Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
  • G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
  • G01N24/082—Measurement of solid, liquid or gas content

Definitions

• the subject of the invention is a method of detection and monitoring by nuclear magnetic resonance of the flocculation kinetics of high molecular weight fractions of a complex fluid.
• the method according to the invention notably has the application of monitoring the flocculation kinetics of generally asphaltenic polar fractions, which are contained in the dissolved state and / or in the stable colloidal state in a liquid hydrocarbon fluid.
• thermodynamic parameters which govern the flocculation processes are numerous (composition, pressure, temperature) and the complexity of the molecular structures involved make prediction and modeling very uncertain. Likewise, certain recovery processes (CO2 injection, acidification) can modify the fluid balances and cause these processes. Thus, it is necessary to carry out measurements but the techniques available do not make it possible to observe the first stages of flocculation and pose significant implementation problems in pressure and temperature or in situ in oil wells. State of the art
• liquid hydrocarbon fluids consisting of crude oil containing heavy fractions, for example asphaltic crude oil
• stain test consists in depositing a little mixture on a filter paper, and to observe the stain which forms.
• the flocculation aggregates which form in a mixture diffuse less quickly than the surrounding liquid.
• the stain is not uniform, it is an indication that it contains flocculating particles.
• the aforementioned methods call for the detection of the variation of a physical quantity, for example absorption coefficient or absorbance of the light rays in the visible or in the infrared domain, electrical conductivity or viscosity, which results from the change of structure of the fluid as a result of flocculation and deposition of heavy fractions.
• a major drawback of such methods is that they are not very selective in the sense that it is not always easy to relate the variation of the physical quantity measured to the flocculation and the deposition of heavy fractions and that they do not are not always sensitive to the deposition of a small amount of such fractions. Certain methods, such as the measurement of absorbance in the infrared, are very sensitive, but difficult to implement under deposit conditions.
• the fluid sample being in the dissolved state and / or in the stable colloidal state, at the entry of a capillary passage a pressure drop is generated between inlet and outlet at least equal to the difference between the pressure of the fluid sample and the bubble pressure of said sample.
• a significant change in the variation as a function of time of ⁇ P is detected (difference between the fluid pressure at the inlet of the capillary and the pressure at its outlet) and by a magnitude D representative of the flow rate of liquid flowing through the capillary passage, which makes it possible to characterize the threshold for depositing heavy fractions of the fluid.
• NMR can be used in particular for measuring certain physical characteristics of mixtures of fluids such as hydrocarbons, in particular viscosity or their gas-liquid ratio or GOR.
• the inventors have observed that the NMR type methods applied to the detection of solid particles could also surprisingly be applied to non-solid particles of high molecular weight in slow rotation which gradually aggregate together, and verified that the this type of method could determine their rate of flocculation.
• the method of detection and monitoring by nuclear magnetic resonance of the kinetics of flocculation of non-solid aggregates of high molecular mass of a complex fluid comprises the application to the fluid of a first static magnetic magnetic field of polarization then of at least a second pulsed magnetic field oscillating perpendicular to the first created by windings connected to an excitation generator to carry out the nuclear magnetic resonance of the nuclei considered and the acquisition of the relaxation signals of the nuclei in the fluid.
• It comprises the detection on the relaxation signals, of a first part representative of the relaxation of these aggregates in the fluid and of a second part representative of the relaxation of the liquid fraction of the fluid, and the determination of the rate flocculation (Tf) of the aggregates by comparison of the extrapolated values at the origin respectively of the acquisition times of the first part and of the second part.
• the proposed method has many advantages. It offers the possibility of continuous monitoring, useful for the analysis of flocculation depending on the chemical composition and the solvent. The entire volume is analyzed. Unlike optical methods, even non-transparent samples can be analyzed. The characterization of the kinetics is easy. Likewise, it is easy to assess the level of aggregates, which can lead to a rough estimate of the molecular weight.
• Figure 1 shows the decrease in transverse magnetization measured on a flocculated mixture
• Figure 2 shows the decay curves of the transverse magnetization measured for a mixture not initially flocculated, then flocculated
