CN106988737B - Method for identifying sedimentary facies by utilizing lithology combination - Google Patents
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- 208000035126 Facies Diseases 0.000 title claims abstract description 66
- 238000000034 method Methods 0.000 title claims abstract description 32
- 230000008021 deposition Effects 0.000 claims abstract description 39
- 230000004069 differentiation Effects 0.000 claims abstract description 22
- 238000011160 research Methods 0.000 claims abstract description 21
- 238000012545 processing Methods 0.000 claims abstract description 5
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- 238000004062 sedimentation Methods 0.000 claims description 7
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- 230000001590 oxidative effect Effects 0.000 claims description 3
- 239000010410 layer Substances 0.000 description 48
- 238000004364 calculation method Methods 0.000 description 9
- 230000009286 beneficial effect Effects 0.000 description 8
- 239000000463 material Substances 0.000 description 6
- 238000007254 oxidation reaction Methods 0.000 description 6
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- 238000004458 analytical method Methods 0.000 description 4
- 230000005484 gravity Effects 0.000 description 4
- 238000005553 drilling Methods 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 239000002356 single layer Substances 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000003921 oil Substances 0.000 description 2
- 239000005416 organic matter Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- MBMLMWLHJBBADN-UHFFFAOYSA-N Ferrous sulfide Chemical compound [Fe]=S MBMLMWLHJBBADN-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000001364 causal effect Effects 0.000 description 1
- 229910001919 chlorite Inorganic materials 0.000 description 1
- 229910052619 chlorite group Inorganic materials 0.000 description 1
- QBWCMBCROVPCKQ-UHFFFAOYSA-N chlorous acid Chemical compound OCl=O QBWCMBCROVPCKQ-UHFFFAOYSA-N 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
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- 239000010419 fine particle Substances 0.000 description 1
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- 229910052595 hematite Inorganic materials 0.000 description 1
- 239000011019 hematite Substances 0.000 description 1
- 229910052900 illite Inorganic materials 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 description 1
- 239000002480 mineral oil Substances 0.000 description 1
- 235000010446 mineral oil Nutrition 0.000 description 1
- VGIBGUSAECPPNB-UHFFFAOYSA-L nonaaluminum;magnesium;tripotassium;1,3-dioxido-2,4,5-trioxa-1,3-disilabicyclo[1.1.1]pentane;iron(2+);oxygen(2-);fluoride;hydroxide Chemical compound [OH-].[O-2].[O-2].[O-2].[O-2].[O-2].[F-].[Mg+2].[Al+3].[Al+3].[Al+3].[Al+3].[Al+3].[Al+3].[Al+3].[Al+3].[Al+3].[K+].[K+].[K+].[Fe+2].O1[Si]2([O-])O[Si]1([O-])O2.O1[Si]2([O-])O[Si]1([O-])O2.O1[Si]2([O-])O[Si]1([O-])O2.O1[Si]2([O-])O[Si]1([O-])O2.O1[Si]2([O-])O[Si]1([O-])O2.O1[Si]2([O-])O[Si]1([O-])O2.O1[Si]2([O-])O[Si]1([O-])O2 VGIBGUSAECPPNB-UHFFFAOYSA-L 0.000 description 1
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- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
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- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
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Abstract
The invention relates to a method for identifying sedimentary facies by utilizing lithology combination, which comprises the following steps: s1, collecting and processing lithology combination indexes of the research interval; s2, judging the deposition environment by using the mudstone color index; s3, judging a sedimentary facies belt by using the mudstone thickness index; s4, judging the source stability by using the sandstone thickness differentiation degree; s5, judging the lithology of the study layer interval by using the lithology index; s6, judging the hydrodynamic strength by using the sandstone grade index; s7, judging granularity dissimilarity by using the sandstone granularity dissimilarity index; s8, judging the source strength by using the sandstone thickness index; s9, for the steps S2 to S8, narrowing the scope of the sedimentary facies step by step according to the obtained combination index of the lithology of the research layer so as to judge the sedimentary facies; wherein the step S2 to the step S8 have no sequence.
Description
Technical Field
The invention relates to the technical field of mineral oil and gas resource exploration, in particular to a method for identifying a sedimentary facies by utilizing lithological combination.
