1. Combined nuclear magnetic vibration logging tool (CMR)
The CMR logging tool uses a permanent magnet with strong magnetism to generate a static magnetic field, puts the magnet into the well, and establishes a uniform magnetic field area in the outer layer of the well, which is 1000 times larger than the geomagnetic field strength. The antenna transmits the spin echo pulse sequence (CPMG) signal and receives the echo signal of the formation. CMR raw data consists of a series of spin echo amplitudes, and T2 relaxation time distribution is obtained after processing. T2 distribution is the main logging output, through which porosity, bound fluid saturation, free fluid saturation and permeability can be obtained.
CMR is a small sliding-type instrument with connection length of 4.33 m, weight 148 kg, rated temperature 177℃ and rated pressure 138 MPa. Its structure and cross section are shown in Figure 5-54.
CMR must use bow spring, eccentric or dynamic caliper to measure eccentricity. The maximum width of the detector polar plate is 5.3 inches, and the maximum total diameter of the bow spring with sliding sleeve is 6.6 inches.
For general drilling conditions, the recommended minimum drilling diameter is 6.25 inches. When the borehole conditions are good, CMR can log in the borehole below 5.785 inches.
Selection of (1)CPMG pulse sequence parameters
Nuclear magnetic resonance measurement is periodic, not continuous. The measurement period consists of waiting time and spin echo acquisition period. Acquisition time is much shorter than waiting time. During the waiting period, the hydrogen nucleus returns to the direction of the instrument magnetic field. The waiting time depends on T 1 of pore fluid. During the acquisition, the transmitting coil of the instrument sends out spin echo quickly. Collect echoes regularly (echo interval).
The waiting time, the number of echoes collected and the echo interval are called pulse sequence parameters. These parameters determine the NMR measurement and must be interpreted before logging. The optimal selection of parameters is related to lithology and fluid type, and whether CMR instrument is used for continuous measurement or point measurement.
Figure 5-54 Experimental Pulse NMR Instrument
1) measurement period. In order to correct the bias of electronic circuits, spin echo sequences are collected in pairs, which are called phase alternating pairs.
The total cycle time of obtaining phase alternating pairs is
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Where TW is the waiting time, s; NE is the echo number; TE is the echo interval, s.
Long cycle time can improve the accuracy of CMR logging. However, for wells with large environmental changes, the long period leads to low velocity measurement and long residence time of measuring points.
2) Speed measurement. In continuous logging, adjust the measuring speed of the instrument to ensure that a new measuring cycle is completed in each sampling rate section (usually 6 in, that is, 15.24 cm) underground. The maximum logging speed is
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Figure 5-55 shows the relationship between the maximum velocity measurement and the waiting time and the number of echoes collected. Most CMR logging speeds are between 45.7 ~ 183 m/h, and the velocity measurement can reach more than 244 m/h under the constrained fluid logging model.
3) Constraints of pulse parameter selection. ① Echo interval. In order to improve the sensitivity of measuring rapidly decaying components (i.e. small pores and high viscosity petroleum), CMR logging usually adopts the minimum echo interval (0.28 ms). With the improvement of hardware, the expected minimum echo interval decreases. In order to enhance diffusion relaxation, the echo interval is also increased. This is suitable for pure formations without a large number of micropores. In order to keep the sensitivity to small pores, the echo interval rarely exceeds1ms2 echo number. The sensitivity of the collected echo is 200,300,600, 1200,1800,3000,5000,8000. When the echo interval is 0.28 ms, the corresponding acquisition times are 0.056 s, 0.084 s, 0. 17 s, 0.34 s, 0.50 s, 0.84 s, 1.40 s and 2.24 s respectively. The maximum number of echoes collected during continuous logging is usually 1800. Computer simulation and field experience show that the change of CMR pore logging caused by the increase of echo number can be ignored. ③ Waiting time. Ideally, the waiting time is long enough to completely polarize the hydrogen nuclei. Because the contribution of incompletely polarized hydrogen to the spin echo amplitude is incomplete. In fact, the waiting time is limited by the efficiency requirements of the well site, and the incomplete polarization should be corrected. Generally, the waiting time is 3 times longer than the average T 1 of pore fluid. ④ Minimum waiting time. Due to the limitation of the bandwidth ratio of the transmitting coil, the minimum waiting time is about twice the acquisition time. Actually, this is not a limitation, because both the waiting time and the acquisition time are controlled by the relaxation time of the pore fluid (T 1 and T2), and the pore fluid with a long T2 also has a long T 1, so a long waiting time is required.
