Measuring and testing – Liquid analysis or analysis of the suspension of solids in a...
Reexamination Certificate
2002-02-06
2003-06-17
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
C073S054090, C073S061410, C073S064560, C073S864720, C073S864870
Reexamination Certificate
active
06578409
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a method for determining the threshold of deposition of heavy fractions, i.e., according to the invention, generally asphaltenic polar fractions, that are contained in the dissolved and/or stable colloidal state in a liquid hydrocarbon-containing fluid. It further concerns a device for implementing said method.
Many petroleum crudes, notably those referred to as asphaltenic petroleum crudes, are liquid hydrocarbon-containing fluids that contain more or less large quantities of heavy fractions in the dissolved and/or stable colloidal state under the pressure and temperature conditions which said fluids are subjected to. When these pressure and/or temperature conditions vary, notably when the pressure decreases, the heavy fractions contained in these fluids tend to flocculate and to settle in the formation surrounding the wells, in the wells and in the production and transfer facilities intended for said fluids. Thus, when a hydrocarbon reservoir containing heavy fractions is developed, the stability of these fractions decreases generally before the bubble point is reached. When the saturation threshold is reached, the heavy fractions flocculate and settle, which can lead to clogging of the porous media and formation of plugs likely to cause severe damage to the production wells and to the surface installations.
For petroleum producers, who have to extract and to convey, through production wells and pipe networks, liquid hydrocarbon-containing fluids consisting of petroleum crudes containing heavy fractions, for example asphaltenic petroleum crudes, coming from production fields, it is therefore important to precisely know the pressure thresholds above which heavy fractions settle, so as to carry out production and transfer of said fluids under pressure and temperature conditions that prevent heavy fraction deposition in the facilities, or to provide a suitable treatment.
BACKGROUND OF THE INVENTION
There are various known methods for determining the deposition threshold of heavy fractions, notably asphaltenes, contained in liquid hydrocarbon-containing fluids consisting of petroleum crudes. These methods are most often optical light transmission or scattering methods, conductimetric methods, or viscometric methods.
The aforementioned methods involve detection of the variation of a physical quantity, for example the absorption coefficient or absorbance of light beams in the visible range or in the infrared, the electrical conductivity, or the viscosity, which is due to a change in the consistency of the fluid as a result of the flocculation and the deposition of the heavy fractions.
A major drawback of such methods is that they are not very selective insofar as the variation of the physical quantity measured cannot be always readily connected to the flocculation and the deposition of heavy fractions, and they are not always sensitive to the deposition of a small amount of such fractions. Some methods, such as the measurement of the absorbance in the infrared, are very sensitive, but difficult to implement under reservoir conditions.
Furthermore, since these methods are often used in the laboratory, the question which must also be considered concerns the representativeness of the samples on which the physical quantity measurements are performed. In fact, for a sample to be representative of the sampled fluid, it is necessary to maintain this sample under the pressure and temperature conditions that prevail for the sampled fluid, for example a reservoir fluid, throughout the sampling, sample transport and storage operations that are carried out prior to measurement.
The invention provides a method for determining the threshold of deposition of heavy fractions, notably asphaltenes, contained in the dissolved and/or stable colloidal state in a liquid hydrocarbon-containing fluid, based on the creation of an increasingly great pressure drop linked with the flow, at increasing flow rate, of a sample of said fluid through a capillary passage. Such a method has an improved selectivity and sensitivity in relation to the aforementioned prior methods and it allows to overcome the drawbacks of these methods. Furthermore, the method according to the invention can be implemented in situ in wells producing fluids, notably asphaltenic fluids, which also provides an answer to the problem of the representativeness of the samples measured.
SUMMARY OF THE INVENTION
The method according to the invention for determining the threshold of deposition of heavy fractions contained in the dissolved and/or stable colloidal state in a liquid, hydrocarbon-containing fluid is characterized in that it consists in:
bringing a sample of said fluid, maintained at a constant pressure and temperature such that the heavy fractions present in said fluid sample are in the dissolved and/or stable colloidal state, to the inlet of a capillary passage comprising an inlet and an outlet, and likely to generate a pressure drop between the inlet and the outlet that is at least equal to the difference between the pressure of the fluid sample and the bubble-point pressure of said sample,
establishing an initial fluid pressure at the outlet of the capillary passage that is substantially equal to the pressure of the fluid sample brought to the inlet of said passage,
generating, by operating at a constant temperature substantially equal to the temperature of the fluid sample, a flow of the liquid fluid, at an increasing flow rate, through the capillary passage, until the pressure at the outlet of the capillary passage has dropped from the original pressure to a predetermined pressure above the bubble-point pressure of the sample,
measuring a difference &Dgr;P between the pressure of the fluid at the inlet of the capillary passage and pressure Ps of the fluid at the outlet of said capillary passage and/or said outlet pressure Ps, as well as a quantity D representative of the flow of liquid flowing through the capillary passage,
detecting a significant shift in the variation of one of quantities &Dgr;P and D as a function of time or as a function of the other quantity or of a quantity representative of this other quantity, and
defining as the deposition pressure of the heavy fractions at the operating temperature, for the liquid hydrocarbon-containing fluid subjected to the test, the fluid pressure at the outlet of the capillary passage which corresponds to a start of said shift, this pressure characterizing the threshold of deposition of the heavy fractions for said fluid.
In particular, the last two aforementioned stages of the method according to the invention can be carried out by representing, in form of a curve, the variation of one of the quantities &Dgr;P and D as a function of time or as a function of the other quantity or of a quantity representative of this other quantity, and by defining as the deposition pressure of the heavy fractions at the operating temperature, for the liquid hydrocarbon-containing fluid subjected to the test, the fluid pressure at the outlet of the capillary passage which corresponds to the start of a change in the slope of the variation curve of quantity &Dgr;P or of quantity D.
According to an embodiment, the capillary passage is filled with a stationary phase that can be selected, for example, from among the stationary phases used in high-pressure liquid chromatography.
Whether filled with a stationary phase or free from such a phase, the capillary passage has a void space advantageously ranging between 1 &mgr;l and 5000 &mgr;l, and more particularly between 10 &mgr;l and 100 &mgr;l.
The pressure of the liquid sample brought to the inlet of the capillary passage can vary quite widely and it can notably range between 5 bars and 1500 bars.
The volume of liquid sample sweeping the capillary passage during operation advantageously represents 50 to 500,000, preferably 10,000 to 100,000 times the void space of the capillary passage.
In a first embodiment of the method according to the invention, the liquid flow is generated at an increasing flow rate throu
Broseta Daniel
Durandeau Marc
Jose Jacques
Robin Michel
Zhou Honggang
Institut Francais du Pe'trole
Larkin Daniel S.
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