Background
A sedimentary facies is a complete picture of a part of the earth's surface over a certain geological time and is a combination of the sedimentary environment and the sedimentary rock (material) features formed in that environment. Oil and gas exploration can deduce the type and series of adjacent areas in the transverse direction according to the sedimentary facies sequence appearing in the vertical direction, and provides basis for optimizing a powerful target area. The sedimentary facies identification mode can be comprehensively judged through data such as field outcrop, rock core, logging, earthquake and the like, but the evaluation mode often excessively depends on the research experience of researchers, belongs to qualitative analysis, and the research period is too long, so that the sedimentary facies identification work of old oil fields becomes complicated, and the workload is large.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for identifying sedimentary facies by utilizing lithological combination, which can describe the sedimentary environment and sedimentary characteristics of a research layer section by counting mudstone color index, mudstone thickness index, sandstone thickness diversity factor, lithological index, sandstone grade diversity factor and sandstone thickness index related to the lithological combination, and further comprehensively judge the sedimentary facies.
The technical scheme for solving the technical problems is as follows: a method for identifying dephasing using lithological combinations, comprising the steps of: s1, collecting and processing lithology combination indexes of the research interval; s2, judging the deposition environment by using the mudstone color index; s3, judging a sedimentary facies belt by using the mudstone thickness index; s4, judging the source stability by using the sandstone thickness differentiation degree; s5, judging the lithology of the study layer interval by using the lithology index; s6, judging the hydrodynamic strength by using the sandstone grade index; s7, judging granularity dissimilarity by using the sandstone granularity dissimilarity index; s8, judging the source strength by using the sandstone thickness index; s9, for the steps S2 to S8, narrowing the scope of the sedimentary facies step by step according to the obtained combination index of the lithology of the research layer so as to judge the sedimentary facies; wherein the step S2 to the step S8 have no sequence.
The invention has the beneficial effects that: and after collecting and processing the lithological combination data of the research layer, further analyzing the multi-representative geological significance of different lithological combination indexes by defining and counting the lithological combination indexes of each layer, and realizing quantitative judgment of the four-level sequence stratified sedimentary combination and the five-level sequence stratified sedimentary combination.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, the method for identifying the sedimentary facies by using the lithology combination includes the steps of determining the lithology combination index through the lithology logging information in step S1, obtaining well position layered data according to the logging information, correcting the sand-shale thickness and the initial interface in the lithology logging information according to the logging curve characteristics, and finally obtaining the lithology combination index of the well position.
The beneficial effect of adopting the further scheme is that: the lithological combination index is based on logging data, the logging data often do not accord with the actual situation in the actual acquisition process, and the logging data can basically discharge artificial influence.
Further, in the method for identifying sedimentary facies by using lithology combination, in step S2, the mudstone color index IciIs defined as
H in formula (1)dgIs the thickness of dark grey mudstone; hgrThickness of grey mudstone; hgGreen mudstone thickness; hprIs red purple brown mudstone thickness; hmIs the mudstone thickness;
in step S3, mudstone thickness index (number of layers of 100m mudstone) ImiIs defined as
N in formula (2)msThe total number of layers of the mudstone; hmThe total thickness of the mudstone;
sandstone thickness differentiation degree I in step S4sdIs defined as
H in formula (3)ssThe average thickness of the siltstone; hfThe average thickness of the fine sandstone; hmsThe average thickness of the medium sandstone; hgThe average thickness of the coarse sandstone; hatIs the average thickness of the sandstone;
lithology index I in step S5lIs defined as:
h in formula (4)mIs the mudstone thickness; hasThe thickness of the argillaceous sandstone; hsIs the thickness of sandstone; hstIs the formation thickness;
sandstone grade index I in step S6fIs defined as:
h in formula (5)ssIs the thickness of the siltstone; hfIs the thickness of the fine sandstone; hmsIs the thickness of the medium sandstone; hgIs the thickness of the coarse sandstone;
particle fraction differentiation degree index I in step S7dIs defined as
α in equation (6)ssα weight percent of siltstone in sandstonefα weight percent of fine sandstonemsα is the percentage of medium sandstone in sandstonegThe percentage of the medium sandstone in the sandstone is shown;
sandstone thickness index (number of sandstone layers of 100 m) I in step S8stIs defined as
N in formula (7)sThe total number of layers of the sandstone; hssIs the thickness of the siltstone; hfIs the thickness of the fine sandstone; hmsIs the thickness of the medium sandstone; hgIs the thickness of the coarse sandstone.
