Application of main parameters of seismic wave in lithology and oil and gas prediction in Tahe Oilfield

(Planning and Design Institute of Northwest Petroleum Bureau of Urumqi 8300 1 1)

Huang He Jianjun

(Chengdu University of Technology, Chengdu 6 10059)

Based on the main parameters of seismic waves, combined with the fine interpretation of seismic data and comprehensive geological research results in the first area of Tahe Oilfield and its adjacent areas, the lithology and oil and gas distribution of Triassic oil groups in this area are emphatically predicted, and good results have been achieved.

Seismic wave; Main parameters; Energy density function; Lithologic prediction in Tahe Oilfield: Oil and gas prediction

It has been many years to study reservoir physical properties and oil-gas bearing property by using seismic wave dynamic characteristics, but it is a new method developed in recent years to analyze and predict formation lithology and oil-gas distribution by using seismic wave main parameters. The so-called main parameters of seismic wave refer to the main parameters of seismic wave dynamics, which can represent the main characteristics of reflected wave or frequency spectrum in time domain, frequency domain or time-frequency domain.

Using principal parameters, it is easy to link time domain information with frequency domain information for analysis, that is, the so-called time-frequency domain principal parameter analysis method. At present, time-frequency analysis includes: along-layer spectrum, integral spectrum, notch frequency and sliding spectrum along time, three instantaneous profiles and main parameter profiles. Huang, Study on Seismic Low Amplitude Structure and Lithologic Oil and Gas Prediction in Aixieke-Santamu Area of Shaya Uplift in Tarim Basin, Xinjiang, 1997.

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Fourier transform is indispensable for studying the variation of amplitude spectrum in horizontal and vertical directions. When the Fourier time window is long, it may include multiple reflection layers, so it is difficult to understand the corresponding relationship between the characteristic values in the spectrum and each reflection layer. In order to make Fourier transform have geological connotation, it is necessary to shorten the time window, but this will reduce the sampling accuracy and resolution in the spectrum.

Instantaneous parameters are obtained by orthogonal transformation of signals [1], which can only describe the amplitude, frequency and phase properties of signals at a certain moment, but cannot reflect the overall characteristics of signals.

Based on the theory of complex energy density function, the main parameter profile extracts the main amplitude, main frequency and main phase which can represent the signal waveform by using time-frequency domain information, and then forms three main parameter profiles. The three main sections give semi-quantitatively (or quantitatively) the main parameters representing the overall characteristics of the reflected wave waveform of each layer and their distribution in time and space domain, which is convenient for people to study the lateral changes of geological structure and stratigraphic structure from macro and micro aspects through time-frequency analysis, and then achieve the purpose of predicting stratigraphic lithology and oil and gas potential.

1 calculation principle of main parameter profile

Accurate spectrum estimation needs an infinite time window, and it is difficult to understand the corresponding relationship between the characteristic parameters and the reflection layer in the spectrum in the long time window, while accurate instantaneous parameter estimation needs an infinite frequency band, which shows that the properties of the signal in frequency domain and time domain are mutually restricted. In order to get the best estimate of reflected wave, it is necessary to analyze both time domain and frequency domain. Therefore, we introduce the concept of energy density function and the distribution characteristics of signal energy in time-frequency domain in the field of signal analysis, thus establishing the relational equation of signal frequency domain characteristic parameters, and according to this relationship, we can calculate the main amplitude, main frequency and main phase of seismic waves.

1. 1 main frequency profile

According to the distribution of signal energy in time domain and frequency domain, the intercept of complex energy focusing on frequency axis is the main frequency of the signal, and the intercept on time axis is the group delay of the signal.