Figure 5-55 Relationship between maximum speed measurement and waiting time and number of echoes collected.
4) Parameter selection. The selection of pulse sequence parameters is based on the previous work plan and field measurement.
The preliminary work plan includes estimating the average relaxation time of pore water and hydrocarbons (original hydrocarbons or oil-based mud) in the invaded zone (average T 1). For general instrument operation, the waiting time is about four times of the larger values of these two T 1.
When estimating the relaxation time of pore fluid, it is usually assumed that the rock is wet with water. In this case, hydrocarbons relax at a volume rate, and the volume relaxation of oil is estimated from the viscosity under reservoir conditions. The volume relaxation of gas is related to reservoir temperature and pressure. The relation curve of T 1 with T2 and fluid viscosity is shown in Figure 5-49.
Pulse sequence detection is usually realized by repeated logging with short waiting time after long waiting time logging in production interval. The shortest waiting time to produce accurate CMR porosity and small polarization correction (for example, less than 2 p.u) is used for main logging.
After several times of CMR logging in an area or formation, the best sequence can usually be determined. This sequence can be used for subsequent CMR recording.
The following are some predefined pulse sequences that have been successfully used in field testing.
A reservoir with medium to high viscosity oil (greater than 4 mPa·s). The T 1 value of medium and high viscosity oil is relatively short, and the CMR pulse sequence is mainly selected according to the T 1 of pore water.
T 1 of pore water is determined by surface relaxation and varies with pore size and lithology. The surface relaxation of carbonate rocks is weaker than that of sandstone, which requires a long waiting time. When rocks have large pores (such as porous carbonate rocks), the relaxation time is close to the value of volume water (as a known temperature function). However, the CMR instrument detected the intrusion zone, in which the primary water was replaced by drilling mud filtrate. Due to the dissolved paramagnetic ions in the filtrate, the T 1 of the volume mud filtrate decreases.
In fact, it is difficult to determine the value of T 1 of pore water, so the pulse sequence depends on the minimum cycle time suitable for most underground environments. According to experience, the recommended pulse sequence for continuous logging is shown in Table 5-3. The second column in the table is the viscosity threshold of oil, which requires a long waiting time. If the reservoir contains particularly large pores (such as high permeability, loose sandstone and porous carbonate rock), it also needs a long waiting time.
Table 5-3 Conventional Continuous Logging
B reservoirs with low viscosity oil (less than 4 mPa·s). When the reservoir contains light oil or oil-based mud is used for drilling, the CMR pulse sequence is determined according to the T 1 of the oil. It requires long waiting time and slow speed measurement. Table 5-4 shows the predefined pulse parameters in MAXIS logging software. If the oil viscosity under reservoir conditions is known, the waiting time of this sequence must be corrected. At this time, the average value T 1 is estimated from Figure 5-49, and the waiting time is set to 3T 1. When borehole conditions permit higher velocity measurement, the sampling rate of 9 inches is recommended, and the velocity measurement is increased by 1.5 times.
Table 5-4 Predefined Pulse Parameters in Maxis Logging Software
C. gas-bearing reservoir. Among the potential gas-bearing layers, the main application of CMR logging is to identify gas layers that are not shown in traditional logging curves (such as neutron density). CMR porosity underestimates the porosity of gas reservoir. The reasons are as follows: the hydrogen index of gas is obviously less than1; In a wide range of temperature and pressure, the length of gas is t1(more than 3s), so it cannot be completely polarized in continuous logging. Due to diffusion, the gas T2 is very short (about 400 μs). Therefore, the high ratio of T 1/T2 makes polarization correction ineffective.
The amplitude of the gas signal is
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Where: HI is the gas hydrogen index; Vg is the gas volume of the invading domain, p.u；; T 1 effect is part of the influence of polarized gas in the waiting time, that is,1-exp (-tw/t1g) (t1g is the t1of gas; Tw is the waiting time).