The beneficial effect of adopting the further scheme is that: and defining each lithology combination index, and quantitatively describing the lithology combination information of the research layer interval by using the 7 lithology combination indexes to provide a basis for quantitatively identifying sedimentary facies and sedimentary facies combination.
Further, in the method for identifying the sedimentary facies by using the lithological combination, in the step S2, the mudstone color index less than 0.1 represents a strong reduction environment, the mudstone color index less than 0.3 and not more than 0.1 represents a weak reduction environment, the mudstone color index less than 0.6 and not more than 0.3 represents a weak oxidation environment, and the mudstone color index more than or equal to 0.6 represents a strong oxidation environment.
The beneficial effect of adopting the further scheme is that: and judging the redox environment of the research layer section by using the mudstone color index, and reducing the possible sedimentary phase combination range.
Further, according to the method for identifying sedimentary facies by using lithology combination, in the step S3, the mudstone thickness index is less than 15, and a deep lake sedimentary facies zone appears; 15 or more than or equal to mud rock thickness index of less than 30, and a half-deep lake sedimentary facies zone appears; the mudstone thickness index is more than or equal to 30, and a sedimentary facies belt of the shoa lake appears.
Further, in the method for identifying the sedimentary facies by using the lithological combination, when the sandstone thickness diversity factor is less than 2 and greater than 0 in the step S4, the sedimentary interval has both a coarse sand layer and a fine sand layer and has the characteristic of sudden change; when the sandstone thickness diversity factor is larger than 2, sandstone with certain lithologic thickness in the sedimentary interval is dominant, and the sedimentary environment is quiet.
The beneficial effect of adopting the further scheme is that: and (3) judging the abrupt change or quiet deposition environment of the study layer section by using the sandstone thickness differentiation degree to distinguish a gravity flow deposition system and a traction flow deposition system.
Further, in the method for identifying the sedimentary facies by using the lithology combination, the lithology index is more than or equal to 0.75 in the step S5 and represents a sand-rich mold; the lithology index is more than or equal to 0.5 and less than 0.75, and represents the sand type; the lithological index is more than or equal to 0.25 and less than 0.5, and represents a sand-containing mold; lithology index <0.25, representing a lean sand mold.
The beneficial effect of adopting the further scheme is that: the lithology combination index is used for judging the relation between the sedimentary region and the source, and the sedimentary facies selection range can be further narrowed by comparing sedimentary facies which may appear in different lithology indexes.
Further, in the method for identifying sedimentary facies by using lithology combination, when the sandstone granularity index is greater than 0.5 in step S6, the method represents a strong hydrodynamic sedimentary environment; sandstone grade index less than 0.5 represents a relatively quiet sedimentary environment.
The beneficial effect of adopting the further scheme is that: and under the condition of traction flow control, reflecting the hydrodynamic condition for carrying the debris substances in the sedimentation process by using the sandstone grade index, and further screening the possibly occurring sedimentary phases according to the strength of the hydrodynamic condition.
Further, in the method for identifying sedimentary facies by using lithology combination, when the sandstone particle fraction differentiation index is less than 0.5 in step S7, rapid sedimentation is represented; when the particle size fraction index is more than 0.5, the drawing flow sedimentation characteristic is realized.
The beneficial effect of adopting the further scheme is that: the sandstone granularity differentiation degree is used for judging the distance of the source, a near-shore near-source fan body is easily formed under the condition of the near source, and a mud-rich sedimentary phase is easily formed far away from the source region.
Drawings
FIG. 1 is a flow chart of the steps of the present invention;
FIG. 2 is a flow chart of a deposition phase combination and a deposition phase identification according to an embodiment of the present invention.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
The material components of the land-based lake basin land-based clastic deposition system mainly comprise clastic substances such as sand, silt, clay and the like, the classification of the currently common deposition system is mainly based on the natural geographic conditions which dominate in the deposition environment, and in practical application, the land-based clastic rock deposition system can be divided into a alluvial fan system, a flood fan system, a river system, a delta system, a braided river delta system, a fan delta system, a gravity flow system and a lake system by combining deposition kinetics, deposition characteristics and other deposition conditions, wherein each deposition system comprises a plurality of deposition phases and deposition phases, as shown in table 1.
