A velocity field correction method based on buried depth tendency in a sparse well pattern area

Abstract

The application provides a sparse well network area velocity field correction method based on a buried depth trend. After a first round of trend correction of an average velocity body by a trend correction formula of a real drilled well, the buried depth change trend and the overall value range of the average velocity body are more in line with the actual situation. The velocity error grid is corrected by a fitting buried depth trend correction formula of each layer, the accuracy of the corrected error grid is higher, a more accurate velocity field can be obtained, and the accuracy of variable speed mapping is improved. The error grid correction method based on the buried depth trend improves the velocity field accuracy of the sparse well network and the area with large structure changes, improves the accuracy of variable speed mapping, and thus can improve the effectiveness of trap identification and the success rate of drilling.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of oil exploration and development, and is used for velocity field correction in a sparse well pattern area. BACKGROUND

[0002] In some areas with severe structural changes, changes in strata and lithology will cause changes in spatial velocity fields, which will directly affect the accuracy of variable velocity mapping and the description of the true form of the structure. In areas with low exploration degree and sparse well pattern, it is more difficult to obtain an accurate velocity field. How to obtain an accurate velocity field in areas with sparse well pattern and severe structural fluctuations and carry out variable velocity mapping has important research significance for oil exploration and development.

[0003] The mainstream correction method of the velocity field model at present is to combine the logging velocity and the seismic velocity: the stacking velocity field provided by processing is converted into an initial layer velocity model or an average velocity model through Dix conversion, a pseudo well velocity curve is extracted from the model, the residual velocity curve is obtained by comparing the pseudo well velocity curve with the logging velocity curve, and the seismic velocity is corrected by using the residual velocity field. This method combines the lateral resolution of the seismic velocity and the vertical resolution of the logging velocity, and can obtain an accurate velocity field in areas with uniform and high-density drilling distribution, but still has deficiencies in areas with low exploration degree and severe structural changes. The main deficiencies are as follows: first, the accuracy of correction is obviously reduced in areas with large structural changes and no well control; second, when the error grid is generated, there are obvious bull's eyes at the wellbores no matter what interpolation method is used, which directly affects the accuracy of the velocity field in the well-free area. This phenomenon is more prominent in areas with severe structural changes.

[0004] Therefore, there is an urgent need for a velocity field correction method suitable for a sparse well pattern area. SUMMARY

[0005] The embodiment of the application provides a velocity field correction method based on the depth trend in a sparse well pattern area, which corrects the error grid by using the relationship between the velocity and the stratum depth, improves the accuracy of the error grid, and further improves the accuracy of the velocity field in the well-free area, so that a more accurate velocity field is obtained.

[0006] In the first aspect, the embodiment of the application provides a velocity field correction method based on the depth trend in a sparse well pattern area, which includes the following steps.

[0007] S1, calculating a logging average velocity curve A on the basis of well-seismic calibration;

[0008] S2, converting a stacking velocity body into an average velocity body through a Dix formula, and extracting a borehole average velocity curve B;

[0009] S3, select a well that meets the preset conditions, crossplot the logging average velocity curve A and the borehole average velocity curve B, and fit to obtain an average velocity body trend correction formula, and use the formula to perform first round trend correction on the average velocity body;

[0010] S4, extract the borehole average velocity curve B' from the average velocity body after the first round of trend correction, and subtract the calculated logging average velocity curve A to obtain a borehole error curve C;

[0011] S5, use the borehole error curve C to interpolate along the stratigraphic-frame model to obtain an average velocity error body;

[0012] S6, extract the average velocity error grid along the layers, and perform crossplot analysis with the interpreted horizons to fit a trend error correction curve for each layer;

[0013] S7, use the error correction curve to correct the average velocity error grid;

[0014] S8, add the corrected error grid and the horizon average velocity after the first round of trend correction to obtain the final average velocity field of the layer.

[0015] S1, on the basis of well-seismic calibration, calculate the logging average velocity curve A, including:

[0016] Well-seismic calibration: use the acoustic time curve of the well in the work area to make a synthetic seismic record, reference geological stratification and seismic response characteristics to carry out well-seismic calibration, and determine the time-depth relationship curve of each well;

[0017] Calculate the logging average velocity curve A: convert the time-depth relationship curve into average velocity, A = 2TVD / T0, A is the logging average velocity, TVD is the depth, and T0 is the two-way travel time.