In many environments, the gas signal is too small to be detected, which occurs in shallow formations (gas hydrogen index is too small) and low to medium porosity formations (containing a small amount of residual gas volume). In these formations, the most effective method is to wait for logging with relatively short time, as long as there is enough time to polarize water (for example, sandstone or carbonate rock sequence). This makes the amplitude of gas signal minimum, and the decrease of CMR porosity may be caused by the influence of gas.
In deep high porosity formation, the gas signal may be greater than 3 p.u or 4 p.u. In these formations, a single CMR logging can identify gas-bearing layers by changing the waiting time and echo interval.
In this way, the distribution of T 1 is changed by changing the waiting time. Waiting time of fully polarized water in the first logging (such as sandstone or carbonate sequence). The second logging uses longer waiting time to increase the amplitude of gas signal. Therefore, gas reservoirs can be identified by CMR porosity increment obtained from secondary logging. The waiting time of the second logging should be selected to obtain at least 4p.u of additional gas signal. The additional gas signal is calculated as follows:
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Where T 1w is the waiting time for the first log record; T2w is the waiting time for the second logging; T 1g is t1of gas.
In a good environment, the diffusion coefficient of pore fluid can be calculated by processing spin echo sequences collected from two logging records with different echo intervals (Flaum et al., 1996). The gas can then be identified by its high diffusion coefficient associated with oil and water. The minimum gas signal of 4 p.u is the expected value, and the required waiting time is calculated by Equation (5-42). Usually, the minimum waiting time is 4 seconds or 5 seconds, and the same waiting time is used for two logins. The pulse sequence in Table 5-5 has been successfully used to calculate the diffusion coefficient of several high porosity sandstones.
Table 5-5 Logging with Different Echo Interval
D. bound fluid. The bound fluid has a low T 1, which is usually less than 50 ms in sandstone and less than 150 ms in carbonate rock. Therefore, the logging curve of bound fluid is obtained through short waiting time and high-speed measurement. Refer to Table 5-6 for recommended parameters of bound fluid logging.
Table 5-6 Bound Fluid Logging
5) Selection of field measurement parameters. The purpose of point measurement is to improve the accuracy of CMR porosity logging and obtain detailed T2 distribution. The principle of measurement is the same as that of continuous logging, but there is no limit to the period of point measurement. Generally, compared with continuous logging, longer waiting time is used to collect more echoes. Table 5-7 shows the predefined pulse sequences of sandstone, carbonate rock and light oil/oil-based mud.
Table 5-7 Pulse sequence of field measurement
(2) signal processing
While developing CMR instrument, we must design an economical and complete data acquisition and signal processing method to analyze hundreds of spin echo amplitude values collected in CPMG pulse sequence. Signal processing is mainly to calculate T2 distribution curve.
In the early stage of instrument development, people realized that inversion method was not suitable for real-time processing of CMR logging data. Especially, the real-time calculation of continuous T2 distribution requires many computers to complete the calculation of a large number of collected data. Because a spin echo sequence consisting of hundreds of spin amplitudes contains only a few linearly related parameters, and the core parameters measured by NMR are approximately linear, the spin echo data is redundant and can be compressed into several values without losing information. T2 distribution can be calculated in real time by using compressed data collected by field computing equipment.
Data compression algorithm must be able to adapt and be compatible with real-time data acquisition and processing environment. Downhole data compression uses the digital signal processing chip in the instrument electronic box, which requires a fast compression algorithm. Downhole data compression reduces the need for telemetry and disk and tape storage. Uncompressed data can also be transferred underground and stored in disk for post-processing. A new inversion and related data compression algorithm-window processing algorithm is developed.
The T2 distribution is calculated by determining the signal amplitude at the preselected T2 value. Then the curve is fitted from the amplitude to show the continuous function. The preselected T2 values are equidistantly distributed on the logarithmic coordinates between T2min and T2max. The number of preselected T2 values is the number of components in the distribution.