TABLE 1 continental clastic rock sedimentary system
Comprehensively judging the sedimentary facies to which the research horizon belongs by extracting lithology characteristics, hydrodynamic conditions, granularity anisotropy, source strength, source stability, sedimentary environment and sedimentary facies band information contained in the lithology combination index, and specifically comprising the following steps of:
and S1, collecting and processing the lithology combination index of the research interval.
And S2, judging the deposition environment by using the mudstone color index.
And S3, judging the sedimentary facies belt by using the mudstone thickness index.
And S4, judging the stability of the source by using the sandstone thickness differentiation degree.
And S5, judging the lithology of the research interval by using the lithology index.
And S6, judging the hydrodynamic strength by using the sandstone grade index.
And S7, judging granularity differential by using the sandstone granularity differential index.
And S8, judging the source strength by using the sandstone thickness index.
S9, for the steps S2 to S8, narrowing the scope of the sedimentary facies step by step according to the obtained combination index of the lithology of the research layer so as to judge the sedimentary facies; wherein the step S2 to the step S8 have no sequence.
The step S2 to the step S8 have no sequence, and are determined according to the specific situation of the research layer.
In step 1), the lithology logging data is one of the main technical methods for determining the lithology combination index, and is limited by the accuracy of the logging data, and the lithology logging data is often corrected according to the logging curve.
Specifically, the lithology logging data is a main data source for determining lithology combination characteristics, but the lithology logging data is influenced by factors such as tripping, single joint jointing, drilling coring, drilling time, drilling fluid circulation flow and the like, so that the resolution of the logging data is reduced, and therefore the logging data needs to be corrected through the logging and coring data. In the process of identifying a sedimentary facies of a certain well, three-level and four-level layering of the well position are obtained according to logging information, the thickness of sand shale in the lithology logging information and an initial interface are corrected according to the characteristics of a logging curve, and finally the lithology combination index of the well is obtained.
And (5) carrying out statistics on basic information of the sand-shale. The lithological combination index is calculated according to the basic information of the sand and the mudstone in the lithological combination section, and is specifically divided into the basic information of the sand and the mudstone, and the two types of data are obtained through a statistical method.
The sandstone basic information comprises sandstone thickness, sandstone layer number, conglomerate thickness, conglomerate layer number, medium sandstone thickness, medium sandstone layer number, fine sandstone thickness, fine sandstone layer number, siltstone thickness, siltstone layer number and the like. The sandstone basic information of the well section is found through statistics, the well does not develop a conglomerate section, and the sandstone basic information is shown in table 2.
TABLE 2 sandstone basic information in each layered section of a well
The sandstone thickness and the sandstone layer number in table 2 respectively represent the total thickness and the total layer number of the layer in which the sandstone layer is located.
The mudstone basic information comprises stratum thickness, mudstone layer number, red-purple-brown mudstone thickness, green mudstone thickness, gray mudstone thickness, dark mudstone thickness, oil shale thickness and the like. The mudstone base statistics for this well are shown in table 3.
TABLE 3 mudstone foundation information in each layered section of a well
And calculating a mudstone color index, a mudstone thickness index, a sandstone thickness differentiation degree, a lithology parameter, a sandstone grade differentiation degree and a sandstone thickness index of each layered section according to the sand mudstone basic information obtained by statistics. The calculation method is shown below by taking the second hole segment as an example:
in step S2, mudstone color index IciIs defined as
H in formula (1)dgIs the thickness of dark grey mudstone; hgrThickness of grey mudstone; hgGreen mudstone thickness; hprIs red purple brown mudstone thickness; hmIs the mudstone thickness.
The mudstone color index is used to evaluate the depositional environment of the study interval. Red and brown mudstones tend to contain oily iron cladding, representing an oxidative deposition environment. The green mudstone contains chlorite and illite, is lack of hematite, organic matter and sulfide and represents a semi-oxidation and semi-reduction environment, and the color of the dark grey and gray mudstone is mainly influenced by organic matter and iron sulfide and represents a reduction environment. The larger the mudstone color is, the more powerful the oxidation potential of sedimentary environments such as the plano phase of delta and the sedimentary phase of fandelta. And (3) judging the possible sedimentary phase combination of each sedimentary interval according to the sedimentary environment represented by different mudstone color indexes and the possible sedimentary phase table shown in the table 4 by counting the mudstone color indexes of each interval.
