Comparative division method for clastic rock buried hill strata

Abstract

The invention relates to the technical field of oil-gas exploration, in particular to a clastic rock buried hill stratum comparison and division method. A clastic rock buried hill stratum comparison and division method comprises the following steps that S1, the structure background of a buried hill in a target area is known, and single-well rock stratum analysis is carried out with stratigraphy as guidance; s2, on the basis of collected single well, well connection and seismic datum plane recognition, cycle analysis of lithology, rock electricity and seismic response is carried out, and well connection and seismic stratigraphic comparison is carried out; s3, in combination with the comparison result of the lithology combination, the rock electricity combination and the seismic response characteristics, the difference of the drilling reveal strata series characteristics between different areas is determined, and a sedimentary reference plane with obvious characteristics and typical phenomena is found according to the comparison result; s4, step-by-step comparison is carried out on the target horizon according to the development characteristics of the strata series between the regions, the preservation condition of each strata series is determined, well-connected rock stratigraphic comparison and division are completed, and a stratigraphic framework is established.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploration, and in particular to a comparative division method of clastic rock buried hill strata. Background Art

[0002] Although there are some methods for comparing and dividing clastic buried hill strata, such as according to the basic principles of stratigraphy, geologists will consider the properties, sequence and changes of rocks, as well as the environmental conditions of deposition. This may include observations of rock color, texture, structure, mineral composition, etc. Some scholars also compare buried hill strata with strata in surrounding areas or other places to establish the consistency and correlation of stratigraphic sequences. This helps to identify stratigraphic changes and connections between different regions.

[0003] U-Pb zircon crystallization age dating and apatite fission track annealing age can also be used. Considering the fossils found in different strata, especially microfossils and macrofossils, they can provide clues to the relative age and sedimentary environment of the strata. Using geophysical methods such as seismic reflection, gravity anomalies, and magnetic anomalies can help researchers obtain underground structural information, so as to better understand the distribution and characteristics of the strata.

[0004] However, clastic buried-hill strata involve a variety of complex geological processes, such as sedimentation, tectonic movement, erosion, etc. The interaction of these processes makes stratigraphic correlation more complicated. Clastic buried-hill strata often undergo complex geological movement transformation, poor preservation conditions, poor seismic imaging effects, and less drilling data, making stratigraphic correlation and division particularly difficult. In particular, after experiencing complex geological movements, the occurrence of clastic buried-hill strata frequently changes, which is quite different from the burial law of conventional clastic strata. On the one hand, it is reflected in the completely changed original occurrence, and on the other hand, it is reflected in the lack of signs for stratigraphic division and correlation. Current exploration practice shows that clastic buried-hill has rich oil and gas resources and great exploration potential. Accurate comparison and division of strata is the premise of oil and gas exploration and the basis of geological research. Therefore, it is necessary to establish a method that can accurately and efficiently compare and divide clastic buried-hill strata. Summary of the invention

[0005] The purpose of the present invention is to provide a comparative division method of clastic buried hill strata, so as to solve the problem that the clastic buried hill strata cannot be accurately compared and divided due to insufficient research data.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A comparative division method for clastic rock buried hill strata comprises the following steps: S1, understand the tectonic background of the buried hill in the target area, identify the unconformity surface data of the target area in combination with the regional geological background data of the area, and conduct single well rock stratigraphic analysis guided by stratigraphy; S2, based on the identification of the collected single well, well-connected and seismic datum surfaces, the bottom interface of the selected wells will be uniformly calibrated to be on the same relative horizontal plane. After calibration, the lithology, rock electricity and seismic response cycle analysis will be carried out from the bottom to the top of the same bottom interface, and the well-connected and seismic stratigraphic comparison will be carried out; S3, combined with the comparison results of lithology, rock-electricity combination and seismic response characteristics, identify typical wells with relatively complete strata and less denudation, compare the typical wells with other wells in the target area, clarify the differences in strata characteristics revealed by drilling in different areas, and find the sedimentary base surface with more obvious characteristics and more typical phenomena based on the comparison results; S4. Based on the comprehensive development characteristics of the inter-regional stratigraphic systems and the restoration of the denuded stratigraphic systems, a comprehensive columnar diagram of typical sequence stratigraphy in each region is established to complete the stratigraphic comparison and division between the clastic rock buried-hill areas. The base level is flattened and, with the base level as a reference, a step-by-step comparison of the target strata is carried out to clarify the preservation status of each stratum, complete the comparison and division of the rock stratigraphy of the connected wells, and establish a stratigraphic framework.