[0018] S2, convert the stacked velocity body into an average velocity body by the Dix formula, and extract the borehole average velocity curve B, including:

[0019] Convert the stacked velocity body obtained after seismic processing into an average velocity body: first convert the stacked velocity body into a layer velocity body using the Dix formula, the formula is:

[0020]

[0021] where, is the layer velocity of the i-th layer, t i is the travel time to the bottom of the i-th layer, t i -t i-1 is the time thickness of the i-th layer, is the stacked velocity of the i-th layer; then convert the layer velocity body into an average velocity body, the formula is:

[0022]

[0023] V A is the average velocity body, is the time thickness of i layer, m is the total number of sample points above the average velocity to be calculated;

[0024] Extract the borehole average velocity curve B along the well trajectory in the average velocity body.

[0025] Wherein, S3, select a well that meets the preset condition, crossplot the logging average velocity curve A and the borehole average velocity curve B, and fit to obtain the average velocity body trend correction formula, use the formula to carry out the first round of trend correction on the average velocity body, including:

[0026] Select a well that meets the preset condition, the preset condition includes that the distance from the well to the well-free area is less than a threshold, crossplot the logging average velocity curve A and the borehole average velocity curve B, and fit to obtain the average velocity body trend correction formula:

[0027] Y=C0+C1x+C2x^2

[0028] Use the formula to carry out the first round of trend correction on the average velocity body.

[0029] Wherein, C0=3940.13, C1=-1.15272, C2=0.000274009, substitute the average velocity body into X, calculate Y through the correction formula, and Y is the corrected average velocity body.

[0030] Wherein, crossplot the logging average velocity curve A and the borehole average velocity curve B, including:

[0031] The borehole average velocity curve B is X in the crossplot, and the logging average velocity curve A is Y in the crossplot, according to the position of the data crossplot point on the crossplot, carry out data analysis.

[0032] Wherein, S5, use the borehole error curve C to interpolate along the stratigraphic framework model to obtain the average velocity error body, including:

[0033] On the basis of the well-seismic calibration carried out in step S1, the seismic reflection event is one-to-one corresponding to the geological horizon, and the horizon interpretation is carried out, and the stratigraphic framework model is established by using the interpreted horizon;

[0034] Use the borehole error curve C to interpolate along the stratigraphic framework model to obtain the average velocity error body.

[0035] Wherein, S6, extract the average velocity error grid along the layer, and carry out crossplot analysis with the interpreted horizon, fit the depth trend error correction curve of each layer, including:

[0036] The average velocity error grid is extracted along the interpreted horizon on the average velocity error volume, and the average velocity error grid is cross analyzed with the interpreted horizon to fit the depth trend correction formula of each interpreted horizon.

[0037] The depth trend correction formula is a first order polynomial Y=C0+C1X.

[0038] The corrected error grid and the average velocity of the horizon after the first round of trend correction are added to obtain the final average velocity field of the horizon, including:

[0039] The average velocity grid of each interpreted horizon is extracted along the horizon on the average velocity volume after the first round of trend correction, and the average velocity grid is added to the average velocity error grid to obtain the final velocity field of each horizon after the second round of correction.

[0040] The velocity field correction method based on the depth trend of the sparse well pattern area has the following beneficial effects:

[0041] The error grid correction method based on the depth trend improves the accuracy of the velocity field in the sparse well pattern area and the area with large structure changes, improves the accuracy of the variable velocity mapping, and thus improves the effectiveness of the trap identification and the success rate of drilling. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The figure is a flowchart of the velocity field correction method based on the depth trend of the sparse well pattern area;

[0043] Figure 2 The figure is another flowchart of the velocity field correction method based on the depth trend of the sparse well pattern area;

[0044] Figure 3 The horizontal axis is the borehole average velocity B, and the vertical axis is the logging average velocity A.

[0045] Figure 4 The figure is a stratigraphic framework model

[0046] Figure 5a The figure is an average velocity error grid before the second round of trend correction;

[0047] Figure 5b The figure is an average velocity error grid after the second round of trend correction;

[0048] Figure 5c The figure is an interpreted horizon in the time domain;

[0049] Figure 6 The horizontal axis is the interpreted horizon in the time domain, and the vertical axis is the borehole error conventional interpolation grid. Detailed Implementation

[0050] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0051] In the following description, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The following description provides multiple embodiments of the invention, which can be substituted or combined with each other. Therefore, this application can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then this application should also be considered to include embodiments containing one or more other possible combinations of A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0052] The following description provides examples and does not limit the scope, applicability, or examples set forth in the claims. Changes may be made to the function and arrangement of the described elements without departing from the scope of this application. Various processes or components may be appropriately omitted, substituted, or added to the examples. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Furthermore, features described with respect to some examples may be combined into other examples.

