Sandwich type shale oil ultrathin reservoir horizontal well earthquake guiding method

Abstract

The invention relates to the field of unconventional oil-gas exploration, in particular to an earthquake guiding method for a horizontal well of a sandwich type shale oil ultrathin reservoir. The problems that an existing interlayer type thin sandstone reservoir is small in thickness, and tracking while drilling of a horizontal well is difficult are mainly solved. Comprising the following steps: analyzing a sedimentary background of a research area, and judging a sandstone distribution range and a pinching direction; performing qualitative depiction on the sandstone distribution range; a marker bed is determined, the depth of the marker bed is constructed into a map, and the map is compared with the actual drilling depth to guide timely adjustment and accurate target entering of a drilling track in the next step; quantitatively predicting the distribution range of the sand body; in-drilling inversion is carried out according to actual drilling lithology information in the while-drilling process, and a next-step guiding scheme is guided; and calculating a stratigraphic dip angle in real time, guiding a well inclination angle and adjusting a drilling strategy in the next step. The interlayer type shale oil ultrathin reservoir horizontal well seismic steering method can be suitable for an interlayer type thin sandstone reservoir with the thickness smaller than 3 m, the predicted sandstone position is accurate, and the drilling rate is high.

Description

Technical Field

[0001] This invention relates to the field of unconventional oil and gas exploration, specifically to a seismic steering method for horizontal wells in interlayered shale oil ultrathin reservoirs. Background Technology

[0002] In the northern Songliao Basin, the interbedded shale oil in the Qingshankou Formation is vertically interbedded between source rocks and developed in the source-reservoir superposition zone. It has obvious zonation with conventional oil and pure shale oil. From 2011 to 2013, wells Ying 47, Ying 54, Ying X56 and Ying X55 were deployed in the Qingshankou Formation and all showed good performance. In 2019, the Yingye 1H well, deployed for the interbedded shale oil in the first section of Qingshankou, achieved a daily production of 28 tons in the initial stage of oil testing. After 770 days of trial production, the cumulative oil production reached 10,261 cubic meters and the gas production reached 590,000 cubic meters, achieving high and stable production. In 2022, the Ha 36 well deployed in the second section of Qingshankou obtained a high-yield industrial oil flow of 52.92 tons per day. In the Qijia area, the "horizontal well + volumetric fracturing" technology was applied to explore interlayer shale oil in the Qingshankou Formation. Multiple horizontal wells were successively drilled and obtained high-yield industrial oil flows, fully demonstrating the exploration potential of interlayer shale oil. At the same time, the horizontal well development method will also become an effective means to increase reserves and production.

[0003] The interlayered shale oil in the Qingshankou Formation of the northern Songliao Basin mainly refers to single-layer shale oil, with shale accounting for 80%–95% and sandstone single layers being 0.2–1.5 m thick. The thin sandstone single layers represent a large resource volume, and breakthroughs in these layers will make them crucial for significant growth in oil and gas reserves and production. Currently, the target sandstone layers in horizontal wells are generally 4–5 m or thicker, but the reservoir thickness encountered during horizontal well drilling is less than 3 m or even thinner, making tracking difficult. Therefore, there is an urgent need for a targeted and widely applicable horizontal well steerable technology to ensure a high success rate in encountering sandstone and oil-bearing formations. Summary of the Invention

[0004] To overcome the shortcomings of existing methods for guiding horizontal wells in thin sandstone reservoirs with small thickness and high difficulty in tracking them during drilling, this invention provides a seismic steering method for ultra-thin sandstone reservoirs in interbedded shale oil. This seismic steering method is applicable to thin sandstone reservoirs with a thickness of less than 3m, accurately predicts the location of sandstone, and has a high drilling encounter rate.

