CN118033771A - Shale stratum partitioning method based on sedimentary environment - Google Patents
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Abstract
The invention belongs to the field of shale oil development, and discloses a shale stratum partitioning method based on a sedimentary environment. It is proposed to characterize shale depositional environment characteristics for simultaneous shale stratigraphic classification and dessert identification. Firstly, testing the total organic carbon and free hydrocarbon content to perform shale oiliness characterization, then optimizing out an element combination sensitive to shale oiliness through correlation analysis according to an element content measurement experiment result, performing shale sedimentary environment characterization from various dimensions by utilizing the parameters, including paleoclimatic conditions, paleoredox environment and paleoproductivity characteristics, constructing a sedimentary environment factor I E by combining the parameters, and finally completing shale oil geological stratification according to the rotation characteristics of I E. The stratum division method provided by the invention can effectively improve the precision of stratum division and avoid uncertainty caused by artificial subjective layering.
Description
Technical Field
The invention belongs to the field of shale oil development, and relates to a shale stratum partitioning method based on a sedimentary environment.
Background
Shale oil is a very important unconventional oil and gas resource. Shale formation fine-classification is the basis for shale dessert identification. Shale lithology, mineral composition, sedimentary structure, organic content heterogeneity are very large, and therefore shale formation classification has been a difficult problem for geologist.
Currently, shale formation classification methods have certain defects or shortcomings in the patent.
The patent application 202110959701.8 'high-precision stratum division method of organic shale' essentially regards a logging curve as a comprehensive signal formed by regular formation change of various geological factors in a depth domain or a time domain, and fourier transformation is carried out on the comprehensive signal to convert the depth domain or the time domain into a frequency domain. An autocorrelation function can be obtained through maximum entropy spectrum analysis, and can be used for increasing the data length and further improving the resolution. Although logging data is one of geological data with high resolution and good continuity can be obtained at present, the rotation of logging information is related to not only stratum characteristics, but also a plurality of factors such as the resolution of the response of logging instruments, the logging environment, logging operation, the stability of the logging instruments and the like, and a plurality of unexpected results obviously exist when the data is applied to the rotation sequence stratum related analysis.
The patent application No. 201610442252.9 is a shale sequence stratigraphic division method, which characterizes the evolution characteristics of a deposition environment by performing element analysis on shale samples, and determines the interface characteristics of a quasi-sequence group according to a sequence gyratory standard by using a sequence stratigraphy principle. The method does not consider the organic matter content and the oil content characteristics of the shale, so that the dessert identification of the beneficial targets of the shale cannot be carried out.
Up to now, there is no method for evaluating the oil content of shale and dividing the shale formation with high efficiency.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a shale stratum division method based on a sedimentary environment, so that the problem that the existing method cannot simultaneously divide shale stratum and identify desserts is solved. The stratum division method provided by the invention can effectively improve the precision of stratum division and avoid uncertainty caused by artificial subjective layering.
The above object of the present invention is achieved by the following technical solutions:
A shale stratum partitioning method based on a sedimentary environment comprises the following steps:
step 1: performing system sampling on the target shale interval;
step 2: performing a total organic carbon and rock pyrolysis experiment on a shale sample to obtain Total Organic Carbon (TOC) and free hydrocarbon (S 1) contents, and calculating an OSI (OSI=S 1/TOC.100) value;
step 3: performing element analysis experiments on shale samples to obtain the main quantity, trace quantity and rare earth element content of the shale samples;
Step 4: performing related analysis on elements and OSI, screening out an element combination sensitive to OSI, and respectively representing paleoclimatic conditions, paleoredox conditions and paleoproductivity characteristics of shale deposition;
Step 5: calculating and obtaining a deposition environment factor I E based on the screened element combination;
Step 6: and drawing a graph by using a deposition environment factor I E, determining a stratum dividing limit according to the rotation characteristic of the graph I E, wherein a curve turning point is a layering mark.
In the step (1), the shale samples are systematically sampled, namely, the shale core samples are uniformly drilled aiming at a section of continuous shale core, the length L of the core and the number x of the cores designed to be sampled, and the interval is L/x.
In the step (2), the sample needs to be pretreated before the sample is subjected to the pyrolysis experiment of the total organic carbon and the rock. The sample was ground to 80-100 mesh powder using a quartz mortar. And (3) fully reacting a dilute hydrochloric acid solution with the concentration of 2mol/L with a sample to remove inorganic minerals such as carbonic acid rock, wherein a TOC experimental instrument is a C-744 carbon-sulfur analyzer, the test error is less than 3%, and the experiment is carried out according to the GB/T19145-2003 standard. The Rock pyrolysis experimental instrument is a Rock-Eval-6 type raw oil Rock analyzer, the test error is less than 3%, and the experiment is executed according to the GB/T18602-2012 standard.