[0007] A further technical solution is that, in said S1, the unconformity surface data include sedimentology, paleontology, base value changes of logging curves, natural energy spectrum logging, natural potential and resistivity curves, and seismic markers.

[0008] A further technical solution is that, in S2, cycles are identified by observing sedimentary features in rock strata.

[0009] A further technical solution is that the sedimentary characteristics include rock type, color, texture, structure, fossil combination and other sedimentological characteristics.

[0010] Compared with the prior art, the present invention has the following beneficial effects: The present invention can overcome the difficulty of changing the original occurrence of clastic buried hill strata affected by tectonic movement without requiring too much production data, and can also accurately compare the rock electrical characteristics of the sedimentary process to find out the corresponding relationship between clastic buried hill strata by comparing between strata. In addition, on the basis of stratum comparison, it can also guide sedimentological research, guide favorable reservoir prediction, and provide basic geological basis for oil and gas exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a layer flattening diagram of the clastic rock buried hill stratum in the present invention. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0013] Figure 1 This is an embodiment of the present invention.

[0014] Example 1 A comparative division method for clastic rock buried hill strata comprises the following steps: S1. Understand the tectonic background of the buried hill in the target area. Combined with the regional geological background data of the area, identify the unconformity surface data such as sedimentology, paleontology, base value changes of well logging curves, natural energy spectrum logging, natural potential and resistivity curves, and seismic markers in the target area. Guided by stratigraphy, conduct single well rock stratigraphic analysis.

[0015] Furthermore, from the perspective of sedimentology, an ancient weathering crust formed by the accumulation of residual materials after long-term weathering has developed on the outcrops in the target area. The surface may also be exposed due to sea level drop and tectonic uplift, encountering weathering and erosion, forming an ancient karst action surface, and karstification and landslides occur near the interface. At the same time, in the drilling and outcrops, the lithology, color, structure, sedimentary structure and lithofacies combination of rocks suddenly change above and below the unconformity surface.

[0016] Furthermore, from the perspective of paleontology, the environment has a strong influence on organisms, and its zoning characteristics are related to the depth of the water body. The mutation of the type and number of paleontology often indicates a change in the sedimentary environment, indicating that there has been a sedimentary interruption or stratum missing at the mutation site, which can be used as a method to identify unconformities. Taking the palynological assemblage as an example, the types of palynological assemblage zones in strata of different ages are also different.

[0017] Furthermore, the unconformity surface can be identified by the change in the base value of the logging curve. Since the lithology, diagenesis and compaction of the strata above and below the unconformity surface are very different, the place where the amplitude, shape and sharpness of various logging curves change suddenly is the unconformity interface.

[0018] Furthermore, in natural energy spectrum logging, the natural gamma intensity is determined by the enrichment of radioactive elements U, K, and Th, so the values ​​of U, Th, and K also have mutations at the unconformity surface. In particular, the enrichment of Th and K is related to clay minerals. A more accurate way to identify unconformity is to calculate the Th / K value, because the Th / K value is inversely proportional to the ancient water depth of deposition. The larger the ratio, the shallower the ancient water depth. When Th / K>7, it means it is in an exposed environment.

[0019] Furthermore, for the natural potential and resistivity curves, if bottom conglomerate is developed under the unconformity, the natural potential curve will deviate from the baseline at the interface and undergo a mutation, and the resistivity curve will generally show a spike-shaped positive anomaly at the interface; if karstification or leaching occurs under the unconformity, resulting in good porosity and connectivity of the stratum, then due to the high fluid content in the pores, a negative abnormal mutation will appear in the resistivity curve at the interface; if the unconformity is a sedimentary cycle conversion interface, the natural potential and resistivity curves at the interface will be a "box-shaped" shape indicating accumulation or a "bell-shaped" shape indicating retroaccretion.