[0005] The technical solution of this invention is: a seismic steering method for horizontal wells in interlayered shale oil ultrathin reservoirs, comprising the following steps: S1. Analyze the sedimentary background of the study area based on the known well characteristics of the strata, and determine the distribution range and pinch-out direction of sandstone; S2. Combining the regional sandstone distribution results in step S1, and under the condition that the synthetic record is accurately calibrated, the seismic reflection characteristics of sandstone are summarized. The maximum peak amplitude and waveform clustering seismic attributes are extracted using different time windows to qualitatively characterize the sandstone distribution range. S3. Determine the marker layer, obtain the time-depth relationship through synthetic record calibration, establish a high-precision velocity field, complete the depth construction mapping of the marker layer, and judge the prediction depth error by comparing it with the actual drilling depth to guide the timely adjustment and accurate target entry of the next drilling trajectory; predict the formation conditions encountered during drilling. S4. Based on the qualitative prediction of the sand body in step S2, the sand body distribution range is quantitatively predicted by inversion, and the sandstone thickness and distribution boundary are predicted. During drilling, inversion is performed based on the actual drilling lithology information to correct the inversion results and guide the next step of the guidance scheme. S5. Using the high-precision velocity field established in step S3, calculate the formation dip angle in real time. Combine the prediction results of steps S2, S3, and S4 to comprehensively analyze the relative position of the drill bit and sandstone, and provide real-time guidance for adjusting the well inclination angle and the next drilling strategy.

[0006] Furthermore, the known well characteristics in step S1 include rock electrical characteristics, heavy mineral analysis, sand-to-soil ratio distribution, and sedimentary facies classification results.

[0007] Furthermore, the sedimentary background of the study area in step S1 includes the source direction, sedimentary facies zone, and paleocurrent direction of the study area.

[0008] Furthermore, in step S3, the predicted formation conditions encountered during drilling include: whether the formation contains small faults or fractures.

[0009] Furthermore, in step S4, the inversion method includes at least one of geostatistical inversion, waveform indicator inversion, and Z-inversion.

[0010] Furthermore, in step S5, if the well inclination angle is close to the formation dip angle, and the gamma curves during drilling are stable, and the cuttings show as oil-stained siltstone, then the current well inclination angle is maintained for stable drilling.

[0011] Furthermore, in step S5, if the upper and lower gamma values ​​show an increasing trend, it is necessary to determine the relative position of the drill bit and the sandstone. If the lower gamma value increases first, the rock cuttings become transitional lithology of argillaceous siltstone, and the drilling angle is increased. If the upper gamma value increases first, the rock cuttings lithology changes from siltstone to argillaceous siltstone, and the drilling angle is decreased.

[0012] This invention offers the following advantages: By employing the aforementioned scheme, this guidance method enables real-time prediction of the target layer depth, assesses the error between the target layer depth and the predicted depth, accurately predicts the formation dip angle, and guides the adjustment of the drilling inclination angle. Precise prediction of sandstone thickness ensures accurate characterization of ultra-thin sandstone thickness, providing a reliable basis for predicting horizontal well productivity and designing subsequent fracturing and testing strategies. Ensuring accurate prediction of sandstone location provides a reference for geologists analyzing the depositional stages of sand bodies. This method is applicable to interlayered thin sandstone reservoirs with a thickness of less than 3m, improving the drilling rate and productivity of horizontal wells, and significantly influencing the deployment of reserve enhancement and even the overall development strategy for the entire region. Attached Figure Description

[0013] Figure 1 This is a flowchart of the present invention; Figure 2 It refers to the physical, electrical, and oil-bearing characteristics of the sandstone in the target layer of the reference well; Figure 3 This shows the development of sandstone in the target layer of the drilled wells in the horizontal well area. Figures a, b, c, and d are composite columnar diagrams of four wells. Figure 4 It is a forward model of sandstone target layer in a horizontal well, where a is the forward model before sand removal and b is the forward model after sand removal; Figure 5 These are the classification characteristics of seismic waveforms corresponding to horizontal well sections; Figure 6 It is the feature of the seismic data along the layer slice after a 90-degree phase rotation; Figure 7 It is a waveform indicator inversion profile of the horizontal well area; Figure 8 It is a plan view of sandstone thickness in a horizontal well area predicted by a combination of multiple inversion methods; Figure 9 This is a horizontal well section frequency-coherent small fault prediction plan; Figure 10 This is a planar map showing the crack development density prediction using ant body tracking technology; Figure 11 It is a horizontal well trajectory tracking formation dip angle calculation profile. Detailed Implementation

