An inversion method for characterizing fractured-cavity reservoirs based on residual impedance

Abstract

The application provides an inversion method for characterizing faulted-dissolved reservoirs based on residual impedance. The background P-wave impedance value of the carbonate rock is obtained by analyzing the logging data of the drilled well, and a straight plate low-frequency P-wave impedance model of the carbonate rock is established; the straight plate low-frequency P-wave impedance model is used for constraint, and constraint sparse inversion is carried out to obtain a P-wave impedance body of the underground carbonate rock; then, the established straight plate low-frequency P-wave impedance model is subtracted from the P-wave impedance body obtained by the constraint sparse pulse inversion to obtain a residual impedance body; the residual P-wave impedance body is used for characterizing the distribution of the faulted-dissolved reservoirs by giving a residual impedance threshold value corresponding to the faulted-dissolved reservoirs.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, and in particular to an inversion method for characterizing fault-dissolved reservoirs based on residual impedance. Background Technology

[0002] In 2015, Lu Xinbian et al. proposed the concept of fault-knot traps, which mainly refer to the dissolution and modification of fracture zones by karst water seeping downwards or surging upwards along the fault direction, forming karst fracture-cavity systems in different three-dimensional spaces. These traps are formed under the cover of overlying marl or laterally dense limestone. For example, in the Tarim Basin, the outer slope area of ​​the Tahe River is influenced by the Upper Ordovician strata. The development of karst fracture-cavities shows a good match with fault zones and tectonic deformation, exhibiting obvious fault-controlled karst characteristics. Dissolution and expansion occur around deep, large fault zones, making this a favorable zone for the development of karst fracture-cavities in the Middle-Lower Ordovician strata. Guided by the fault-knot reservoir model, with the deepening of exploration and development, the Shunbei large-scale fault-knot type oil and gas field was discovered. Currently, the Shunbei oil and gas field has identified 18 strike-slip fault zones related to fault-knot development, with a resource scale of 17×10⁸ t oil equivalent, demonstrating the good exploration and development prospects of the Shunbei area.

[0003] Current research suggests that dissolution pores, cavities, and fractured reservoirs developed within carbonate strata exhibit low P-wave impedance characteristics. The more developed the reservoir, the lower its P-wave impedance value, and the greater the difference from the background P-wave impedance of carbonate rocks. The main reservoir spaces within fault-dissolved bodies are caves associated with strike-slip faults, high-angle tectonic fractures, and cavities formed by dissolution along fractures. These spaces are highly heterogeneous, distributed laterally along fault zones with segmentation, and longitudinally in a network pattern with irregularity. Seismically, they exhibit various reflection characteristics, including strong amplitude, weak amplitude, and chaotic reflections. Conventional seismic attributes and seismic inversion are insufficient to effectively characterize the internal reservoirs within fault-dissolved bodies. Existing seismic structural attributes such as structural tensors can characterize fault-dissolved body boundaries, but they suffer from insufficient resolution, making it difficult to effectively characterize the internal reservoir structure. Conventional seismic inversion also yields unsatisfactory prediction results for fault-dissolved reservoirs dominated by chaotic weak reflections.

[0004] For example, patent CN110794476B describes an inversion method based on fault-dissolved body phase control. This method primarily utilizes tensor properties to characterize the fault-dissolved body boundary, establishing a low-frequency model of the boundary. This low-frequency model is then incorporated into the conventional inversion process to obtain the wave impedance volume under the seismic phase control of the fault-dissolved body, thereby achieving a quantitative or semi-quantitative characterization of the "fault-dissolved body" reservoir and ultimately completing the effective reservoir quantification. However, this method only considers the external morphology of the fault-dissolved body and does not take into account the complex fracture-vuggy system within it.

[0005] Patent CN107390264B describes a method for characterizing the internal structure of carbonate fractured-dissolved bodies. This method primarily utilizes post-stack conventional inversion to obtain subsurface P-wave impedance data, determines the P-wave impedance data threshold representing fractured-vuggy reservoirs, and performs a hollowing-out process on the subsurface P-wave impedance data. It then calculates the tensor properties of seismic data, performs spatial smoothing on the tensor properties, determines the tensor property threshold representing the fractured region of the fractured-dissolved body, and obtains the contour of the fractured-dissolved body. Using the contour of the fractured-dissolved body as the boundary, the tensor properties and the subsurface P-wave impedance data are displayed within the contour, thus achieving the characterization of the external contour and internal structure of the fractured-dissolved body. This method uses P-wave impedance properties to characterize the porous reservoirs inside the fractured-dissolved body and tensor properties to characterize the external morphology of the fractured-dissolved body boundary. However, this invention uses properties of different dimensions to characterize the external morphology and internal structure of the fractured-dissolved body separately, and cannot characterize the spatial distribution and connectivity of the reservoirs inside the fractured-dissolved body.