[0053] Example 1

[0054] like Figure 1 As shown, this application provides a method for velocity field correction in sparse well network areas based on burial depth trends, including: S1, calculating the well logging average velocity curve A based on well seismic calibration; S2, converting the superimposed velocity volume into an average velocity volume using the Dix formula, and extracting the wellbore average velocity curve B; S3, selecting a well that meets preset conditions, performing cross-sectional analysis on the well logging average velocity curve A and the wellbore average velocity curve B, fitting the average velocity volume trend correction formula, and using this formula to perform the first round of trend correction on the average velocity volume; S4, after the first round of trend correction, the average velocity... S5. Extract the average velocity curve B' from multiple wells and subtract it from the calculated average velocity curve A to obtain the wellbore error curve C; S6. Use the wellbore error curve C to interpolate along the formation-frame model to obtain the average velocity error volume; S7. Extract the average velocity error grid along the layers and perform cross-intersection analysis with the interpreted layers to fit the depth trend error correction curves of each layer; S8. Use the error correction curves to correct the average velocity error grid; S9. Add the corrected error grid with the layer average velocity after the first round of trend correction to obtain the final average velocity field of the layer.

[0055] The application proposes a method for correcting error grids by using the relationship between velocity and stratum burial depth, improving the accuracy of error grids, and further improving the accuracy of velocity field in well-free areas to obtain more accurate velocity field.

[0056] Embodiment two

[0057] The application based on the velocity field correction method of sparse well grid area according to burial depth trend comprises the following steps:

[0058] On the basis of well-to-seismic calibration, calculate the well logging average velocity curve A.

[0059] Convert the stacking velocity body into the average velocity body through the Dix formula, and extract the borehole average velocity curve B.

[0060] Select a typical well (preferably the well closest to the well-free area) to crossplot A and B, and fit to obtain the average velocity body trend correction formula. Use the formula to carry out the first round of trend correction on the average velocity body.

[0061] Extract the multi-well borehole average velocity curve B' from the average velocity body after the first round of trend correction, and subtract the multi-well logging average velocity curve A calculated to obtain the borehole error curve C.

[0062] Use the multi-well borehole error curve C to interpolate along the stratum-frame model to obtain the average velocity error body.

[0063] Extract the average velocity error grid along the layer, and carry out crossplot analysis with the interpreted horizon to fit the burial depth trend error correction curve of each layer.

[0064] Use the error correction curve to correct the average velocity error grid so that the average velocity error and the burial depth trend have consistency.

[0065] Add the corrected error grid and the horizon average velocity after the first round of trend correction to obtain the final average velocity field of the layer.

[0066] Although the prior art also uses the borehole error curve to interpolate along the stratum-frame model to form a body, under the condition of sparse well grid, no matter what interpolation method is used, the average velocity error body will form several very obvious velocity anomaly points, which directly affects the accuracy of velocity correction. In the present application, the average velocity body is first corrected by using the velocity curve of a typical well, which greatly makes the velocity body of the well-free area more consistent with the actual velocity. Further, the burial depth trend error correction curve is fitted according to each interpreted horizon, so that the average velocity error and the burial depth trend have higher consistency.

[0067] The present application is not only suitable for sparse well grid areas with dramatic structural changes, but also suitable for areas with higher exploration degree but uneven drilling distribution.

[0068] Specifically, as Figures 2-6 shown, the application based on the buried trend sparse well pattern area velocity field correction method includes:

[0069] Step one, well-seismic calibration:

[0070] Use the acoustic travel time curve of the well in the work area to make a synthetic seismic record, reference geological stratification and seismic response characteristics to carry out well-seismic calibration, and determine the time-depth relationship curve of each well.

[0071] Step two, calculate the logging average velocity curve A, method: convert the time-depth relationship curve into average velocity according to the formula, A = 2TVD / T0 (A is the logging average velocity, TVD is the depth, T0 is the two-way travel time).