The complex energy density function is defined as

Essays on exploration and development of oil and gas fields in northern Tarim basin

formula

Essays on exploration and development of oil and gas fields in northern Tarim basin

Where u(t), x(t) and y(t) are complex trajectories, real trajectories and imaginary trajectories respectively, and 〓(f is the conjugate of u(t) spectrum, which can be expressed as

Essays on exploration and development of oil and gas fields in northern Tarim basin

At this time, the energy density function can be expressed as

Essays on exploration and development of oil and gas fields in northern Tarim basin

If F is taken as the ordinate and T as the abscissa, the plane distribution of energy | ε (t, f) | in the f-t domain can be made. By differentiating the phase of equation (2), the longitudinal and transverse coordinates of the energy focus can be obtained, and the following two equations can be solved:

d[ψ(f)-θ(t)+2πft]/dt=0

d[ψ(f)-θ(t)+2πft]/df=0

get

Essays on exploration and development of oil and gas fields in northern Tarim basin

Where and x are the frequency value at the energy focus and the group delay of the reflected wave respectively. A fast algorithm for calculating the main frequency of the signal is obtained.

1.2 main phase profile

If the real seismic trace and its corresponding virtual trace are respectively

x(t-tEmax)= e(-at2)cos[2πf(t-tEmax)+ψ(f)]

y(t-tEmax)= e(-at)sin[2πf(t-tEmax)+ψ(f)]

Its phase is

Essays on exploration and development of oil and gas fields in northern Tarim basin

According to the properties of Fourier transform, the delay phase is

Essays on exploration and development of oil and gas fields in northern Tarim basin

party history

Essays on exploration and development of oil and gas fields in northern Tarim basin

Equation (6) is an expression for calculating the main phase of seismic waves.

1.3 Principal amplitude profile

According to the point where | ε (t, f )| differential equals zero, the principal amplitude is extracted and the principal amplitude profile is constructed.

Essays on exploration and development of oil and gas fields in northern Tarim basin

According to the above mathematical principles, the profile or plane distribution of main parameters can be obtained.

Application of two main parameters in seismic data interpretation

Because the amplitude is mainly related to the reflection intensity, that is, the wave impedance difference, which is mainly related to the change of formation lithology, the formation lithology and its attributes can be distinguished according to the change of amplitude parameters [2].

Phase parameters have little to do with reflection intensity [3], but mainly with wave continuity (that is, wave coherence), so they can be used to study the phenomena of stratum pinch-out, fracture and overlap.

For the frequency, different strata have different lithologic absorption intensities and different frequencies. Therefore, we can judge the stability of lithofacies or stratigraphic deposition by frequency and stability. In addition, in the oil and gas accumulation area, because of its strong absorption of high frequency, the frequency tends to become lower. Therefore, oil and gas accumulation zones can also be found by using the characteristics of low abnormal frequency and low complex wave velocity.

In seismic interpretation, the main parameters have the characteristics of the above-mentioned common seismic wave dynamic parameters, and have the following characteristics superior to the general dynamic parameters:

(1) Because the main parameters are separated from the seismic signals, the constraint is lost, so the weak reflection layer can be highlighted in the main frequency profile, which is beneficial to the continuous comparison and tracking of reflected waves.

② It is beneficial to the comparison between Apollo Formation and faults. In the profile of main parameters, not only the accurate time position and the relationship between layers, time and thickness can be used to compare wave groups, but also the characteristics that the main parameters change basically in the same wave group can be used to compare wave groups and faults.

③ It is helpful to determine the position and nature of strata and pinch points. The profile wave may be submerged in the interference background in the superimposed profile, but it may be displayed in the main parameter profile. The characteristics of the same main parameters on both sides of the fault can be used to judge the nature of the fault. By using the similar main parameters of the same layer on both sides of the pinch-out point, it can help to judge whether it is the bottom overload or the top overload.

④ It is used for seismic stratigraphic interpretation, which facilitates the division of seismic facies and contributes to the division of sedimentary cycles. For different sedimentary cycles, the main amplitude and frequency are different from shallow to deep, which can be used to divide parallel and sub-parallel sedimentary cycles of continental deposits.

⑤ For reservoir description, we can analyze and summarize the variation law of main parameters along the layer, and study the thickness variation of the reservoir in the lateral direction, which is helpful to determine the boundary of the reservoir.

⑥ It is helpful to study ancient landforms. On the surface of the ancient landform, some loose weathered materials will be filled in the low depressions, so the valleys should have the characteristics of low frequency. Therefore, the main parameters can help to study ancient landforms. In thin layer tuning, the situation will be different, which needs to be analyzed in detail with forward simulation.