[0006] Existing methods for characterizing reservoirs within fault-defect bodies are limited to the external morphology of the body, or they combine two seismic attributes—tensor and P-wave impedance—that reflect the external morphology and internal structure of the fault-defect body for different targets, to characterize its external morphology and internal structure. Due to the large dimensional differences between these attributes, they can only qualitatively reflect the external morphology and internal structure of the fault-defect body, and cannot quantitatively describe the spatial distribution of reservoirs within it. Summary of the Invention

[0007] To address the shortcomings of existing technologies in characterizing fracture-dissolve reservoirs, this invention proposes an inversion method based on residual impedance to characterize fracture-dissolve reservoirs. This method solves problems such as weak reflection energy within fracture-dissolve reservoirs and the difficulty in predicting fracture-vuggy systems, providing important evidence for the exploration and development of fracture-vuggy oil reservoirs.

[0008] In a first aspect, the present invention proposes an inversion method for characterizing the internal reservoir of a fractured solution based on residual impedance, comprising the following steps:

[0009] S1: Establish a low-frequency model of a straight carbonate rock plate using logging data from actual drilling.

[0010] S2: Using the low-frequency model of the carbonate rock straight plate obtained in step S1, constrained sparse pulse inversion is performed on the original seismic data to obtain subsurface P-wave impedance data.

[0011] S3: Subtract the underground P-wave impedance data obtained in step S2 from the low-frequency model of the carbonate rock straight plate obtained in step S1 to obtain the residual P-wave impedance data reflecting the fault-dissolved reservoir.

[0012] S4: Using the drilling results, determine the threshold value of the fault-dissolved reservoir corresponding to the remaining P-wave impedance data, and use the remaining P-wave impedance data obtained in step S3 to characterize the distribution of the fault-dissolved reservoir.

[0013] As a specific embodiment of the present invention, the step S1 of establishing a low-frequency model of a carbonate rock straight plate using logging data from actual drilling includes: using logging data from actual drilling, interpolating a low-frequency model using the P-wave impedance value of a single well for clastic rock formations, and establishing a low-frequency model of a carbonate rock straight plate by giving the P-wave impedance background value of the carbonate rock formation.

[0014] As a specific embodiment of the present invention, the P-wave impedance background value of the carbonate rock formation is obtained in step S1 by the following method: For the carbonate rock formation, a P-wave impedance histogram is established based on the P-wave impedance of the drilled wells, and the median value of the histogram is read as the unified impedance background value of the carbonate rock formation.

[0015] As a specific embodiment of the present invention, step S2 specifically includes: extracting seismic wavelets from carbonate rock strata through drilling and seismic calibration; inputting the seismic wavelets and the low-frequency model of carbonate rock straight plate established in step S1 into the constrained sparse pulse inversion software engine; performing seismic inversion to obtain subsurface P-wave impedance data.

[0016] As a specific embodiment of the present invention, step S3 specifically includes: subtracting the inverted longitudinal wave impedance data obtained in step S2 from the longitudinal wave impedance straight plate low-frequency model obtained in step S1 to obtain residual impedance data, which reflects the anomaly caused by the reservoir inside the fractured solution.

[0017] As a specific embodiment of the present invention, in step S4, based on the reservoir inside the fault-dissolved body encountered by the drilled well, the vertical position of the reservoir is determined by drilling and seismic calibration. This position corresponds to the residual impedance value obtained in step S3. The residual longitudinal impedance value is used as a threshold value to spatially characterize the spatial distribution of the reservoir inside the fault-dissolved body.

[0018] Secondly, the present invention provides the application of the inversion method for characterizing fractured solution reservoirs based on residual impedance in the field of heterogeneous reservoirs.

[0019] As a specific embodiment of the present invention, the heterogeneous strata include carbonate rocks, igneous rocks, salt bodies and / or sandstone lenses.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The inversion method for characterizing fractured-dissolved reservoirs based on residual impedance provided by this invention can characterize the spatial distribution of reservoirs within carbonate fractured-dissolved bodies. The residual impedance volume reflects the three-dimensional distribution of fractured-dissolved reservoirs, and can not only reflect the external morphology of the fractured-dissolved body, but also provide a good and intuitive characterization of the residual impedance exhibited by the fractures and cavities within the fractured-dissolved body.