[0072] Step three, convert the stacking velocity body obtained after seismic processing into average velocity body through calculation, this step is realized through two formulas, first convert the stacking velocity body into interval velocity body using Dix formula. The formula is:

[0073]

[0074] V i is the interval velocity of the i layer, t i -t i-1 is the time thickness of the i layer, is the stacking velocity of the i layer.

[0075] Then convert the interval velocity body into average velocity body, the formula is:

[0076]

[0077] V A is the average velocity body, is the time thickness of the i layer, m is the total number of samples above the average velocity to be calculated.

[0078] Step four, extract the borehole average velocity curve B along the well track in the average velocity body;

[0079] Step five, as Figure 3 shown, preferably a typical well (usually select a well that drilled through a complete formation, high quality logging curve, and adjacent to the well area), the application selects XHY1-1 well, crossplot the logging average velocity curve A and the borehole average velocity curve B of this well, fit the trend correction formula, and carry out the first round of trend correction on the average velocity body. The correction formula is:

[0080] Quadratic polynomial Y = C0 + C1x + C2x^2

[0081] In the application, C0= 3940.13; C1=-1.15272; C2=0.000274009.

[0082] In the correction process, the average velocity body is directly calculated by using the correction formula, and the average velocity body is substituted into X and Y to obtain the corrected average velocity body.

[0083] The crossplot method is a data analysis technique for studying the relationship between different data. Figure 3 For a typical crossplot, curve B is taken as X in the crossplot, and curve A is taken as Y in the crossplot, and according to the position of the data intersection point on the crossplot, data analysis can be carried out.

[0084] Since the logging average velocity curve A comes from a real drilled well, the velocity reflected is more true and accurate, and thus the corrected average velocity body is more in line with the actual trend and value range.

[0085] Step six, on the basis of the average velocity body after the first round of trend correction, the borehole average velocity curve B' of multiple wells in the work area is extracted, and the error calculation (subtraction) is carried out with the logging average velocity curve A to obtain the borehole error curve C.

[0086] Step seven, as shown in the figure, a stratigraphic-framework model is built from bottom to top using the input interpreted horizon. Figure 4 On the basis of the well-seismic calibration carried out in step one, the seismic reflection event can be one-to-one corresponding to the geological horizon, and horizon interpretation can be carried out. The interpreted horizon can be used to establish a stratigraphic-framework model.

[0087] Step eight, the borehole error curve C is used to interpolate along the stratigraphic-framework model, that is, the curve is interpolated in the model to obtain the average velocity error body.

[0088] Step nine, the average velocity error grid is extracted along the interpreted horizon on the average velocity error body (that is, the average velocity error value on a certain interpreted horizon is extracted), and the interpreted horizon is crossplotted to fit the burial depth trend correction formula of each interpreted horizon. The correction formula is in the form of a first-order polynomial Y=C0+C1X, and in the application, C0=781.125 and C1=-275.

[0089] Step ten, the average velocity error grid of each layer is corrected using the fitted burial depth trend correction formula.

[0090] Step eleven, the average velocity grid of each interpreted horizon is extracted along the layer on the average velocity body after the first round of trend correction, and the average velocity error grid is added to obtain the final accurate velocity field of each layer after the second round of correction.

[0091] The advantages of the application are as follows:

[0092] 1. After conducting the first round of trend correction on the mean velocity body using the trend correction formula from actual drilling, the burial depth variation trend and overall value range of the mean velocity body will be more consistent with reality.

[0093] 2. The velocity error grid is corrected by fitting the burial depth trend correction formula of each layer. The corrected error grid has higher accuracy and can obtain a more accurate velocity field, thereby improving the accuracy of variable velocity mapping.

[0094] This application improves the accuracy of velocity fields in areas with sparse well networks and large structural changes by using an error grid correction method based on burial depth trends. This improves the accuracy of variable velocity mapping, thereby enhancing the effectiveness of trap identification and the success rate of drilling.