Application of three main parameters in rock oil and gas prediction in the first area of Tahe Oilfield and its adjacent areas

3. 1 Main achievements of research work

On the basis of interpreting the fine structure of the work area and compiling more than 10 maps, the project research team applied the main parameters of seismic waves in time-frequency domain and time-space domain, and combined with the comprehensive research results of drilling, logging and geological data, drew the profile, plane, lithology and oil-gas distribution map of the main parameters of Upper, Middle and Lower Triassic oil groups in this area. The lithology and oil-gas bearing property of Triassic in the work area are preliminarily predicted, and the plane position of Jianyi well is submitted as shown in Figure 1.

Fig. 1 Tahe oilfield 1 local structural map (isoline numerical unit m) around Jianyi well at the top of Triassic oil formation in block 1 local structural map around Jianyi well at the top of Triassic T-II in Tahe oilfield (No.1).

1- Normal fault; 2- depth contour; 3— Drilling site; 4— Suggested well location

3.2 Application of main parameters in lithology and oil and gas prediction of Triassic oil formation in this area

3.2. 1 Zhong You Formation Lithology and Oil and Gas Prediction Basis

(1) favorable factors.

(1) There are a large set of sandstone reservoirs in Zhong You Formation in the study area, and local structures are developed, which provides a geological basis for effective traps.

(2) The Triassic faults in the work area are developed, which facilitates the secondary migration of oil and gas.

(3) There are many sets of reservoir-cap assemblages in Triassic, which create conditions for oil and gas accumulation.

(2) shortcomings.

(1) Faults are mostly in Triassic, and there is no good channel for upward migration of deep oil and gas.

(2) Effective traps are mostly restricted by factors such as low structural amplitude and small area.

(c) The formation lithology has certain heterogeneity, which leads to the dispersion and accumulation of oil and gas.

3.2.2 Prediction and evaluation of favorable reservoirs and oil and gas distribution in Zhong You Formation.

Zhong You Formation is one of the most important oil and gas producing zones in the study area. The lithology and oil and gas prediction of this layer are mainly based on the main amplitude profile, the plane distribution of main amplitude along the layer and the plane distribution of main frequency.

Through comprehensive analysis of main parameters and actual drilling, it is confirmed that on the main amplitude profile, the strong main amplitude corresponds to the industrial oil and gas flowing horizon, as shown in Figure 2 (a) Well S29 (CDP900, T). The value is about 3085 ms). And in fig. 2 (a) (CDP 772, T. the value is about 3090 ms). Zhong You Formation in S40 well location and Figure 2 (b) (CDP 6 10, t. value is about 3080 ms) are in the middle oil formation of S4 1 well, and the oil and gas productivity is very low due to the weak main amplitude. Building a well is proposed according to the characteristics of strong principal amplitude, as shown in Figure 3(CDP486, t0 value is about 3090ms).

Fig. 2 (a) Seismic principal amplitude and amplitude-preserving profile (88E76) passing through wells S40 and S29 Fig. 2(a) Seismic dominant parameters and relative amplitude-preserving profile passing through wells S40 and S29.

The above-mentioned characteristics of judging the oil-gas bearing property of the formation directly from the main amplitude profile cannot be reflected in the amplitude-preserving superimposed profile (Figure 2(a), Figure 2 (b) and the lower part of Figure 3), which is one of the characteristics that the main parameters are different from ordinary dynamic parameters.

According to the tuning theory, when the thickness of thin layer is large (about 17 m in this area), its amplitude value increases with the increase of thickness. Because of the thickness of this layer of sandstone, the area with higher amplitude of this layer may correspond to the area with greater thickness of sandstone. The research shows that the plane distribution trend of apparent amplitude and main amplitude is consistent. On the plane distribution map of principal amplitude (Figure 4), it can be considered that the area with higher principal amplitude (greater than 6200) is likely to contain oil and gas. If the principal amplitude is bounded by 1. 1× 104, all areas larger than 1. 1× 104 are favorable oil and gas-bearing areas.

Fig. 2 (b) Main amplitude and amplitude retention profile of the earthquake passing through S4 1 well (89N 137.5) Fig. 2(b) Seismic dominant parameters and relative amplitude retention profile of the earthquake passing through S4 1 well.