[0014] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Depend on Figure 1As shown, a seismic steering method for horizontal wells in ultra-thin interlayer shale oil reservoirs includes the following steps: S1. Analyze the sedimentary background of the study area based on the known well characteristics of the strata to determine the distribution range and pinch-out direction of sandstone. Known well characteristics include lithological electrical properties, heavy mineral analysis, sand-to-soil ratio distribution, and sedimentary facies classification results. The sedimentary background of the study area includes the provenance direction, sedimentary facies zones, and paleocurrent direction. Specifically, based on the known well lithological electrical properties, heavy mineral analysis, sand-to-soil ratio distribution, and sedimentary facies classification results of the Qingshankou Formation in the study area, analyze the provenance direction, sedimentary facies zones, and paleocurrent direction to determine the distribution range and pinch-out direction of sandstone.

[0016] S2. Combining the regional sandstone distribution results in step S1, and assuming accurate calibration of the synthetic record, summarize the seismic reflection characteristics of sandstone, extract the maximum peak amplitude using different time windows, cluster the seismic attributes of the waveform, qualitatively characterize the sandstone distribution range, and determine whether the rock strata are sandstone.

[0017] S3. To ensure accurate target entry of the horizontal well, the interface between the upper part of the target layer and the sandstone layer closest to it, and with the most stable sedimentation, is selected as the marker layer. Accurate time-depth relationships are obtained through reasonable calibration of the synthetic record, a high-precision velocity field is established, and a depth structure map of the marker layer is completed. By comparing this map with the actual drilling depth, the predicted depth error is determined, guiding timely adjustments to the drilling trajectory and ensuring accurate target entry in the next step. Simultaneously, precise predictions of potential encounters during drilling are made using methods such as detailed interpretation of small faults and fracture prediction.

[0018] The establishment of a high-precision velocity field firstly ensures that the error of the depth structure map is minimized, and the depth of the target layer is predicted in real time by comparing it with known wells in real time, and the error between the target layer depth and the predicted depth is judged; secondly, it ensures that the trajectory position can be accurately marked on the inversion profile, which is used to determine the predicted sandstone position of the drill bit; and thirdly, it can accurately predict the formation dip angle, guiding the adjustment of the drilling inclination angle.

[0019] S4. Based on the qualitative prediction of the sand body in step S2, the distribution range of the sand body is quantitatively predicted by inversion, and the thickness and distribution boundary of the sandstone are predicted. During the drilling process, in-drill inversion is performed based on the actual drilling lithology information to correct the inversion results. At the same time, the waveform and amplitude are analyzed in conjunction with the results of formation slicing, waveform clustering and other methods to further guide the next step of the guidance scheme.

[0020] When making quantitative predictions about the distribution range of sand bodies, multiple inversion methods can be used for cross-validation, including at least one of geostatistical inversion, waveform indicator inversion, and Z-inversion methods.

[0021] Accurate prediction of sandstone thickness serves two purposes: first, it ensures that the thickness of ultrathin sandstone can be precisely characterized, providing a reliable basis for predicting horizontal well productivity and designing subsequent fracturing and oil testing schemes; second, it ensures that the predicted sandstone location is accurate, providing a reference for geologists to analyze the depositional stages of sand bodies.

[0022] S5. Using the high-precision velocity field established in step S3, calculate the formation dip angle in real time. If the well inclination angle is close to the formation dip angle, and the upper and lower gamma curves during drilling are stable with values ​​between 80-100 API, and the cuttings appear to be oil-stained siltstone, then maintain the current well inclination angle and continue drilling steadily. If the upper and lower gamma values ​​show an increasing trend, it is necessary to determine the relative position of the drill bit and the sandstone. If the lower gamma value increases first, and the cuttings become transitional lithology of argillaceous siltstone, it indicates that the drill bit is more likely to emerge from the lower part of the sandstone, and drilling should be increased inclination. If the upper gamma value increases first, and the cuttings lithology changes from siltstone to argillaceous siltstone, it indicates that the drill bit is more likely to emerge from the upper part of the sandstone, and drilling should be increased inclination. Because the sandstone changes rapidly laterally and has complex combinations, when the lithology changes, it is also necessary to combine the waveform and amplitude changes with the prediction results of steps S2, S3, and S4 to comprehensively analyze the relative position of the drill bit and the sandstone, and provide real-time guidance for adjusting the well inclination angle and the next drilling strategy.