[0020] Furthermore, seismic signs can be used to identify different types of unconformities through their reflection termination morphology on seismic sections. When erosion, truncation, and top overlap occur, it indicates an obvious exposure discontinuity, and the corresponding sequence interface is called "terrestrial unconformity" or "erosion-type unconformity"; when the reflection termination morphology appears on top or on the bottom, it means that the sea level or lake level is relatively rising or static, and the corresponding sequence interface is a sedimentary unconformity; when salt diapir appears in the seismic morphology, it is mostly a tectonic unconformity. After judging the reflection termination morphology, according to the differences in external morphology, internal characteristics, and seismic attributes shown on the seismic section, combined with the sedimentary facies belt in which it is located, different seismic phases can be identified and divided, and further seismic sequence division and sedimentary environment identification can be carried out.

[0021] Furthermore, the external shapes include sheet-like, plate-like, wedge-like, etc., the internal characteristics include parallel reflection, sub-parallel reflection, blank reflection and chaotic reflection, and the seismic attributes include the size of the seismic amplitude, the strength of the frequency, the degree of continuity, etc.

[0022] S2, based on the identification of the collected single wells, well connections and seismic datums, the bottom interface of the selected wells will be uniformly calibrated to be on the same relative horizontal plane. After calibration, the lithology, rock electricity and seismic response cycle analysis will be carried out from the same bottom interface from bottom to top, and well connection and seismic stratigraphic comparison will be carried out.

[0023] Further, potential cycles are identified by observing sedimentary features in rock formations. These features include rock type, color, texture, structure, fossil assemblages, and other sedimentological features. Identify repetitive patterns. Look for repetitive patterns in the target formations, which may indicate alternations or periodic changes in sedimentary environments. For example, a continuous sequence of mudstone, sandstone, and shale may indicate an alternation between terrestrial and marine environments, which may be a sign of a cycle. Examine discontinuities between formations, such as unconformities, erosional surfaces, or metamorphic surfaces. These discontinuities may represent hiatuses between cycles or transitions between different sedimentary environments. Use stratigraphic sequence analysis methods to study the connections and evolution between different formations. This includes the interpretation of inter-stratigraphic connections, the construction of stratigraphic sequences, and the reconstruction of sedimentary environments. Finally, based on the observed geological evidence and the analysis results of the stratigraphic sequence, a cycle model is developed, which divides the stratigraphic sequence into different cyclic units. These cyclic units can be named and described based on factors such as sedimentary environment, sedimentary features, and inter-stratigraphic discontinuities.

[0024] S3. Combined with the comparative results of lithologic combinations, rock-electric combinations, and seismic response characteristics, identify typical wells with relatively complete strata and less denudation, compare the typical wells with other wells in the target area, clarify the differences in stratum characteristics revealed by drilling between different areas, and find the sedimentary base surface with more obvious characteristics and more typical phenomena based on the comparative results.

[0025] Furthermore, in terms of lithologic combinations, the formation methods or processes of different types and percentages of lithologies or lithologic combinations are not almost the same. For example, large sets of massive coarse clastic sandstone, large sets of massive mudstone, or interlayers of thin sandstone and mudstone can all be used as effective identification marks for stratigraphic correlation.

[0026] Furthermore, in terms of rock-electric combination, logging curves of different lithologies (combinations) have different logging curve shapes. Several common logging curve shapes include bell-shaped, box-shaped, funnel-shaped, high-amplitude tooth-shaped, low-amplitude tooth-shaped, etc. By comparing these basic shapes and their combinations among wells, effective stratigraphic comparison can be carried out.

[0027] Furthermore, in terms of seismic response characteristics, seismic response characteristics are the geophysical characteristics of various types of rocks in the area, which mainly include five basic characteristics, such as amplitude, frequency, continuity, external geometry and internal reflection configuration. Based on the detailed description of the above five elements, by comparing the seismic response element characteristics between different regions, the comparative division of strata or strata can be completed more accurately.