Fig. 3 Main amplitude and amplitude maintenance profile of Guo Jian 1 Well (9 1n 135b) Fig. 3 Dominant parameters and relative amplitude maintenance profile of well construction.

Fig. 4 Plane distribution of principal amplitude at the top of Triassic oil group in Tahe Oilfield 1 block and its adjacent area Fig. 4 Dominant amplitude at the top of Triassic T-II in Tahe Oilfield (1) and its adjacent area.

Fig. 5 Plane distribution of top frequency of Triassic oil formation in Tahe Oilfield 1 block and its adjacent area Fig. 5 Top frequency of Triassic T-II in Tahe Oilfield (1) and its adjacent area.

Fig. 6 Prediction map of reservoir lithology and oil and gas distribution of Triassic Zhongyou Formation in Tahe Oilfield 1 block and its adjacent area (Fig. 6 Lithologic reservoir and oil and gas distribution map of Triassic T-II in Tahe Oilfield (No.1) and its adjacent area).

1 block (oil-rich area); 2- secondary block (favorable oil and gas area); Block 3-3 (favorable oil and gas area); Block 4-4 (unfavorable oil and gas area); 5— Missing area of Zhong You Formation.

Judging from the two frequency distributions, the main frequency value of the integral spectrum is too concentrated, and the influence on the well is not obvious. On the main frequency plane distribution map (Figure 5), all wells with industrial oil and gas flow are located in the middle and low frequency (less than 53 Hz) area.

Based on the distribution and quantitative analysis of the main parameter values of the middle oil group in the work area, combined with the structural map of the top of the middle oil group, the division of sedimentary microfacies and the study of lithologic heterogeneity, the lithology and oil and gas distribution of the middle oil group in this area are divided into four blocks with different levels of lithology (I, II, III and IV), and block V is the missing area of the middle oil group (Figure 6).

(1) I 1-I2 block: Tahe Oilfield 1 block where Well S29 and Well S4 1 are located and Cidalia structural area where Well S22 is located. This area is the most favorable facies area in the work area, and it is also the two most favorable oil and gas enrichment areas (Figure 6). The lower oil group in this area is also a favorable oil and gas enrichment area.

(2)I3 block: located to the east of LN37, in a favorable phase area. There is a southeast structure of LN37 in this area, and faults are relatively developed, so this area is classified as a first-class oil and gas area. However, due to the small structural scale, small closed area and amplitude, faults are concentrated in Triassic, and this block does not have the conditions to form large oil and gas reservoirs.

(3) Block II1-Ⅱ 7: Most of these blocks in the scattered study area are small areas, which are in favorable facies areas, and most of them are homogeneous reservoir areas formed by lithologic plane changes, but the structures and faults in the blocks are not developed, so they are classified as Class II blocks. Among them, Block II1is located in Santamu and its southern area, which has a good overlap with Santamu structure, and is in a favorable sedimentary facies zone and a homogeneous and high-quality reservoir distribution area. Faults in this area are well developed, but the scale is small, all of which are developed in Triassic, which may restrict this area from becoming an area with rich oil and gas reserves (compared with Tahe Oilfield 1 block and Sidari Ya). Due to the above other advantages, this area is still one of the favorable oil and gas exploration blocks in the study area.

(4) Class III block: This kind of block is the area where the favorable facies belt is located, but the structure is undeveloped and the lithology heterogeneity is serious, and most of them belong to relatively dense reservoir rocks (relative to Class I and II blocks), which can be listed as a prospective planning area for oil and gas exploration.

(5) Class IV blocks: Most of these blocks belong to sheet sand microfacies environment, with dense lithology and no structure locally, which is not conducive to oil and gas accumulation.

(6)V region is the missing region of Zhong You group.

Effect analysis of four main parameters in lithology and oil and gas prediction in the study area

4. 1 The vertical and horizontal distributions of main parameters are consistent with the known drilling oil and gas productivity.

Display (1) main amplitude on the known cross-well profile.