[0023] The success of horizontal well drilling directional drilling largely tests the analytical capabilities of geologists and the predictive capabilities of seismic technology. As exploration becomes more difficult, the successful drilling and increased production capacity of horizontal wells largely determine the deployment of reserve improvement and even the development plan for the entire field. Example

[0024] The following example illustrates the implementation process of this method using the drilling steerable tracking technology for horizontal wells in the shallow-water deltaic sedimentary system of the northern Songliao Basin in the Daqing exploration area.

[0025] 1. Research Background In the western part of the Gulong Formation in the northern Songliao Basin, the Qingshankou Formation's first and second sections exhibit two major sedimentary systems from the northern and western sources. The source-source convergence area is located in the western slope region, encompassing a large lacustrine area. The Qijia-Gulong Depression features shallow and semi-deep lacustrine deposits, while the surrounding depression zone exhibits a fan-delta front sedimentary system. Interbedded shale formations are found in the lake-entry areas. The interbedded shale oil in the Gulong area originates from delta front sediments entering the lake, extending into the source rock. It is a tight sandstone composed of "two sources plus silt," with a porosity of less than 12%. In 2019, a risk well test yielded 28 tons per day, with a cumulative production of 10,882 cubic meters, demonstrating the effectiveness of the "horizontal well + volumetric fracturing" technology in increasing production. Therefore, accelerating the scale and efficient utilization of interbedded shale oil reserves is imperative.

[0026] In this embodiment, the horizontal well is located on the west side of the Gulong Depression, in the lower part of the second member of the Qingshankou Formation. The target sandstone layer of the reference well has a thickness of 5.0 mm, consisting of oil stains and traces in siltstone, with a porosity of 14.2% and a permeability of 4.17 mD. The daily oil production during the test was 52.92 t. Figure 2 .

[0027] 2. Accurate target entry and formation dip prediction for horizontal wells The Gaotaizi oil layer in the Qingshankou Formation is different from the Fuyu oil layer. The top surface of the Fuyu oil layer, i.e. the top surface of the Quantou Formation, is a very stable sedimentary interface. During the drilling process, the design depth or shallowness of the target depth can be determined by calculating the structural mapping error, and the inclination angle of the well can be adjusted in real time.

[0028] In this embodiment, mudstone is developed above and below the target sandstone in the horizontal well. Therefore, the amplitude of the axial wave peaks in the same direction can basically reflect the degree of sandstone development. The top surface of the target sandstone corresponds to a stable, traceable set of strong reflections. (See...) Figure 3 This method can be used as a reference interface for depth calculation. After tracking, a high-precision velocity field is established, and a structural map of the top surface of the target sandstone layer is created. The elevation depth of the top surface of the sandstone layer at target point A is -1996.22m, the measured core height is 140.6m, and the distance between the top surface of the reference well sandstone and the top surface of the target sandstone layer is 29m. The predicted penetration depth of target point A is 2165.8m, and the design depth of target point A using the time-depth relationship method is 2165.1m, with a small error. This method is a stepwise approximation method. By predicting the depth of the stable sedimentary interface of the target sandstone layer, the depth of the target sandstone layer is predicted, and the conclusions of the geological sub-layers are combined to comprehensively determine the depth of target point A, ensuring that the target is penetrated at the optimal angle.