T2 calculation and logging curve output firstly select a set of processing parameters: the number of components in the multi-exponential relaxation model; T2 maximum T2max and T2 minimum T2min are in the calculated T2 distribution; Cut-off value of free fluid; Enter t1/t2; Relaxation time of mud filtrate. Input the above parameters, and calculate the T2 distribution, the relative amount of porosity of free fluid and bound fluid, and the average relaxation time.
1) components. The simulation and processing of field data show that if at least 10 component model is used, the influence of component number on CMR logging output can be ignored. In order to obtain a smooth T2 distribution, more components must be added. Usually, 30 component models are used for continuous logging and 50 component models are used for point measurement.
2)T2min. According to the inherent sensitivity of measurement to short relaxation time, determine the minimum T2 value, which is related to the measured echo interval. When the echo interval is 0.28 μs, T2min is 0.5 μs s. ..
3) The choice of 3)T2max .T2max value is a compromise between the longest relaxation time in T2 distribution and the longest relaxation time that can be resolved by measurement, and the latter is determined according to the acquisition time (that is, the number and interval of acquired echoes). The simulation results show that, within a reasonable range, CMR logging output is insensitive to T2max value. For continuous logging with 600 ~ 1800 echoes, T2max needs 3000 μ s. Generally, 3000 ~ 8000 echoes are collected for point measurement, and T2max is set to 5000 μ s. ..
4)T 1/T2 ratio. Polarization correction requires T 1/T2. When the reservoir contains viscous oil, T 1/T2 is recommended to be 2. When light oil exists, T 1/T2 increases to 3.
(3) Calibration and correction
In the workshop, a mixture containing nickel chloride diluent is used to complete the accurate calibration. The signal amplitude of the solution represents the standard100 p.u.
Electronic calibration is completed within the waiting time of the measurement cycle. During this time, a small signal is sent to the test coil located on the antenna. The signal is collected and processed by the antenna, and then the signal amplitude is used to correct the gain change of the system caused by the operating frequency, temperature and periodic dielectric conductivity.
The signal amplitude must be corrected by temperature, magnetic field strength (magnetic field strength varies with temperature and the amount of metal debris attached to the magnet) and fluid hydrogen index (this correction is very important when the salinity of formation water or mud filtrate is high).
Figure 5-56 MRIL Instrument Block Diagram
In addition, CMR logging must correct the incomplete polarization of hydrogen nuclei.
(4) Logging quality control
Logging quality control includes: instrument positioning, sampling rate and velocity measurement, stacking and accuracy, instrument tuning, mud filtrate relaxation time, etc.
2. Magnetic resonance (imaging) logging (MRIL)
(1) instrument description
The MRIL instrument consists of three parts: a probe (8 inches long and 4.5 inches or 6.0 inches in diameter); An electronic circuit connector with a length of 13 feet and a diameter of 3.626 inches and an energy storage connector with a length of 10 feet and a diameter of 3.626 inches (Figure 5-56).
The probe of the instrument consists of a permanent magnet, a tuned radio frequency (RF) antenna and a sensor for measuring the amplitude of RF magnetic field. The magnetic field is cylindrical symmetry, the magnetic lines point to the stratum, and the amplitude of the magnetic field is inversely proportional to the square of the radial distance. Adjust the shape of RF magnetic field to make it conform to the spatial distribution of magnetic field, and make RF magnetic field and static magnetic field perpendicular to each other. This structure forms a cylindrical vibration region. Its length is 43 inches (or 24 inches, depending on the opening angle of the RF antenna) and its rated thickness is 0.04 inches. There are two kinds of probes to choose from. The standard probe with a diameter of 6 inches is used for drilling holes with a diameter of 7.785 ~ 12.25 inches. A slim hole probe with a diameter of 4.5 inches is used for drilling holes with a diameter of 6.0 ~ 8.5 inches. The working frequency of the instrument is 650~750 kHz, and the radius of the * * vibration area is 19.7 ~ 2 1.6 cm (for standard probes).
The instrument is digitized, the original echo is digitized according to the carrier wave, and all subsequent filtering and detection are realized in the digital domain.
(2) Instrument characteristics
1) multi-frequency operation. MRIL's Type C instrument has flexible frequency conversion characteristics and can jump from one frequency to another. For the rated magnetic field gradient of 17× 10-4 T/cm, the frequency jump of 15 kHz corresponds to the radius change of * * * vibration zone of 0.23 cm, and the design also supports simultaneous measurement of two frequencies. The geometric schematic diagram of dual-frequency measurement is shown in Figure 5-57.
