Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
  • G01N17/008—Monitoring fouling

Definitions

• the present invention relates to a method for detecting and identifying in-situ the composition of scale deposits found onto the inner surfaces of passages through which certain fluids flow. More specifically the present invention relates to detecting and identifying in-situ the composition of scale deposits in oilfield tubing and piping (hereinafter referred to as "tubulars").
• Oilfield scale forms in the presence of oil and gas, waxes and surfactants, metal corrosion, and in turbulent and high velocity flow. Oilfield scale often is composed of more than one mineral. It is not uncommon for several different compounds to be deposited together or in layers. Wax, oil and iron oxide can be trapped within the scale formation. Even the density of the scale can vary, depending on the depositional conditions.
• Treating oilfield scale is a complex problem.
• treatments to prevent or minimize scale formation are commonly practiced.
• These techniques, including removal and/or inhibition of scales are not 100% effective.
• a removal or inhibition treatment applied uniformly to several wells with different scaling tendencies may result in some wells being under-treated and thus still displaying scales.
• an inhibition treatment can lose effectiveness over time, as the production environment changes, leading to occurrence of certain conditions favourable to scale formation.
• scales include more than one mineral the response to the inhibition treatment is partial.
• Oilfield scale management programs have been designed to prevent scale deposition or, when the prevention is not feasible, to detect the early occurrence of scale deposition and to use the most efficient method to remove the deposits and inhibit further growth. Effective scale management also requires on-line monitoring of scaling tendencies as well as the detection and identification of scale deposits. A direct measurement of scale deposition not only would benefit the selection/design of an effective inhibitor for the treatment of scales, but it could signal changes in scaling conditions, indicating when a scale treatment needs to be modified. A simple, reliable method to continuously monitor for scale formation is needed in a strategy to elude scale-fighting's costly effects.
• a process of scale management typically involves: detection, identification (location composition, quantification), removal, inhibition or prevention, and monitoring. Detection is important because a whole sequence of reactionary events follows detection. Detection of scale all too often comes after production begins to decrease. Successful early detection is the first step to minimizing the effects of scale.
• a commonly practiced method of scale detection, in one field where scale formation is undesirable, is monitoring for abnormal decline in oil production and/or pressure drop across the length of the tubular.
• monitoring the existence of decline in oil production and/or pressure drop alone is generally not efficient to detect the presence of scales.
• RDE rotating disk electrode
• Scale is often detected when chokes or control valves are removed and inspected after a decline in performance. Pig runs can recover scale from pipelines. In some installations, a corrosion probe is used to make routine checks for scale deposits. Visual inspection, however, requires human intervention and is limited by the frequency of the inspections.
• a scale control program may be optimized so that a treatment for scale is provided whereby the cost of treatment is offset by a reduction in production losses otherwise occurring in the absence of the treatment. Due to the difficulty in identifying and quantifying scale deposits in-situ, such steps are frequently neglected. Instead, knowledge of regional formation water chemistry and scale tendencies is often used to assess possible scale composition. Based on such assessment of scale composition, a removal and inhibition treatment is devised by chemical treatment. The evaluation of inhibition treatments is usually performed in laboratory environments, which cannot duplicate real oilfield pipe conditions.
• the present invention provides in one embodiment thereof a method of identifying scales on a surface of a passage through which a fluid is passing.
• the method includes the following steps. First, second, and third values are determined.
• the first, second and third values are related to attenuation of the fluid for first, second, and third energy levels respectively at which energy is emitted through the fluid. It is determined first and second fluid ratios rlf and r2f between the first and second values and between the second and third values respectively.