[0029] 3. Qualitative prediction of sandstone encountered during horizontal well drilling Seismic homing axes represent the superimposed responses of multiple sand bodies. By extracting attributes such as frequency, phase, and amplitude of these homing axes, the planar distribution range of the sand bodies can be predicted, and the lithological variations in horizontal segments can be comprehensively assessed. The strength of the homing axis amplitude is the most direct reflection of the presence and thickness of sandstone. Furthermore, forward modeling reveals… Figure 4 The amplitude of wave troughs is also correlated with sandstone thickness; the thicker the sandstone, the smaller the wave trough amplitude. Therefore, extracting the maximum wave trough amplitude attribute can predict the sandstone thickness distribution to some extent. Waveform clustering utilizes the waveform characteristics of seismic data and employs a neural network method to obtain model traces, classifying the seismic traces. This can be approximately understood as the classification of similar sedimentary environments, i.e., seismic facies. (See...) Figure 5 .

[0030] During drilling, the lithology at the drill bit's location can be determined by the drilling time curve, the gamma ray curves during drilling, and the cuttings returned from the bottom of the well. This helps determine whether the drill bit is at the top, middle, or bottom of the sandstone encountered in the target pre-drilling. Due to limited seismic resolution, there are often transitional lithologies (argillaceous siltstone or silty mudstone) between two closely spaced sandstone layers. Therefore, in addition to determining the sandstone distribution, it is also necessary to determine the drill bit's location. Theoretically, when only one sandstone layer is developed and its thickness is less than the tuning thickness, the seismic waveform corresponding to the single interface is a zero-phase wavelet waveform, which is symmetrical and has the maximum energy. If it is a 90-degree phase wavelet, the waveform is symmetrical, and the maximum energy is greater than that of the non-90-degree phase wavelet. In actual data, this can be approximated as the waveform corresponding to two relatively close thin layers. The lithological interface can be approximated by a 90-degree phase conversion profile (initial phase is zero phase). In horizontal well tracking, after performing a 90-degree phase transformation on the seismic data volume and extracting slices along the layers, the planar amplitude attribute characteristics can be approximated as the planar attribute changes caused by lithological variations. This can be used to determine the lithological changes at the drilling location of the horizontal well. (See...) Figure 6 .

[0031] 4. Quantitative prediction of sandstone encountered during horizontal well drilling In this embodiment, the sedimentary facies zone of the horizontal well is a delta front facies zone, so the sand bodies are relatively continuous, and the waveform can well reflect the changes in the sand bodies. A waveform indication inversion method is used, driven by seismic waveforms, to extract common structural information contained in well logging curves corresponding to similar waveforms, and to perform seismic prior finite sample point simulation. This inversion method is based on facies control, which makes the inversion results gradually determine rather than completely random, providing a better technical solution for horizontal well steering tracking. See [link to relevant documentation]. Figure 7 Based on the combined qualitative prediction results of comprehensive attributes and the quantitative prediction results of waveform indicators, the thickness of sandstone is predicted. (See...) Figure 8 It provides information on the thickness variation of sandstone in a plane, guiding adjustments to the drilling plan during drilling.

[0032] 5. Prediction and early warning of faults and fractures encountered during horizontal well drilling (1) Prediction of small faults and fractures Small faults respond differently at different frequencies; higher frequencies are easier to characterize small faults (generally, 50-60Hz frequency division coherence yields the best results). In this embodiment, the frequency division dip angle coherence method is applied to finely characterize small faults encountered in the formation during horizontal well drilling. Figure 9 Based on the prediction results, horizontal wells do not encounter well-developed small faults in the formation.

[0033] This embodiment primarily utilizes post-stack ant colony attribute extraction technology for fracture prediction in horizontal well sections. This technology leverages the ability of ants to find the optimal path to food sources during their search, and to quickly bypass obstacles and find the optimal path again when that path is blocked. Fault attribute volumes exhibit local maxima or minima at fault locations; for example, coherence volumes show local minima of coherence values ​​at fault locations. Based on this characteristic, directional ant colony algorithms can be used to track and identify fractures in coherence profiles or horizontal slices. The fracture prediction results from post-stack data show… Figure 10 The horizontal section has fewer cracks, which can serve as an early warning during the drilling process.