TABLE 4 depositional environments and possible combinations of depositional phases represented by different mudstone color indexes
In the examples, the thickness H of the dark grey mudstone in the second section of the hole is shown in Table 3dgIs 35.5 m; thickness H of gray mudstonegrIs 12.5 m; green mudstone thickness HgIs 0 m; red purple brown mudstone with thickness of HprIs 21 m; thickness H of mudstonem100.5m, substituting equation (1):
the color index of the mudstone at the second section of the hole is 0.32, which is calculated to be a weak oxidation deposition environment as shown in table 4.
In step S3, mudstone thickness index (number of layers of 100m mudstone) ImiIs defined as
N in formula (2)msThe total number of layers of the mudstone; hmIs the total thickness of the mudstone.
The mudstone thickness index refers to the number of layers contained in 100 meters of mudstone, and the larger the value, the smaller the average single-layer mudstone thickness is indicated. The facies zones of mudstone development are, in turn, a shoa lake, a semi-deep lake and a deep lake, and the thickness of the mudstone developed in the different facies zones is different as shown in table 5. The thickness of the single-layer dark mudstone in the half-deep lake area is gradually reduced towards the direction of the shoreside lake. The sedimentary facies zone of the interval under study may be indicated by the size of the mudstone thickness index. The mudstone thickness index, when smaller, represents the deep lake-semi-deep lake sedimentary facies. When the mudstone thickness index is larger, the sedimentary environment of the shores lake is indicated.
TABLE 5 relationship between mudstone thickness index and sedimentary facies belt
| Mudstone thickness index | Possible occurrence of sedimentary phase belt |
| (Imi<15) | Deep lake |
| (15≤Imi<30) | Half-deep lake |
| (Imi≥30) | Shoreside lake |
In the examples, the total number of layers N of mudstone in the second section of the hole is shown in Table 3ms39 layers, total thickness H of mudstonemIs 100.5m, substituting equation (2):
the thickness index of the shale at the second section of the hole is 38.81 through calculation, and as shown in the table 5, the thickness stability of the shale is moderate and the shale is expressed as a shoa lake phase zone.
Sandstone thickness differentiation degree I in step S4sdIs defined as
H in formula (3)ssThe average thickness of the siltstone; hfThe average thickness of the fine sandstone; hmsThe average thickness of the medium sandstone; hgThe average thickness of the coarse sandstone; hatIs the average thickness of the sandstone.
The sandstone thickness differentiation indicates the difference between different lithologic sand body thicknesses. When the sandstone thickness diversity factor is less than 2 and more than 0, the sandstone thickness diversity factor indicates that the deposition layer section has both a coarse sand layer and a fine sand layer, the deposition environment is relatively complex, the sandstone thickness diversity factor has the characteristic of sudden change, fine particle deposition is received in a certain period, and sediments with coarser granularity appear in another period, and the sandstone thickness diversity factor has the characteristic of event deposition. When the sandstone thickness diversity factor is larger than 2 and larger than 0, sandstone with certain lithologic thickness in the sedimentary interval is dominant, and the index is quieter sedimentary environment. Sandstone thickness differentiation can be used to distinguish gravity flow sedimentary systems from drag flow sedimentary systems.
In the examples, as shown in table 2, the thickness of the two-stage-hole siltstone was 67.5m, the number of layers of the siltstone was 27, and the average thickness H of the siltstone wasssIs 2.5; the thickness of the fine sandstone is 32m, the number of the fine sandstone layers is 14, and the average thickness H of the fine sandstonefIs 2.3; the thickness of the medium sandstone is 2m, the number of the medium sandstone layers is 1, and the average thickness H of the medium sandstonemsIs 2 m; the thickness of the sandstone is 101.5m, the number of the sandstone layers is 42, and the average thickness H of the sandstone isatIs 2.4, the parameters are substituted into a sandstone differentiation degree calculation formula (3)
And calculating to obtain that the thickness diversity of the sandstone at the hole section is 1.73, the sandstone type mainly comprises siltstone, the single-layer thickness difference of the siltstone is not large, and the sandstone has large thickness diversity and is expressed as traction flow deposition.
Lithology index I in step S5lIs defined as:
h in formula (4)mIs the mudstone thickness; hasThe thickness of the argillaceous sandstone; hsIs the thickness of sandstone; hstIs the formation thickness.