[0022] 2. After the implementation of this invention, by spatial characterizing the remaining impedance body, drilling can be carried out on individuals with large scale and well-developed reservoirs, which can improve the production of single wells and development benefits.

[0023] 3. This invention has a wide range of applications. It is not only suitable for carbonate rock fractures, but also has good practicality for strata with significant spatial differences in longitudinal wave impedance, such as igneous rocks, salt bodies, and sandstone lenses. Attached Figure Description

[0024] Figure 1 This is a diagram illustrating the implementation steps of characterizing fractured solution reservoirs based on residual longitudinal wave impedance in an embodiment of the present invention.

[0025] Figure 2 This is a low-frequency model of a straight carbonate rock plate passing through the seismic profile of well A in Embodiment 1 of the present invention;

[0026] Figure 3 The data are the subsurface longitudinal wave impedance data of the low-frequency model of the straight plate model profile through well A in Embodiment 1 of the present invention;

[0027] Figure 4 This is the longitudinal wave impedance inversion profile of well A in Embodiment 1 of the present invention, showing the remaining longitudinal wave impedance of the fractured solution reservoir;

[0028] Figure 5 This is the residual longitudinal wave impedance profile through well A in Embodiment 1 of the present invention;

[0029] Figure 6 The maximum likelihood root mean square attribute of a certain three-dimensional region in Shunbei in Embodiment 1 of the present invention is T74_0_100ms.

[0030] Figure 7 This is the seismic profile through well B in Embodiment 1 of the present invention;

[0031] Figure 8 This is the longitudinal wave impedance inversion profile through well B in Embodiment 1 of the present invention;

[0032] Figure 9 This is the residual longitudinal wave impedance profile through well B in Embodiment 1 of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0034] Example

[0035] This embodiment provides an inversion method for characterizing fractured solution reservoirs based on residual impedance, such as... Figure 1 As shown, this method was applied to oil and gas exploration in a three-dimensional area of ​​the Ordovician carbonate rock fault-dissolved body in the Shunbei region of the Tarim Basin. Specific details are as follows:

[0036] The Ordovician Yijianfang Formation faults in a certain three-dimensional area of ​​Shunbei exhibit a northeast-southwest trend on the plane, such as... Figure 6 As shown, the fractured solution is distributed along the fracture zone. Currently, two wells, A and B, have been drilled for exploration of this fractured solution. The fractured solution reservoir is characterized using the inversion method of this invention.

[0037] Step 1: Using logging data from actual drilling, for clastic rock formations, interpolate the low-frequency model using the P-wave impedance value of a single well; for carbonate rock formations, given the P-wave impedance background value of the carbonate rock formation, establish a low-frequency model for a straight plate, such as... Figure 2 As shown, the seismic profile through well A shows that the boundary of the fault-dissolved body is blurred and there are "beaded" reflections inside the fault-dissolved body, which may be related to the cave-type reservoir. Figure 2 The boundaries of the interrupted melt are unclear, and the interior of the interrupted melt contains "beaded" reflections;

[0038] Step 2: Using a low-frequency model of a straight carbonate rock plate, constrained sparse pulse inversion is performed on the original seismic data to obtain subsurface P-wave impedance data, such as... Figure 3 As shown, the low-frequency impedance model below the T74 earthquake reflection layer is the background value of the P-wave impedance of carbonate rocks, while the low-frequency impedance model above it is the interpolated low-frequency impedance model of clastic rocks.

[0039] Step 3: Subtract the subsurface P-wave impedance data obtained in Step 2 from the low-frequency model of the carbonate rock straight plate obtained in Step 1 to obtain the residual P-wave impedance data reflecting the fault-collapsed reservoir, such as... Figure 4 As shown, the P-wave impedance profile is obtained by post-stack constrained sparse pulse inversion using a low-frequency model of a straight carbonate rock plate. Figure 4 The boundaries of the interrupted melt are unclear, and the "beaded" reflections inside the interrupted melt are relatively... Figure 3 More noticeably, the "beaded" reflections inside the fractured solution are significantly improved, but the boundaries of the fractured solution are blurred;

[0040] Step 4: Using the drilling results, determine the threshold value of the fault-collapsed solution reservoir corresponding to the remaining P-wave impedance, and use the remaining P-wave impedance volume to characterize the distribution of the fault-collapsed solution reservoir, such as... Figure 5 As shown, Figure 5 It visually reflects the outline of the fractured solution and the longitudinal and lateral distribution of the fracture-vuggy reservoir system inside the fractured solution. The darker the color, the greater the residual impedance value, reflecting better reservoir properties. The residual impedance results show that the boundary of the fractured solution is clear, and the longitudinal and lateral distribution and connectivity of the fracture-vuggy reservoir system inside the fractured solution are obvious.