2) Measure low resistance wells. The low impedance well is equivalent to a load on the RF antenna, and the load is often expressed by the antenna factor Q. In a borehole with a diameter of 8.5 inches, the antenna q value in a freshwater mud borehole with RM >10 ω m is100; However, in the borehole with RM = 0.02 Ω m, the q value becomes 7, and the low q value has a bad influence on the signal quality of MRIL.
3) High signal-to-noise ratio (SWR). When the measuring frequency is 725 kHz, the single echo signal-to-noise ratio (SWR) of the instrument is 70∶ 1 in the borehole environment of fresh water mud. Multiple echoes improve the signal-to-noise ratio of the calculated results, and the signal-to-noise ratio of the free fluid index is 240∶ 1.
4) AM and PM functions. Model C instrument provides complete amplitude and phase modulation for each echo.
5) Speed measurement is fast. Velocity measurement depends on the signal-to-noise ratio of MRIL single experiment output, the expected longitudinal angle of logging accuracy and the allowable measurement cycle time Tc of underground T 1. In a single oscillator, the recovery time TR must meet the following requirements:
Figure 5-57 Schematic Diagram of MRIL Dual-frequency Measurement
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Due to multi-frequency operation, the cycle time is slightly longer than T2 of the frequency number used for standardization. In the case of dual-frequency operation, TC=TR/2. Under the conditions of T 1=500 ms, 1000 ms and 2000 ms, the corresponding periods of complete recovery of formation polarization are 750 ms, 1500 ms and 3000 ms. According to different logging environments, the speed of type C instrument is about 4.4 ~14.
6) High vertical resolution. By reducing the longitudinal angle of RF antenna, higher resolution can be obtained. At present, the design angle of the probe is 43 inches, and Class C instruments can be compatible with a smaller angle (24 inches).
(3) Selection of pulse parameters
MRIL uses CPMG pulse sequence to measure T2. The pulse parameter selection method of CPMG is basically the same as that of CMR.
Figure 5-58 Cross-sectional view of dual-frequency MRIL probe and detection area
The echo interval of type C instrument at each sounding point is about 1 ms, and the recorded echo string is: about 1200 echoes in fresh water mud borehole; There are about 300 ~ 500 echoes in the borehole with saline mud.
(4) Vertical resolution and signal-to-noise ratio of 4)MRIL.
The longitudinal resolution of NMR instrument is controlled by the shape of permanent magnetic field and RF magnetic field, that is, by the physical dimensions of magnet and RF antenna. Theoretically, the detection volume of MRIL instrument is a ring (Figure 5-58), and the size of the ring is affected by the opening angle of RF antenna.
The vertical resolution and signal-to-noise ratio of MRIL data are not only controlled by the physical characteristics of NMR and sensor design, but also related to the data acquisition and processing process. The working mode of Class C instruments is dual-frequency and biphasic alternating mode. The pulse sequence is: frequency 2, original phase; Frequency 1, original phase; Frequency 1, inverted; Frequency 2, out of phase. Phase alternation changes the sign of NMR echo, while the phase of interference signal remains unchanged. By changing the sign of all the echoes and adding all the measured values, coherent interference is eliminated. According to the borehole environment, additional averaging is needed to improve the signal-to-noise ratio before the echo data conversion is completed. Apply filtration technology to the well site or subsequent treatment for subsequent treatment.
By using time series analysis method, the longitudinal resolution and signal-to-noise ratio can be quantitatively evaluated by comparing two or more logging data in a specific interval. Three pairs of logging curves were obtained by repeated logging at 0.9 m min- 1+0, 3.0 m min- 1+0 and 9. 1 m min- 1 respectively, and the relationship between correlation coefficient and signal-to-noise ratio and spatial frequency was calculated through time series analysis. The average low-frequency signal-to-noise ratio characteristics are shown in Table 5-8.