Sandstone is formed in basin by weathering, denudation and transportation of source region rock, and the distribution characteristics of sandstone distribution on space reflect depositionThe relationship between the region and the source. The places with larger lithology indexes of the sandstone often appear in places with more intense influence on the material source. The invention adopts lithology index I1To represent the lithology of the research interval, and according to the lithology index, the research interval is divided into rich sand (I)lNot less than 0.75), sandy (not less than 0.5 and not more than I)l<0.75) sand (I is more than or equal to 0.25)l<0.5) and lean sand (I)l<0.25)4 levels. The lithology indices may be used to discriminate between dephasing within the causal phase combination, as shown in table 6, for which the dephasing may occur differently for different lithology indices.
TABLE 6 possible sedimentary phases with different sand contents
In the examples, the thickness H of the sandstone in the second section of the hole is shown in tables 2 and 3s101.5m, mudstone thickness Has100.5m, formation thickness Hst325.5m, substituting into lithology index formula (4)
The lithology index of the second section of the hole was calculated to be 0.31, which is shown in Table 4 as sand-containing mold.
Sandstone grade index I in step S6fIs defined as:
h in formula (5)ssIs the thickness of the siltstone; hfIs the thickness of the fine sandstone; hmsIs the thickness of the medium sandstone; hgIs the thickness of the coarse sandstone.
The sediment characteristics can reflect hydrodynamic conditions when sediment is deposited, coarse sand is stronger than fine sand in hydrodynamic force required by the sediment in the process of carrying, and the sandstone grade index can reflect hydrodynamic strength of the sediment period of an interval under study. A size fraction index greater than 0.5 represents a strong hydrodynamic deposition environment and a size fraction index less than 0.5 represents a relatively quiet deposition environment.
In the examples, the thickness H of the two-stage siltstone in the hole is shown in Table 2ss67.5m, fine sandstone thickness Hf32m, medium sandstone thickness HmsIs 2m, the thickness of the coarse sandstonegThe parameters are substituted into sandstone grade index calculation formula (5) to be 0m
The calculation shows that the sandstone grade index of the hole section is 0.34, the hydrodynamic condition is weak, the siltstone sedimentation is dominant in the interval, the coarse debris particles are less, and the characteristic of far-source sedimentation is shown.
In step S7, the particle fraction differentiation degree index IdIs defined as
α in equation (6)ssα weight percent of siltstone in sandstonefα weight percent of fine sandstonemsα is the percentage of medium sandstone in sandstonegIs the percentage of the medium sandstone in the sandstone.
The sand fraction is used to describe the size fraction characteristic of the sedimentary interval, which can be used to indirectly indicate the sortability characteristic of the horizon. When the grade differentiation index is less than 0.5, the sandstone proportion of the grade of the research layer section is indicated to be relatively balanced, the separation is poor, and the characteristic of mixed deposition is shown, which represents the characteristic of rapid deposition, such as a fan delta, a delta and a gravity flow deposition system. When the grain fraction differentiation index is larger than 0.5, the sandstone component in the interval to be researched is indicated to be relatively uniform, has good sorting property and has traction flow sedimentary characteristics, such as beach bar sand sedimentary facies.
In the examples, as shown in Table 2Thickness H of hole two-section siltstoness67.5m, fine sandstone thickness Hf32m, medium sandstone thickness HmsIs 2m, the thickness of the coarse sandstoneg0m, total sandstone thickness of 101.5m, and siltstone content of αss0.67 percent of fine sandstone αf0.31, and α percent of medium sandstone in sandstonemsTo 0.02, this data was substituted into the calculation formula (6) for the degree of particle size differentiation index
The calculation result shows that the grain size differential degree of the sandstone at the two sections of the hole is 0.46, and the differential degree is small, which shows that the section of the sand has relatively good sorting property and has the Delta front edge sedimentation characteristic controlled by the traction flow.
Sandstone thickness index (number of layers of sandstone of 100 m) I in step S8stIs defined as
N in formula (7)sThe total number of layers of the sandstone; hssIs the thickness of the siltstone; hfIs the thickness of the fine sandstone; hmsIs the thickness of the medium sandstone; hgIs the thickness of the coarse sandstone.
