Threaded borehole density curve correction method based on numerical simulation and frequency domain filtering

Abstract

The invention discloses a threaded borehole density curve correction method based on numerical simulation and frequency domain filtering, and relates to the technical field of petroleum and natural gas development, and the process is as follows: obtaining stratum apparent density results under different thread depths by using threaded borehole stratum simulation models with different thread depths; performing frequency domain filtering processing on the stratum apparent density result to obtain a density curve frequency domain filtering processing result under each thread depth condition; then establishing a mathematical relationship between the deviation value and the corresponding thread depth to obtain a density deviation value chart suitable for frequency domain filtering under different thread depths; performing frequency domain filtering processing on the actually measured density curve, and outputting a frequency domain filtering result of the density curve; and finally, superposing the deviation value to a frequency domain filtering result of the actual measurement density curve to obtain a final correction result. According to the method, the density deviation value charts under different threaded well hole conditions are established through a numerical simulation method, the density curve after frequency domain filtering is corrected, and the accuracy of the density logging curve is improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas development, and in particular to a threaded wellbore density curve correction method based on numerical simulation and frequency domain filtering. Background Art

[0002] During the exploration and development of oil and gas, due to the influence of drilling technology, formation characteristics and other factors, threaded boreholes appear in some sections of the wells. A threaded borehole refers to an uneven shape similar to a thread on the inner wall of the borehole, which is reflected in the logging curve as periodic fluctuations in the well diameter curve and density curve. For density logging, it is greatly affected by the change in well diameter. In a threaded borehole, due to the irregular well wall, the size of the gap between the well wall and the density instrument plate shows a sinusoidal change law with depth, resulting in periodic fluctuations in the density curve. This periodic jitter makes it impossible to identify the lithology interface and divide the reservoir when interpreting the logging data, which in turn leads to deviations in the calculation of reservoir parameters.

[0003] When correcting the density logging curve of threaded boreholes, the commonly used methods are the envelope method and the frequency domain filtering method. The envelope method can identify and eliminate abnormal responses caused by borehole irregularities, thereby obtaining a more accurate logging curve; the frequency domain filtering method focuses on filtering the logging signal in the frequency domain to remove the influence of noise and borehole irregularities. Due to the complex and changeable structure of threaded boreholes, in the process of actual application, these two methods often have the problem of deviation between the corrected density and the true density when correcting the density curve in the threaded borehole. In order to solve the above problems, a threaded borehole density curve correction method based on numerical simulation and frequency domain filtering is proposed. Summary of the invention

[0004] In order to solve the above technical problems, the present invention discloses a threaded wellbore density curve correction method based on numerical simulation and frequency domain filtering. The numerical simulation method is used to establish a density deviation map under different threaded wellbore conditions, so as to correct the density curve after frequency domain filtering and improve the accuracy of the density logging curve.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The threaded borehole density curve correction method based on numerical simulation and frequency domain filtering is characterized in that the specific steps include:

[0007] Step 1: Establish a density logging-threaded wellbore formation simulation model with different thread depths based on the Monte Carlo method;

[0008] Step 2: Using the density logging-threaded borehole environment simulation model of step 1 to simulate the logging response of the density logging instrument at different thread depths, the formation apparent density results at different thread depths are obtained, which have deviations from the true density of the formation. The true density of the formation refers to the density value set for the formation in the model;

[0009] Step 3: Perform frequency domain filtering on the formation apparent density result obtained in step 2 to obtain the frequency domain filtering result of the density curve under each thread depth condition;

[0010] Step 4: extract the deviation between the frequency domain filtering result of the density curve in step 3 and the actual formation density, and make an intersection diagram of the deviation and the thread depth to obtain a density deviation map at different thread depths suitable for frequency domain filtering, and derive a density deviation calculation formula based on the density deviation map;

[0011] The above deviation refers to the difference between the frequency domain filtering result of the density curve and the actual formation density.

[0012] The density deviation chart is obtained by fitting the density deviation under different thread depths, wherein the horizontal axis is the thread depth and the vertical axis is the density deviation.

[0013] Step 5, extracting the wellbore curve and density curve corresponding to the threaded wellbore layer section in the measured data, and performing frequency domain filtering on the measured density curve to output the frequency domain filtering result of the density curve;

[0014] The measured density curve processed by frequency domain filtering refers to the density curve obtained by eliminating the periodic fluctuation of the threaded wellbore through frequency domain filtering of the actual density curve.