• Figure 1 illustrates an apparatus that may be used for one embodiment of the method of the present invention
• Figure 2 illustrates various solution triangles for dual-energy spectral gamma ray hold-up measurement in the presence of scale
• Figure 3 illustrates a diagram showing the attenuation ratios for various fluids (gas, oil, water) and major types of scales produced by way of a dual energy attenuation measurement
• Figure 4 illustrates a chart showing how scale compound may be estimated using the slope of the gas point translation (line);
• Figure 5 illustrates an energy distribution in the presence and in the absence of scale deposit for three energy levels used at 32 keV, 80 keV and 356 keV;
• Figure 6 illustrates a chart used for identification of scales by way of the method according to the present invention
• Figure 7 illustrates a simulation of case with 50% gas volume fraction (GVF), 50% water liquid ratio (WLR) and increasing scale thickness of 0, 10, 25, 100, 250, 400 and 550 microns;
• VVF gas volume fraction
• WLR water liquid ratio
• Figures 8 to 12 show simulation data created using a random generator that produce a stochastic flow with added statistical noise to account for the Poisson nature of gamma ray detection
• One embodiment of the method of the present invention utilizes principles related to the attenuation of a beam of gamma or X rays emitted through a fluid.
• the presence of scales may be detected and their nature identified as a modification (increase) in the attenuation observed in the path of the beam of gamma or X rays emitted.
• the reason for the change in the attenuation is due to fact that scales are typically composed of atomic elements that are heavier, and that cause a higher attenuation of the gamma rays, than the hydrocarbons (oil and gas) and water existent in the fluid.
• Figure 1 illustrates an embodiment of an apparatus 100 that may be used by the method of the present invention.
• Apparatus 100 may be placed in the structures (piping and tubing in one embodiment) through which a fluid is flowing.
• the fluid may be a multiphase fluid including oil, gas, and water, but the present invention is not limited in this respect to this composition.
• Apparatus 100 includes a tubular portion 101 with a passage 106 through which the fluid may flow.
• Apparatus 100 also includes a measurement section 102 where a source 104, which may be a radioactive chemical source emits energy in the form of gamma rays or X rays at different energy levels.
• the source 104 may be an X-ray generator. The following description makes reference to gamma rays but it also applies to embodiments where the source emits X-rays.
• the source 104 emits gamma rays at three distinct energy levels through the fluid circulating through main passage 106 of the apparatus.
• the source 104 is encapsulated except for a small opening on the detector side, permitting a collimated beam of gamma rays to pass across dio the detector 108.
• the detector 108 may include in one embodiment a conventional scintillator crystal such as Nal.
• a photo multiplier 110, coupled to the detector 108 converts light pulses detected by the detector into electrical signals, also referred to as count rates, which are digitally processed.
• the source 104 emits gamma rays at a single energy level.
• the gap between the source and the detector is filled with substance, s , making up the fluid, of density, p s . If we consider a single energy of the source emission, the mass attenuation, M , of the substance can be determined as follows:
• N vac and N are the number of gamma ray counts detected over a given time after passing through a vacuum and through the
• the detector 108 produces two series of signals NH and NL (count rates), representative of the numbers of photons detected per sampling period resulting from the emission of gamma rays through the fluid.
• the mass attenuation of the mixture Mm or compound is determined as the mass fraction weighted average of the mass attenuations of its components or elements i:
• the mass attenuation of each phase can be shown as:
• the mass attenuations for oil, water, gas and scale can be calculated from the NIST tables (NIST X-Ray & Gamma-ray Attenuation Coefficients & Cross Sections, 1990, US. Dept. of Commerce) or measured directly.
• the attenuation of a mixture is the volume fraction average of the attenuations of it components:
• Equation (4) may be expressed in two independent forms, i.e., for attenuations ⁇ (high) and A m L (low) at the two different energy levels.