The sandstone thickness index is the number of layers contained in 100 meters of sandstone, and the larger the number of layers, the smaller the thickness of a single sand body, and the index can indicate the strength of a source or the strength influenced by the source. When the sandstone thickness index is greater than 50, it indicates that the deposition zone is less affected by the source. When the sandstone thickness index is less than 20, the material source supply capacity is high, the sedimentary sand body is relatively stable, the range influenced by the material source is wide, and a sand-rich sedimentary phase is easy to form.
In the examples, the total number of layers N of sandstone in two stages of the hole, as shown in Table 2s42 layers, sandstone total thickness (H)ss+Hf+Hms+Hg) Is 101.5m, the parameter is substituted into the sandstone thickness index calculation formula (7)
The calculation result shows that the thickness index of the sandstone at the second section of the hole is 41.38, which represents that the sandstone at 100m comprises 38 layers of sandstone, and the sandstone has a medium thickness index value.
The sandstone combination data for the remaining horizons can be derived by the same method, as shown in table 7:
TABLE 7 major stratified section sandstone combined data table for a certain well
In step S9, after determining the depositional environment, depositional facies zone, source stability, lithology, hydrodynamic strength, particle size anisotropy, and source strength parameters of the study interval, and comparing with the ground facies clastic rock deposition system in table 1 in combination with the study background data, a reasonable determination can be made on the depositional facies of the interval.
In the actual operation process, sedimentary facies (combinations) are determined according to the hierarchies, the corresponding hierarchy under the three-level hierarchical trellis can identify the sedimentary facies combinations, and the corresponding hierarchy under the four-level hierarchical trellis can further identify the sedimentary facies. As shown in fig. 2, the two-section hole is judged to be a weak oxidation deposition environment according to the mudstone color index, the deposition combination range of the two-section hole can be reduced to the phases of the fan heel, the river channel, the river flood beach, the delta plain, the plait river delta plain, the fan delta leading edge and the delta leading edge, the two-section hole can be judged to belong to the shoal lake facies according to the mudstone thickness index, the deposition combination of the two-section hole can be further reduced to the river channel, the fan delta leading edge and the delta leading edge, the whole two-section hole is judged to be a weak hydrodynamic condition through the sandstone grain index, and the deposition combination of the two-section hole is finally judged to be the delta leading edge. After determining the sedimentary phase combination, the pore-two sedimentary phase can be further identified according to a four-level sequence layering: the delta front edge comprises five sedimentary facies of an underwater diversion river channel, an underwater diversion river channel space, a estuary dam, a far sand dam and mat sand, the two sections of the hole are judged to be sand-containing levels through lithology indexes, the sedimentary facies range is narrowed to the estuary dam and the far sand dam, the two sections of the hole are determined to be greatly influenced by a material source according to the sandstone thickness index, and the two sections of the hole are judged to be estuary dam facies.
According to the idea and the flow, sedimentary phase combination and sedimentary phase analysis are sequentially carried out on each layer of a well, and the analysis results are shown in tables 8-1 and 8-2.
TABLE 8-1 analysis table of main stratified facies (combinations) of a well
TABLE 8-2 analysis table of main stratified facies (combinations) of a well
The lithology combination index of the same layer was also reviewed in conjunction with tables 8-1 and 8-2, and the sedimentary facies (combination) results were reviewed in table 8-2.
The method can quantitatively analyze sedimentary facies through lithology combination index, and for those skilled in the art, the specific examples are only illustrative descriptions of the present invention, and it is obvious that the specific implementation of the present invention is not limited by the above-mentioned manner, and it is within the protection scope of the present invention as long as various insubstantial modifications are made by using the method concept and technical scheme of the present invention, or the concept and technical scheme of the present invention is directly applied to other occasions without modification.
