squeeze treatment asphaltene scale inhibitors exhibit a useful lifetime after addition in some oil fields of only about 2 months, while inorganic scale inhibitors exhibit useful lifetimes on the order of years. The increased addition frequency of squeeze treatment asphaltene scale inhibitors undesirably increases the cost of asphaltene scale deposition squeeze treatment as a result of increased well interventions, well shut-ins and higher chemical volumes.

[0013] According to one embodiment, longer lasting asphaltene scale deposition squeeze treatment inhibitors are provided. The asphaltene scale deposition squeeze treatment inhibitors may exhibit a lifetime of at least about 6 months, such as at least about 7 months, about 8 months, about 9 months, about 10 months, about 11 months, about 12 months, or more. The squeeze treatment asphaltene scale inhibitors may exhibit a lifetime of at least about 300% greater than pre-existing squeeze treatment asphaltene scale inhibitors, such as at least about 400% greater, about 500% greater, or about 600%) greater. The longer lasting asphaltene scale deposition squeeze treatment inhibitors may reduce operational costs and well downtime in comparison to pre-existing asphaltene scale deposition squeeze treatment inhibitors.

[0014] As utilized herein, lifetime may refer to the time which the squeeze treatment asphaltene scale inhibitors remain effective in preventing or reducing asphaltene scale deposition after addition to the hydrocarbon reservoir. The squeeze treatment asphaltene scale inhibitors may be considered effective in preventing or reducing asphaltene scale deposition when the asphaltene scale inhibitor concentration in the hydrocarbon reservoir is greater than a minimum inhibitor concentration (MIC) necessary to keep asphaltenes in solution. The MIC may vary based on the longer lasting asphaltene scale deposition squeeze treatment inhibitor and the hydrocarbon reservoir conditions.

[0015] The squeeze treatment asphaltene scale inhibitor may include an asphaltene inhibitor modified with a functional group that controls adsorption-desorption kinetics of the squeeze treatment asphaltene scale inhibitor in the rocks of a hydrocarbon reservoir. The asphaltene inhibitor may be any suitable asphaltene inhibitor, such as a chemical stabilizer that controls asphaltene precipitation. According to one embodiment, the asphaltene inhibitor may be at least one of a resorcinol, sulfonic acid, phenol, phenolic acid, organosulfate, sulfonate and aromatic hydrocarbon. For example, the asphaltene inhibitor to be modified with a a functional group that controls adsorption-desorption kinetics may be at least one of (1) dodecyl resorcinol (DR), (2) linear alkyl benzene sulfonic acid (LABS), (3) ethoxylated nonyl phenol, (4) salicylic acid, (5) sodium dodecyl sulfate, (6) benzene, (7) toluene, (8) xylenes, (9) cetylpyridnium chloride, (10) dodecyl benzene sulfonic acid (DBSA) and (11) petroleum sulfonate, as shown in Figure 1.

[0016] The functional group that controls adsorption-desorption kinetics may be any suitable functional group, such as a functional group that controls the adsorption- desorption kinetics of pre-existing squeeze treatment inorganic scale inhibitors. The functional group that controls adsorption-desorption kinetics may be a functional group that slows the desorption rate of the squeeze treatment asphaltene scale inhibitor from the rocks that form a hydrocarbon reservoir, such that the squeeze treatment asphaltene scale inhibitor is released from the rocks over a longer period of time. The functional group that controls adsorption-desorption kinetics may be a functional group that increases the adsorption rate at which the squeeze treatment asphaltene scale inhibitor is adsorbed to the rocks that form a hydrocarbon reservoir, such that a larger amount of the squeeze treatment asphaltene scale inhibitor is adsorbed to the rocks. According to one

embodiment, the functional group that controls adsorption-desorption kinetics may be a functional group that slows the desorption rate of the squeeze treatment asphaltene scale inhibitor from the rocks that form a hydrocarbon reservoir and increases the adsorption rate at which the squeeze treatment asphaltene scale inhibitor is adsorbed to the rocks that form a hydrocarbon reservoir.

[0017] According to another embodiment, the squeeze treatment asphaltene scale inhibitor may include a pre-existing asphaltene scale deposition inhibitor modified by a functional group that may also be utilized to control the adsorption-desorption kinetics of a squeeze treatment inorganic scale inhibitor. The functional group that controls adsorption- desorption kinetics may produce the desired effect at ambient temperature and pressure, high temperature and pressure, or both. The squeeze treatment asphaltene scale inhibitor may include a plurality of functional group that controls adsorption-desorption kinetics.

[0018] The longer lasting asphaltene scale deposition squeeze treatment inhibitors may not block the pores of, degrade or damage the rocks forming the hydrocarbon reservoir. The longer lasting asphaltene scale deposition squeeze treatment inhibitors may preserve the integrity of the hydrocarbon reservoir after addition to the hydrocarbon reservoir.

[0019] The longer lasting asphaltene scale deposition inhibitors may be added to a well and/or hydrocarbon reservoir by any suitable process. According to one embodiment the addition process may be a squeeze treatment process. The squeeze treatment process may include an addition period and a well shut-in period. The squeeze treatment process may take place over a period of less than about 4 days, such as a period in the range of about 2 to about 3 days.