(a) As shown in Figure 2(a), the main amplitude of well S29 on E76 line is stronger than that of well S40, which is consistent with the fact that the oil and gas productivity of well S29 is better than that of well S40 (completely consistent with the actual drilling).

(b) Comparing Figure 2(a) and Figure 2(b), it can be found that the main amplitude characteristics of oil group in well S4 1 are much smaller than that in well S29, and the actual oil group productivity in well S4 1 is much smaller than that in well S29 (confirmed by drilling).

(c) On the N 135B line (as shown in Figure 3), the main amplitude characteristics of the middle and lower oil groups are located in the well under construction. Although the well Jian-1 was not drilled, TK 104H (horizontal well) next to the well Jian-1 (prediction well) encountered high-yield industrial oil gas flow in the middle and lower Triassic oil formation, which fully proved the correctness of the study on the main amplitude of the construction well site.

(2) The distribution of the main amplitude on the plane.

As mentioned above, the middle-low frequency region less than 53 Hz and the section with the principal amplitude value greater than 6200 are oil-bearing and possible oil-bearing regions, especially when the principal amplitude value is greater than 1. 1× 104, the corresponding regions are favorable oil-bearing regions. This has been confirmed in Tahe 1 Area T 10 1, T 102, TK 103, TK 104H-TK 106H, and it has been used in the west.

4.2 Main parameters predict lithology and oil and gas distribution

We only briefly discuss the first two of the four types of blocks discussed above.

① For the Ⅱ1-Ⅱ 77 block, there is no drilling revelation, which needs to be studied in the future.

② For block Ⅰ 2, it has been verified in many wells (known areas) such as S22 in west Daria structure, which is consistent with the research results of principal amplitude.

③ Block Ⅰ 3 has not been drilled and needs further verification.

④ Ⅰ1block (including the scope of Ⅰ1block in Tahe Oilfield), S29, S4 1, t1,T 102 and tk/kloc beside the construction well (prediction well). Obviously, the study of predicting formation lithology and oil and gas distribution by using principal parameters has achieved great success, and the prediction effect is good, which shows the broad application prospect of seismic wave principal parameters in lithology and oil and gas prediction.

5 conclusion

The application of seismic wave main parameter analysis method in formation lithology and oil and gas prediction in Tahe Oilfield has achieved good results and has been confirmed by drilling.

The main parameter profile is not only helpful for structural interpretation, but also more suitable for formation lithology analysis and reservoir oil and gas prediction. By analyzing the plan of main parameters, we can intuitively understand the spatial distribution characteristics of main amplitude and main frequency related to formation lithology and the favorable oil and gas anomaly areas. Using the distribution law of main parameters, stratigraphic interpretation and sedimentary facies zone division can be carried out, and then oil-bearing areas can be delineated, thus improving exploration accuracy and drilling hit rate.

We believe that with the continuous development and deepening of geophysical exploration technology, principal parameter analysis combined with other technologies will play a greater role in oil and gas exploration and development.

In the process of writing this paper, I got the guidance from Qiu Shengde of Northwest Petroleum Bureau, Ye Desheng and Zhou Dikang of Southwest Petroleum Bureau. Thank you!

refer to

[1] Zhao Hongru's full-wave phase analysis. Beijing: seismological press,1991.163 ~166.

Huang et al. Digital processing of seismic exploration data. Beijing: Geological Publishing House, 1990.203 ~ 208.

Liu. Using seismic information to predict oil and gas. Beijing: Petroleum Industry Press, 1994.38 ~ 45.

Application of seismic dominant parameters in lithology and reservoir prediction in Tahe Oilfield

Zhao Xuboping

Design and Planning Institute of Northwest Petroleum Geology Bureau? Ramch 8300 1 1)

Huang He Jianjun

(Chengdu University of Technology, Chengdu 6 10059)

Abstract: According to the characteristics of seismic dominant parameters, this paper discusses the use of seismic dominant parameters, combined with the fine interpretation of seismic data in Tahe Oilfield (1) and its adjacent areas and the comprehensive geological research results, and predicts the Triassic lithology and the distribution of reservoirs in Zhongyou Formation, and obtains good results.

Keywords: seismic dominant parameter energy density function Lithology prediction and oil and gas prediction in Tahe Oilfield