• - Figure 4 shows the relaxation signal of an asphaltene / toluene / heptane solution
• - Figure 5 shows the evolution of the coefficient A of a function modeling the relaxation signal of Figure 4, which identifies the value of the flocculation threshold.
• the NMR analysis technique essentially consists, as it is recalled, of applying to a test object a first static magnetic magnetic field Bo of polarization intended to align the nuclei of the hydrogen protons initially oriented at random, in the direction of the field and then to a second pulsed magnetic field oscillating at the Larmor frequency perpendicular to the first created by windings excited by a control signal to carry out a nuclear magnetic resonance experiment.
• a first static magnetic magnetic field Bo of polarization intended to align the nuclei of the hydrogen protons initially oriented at random, in the direction of the field and then to a second pulsed magnetic field oscillating at the Larmor frequency perpendicular to the first created by windings excited by a control signal to carry out a nuclear magnetic resonance experiment.
• this impulse field ceases, the return of the nuclei to their initial state or relaxation, generates electromagnetic signals (echoes) which are detected and analyzed. From the amplitude characteristics of these signals, the presence of this or that substance and some of its physical parameters are determined.
• the analysis of the relaxation of the transverse magnetization M x (t) of the protons of a liquid considered, observed at short times is applied both to the detection of flocculation, the determination of the rate of large structures formed in suspension in a liquid and the characterization of the kinetics governing this formation process.
• a pulse field B ⁇ (t) is applied by means of the windings 3 which has for example a falling edge and a time of receiver desaturation less than a few microseconds.
• a series of at least two so-called 90 ° pulses separated by a time interval ⁇ will be applied, with an interposed 180 ° pulse intended to focus the magnetization and thus to overcome the diamagnetic heterogeneities of the material.
• the instants of application of the pulses are separated by time intervals of duration ⁇ / 2.
• the sequence can be diagrammed in time as follows:
• the relaxation signal has two very distinct parts corresponding to the appearance of large structures in the liquid: a first part which decreases very rapidly over twenty microseconds and whose importance increases regularly with the formation of flocculated structures, and a second part which decreases very slowly over several hundred milliseconds and corresponds to the liquid part of the fluid (Fig. 2).
• the flocculated structures produce a rapid decrease in magnetization because they can be considered as frozen
• a graphical method can be used when, as in the example in Fig.l, the distribution of the points relating to the liquid part of the fluid analyzed is substantially linear.
• One can also search for example a polynomial of sufficient degree or if necessary a sum of exponential functions modeling the distribution of the points of the liquid part, and to deduce from it the extrapolated value at time t 0.
• the detection of the first part of the relaxation distribution (Fig. 1) supposes that the relaxation signals are acquired practically from the origin of the times, that is to say within an interval much less than 1 ms, which is not the case with conventional methods using NMR analysis apparatus.
• FIG. 4 shows an example of the transverse magnetization signals (Mx (t)) obtained on these solutions.
• the parts PI and P2 previously described are connected to it by an intermediate part P3.
• the signals are correctly described by a function which is a sum of exponentials. In the following function:
• Equation 2 is useful for separating the high molecular weight part characterized by very short relaxation times (order of magnitude ⁇ ), from that of the heptane / toluene mixture (order of magnitude T 2 s).
• the first term describes the PI part as well as the intermediate part P3. For the mixture considered, the high molecular weight buildings are visible before flocculation.
• the NMR measuring device used for implementing the method can be miniaturized for the purpose of being installed in an oil well in conjunction with a fluid sampler of a type known in any other surface installation for monitoring. flocculation phenomena. Whatever the analysis conditions, approximately 50 mg of substance is sufficient in practice.

Landscapes

• Physics & Mathematics (AREA)
• High Energy & Nuclear Physics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=8871302

Family Applications (1)

Country Status (6)

Families Citing this family (5)

Family Cites Families (8)

• 2002
  • 2002-01-16 FR FR0200466A patent/FR2834792B1/fr not_active Expired - Fee Related
• 2003
  • 2003-01-16 US US10/501,524 patent/US7009393B2/en not_active Expired - Fee Related
  • 2003-01-16 WO PCT/FR2003/000127 patent/WO2003060539A1/fr not_active Ceased
  • 2003-01-16 EP EP03712250A patent/EP1468304A1/de not_active Withdrawn
  • 2003-01-16 CA CA002472087A patent/CA2472087A1/fr not_active Abandoned
  • 2003-01-16 AU AU2003216731A patent/AU2003216731A1/en not_active Abandoned

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events