[0028] Based on the analysis of lithologic combinations, rock-electric combinations, and seismic response characteristics, a datum plane for stratigraphic correlation is determined. Its main characteristics are that it has typical lithologic, rock-electrical or seismic response characteristics that can be used for regional correlation, such as widely developed coal-bearing strata, regionally stably distributed mudstone layers, or well logging curves with special morphology, such as the high-Foshan finger shape that appears in the large set of teeth, or the large reflection that appears in the amplitude stability curve, all of which can serve as a good basis for datum plane identification.

[0029] S4. Based on the comprehensive development characteristics of the inter-regional stratigraphic systems and the restoration of the denuded stratigraphic systems, a comprehensive columnar diagram of typical sequence stratigraphy in each region is established to complete the stratigraphic comparison and division between the clastic rock buried-hill areas. The base level is flattened and, with the base level as a reference, a step-by-step comparison of the target strata is carried out to clarify the preservation status of each stratum, complete the comparison and division of the rock stratigraphy of the connected wells, and establish a stratigraphic framework.

[0030] Furthermore, combined with the existing information on lithologic combinations, rock-electric combinations, seismic response characteristics, etc., a typical sequence stratigraphic comprehensive columnar diagram is drawn, and the lithologic characteristics, logging curve shapes, cyclic characteristics, etc. corresponding to different depths are marked on the diagram. Combined with the previously determined stratigraphic comparison base plane, the clastic buried-hill strata with different occurrences in the study area are flattened. After the layers are flattened, the lithologic combinations, rock-electric combinations, and cyclic characteristics of the strata in the clastic buried-hill area are compared, which can more intuitively identify the differences between different bottom layers.

[0031] Although the present invention is described herein with reference to a number of illustrative embodiments of the present invention, it will be appreciated that those skilled in the art may devise many other modifications and implementations that fall within the scope and spirit of the principles disclosed herein. More specifically, within the scope of the drawings and claims disclosed herein, a variety of variations and modifications may be made to the components and / or layout of the subject combination layout. In addition to the variations and modifications made to the components and / or layout, other uses will also be apparent to those skilled in the art.

Claims

1. A comparative division method for clastic buried hill strata, characterized by: The following steps are involved: S1, understand the tectonic background of the buried hill in the target area, identify the unconformity surface data of the target area in combination with the regional geological background data of the area, and conduct single well rock stratigraphic analysis guided by stratigraphy; S2, based on the identification of the collected single well, well-connected and seismic datum surfaces, the bottom interface of the selected wells will be uniformly calibrated to be on the same relative horizontal plane. After calibration, the lithology, rock electricity and seismic response cycle analysis will be carried out from the bottom to the top of the same bottom interface, and the well-connected and seismic stratigraphic comparison will be carried out; S3, combined with the comparison results of lithology, rock-electricity combination and seismic response characteristics, identify typical wells with relatively complete strata and less denudation, compare the typical wells with other wells in the target area, clarify the differences in strata characteristics revealed by drilling in different areas, and find the sedimentary base surface with more obvious characteristics and more typical phenomena based on the comparison results; S4. Based on the comprehensive development characteristics of the inter-regional stratigraphic systems and the restoration of the denuded stratigraphic systems, a comprehensive columnar diagram of typical sequence stratigraphy in each region is established to complete the stratigraphic comparison and division between the clastic rock buried-hill areas. The base level is flattened and, with the base level as a reference, a step-by-step comparison of the target strata is carried out to clarify the preservation status of each stratum, complete the comparison and division of the rock stratigraphy of the connected wells, and establish a stratigraphic framework.

2. The comparative division method of clastic rock buried hill strata according to claim 1 is characterized by: In the S1, the unconformity surface data include sedimentology, paleontology, changes in base value of logging curves, natural energy spectrum logging, natural potential and resistivity curves, and seismic marks.

3. The comparative division method of clastic rock buried hill strata according to claim 1 is characterized by: In said S2, cycles are identified by observing sedimentary features in the rock formations.

4. The comparative division method of clastic rock buried hill strata according to claim 3 is characterized by: The sedimentary characteristics include rock type, color, texture, structure, fossil assemblages and other sedimentological features.

Images