Claims (8)
1. A method for identifying sedimentary facies using lithological combinations, comprising the steps of:
s1, collecting and processing lithology combination indexes of the research interval;
s2, judging the deposition environment by using the mudstone color index,
wherein, mudstone color index IciIs defined as:
wherein Hdg is the thickness of dark grey mudstone; hgrThickness of grey mudstone; hgGreen mudstone thickness; hprIs red purple brown mudstone thickness; hmIs the mudstone thickness;
s3, judging a sedimentary facies belt by using the mudstone thickness index,
wherein, the mudstone thickness index I of the layer number of 100m mudstonemiIs defined as:
wherein N ismsThe total number of layers of the mudstone; hmThe total thickness of the mudstone;
s4, judging the stability of the source by the sandstone thickness differentiation degree,
wherein, the sandstone thickness differentiation degree IsdIs defined as:
wherein HssThe average thickness of the siltstone; hfThe average thickness of the fine sandstone; hmsThe average thickness of the medium sandstone; hgThe average thickness of the coarse sandstone; hatIs the average thickness of the sandstone;
s5, judging the lithology of the research layer section by using the lithology index,
wherein, lithology index IlIs defined as:
wherein HmIs the mudstone thickness; hasThe thickness of the argillaceous sandstone; hsIs the thickness of sandstone; hstIs the formation thickness;
s6, judging the hydrodynamic strength by the sandstone granularity index,
wherein, sandstone grade index IfIs defined as:
wherein HssIs the thickness of the siltstone; hfIs the thickness of the fine sandstone; hmsIs the thickness of the medium sandstone; hgIs the thickness of the coarse sandstone;
s7, judging granularity dissimilarity by the sandstone granularity dissimilarity index,
wherein, the index of particle size fraction differentiation degree IdIs defined as:
wherein, αssα weight percent of siltstone in sandstonefα weight percent of fine sandstonemsα is the percentage of medium sandstone in sandstonegThe percentage of the medium sandstone in the sandstone is shown;
s8, judging the source strength by the sandstone thickness index,
sandstone thickness index I of 100m sandstone layersstIs defined as:
wherein N issThe total number of layers of the sandstone; hssIs the thickness of the siltstone; hfIs the thickness of the fine sandstone; hmsIs the thickness of the medium sandstone; hgIs the thickness of the coarse sandstone;
s9, for the steps S2 to S8, narrowing the scope of the sedimentary facies step by step according to the obtained combination index of the lithology of the research layer so as to judge the sedimentary facies; wherein the step S2 to the step S8 have no sequence.
2. The method as claimed in claim 1, wherein the lithology combination index is determined according to lithology logging data in step S1, the well location layered data is obtained according to the logging data, the mudstone thickness and the initial interface in the lithology logging data are corrected according to the logging curve characteristics, and finally the lithology combination index of the well location is obtained.
3. The method for identifying the sedimentary facies using lithological combination as claimed in claim 2, wherein mudstone color index <0.1 represents a strong reducing environment, mudstone color index < 0.1.3 or more represents a weak reducing environment, mudstone color index <0.3 or more represents a weak oxidizing environment, and mudstone color index > 0.6 represents a strong oxidizing environment in step S2.
4. The method for identifying dephasing by using lithology combination as claimed in claim 2, wherein in step S3, mudstone thickness index is <15, deep lake dephasing zone occurs; 15 or more than or equal to mud rock thickness index of less than 30, and a half-deep lake sedimentary facies zone appears; the mudstone thickness index is more than or equal to 30, and a sedimentary facies belt of the shoa lake appears.
5. The method for identifying the sedimentary facies by using the lithological combination as claimed in claim 2, wherein in step S4, when the sandstone thickness variation is less than 2 and greater than 0, the sandstone thickness variation indicates that the sedimentary interval has both coarse sand layers and fine sand layers and has the characteristic of abrupt change; when the sandstone thickness diversity factor is larger than 2, sandstone with certain lithologic thickness in the sedimentary interval is dominant, and the sedimentary environment is quiet.
6. The method for identifying sedimentary facies by using lithological character combination as claimed in claim 2, wherein the lithological character index is not less than 0.75 in step S5 and represents a sand-rich model; the lithology index is more than or equal to 0.5 and less than 0.75, and represents the sand type; the lithological index is more than or equal to 0.25 and less than 0.5, and represents a sand-containing mold; lithology index <0.25, representing a lean sand mold.
7. The method for identifying dephasing using lithology combination as claimed in claim 2, wherein the sandstone particle size index of step S6 is greater than 0.5, which represents a strong hydrodynamic deposition environment; sandstone grade index less than 0.5 represents a relatively quiet sedimentary environment.
8. The method for identifying dephasing using lithology combination as claimed in claim 2, wherein step S7 is performed when the sandstone particle fraction differentiation index is less than 0.5, which represents fast deposition; when the particle size fraction index is more than 0.5, the drawing flow sedimentation characteristic is realized.
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