[0015] Step six, use the measured wellbore curve to calculate the thread depth, calculate the deviation of the actual density curve based on the actual thread depth information and the density deviation chart, and superimpose the deviation on the frequency domain filtering result of the measured density curve to obtain the final correction result.

[0016] Furthermore, in step one, the density logging instrument in the density logging-threaded borehole formation simulation model is based on the parameters of the actual logging instrument. The threaded borehole formation parameters are mainly the thread depth. The thread depth is calculated using the wellbore curve of the threaded well section, which is equal to the maximum value of the wellbore curve minus the minimum value of the wellbore curve, which is 0-3cm. The thread depth period usually fluctuates around 1.0m in the actual threaded layer section. Due to the relatively small range of variation, it is usually set to 1.0m.

[0017] Furthermore, in step 2, the formation apparent density result is obtained by converting the simulated logging response into the formation apparent density result using a calibration formula and a density ridge diagram.

[0018] Furthermore, in step three, frequency domain filtering processing is to perform fast Fourier transform on the simulated formation apparent density results, use a specific low-pass filter to filter the simulated formation apparent density results, obtain the formation apparent density frequency domain distribution results, and achieve the filtering effect by cutting the contribution corresponding to the threaded wellbore signal frequency to 0. The threaded wellbore signal frequency refers to the frequency value corresponding to the peak position on the formation apparent density frequency domain distribution result due to the periodic repetition of the threaded wellbore signal. The frequency domain filtering result of the density curve refers to the density curve after the contribution of the threaded wellbore signal is eliminated through frequency domain filtering.

[0019] The beneficial effects of the present invention are as follows: first, a simulation model of a threaded wellbore formation with different thread depths is used to obtain the formation apparent density results at different thread depths; then the formation apparent density results are subjected to frequency domain filtering processing to obtain the frequency domain filtering processing results of the density curve under each thread depth condition; then a mathematical relationship is established between the deviation amount and the corresponding thread depth to obtain a density deviation chart at different thread depths suitable for frequency domain filtering; the measured density curve is subjected to frequency domain filtering processing to output the frequency domain filtering result of the density curve; finally, the deviation amount is superimposed on the frequency domain filtering result of the measured density curve to obtain the final correction result.

[0020] This method uses numerical simulation methods to establish density deviation charts under different threaded borehole conditions, thereby correcting the density curve after frequency domain filtering. This method significantly eliminates the periodic fluctuations of the density curve, and the curve can better reflect the real density information.

[0021] The method combines numerical simulation technology and frequency domain filtering technology. The numerical simulation technology provides a density deviation map, which solves the problem that only frequency domain filtering is used for correction, resulting in deviation between the corrected density and the true density. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a threaded wellbore formation simulation model in an embodiment of the present invention;

[0023] Figure 2 It is a density curve spectrum diagram in an embodiment of the present invention;

[0024] Figure 3 is a frequency domain filtering result diagram of a density simulation curve in an embodiment of the present invention;

[0025] Figure 4 It is a density thread wellbore deviation amount chart in an embodiment of the present invention;

[0026] Figure 5 This is the calibration result of the measured threaded borehole data in the embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The present invention discloses a threaded borehole density curve correction method based on numerical simulation and frequency domain filtering, and the specific process is as follows:

[0029] (1) Based on the Monte Carlo method, a simulation model of the well logging-thread wellbore environment with different thread depths is established, such as Figure 1 As shown in the figure, in this example, the density logging instrument refers to the actual density logging instrument, and the source distance is set to 20cm and 40cm. The borehole water in the model is set to fresh water, and the formation is partially filled with saturated limestone with a density of 2.5390g / cm 3 , the porosity is 10 p.u., the thread period is 1 m, and the model sets the thread depths of 0.0 cm, 0.5 cm, 1.0 cm, 1.5 cm, 2.0 cm, 2.5 cm, and 3.0 cm to simulate the density response at different thread depths.

[0030] (2) The logging-threaded borehole environment simulation model of step (1) simulates the logging response of the density logging instrument at different thread depths to obtain the formation apparent density results at different thread depths, which deviate from the true density of the formation.