• the three phase volume fractions a 0 ,a w ,a g be computed by solving three equations for three unknowns.
• the presence of scales in the passage 106 may be determined by way of dual energy attenuation measurements whereby values A" and
• a m L are determined.
• the presence of scale causes an increase in the attenuations observed in the path of the gamma rays, as scale is composed of atomic elements that are heavier causing a higher attenuation than hydrocarbons and water existent in the fluid. Common oilfield scales attenuate preferentially the lower energy.
• Fig. 2 illustrates various solution triangles for dual-energy spectral gamma ray hold-up measurement in the presence of scale.
• the triangle shown on the right of the figure in continuous lines is obtained by drawing three lines that connect every two of the three operating points of the fluid for water, oil, and gas (the apexes of the triangle).
• the additional attenuation caused by the scale deposits produce a shift, corresponding to the effect of scale, in the triangle shown in continuous lines resulting in the triangle shown in dotted lines.
• a measurement is normally made in the presence of gas (known composition) by way of the apparatus of Figure 1 bypassed, with any liquids settling below the measure point.
• gas known composition
• any change in attenuation in successive reference measurements may be attributed to scale formation.
• Similar reference measurements may be made for oil and water. As scale accumulates, the gas, oil, and water reference points progress linearly in the direction of the unknown scale point. The intersection of these lines defines the scale point (the leftmost point in the figure). The slope of a line passing through the scale point and the vacuum point (the origin of the X-Y axes) is unique for most common oilfield scales and indicates the nature of the scale.
• the ratio of the low energy attenuation to high-energy attenuation, A /A H is used.
• the ratio A L j A H may vary significantly for different materials as one may see from (Fig 3).
• Fig 3 illustrates by way of a chart dual-energy attenuation ratios for gas, oil, water and various types of scale.
• the type of scale may be determined from this chart from the ratio Al/Ah by looking up the scale corresponding to this ratio. This ratio may be determined as the slope of the scale line of Figure 2. Because generally it is inconvenient to make the three reference measurements, the scale compound may be estimated using the slope of the gas point translation (line), as this slope is close to the slope of the scale point-vacuum point line (Fig 4).
• the fractions of oil, water and gas are:
• the scale thickness is roughly estimated by:
• An improved method of identification of scales provided in one embodiment of the present invention is based on continuous triple-energy spectral gamma-ray attenuation measurements made in-situ by using the apparatus shown in Figure 1.
• This method provides quick detection and identification of scale deposits on pipe walls such as the walls of the apparatus of Figure 1 without disrupting the flow of the fluid.
• the advantage of this method is an immediate scale identification, without time-lapse. The example below is given for 3 different energy peaks emitted by a 133 Ba source at 32 keV, 80 keV and 356 keV ( Figure 5).
• Figure 5 illustrates a graph showing the energy distribution (represented as a count rate) in the presence and absence of scale for the gamma rays emitted by the source of the apparatus of Figure 1.
• the accumulated counts at each energy are measured as N , N and N .
• the corresponding vacuum values, 80 3S6 defined at calibration time, are respectively 7V v,ac i tV vac a ⁇ n"H u N vac
• the single-phase attenuations of oil, water, gas and scale can then be defined as:
• a o,w,g,_ Po, W ,g,s dM -,w,g,s (12) where represents the mass attenuations for oil, water, gas and scale determined at each of three energies.
• the ratios of the attenuations are equal to the ratios of the mass attenuations for each phase, and consequently, are independent of the phase density and the diameter of the measuring section.
• Oil, water, gas and the various scale minerals may be represented on a Cartesian plot, 80/356 vs 32/80 .
• a scales identification chart illustrates several common scales encountered in oilfield wells (Fig, 6).
• the gas point is represented by CH .
• the oil point is represented by CH2, which corresponds to the carbon/hydrogen ratio in oil.
• a point defined as operating point (rlf, r2f) 80 356 , 32 80 ) is determined for the fluid mixture at a given moment in time.