Table 5-8
(5) instrument calibration and environmental impact
Model C MRIL is calibrated with 100% standard water, which is packed in a shielded container with a height of 1 m, a length of 2 m and a width of 1 m (working in amplitude modulation frequency band). The way to change the borehole load is to add borehole fluid or increase the resistance of RF antenna. In the presence of borehole load, the echo amplitude is calibrated by comparing with the simple exponential attenuation of known standard water. This instrument needs to be recalibrated. In addition, in the well site, before and after logging, the electronic circuit should be calibrated with standard probes, and all parameters of the instrument should be recorded and compared with the standard values.
For the new 24-inch angle MRIL instrument, it can be seen that when the 24-inch angle instrument collects data for time series analysis of field curves, the data shows obvious layer boundaries and can distinguish thin layers. The results of time series analysis are shown in Table 5-9. Compared with the results of 43-inch opening angle in Table 5-8, the vertical resolution of 24-inch opening angle is improved. There is no difference between low frequency signal-to-noise ratio and low frequency signal-to-noise ratio. According to simple geometric reasoning, we predict that the signal-to-noise ratio of 24-inch opening angle will be reduced by 2.5 dB. This reduction in signal-to-noise ratio has nothing to do with speed measurement. The time series analysis of test wells shows that the signal-to-noise ratio is reduced to below 5 dB.
Table 5-9
The amplitude of NMR echo decreases with the increase of formation temperature, and the ratio of formation temperature to calibration temperature is used to correct echo output. MRIL production is sensitive to hydrocarbon density, so it is necessary to correct the influence of temperature and pressure on liquid hydrocarbon density. Natural gas can reduce the porosity of MRIL, but it cannot be corrected.
(2) signal processing and output
The raw data measured by MRIL is the received echo string, as shown in Figure 5-59. It is the basis for finding various parameters and applications.
At present, the signal processing method adopted by Type C instrument is to extract T2 distribution spectrum from the original echo string (as shown in Figure 5-60).
For porous systems, there may be multiple relaxation components T2i, and each echo is the overall effect of multiple relaxation components. Usually, the attenuation rate of echo string presents double exponential or multi-exponential characteristics; Therefore, the echo amplitude can be regarded as the sum of multiple exponential components.
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Where: ai is the echo amplitude corresponding to the ith transverse relaxation time; T2i is the i-th transverse relaxation time; N is the number of dividing T2i, usually n is 8.
Figure 5-59 Echo String Measured by MRIL
The echo string is fitted by a set of fixed T2 relaxations (4 ms, 8 ms, 16 ms, 32 ms, 64 ms, 128 ms, 256 ms and 5 12 ms). Such a set of nuclear magnetic resonance measurement signals (echo) Aj(t) (where m, m > n) can obtain a set of overdetermined equations, and the least square solution of the equations can obtain a set of ai corresponding to the fixed division of T2i, and the T2 distribution spectrum can be obtained after interpolation smoothing. Each delineated T2 corresponds to a part of pores, and all T2 components ai are summed and calibrated to obtain φ NMR; FFI is the sum of pores with T2 greater than or equal to 32 ms, and φ FFI is obtained by scaling (normalizing) the sum of ai with T2 greater than the cutoff value; BVI is the sum of partial pores corresponding to T2 values of 4ms, 8ms and 16ms, and φbvi is obtained by scaling (normalization) from the sum of ai with T2 less than the cutoff value.
Figure 5-60 Multiple Exponential Fitting and T2 Distribution Spectrum of Spin Echo Sequence
By reasonably setting the measurement parameters TR and TE of MRIL, two or more groups of echo strings are measured, and different T2 distribution spectra are obtained. Through spectral difference or spectral offset processing, the fluid types in reservoirs can be qualitatively identified.
(3) Measurement mode of nuclear magnetic resonance vibration logging (MRIL-C instrument)
1. Standard T2 logging
Provide general reservoir parameters, such as effective porosity, free fluid volume, bound fluid volume, permeability, etc.
Generally, the waiting time TW = 3 ~ 4 s, the standard echo time interval Te= 1.2 ms, and the echo number Ne≥200 are selected.
2. Double TW logging
According to the different relaxation response characteristics of oil, gas and water, we can qualitatively identify the fluid properties by measuring different waiting time TW:
Short waiting time TWS: the water signal can be completely recovered, but the hydrocarbon signal cannot be completely recovered;
Long waiting time TWL: Water signal can be completely recovered, and hydrocarbon signal can also be completely recovered.