[0031] (3) Perform fast Fourier transform on the formation apparent density results at different thread depths obtained in step (2) to obtain the formation apparent density frequency domain distribution results. Figure 2 As shown in the figure, there will be an obvious peak at the frequency of the threaded borehole. In this example, the frequency of the spectrum peak is 1Hz. The contribution corresponding to the threaded borehole signal frequency is cut off to 0 to achieve the filtering effect, and the density curve frequency domain filtering result is output.

[0032] The results show that the density frequency domain filtering results at each thread depth have obvious deviations (ΔDEN) from the true formation density. Figure 3 shown.

[0033] (4) Calculate the deviation (ΔDEN) between the density curve frequency domain filtering result of step (3) and the true formation density, and fit the thread depth and the deviation to obtain a density deviation chart at different thread depths suitable for frequency domain filtering, such as Figure 4 shown. Figure 4The horizontal axis is the thread depth, and the vertical axis is the density deviation calculated by simulation. When using the density deviation chart, substitute the measured thread depth into the density deviation chart to obtain the corresponding density deviation.

[0034] (5) Extract the borehole diameter curve and density curve corresponding to the threaded borehole layer section in the measured data, and use the measured borehole diameter curve to calculate the thread depth. The thread depth is equal to the maximum value of the borehole diameter curve minus the minimum value of the borehole diameter curve. The measured density curve is subjected to frequency domain filtering to eliminate the periodic jitter of the threaded borehole and output the frequency domain filtering result of the density curve; Figure 5 The third track is shown. Figure 5 The third track is the measured density curve, which has been initially processed by frequency domain filtering. Its periodic jitter is basically eliminated, but it still needs further processing due to its deviation from the actual density.

[0035] (6) Based on the actual thread depth information and the density deviation plate, the deviation (ΔDEN) of the actual density curve is calculated, and the deviation (ΔDEN) is superimposed on the frequency domain filtering result of the measured density curve to obtain the final correction result; the effect is as follows: Figure 5 As shown in the fourth track. Figure 5 The fifth track is the final correction result. The influence of threaded wellbore on density curve is basically eliminated, and the correction result is close to the real density, which can truly reflect the formation information.

[0036] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A threaded borehole density curve correction method based on numerical simulation and frequency domain filtering, characterized in that: The specific steps include: Step 1: Establish a density logging-threaded wellbore formation simulation model with different thread depths based on the Monte Carlo method; Step 2: using the density logging-threaded borehole environment simulation model of step 1 to simulate the logging response of the density logging instrument at different thread depths, and obtain the formation apparent density results at different thread depths; Step 3: Perform frequency domain filtering on the formation apparent density result obtained in step 2 to obtain the frequency domain filtering result of the density curve under each thread depth condition; Step 4: extract the deviation between the frequency domain filtering result of the density curve in step 3 and the real formation density, and make an intersection diagram of the deviation and the thread depth to obtain a density deviation diagram at different thread depths suitable for frequency domain filtering; Step 5, extracting the wellbore curve and density curve corresponding to the threaded wellbore layer section in the measured data, and performing frequency domain filtering on the measured density curve to output the frequency domain filtering result of the density curve; Step six, use the measured wellbore curve to calculate the thread depth, calculate the deviation of the actual density curve based on the actual thread depth information and the density deviation chart, and superimpose the deviation on the frequency domain filtering result of the measured density curve to obtain the final correction result.

2. The threaded borehole density curve correction method based on numerical simulation and frequency domain filtering according to claim 1 is characterized in that: In step 1, the density logging instrument in the density logging-threaded borehole formation simulation model is based on the parameters of the actual logging instrument. The threaded borehole formation parameters are mainly the thread depth, which is equal to the maximum value of the wellbore curve minus the minimum value of the wellbore curve, which is 0-3cm.

3. The threaded borehole density curve correction method based on numerical simulation and frequency domain filtering according to claim 2 is characterized in that: In step 2, the formation apparent density results are obtained by converting the simulated logging response into the formation apparent density results using the calibration formula and the density ridge diagram.

4. The threaded borehole density curve correction method based on numerical simulation and frequency domain filtering according to claim 3 is characterized in that: In step three, the frequency domain filtering process is to perform fast Fourier transform on the simulated formation apparent density results, and use a low-pass filter to filter the simulated formation apparent density results to obtain the formation apparent density frequency domain distribution results.

Images