• the scales are identified by comparing the operating point of the fluid defined by (rlf, r2f) with the various scale ratios (r1s, r2s).
• the scale having its ratios ( s, r2s) closest to the ratios (rlf, r2f) are the most likely to be present in the pipe and thus identified.
• the operating point of a gas/oil mixture will typically remain on the "hydrocarbon point" whatever the gas fraction value is.
• the operating point of a gas/oil/water mixture without presence of scale, remains on the line between the hydrocarbon point (gas, oil in the chart) and the water point (H20).
• the operating point for a given fluid at a given time lies on the line shown in Figure 6 between the hydrocarbon point and the water point initially determined.
• the scale points lie above the hydrocarbon/water line. If scale gets deposited on the wall of the pipe, it causes an increase the 80 356 ratio, moving the operating point above the hydrocarbon/water line. Scale presence also moves the operating point strongly to the right, to higher 32/80 ratios.
• Scale composition may thus be determined independently of oil, water and gas flow rates. As scale accumulates over time, the accumulation displaces the operating point of the fluid mixture on the scale identification plot. The operating point, as seen in the plot illustrated in Figure 7, tracks along a curve that seeks the scale point and eventually ends at that point when the scale nearly clogs the pipe.
• Figure 7 shows the curve traced by the operating point in a fluid mixture having 50% gas volume fraction (GVF), 50% water liquid ratio (WLR) and increasing scale thickness of 0, 10, 25, 100, 250, 400 and 550 microns for the BaS04. scale. As one may see from Figure 7, as the thickness of scale increases, the operating point moves closer to the scale point identifying BaS04. small deposit of scale are thus sufficient to identify the scale minerals.
• VVF gas volume fraction
• WLR water liquid ratio
• Figures 8 to 12 show that scale may also be identified when its thickness is constant. Simulation data was created using a random generator to produce a stochastic flow, then adding statistical noise to account for the Poisson nature of gamma ray detection. As the gas fraction fluctuates, the high gas fraction points in the statistical set tend to distribute themselves narrowly towards the unknown pure scale point. This trend may be obtained in a few minutes, depending on the flow regime.
• the mean value is indicated by a cross within the "cloud” shown which represents a collection of operating points measured within a given period of time. The location of the mean value, as well as the shape of the statistical set, clearly indicates the presence of scale. Figure 12 shows the case when no scale is present.
• the thickness of the scale deposit may be determined as follows.
• the oil, water, gas and scale densities at line conditions, p 0jWjgjS , and their respective mass attenuations at three energies 32 ,; 8 "; 3 6 are known.
• the attenuations of the gamma ray beam through four phase mixture, ⁇ 32 ' 80 ' 356 are measured for each energy within the instrument of internal diameter, d .
• a linear system of four equations with four unknowns may be constructed to compute a o,w,g,s ⁇ tne fractions of oil, gas, water and scale in the pipe.
• the gas fraction, gf a g
• the gas and liquid fractions may be used in pressure drop calculations and as indicators of flow regime.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Biodiversity & Conservation Biology (AREA)
• Ecology (AREA)
• Environmental & Geological Engineering (AREA)
• Environmental Sciences (AREA)
• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Analysing Materials By The Use Of Radiation (AREA)
• Measurement Of Radiation (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Testing Of Devices, Machine Parts, Or Other Structures Thereof (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23298955

Family Applications (1)

Country Status (6)

Cited By (2)

Families Citing this family (1)

Citations (3)

• 2002
  • 2002-11-14 WO PCT/EP2002/012974 patent/WO2003042675A1/en not_active Application Discontinuation
  • 2002-11-14 CA CA2466500A patent/CA2466500C/en not_active Expired - Lifetime
  • 2002-11-14 BR BR0214114-0A patent/BR0214114A/pt not_active IP Right Cessation
  • 2002-11-14 GB GB0410563A patent/GB2400436B/en not_active Expired - Lifetime
  • 2002-11-14 MX MXPA04004436A patent/MXPA04004436A/es active IP Right Grant
• 2004
  • 2004-06-15 NO NO20042492A patent/NO20042492L/no not_active Application Discontinuation

Patent Citations (3)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events