Crude oil products are globally obtained from subterranean reservoirs using techniques such as drilling and hydraulic fracturing. Transportation of crude oil products from the subterranean reservoir, required to refine or process the crude oil, is accomplished by moving the crude oil through pipes and into storage/transportation means such as rail cars, tanks, and the like. During the moving and/or storage, the crude is often subjected to ambient temperatures between −40° C. and 60° C.
Crude oil products include linear and branched alkanes having the general formula CnH2n+2 wherein n is typically about 1-50, although minor amounts of longer hydrocarbon chains do occur. The higher molecular weight alkanes can be problematic in that their melting points tend to be greater than ambient temperatures in some cases. For example, nonadecane has a melting point of 33° C.; higher alkanes can have melting points in excess of 60° C. for example.
The high melting alkane fractions lead to phase separation of paraffinic residue that solidifies and deposits on the sides and bottoms of pipes, storage vessels, and transportation vessels (rail cars, ocean tankers, etc.). The solid, phase separated paraffinic residue, also known as “paraffin wax”, not only reduces the effective volume of the structure within which it is contained but also represents a loss of a valuable component from the body of the crude oil. Excessive paraffin wax buildup reduces the efficiency of transporting crude oil and leads to increased costs related to added downtime for cleaning of the pipes and/or vessels as well as disposal of residues removed from the vessel which increase environmental burden. While the pipelines and vessels can be cleaned to remove the paraffinic residue, the process generates hazardous waste, takes the vessel out of service during the cleaning period, and is expensive.
The phase separation of paraffin wax can be reduced by additives, called “paraffin inhibitors” (PI) which interfere with the crystallization process of wax and/or suspend wax crystals in the oil. Typical paraffin inhibitor polymers include, e.g. ethylene polymers and copolymers thereof with vinyl acetate, acrylonitrile, or α-olefins such as octene, butene, propylene, and the like; comb polymers with alkyl side chains such as methacrylate ester copolymers, maleic-olefinic ester copolymers, and maleic-olefinic amide copolymers; and branched copolymers having alkyl side chains such as alkylphenol formaldehyde copolymers and polyethyleneimines.
The phase separation of paraffin wax can also be reduced by additives, called “paraffin dispersants” (PD), which disperse wax and/or paraffin crystals which form in the oil. Many paraffin dispersants are oligomeric or small surfactant molecules. Examples of paraffin dispersants include nonyl-phenol formaldehyde resins, and dodecyl benzene sulfonic acid-.
The addition of a paraffin suppressant (a paraffin inhibitor or a paraffin dispersant or both) or a “paraffin suppressant concentrate” (PSC) to the crude oil is effective in dispersing paraffinic residue, thereby reducing the formation of residues in the pipelines and vessels to the benefit of the oil and gas industry. Paraffin suppressant effectively reduces the formation of paraffinic residues during storage and transportation of the crude oil products, mitigating economic loss and decreasing environmental impact. A majority of operators in the oil and gas industry employ paraffin suppressant as their primary mode of paraffinic residue control in production pipelines. Non-aqueous formulations including such paraffin suppressant concentrate (PSC) are transported to and stored at the field locations where crude oil is recovered so that it can be applied as needed to pipes, vessels, and the like. Providing PSC in a fluid format—i.e. in solution or dispersion—is highly advantageous for applying PI in the field because pumping equipment suitable to meter the desired amount of PI into a pipe or vessel is readily available.
A suite of laboratory tests under simulated field conditions are conventionally conducted before field deployment to identify the preferred paraffin suppressant and the optimal paraffin suppressant dosage to reach the operator's various performance requirements. Such laboratory tests include cold-finger experiments and cold filter plugging tests. When used in the field, paraffin suppressant is added to crude oil products in production equipment such as pipes and tanks at a rate initially to target a laboratory-determined concentration of paraffin suppressant to prevent and/or disperse paraffinic residue. Because of differences between the laboratory and field environments, it is advantageous to optimize the paraffin suppressant addition rate in the field, typically based on paraffin monitoring which is assumed to be representative of the system. The paraffin monitoring is further complemented with paraffin suppressant residual analysis, that is, measurement of residual paraffin inhibitor and/or paraffin dispersant concentration at the end of a pipe. However, in systems lacking means of paraffin monitoring, operators often rely solely on residual paraffin suppressant monitoring to ensure that the concentration of the paraffin suppressant concentration is within a targeted range. For example, samples can be sent to a laboratory for liquid chromatography/mass spectroscopy analysis. However, at present there is no method for paraffin suppressant analysis of oilfield samples in the field. A field method for residual paraffin suppressant analysis would be advantageous, because results could be obtained more quickly, and real-time adjustments to addition rate and/or other dosage means to control paraffin suppressant concentration in the oil could be made, maintaining an effective and economic dosage of paraffin suppressant to prevent paraffin deposition without use of excessive quantities of paraffin suppressant.
Therefore, there is a need for paraffin suppressants and paraffin suppressant compositions that can be applied to crude oil or compositions containing crude oil in oil-recovery, oil transportation, and oil processing facilities, and wherein the paraffin suppressant concentration can be determined in situ at various selected locations, including those in the field distant from laboratory facilities, and can be monitored by sampling at different locations of the facilities.