[0041] Well A's bottom is located at the edge of the fractured solution characterized by residual impedance. During drilling, mud loss occurred at the bottom of the well, which may have led to the encounter of a fractured reservoir within the fractured solution, ultimately resulting in high-yield oil and gas production, which matches the reservoir predicted by residual impedance.

[0042] like Figures 6-9 As shown, well B is located southwest of well A. Figure 7 Seismic profile of well B and Figure 8 The impedance profile obtained from conventional inversion shows that the boundaries of the fractured solution and the reservoir inside the fractured solution are unclear, while Figure 9 The residual impedance profile shows that the boundaries of the fractured solution and the reservoir inside the fractured solution are clear, and the fractured-vuggy reservoir is longitudinally and laterally connected.

[0043] During drilling, Well B experienced a venting near the bottom of the well and encountered a cavern. This location was exactly in the predicted reservoir development area. The well eventually achieved a high-yield oil flow during testing, and the actual drilling results matched the prediction.

[0044] In summary, the inversion method for characterizing fractured-dissolved reservoirs based on residual impedance of the present invention can characterize the spatial distribution of reservoirs inside carbonate fractured-dissolved bodies, intuitively characterize the development scale of reservoirs inside fractured-dissolved bodies, provide a reliable basis for well location deployment for efficient exploration and development, and improve exploration and development efficiency.

[0045] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0046] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. An inversion method for characterizing the internal reservoir of a fractured solution based on residual impedance, characterized in that, Includes the following steps: S1: Establish a low-frequency model of a carbonate rock straight plate using logging data from actual drilling. Step S1 involves: using logging data from actual drilling, interpolating the low-frequency model using the P-wave impedance value of a single well for clastic rock formations; and establishing a low-frequency model of a carbonate rock straight plate given the P-wave impedance background value of the carbonate rock formation. The P-wave impedance background value of the carbonate rock formation is obtained in step S1 using the following method: for carbonate rock formations, a P-wave impedance histogram is established based on the P-wave impedance of drilled wells, and the median value of the histogram is used as the unified impedance background value for the carbonate rock formation. S2: Using the low-frequency model of the carbonate rock straight plate obtained in step S1, constrained sparse pulse inversion is performed on the original seismic data to obtain subsurface P-wave impedance data. S3: Subtract the underground P-wave impedance data obtained in step S2 from the low-frequency model of the carbonate rock straight plate obtained in step S1 to obtain the residual P-wave impedance data reflecting the fault-collapsed reservoir. S4: Using the drilling results, determine the threshold value of the fault-dissolved reservoir corresponding to the remaining P-wave impedance data. Use the remaining P-wave impedance data obtained in step S3 to characterize the distribution of the fault-dissolved reservoir. In step S4, based on the fault-dissolved reservoir encountered in the drilled well, determine the vertical position of the reservoir through drilling and seismic calibration. This position corresponds to the remaining impedance value obtained in step S3. Use the remaining P-wave impedance value as the threshold value to characterize the spatial distribution of the reservoir inside the fault-dissolved reservoir in space.

2. The inversion method according to claim 1, characterized in that, Step S2 specifically includes: extracting seismic wavelets from carbonate rock strata through drilling and seismic calibration; inputting the seismic wavelets and the low-frequency model of the carbonate rock straight plate established in step S1 into the constrained sparse pulse inversion software engine; performing seismic inversion to obtain subsurface P-wave impedance data.

3. The inversion method according to claim 1 or 2, characterized in that, The specific steps of step S3 include: subtracting the inverted longitudinal wave impedance data obtained in step S2 from the longitudinal wave impedance straight plate low-frequency model obtained in step S1 to obtain the residual impedance data, which reflects the anomaly caused by the reservoir inside the fractured solution.

4. The application of the inversion method according to any one of claims 1-3 in the field of heterogeneous strata.

5. The application according to claim 4, characterized in that, The heterogeneous strata include carbonate rocks, igneous rocks, salt bodies, and / or sandstone lenses.

Images