[0095] In this application, the stacked velocity volume is converted into an average velocity volume using the Dix formula, and two rounds of trend correction are performed on the average velocity volume. An alternative approach is to convert the stacked velocity volume into a layered velocity volume using the Dix formula, perform corrections on the layered velocity volume first, and then convert it back into an average velocity volume after the corrections are complete.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for velocity field correction in a sparse well network area based on burial depth trends, characterized in that, include: S1, based on the well vibration calibration, calculate the average logging velocity curve A; S2, convert the superimposed velocity volume into an average velocity volume using the Dix formula, and extract the borehole average velocity curve B; S3. Select a well that meets the preset conditions, perform cross-sectional analysis on the well logging average velocity curve A and the wellbore average velocity curve B, and fit the average velocity volume trend correction formula to obtain the formula. Use this formula to carry out the first round of trend correction on the average velocity volume; including: Select a well that meets preset conditions, including a distance from a no-well zone that is less than a threshold. Perform cross-plot analysis on the well logging average velocity curve A and the wellbore average velocity curve B, and fit the average velocity volume trend correction formula: Y = C0 + C1x + C2x^2 The formula is used to perform the first round of trend correction on the average velocity volume; a cross-plot analysis is performed on the well logging average velocity curve A and the wellbore average velocity curve B, including: the wellbore average velocity curve B is used as x in the cross-plot, and the well logging average velocity curve A is used as Y in the cross-plot. Data analysis is carried out based on the position of the data cross-plot point on the cross-plot. S4. Extract the average velocity curve B' of the multi-well hole from the average velocity body after the first round of trend correction, and subtract it from the calculated average logging velocity curve A to obtain the hole error curve C. S5. Using the borehole error curve C, interpolation is performed along the formation-frame model to obtain the average velocity error volume; S6, extract the average velocity error grid along the layer, perform cross-intersection analysis with the interpreted layer, and fit the burial depth trend error correction curve for each layer; including: The mean velocity error grid is extracted along the interpretation layer on the mean velocity error volume, and cross-intersection analysis is performed with the interpretation layer to fit the burial depth trend correction formula for each interpretation layer; the burial depth trend correction formula is in the form of a first-order polynomial Y'=C0'+C1'X'; S7, use the error correction curve to correct the average velocity error grid; S8, add the corrected error grid and the layer average velocity after the first round of trend correction to obtain the final average velocity field of the layer.

2. The velocity field correction method for sparse well network areas based on burial depth trend according to claim 1, characterized in that, S1, based on the well vibration calibration, calculate the average logging velocity curve A, including: Well-seismic calibration: Synthetic seismic records are generated using the sonic transit time curves of wells within the work area. Well-seismic calibration is carried out with reference to geological stratification and seismic response characteristics to determine the time-depth relationship curve for each well. Calculate the logging average velocity curve A: Convert the time-depth relationship curve into an average velocity, A = 2TVD / T0, where A is the logging average velocity, TVD is the depth, and T0 is the two-way travel time.

3. The velocity field correction method for sparse well network areas based on burial depth trend according to claim 2, characterized in that, S2, convert the superimposed velocity volume into an average velocity volume using the Dix formula, and extract the borehole average velocity curve B, including: To convert the stacked velocity volume obtained after seismic processing into an average velocity volume: First, the stacked velocity volume is converted into a layer velocity volume using the Dix formula, which is as follows: in, Let t be the layer velocity of layer i. i For the journey to the bottom of the i-th level, t i -t i-1 The time thickness of layer i. Let i be the stacking velocity of layer segment i; then convert the layer velocity volume into an average velocity volume using the following formula: V A For average velocity body, Let i be the time thickness of layer i, and m be the total number of sampling points above the point where the average velocity is to be calculated. Extract the borehole average velocity curve B along the well trajectory in the average velocity volume.

4. The velocity field correction method for sparse well network areas based on burial depth trend according to claim 1, characterized in that, C0 = 3940.13, C1 = -1.15272, C2 = 0.000274009. Substituting the average velocity volume into x, we can calculate Y using the correction formula. Y is the corrected average velocity volume.

5. The velocity field correction method for sparse well network areas based on burial depth trends according to any one of claims 1-3, characterized in that, S5, using the borehole error curve C, interpolation is performed along the formation-frame model to obtain the average velocity error volume, including: Based on the well-seismic calibration carried out in step S1, the seismic reflection phase axes are matched one-to-one with the geological strata, and the strata are interpreted. The interpreted strata are then used to establish a stratigraphic-frame model. Using the borehole error curve C, interpolation is performed along the formation-frame model to obtain the average velocity error volume.

6. The velocity field correction method for sparse well network areas based on burial depth trend according to any one of claims 1-3, characterized in that, S8, the corrected error grid and the layer-averaged velocity after the first round of trend correction are added to obtain the final average velocity field of the layer, including: The average velocity grid of each interpretation layer is extracted along the average velocity volume after the first round of trend correction, and added to the average velocity error grid to obtain the final velocity field of each layer after the second round of correction.

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