[0034] (2) Prediction of stratigraphic dip angle This embodiment of horizontal well tracking technology extracts wellpoint velocities from a time-depth table. Based on the analysis of lateral, longitudinal, and spatial velocities, a velocity model and average velocity field are established. Stratigraphic framework subdivision is performed using stratigraphic information and the time-depth relationship of a single well. Time-depth conversion of the seismic body is then performed, thereby completing rapid modeling of the attribute profile. During horizontal well tracking, the dip angle of the formation at different horizontal distances is calculated. Simultaneously, through fitting characteristic curves, the drilling direction is updated in real time to adjust the drilling angle accordingly. (See...) Figure 11 .

[0035] The method of this invention has been applied to drill two horizontal wells with good results. The first well was in the Qing 2 Formation sandstone, with a target sandstone layer of 4.2 meters. The actual drilled sandstone thickness was only 1 meter. Through the application of this invention, the actual drilling depth at target point A was only 0.3 meters ahead of the predicted depth. Using a combination of technologies, the horizontal well section was 1740 meters long, with a sandstone encounter rate of 81.1% and an oil-bearing sandstone encounter rate of 81.1%. The second well was in the lower Qing 2 Formation, with a target sandstone layer of 5 meters thick. The sandstone layer could be divided into three parts: an upper 1.8-meter sandstone layer, a middle 0.6-meter mudstone interlayer, and a lower 2.6-meter sandstone layer. The entire horizontal section was drilled within the upper 1.8-meter sandstone layer, with a horizontal section length of 1345 meters. The sandstone encounter rate was 85.1%, and the oil layer encounter rate was 85.1%. This method has been well validated in actual drilling.

[0036] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method of seismic steering for a sandwich-type shale oil ultra-thin reservoir horizontal well, characterized in that: The method comprises the following steps: S1, analyzing the sedimentary background of the study area according to the known well characteristics of the stratum, judging the distribution range and pinch-out direction of the sandstone; S2, combining the regional sandstone distribution result in step S1, summarizing the seismic reflection characteristics of the sandstone under the condition of accurate synthetic record calibration, using different time windows to extract the maximum peak amplitude and waveform clustering seismic attribute, and qualitatively describing the distribution range of the sandstone; S3, determining the marker layer, obtaining the time-depth relationship through synthetic record calibration, establishing a high-precision velocity field, completing the depth structure mapping of the marker layer, comparing with the actual drilling depth to judge the prediction depth error, guiding the next drilling trajectory and timely adjustment and accurate target entry, and predicting the drilled stratum; S4, on the basis of the qualitative prediction of the sand body in step S2, quantitatively predicting the distribution range of the sand body through inversion, predicting the thickness and distribution boundary of the sandstone, and correcting the inversion result according to the drilling lithology information in the process of drilling while drilling to guide the next steering scheme; S5, using the high-precision velocity field established in step S3 to calculate the stratum dip angle in real time, combining the prediction results of steps S2, S3 and S4 to comprehensively analyze the relative position of the drill bit and the sandstone, and guiding the hole inclination angle and the next drilling strategy adjustment in real time.

2. The method of claim 1, wherein: The known well characteristics in step S1 include rock-electricity characteristics, heavy mineral analysis, sandstone ratio distribution and sedimentary facies division results.

3. The method of claim 2, wherein: The sedimentary background of the study area in step S1 includes the source direction of the study area, sedimentary facies belt and paleocurrent direction.

4. The method of claim 3, wherein: In step S3, the predicted drilled stratum includes whether the stratum contains small faults and fractures.

5. The method of claim 4, wherein: In step S4, the inversion method includes at least one of the geological statistics inversion, waveform indication inversion and Z inversion method.

6. The method of claim 5, wherein: In step S5, if the hole inclination angle is similar to the stratum dip angle, and the up and down gamma curves are stable while drilling, and the cuttings show oil spot siltstone, the current hole inclination angle is kept stable.

7. The method of claim 6, wherein: In step S5, if the up and down gamma values have an increasing trend, the relative position of the drill bit and the sandstone needs to be judged, if the down gamma value rises first and the cuttings change to argillaceous siltstone, the hole inclination angle is increased, and if the up gamma value rises first and the cuttings change from siltstone to argillaceous siltstone, the hole inclination angle is decreased.

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