Subtracting the T2 distribution measured by two kinds of waiting time (TWS and TWL) can basically eliminate the water signal and leave some hydrocarbon signals, thus achieving the purpose of identifying oil and gas reservoirs.
3. Double TE logging
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Where: T2CPMG is the relaxation time measured by CPMG pulse method; D is the diffusion coefficient of formation fluid; G is the magnetic field gradient; TE is the echo interval; γ is the gyromagnetic ratio of hydrogen nucleus.
As can be seen from the above formula, increasing the echo interval te will lead to the decrease of T2; And the T2 distribution will shift to a decreasing direction (shift spectrum). Because of the different diffusion coefficients of oil, gas and water, the influence on T2 distribution in gradient magnetic field of MRIL-C logging tool is also different. Using long-term and short-term TE logging, the T2 distribution of oil, gas and water changes in different degrees, so the fluid properties can be qualitatively identified.
(4) Measurement mode of nuclear magnetic resonance vibration logging (MRIL-P instrument)
Measurement mode is a series of parameters of control instrument in logging process. There are four basic measuring methods for MRIL-P logging tool, which are combined into 77 logging modes according to different parameters.
1.DTP mode
For the waiting time TW and clay bound water model. It is divided into five frequency bands and two groups of measurement methods (A, PR). There is a PR signal in the fourth frequency band (TE=0.6 ms, NE= 10, TW=0.02 s), and * * * collects eight echo strings to calculate the bound water volume of clay. In the 0 ~ 3 frequency band, it is a set of signals (TE and TW are customized), and * * * collects 16 TW signals. There are 24 echo strings per cycle. This method is mainly used to calculate the total porosity and effective porosity; Determine the parameters such as movable fluid volume, capillary bound fluid volume, clay bound fluid volume and permeability.
2.DTW mode
Also known as dual TW mode. This mode adopts five frequency bands and three groups of measurement modes (A, B, PR). In frequency band 4, there are PR signals (TE=0.6 ms, NE= 10, TW=0.02 s), and * * * echo strings are collected to calculate the bound water volume of clay. Group A and Group B collected 16 signals in 0 ~ 3 frequency bands. The echo interval TE of Group A and Group B is the same, but the waiting time TW is different. The waiting time TWL between Group A and Group B is longer, and the waiting time TWS between Group B and Group A is shorter ... There are 40 echo strings in each cycle * * *, and oil and gas can be identified according to T2 spectra of different waiting times.
3.DTE mode
Also known as dual TE mode. This mode adopts five frequency bands and three groups of measurement modes (A, B, PR). In frequency band 4, there are PR signals (TE=0.6 ms, NE= 10, TW=0.02 s), and * * * echo strings are collected to calculate the bound water volume of clay. The 16 signals of group A and group B are collected in 0 ~ 3 frequency bands, and the * * * waiting time TW of group A and group B is the same, but the echo interval TE is different. Group A is a short-distance round-trip Boeing TES, and Group B is a long-distance round-trip telephone with ***40 echo strings. Its main purpose is to use the data of two different echo intervals for diffusion weighting and gas detection.
4.DTWE mode
Also known as dual TW+ dual TE mode. This mode adopts five frequency bands and five groups of measurement modes (A, B, D, E, PR). In frequency band 4, there are PR signals (TE=0.6 ms, NE= 10, TW=0.02 s), and * * * echo strings are collected to calculate the bound water volume of clay. Eight groups of A and B signals are collected in 0 ~ 1 frequency band, and eight groups of D and E signals are collected in 2 ~ 3 frequency band, where A and B are in short TE dual TW mode and D and E are in long TE dual TW mode. ***40 echo strings. Including dual TE and dual TW logging, all information can be obtained in one trip, which greatly improves the work efficiency.
In the actual logging process, after determining the basic measurement mode, according to different measurement parameters, the appropriate mode is selected from 77 measurement modes for logging. Table 5- 10 lists the commonly used measurement mode parameters of 10.
Table 5- 10 10 Common Parameters of Measurement Mode