In the step (2), the oil saturation index OSI can be used for not only characterizing the shale oil content but also characterizing the shale oil mobility.
In the step (3), the sample was ground to 200 mesh powder using a quartz mortar before the element measurement experiment. The content of the principal element is measured by an alkali-fusion glass sheet method, and an experimental device is an X-ray fluorescence spectrometer (XRF). The loss on ignition test method is to heat the sample in a ceramic crucible at 1000 ℃ for 1 hour, and measure the weight change of the sample before and after the experiment. The principal component element measurement experiment method comprises the following steps: 1g of the calcined powder sample to be measured was taken, and after being uniformly mixed with 6g of Li 2B4O7/LiBO2 in a ceramic crucible, the mixture was heated to 1050℃to prepare a molten glass sheet. Relevant test standards are performed according to GB/T14506.14-2010 and GB/T14506.28-2010.
The trace elements and rare earth elements are measured by an acid dissolution method, and the experimental instrument is an inductively coupled plasma mass spectrometer. The sample was ground to a 200 mesh powder using a quartz mortar prior to the experiment, and a 2mol/L HCl solution was used to react well with the sample to remove carbonates and calcareous minerals. The experimental procedure is carried out according to GB/T14506.30-2010, and the analysis accuracy is better than 5.00%.
Wherein the principal element content determination includes, but is not limited to ：SiO2,Al2O3,Fe2O3,CaO,MgO,K2O,BaO,Cr2O3,MnO,Na2O,P2O5,SrO,TiO2, units in wt%.
Trace element content measurements include, but are not limited to ：Li,Be,B,Sc,V,Cr,Co,Ni,Cu,Zn,Ga,Ge,As,Se,Rb,Sr,Zr,Nb,Mo,Ag,Cd,Sn,Sb,Te,Cs,Ba,Hf,Ta,W,Au,Tl,Pb,Bi,Th,U, units in ppm (parts per million).
Rare earth element content assays include, but are not limited to: la, ce, pr, nd, sm, eu, gd, tb, dy, Y, ho, er, tm, yb, lu in ppm (parts per million).
In the step (4), the shale deposition environment disclosed by the invention comprises three aspects, namely paleo-climate conditions, paleo-redox conditions and paleo-productivity characteristics during shale deposition are respectively represented, and the specific selection reasons and methods are as follows:
1. Ancient climate parameters:
C-value: fe, mn, cr, V, ni, co elements are enriched in humid climates, while Ca, mg, K, na, sr and Ba elements are enriched in high salt drought climates. Based on these microelements, C-value is commonly used to evaluate paleoclimatic conditions.
C-value＝∑(Fe+Mn+Cr+V+Ni+Co)/∑(K+Na+Ca+Mg+Sr+Ba)
C-value <0.2 indicates arid climate, 0.2< C-value <0.4 indicates semiarid climate, 0.4< C-value <0.6 indicates semiarid semi-humid climate, 0.6< C-value <0.8 indicates semi-humid climate, C-value >0.8 indicates humid climate;
Sr/Cu: <5 indicates a warm humid climate, 5< Sr/Cu <10 indicates a semi-warm humid-semi-dry hot climate, sr/Cu >10 indicates a dry hot climate;
CIA: chemical weathering index for evaluating ancient climate change, when CIA is between 50-65, reflecting dry and cold climate under low chemical weathering background; when CIA is between 65 and 85, the warm-wet climate under the medium chemical weathering background is reflected; when CIA is greater than 85, it reflects a hot humid climate in the background of strong weathering.
Na/Al: under the humid climate condition, the fresh water input is increased, the water body is deepened, the salinity is reduced, and the content of Al element in sedimentary rock is higher; under drought climate conditions, the water body is evaporated strongly, the salinity is increased, the alkalinity is enhanced, and Na element is enriched in sedimentary rock in the form of salt. Thus, a low Na/Al value indicates humid paleo-climate conditions and a high Na/Al value indicates drought paleo-climate conditions.
2. Paleoredox parameters:
Sr/Ba: the chemical properties of the trace elements Sr and Ba are similar, and the trace elements Sr and Ba can enter the solution in the form of soluble salt and are sensitive to ancient salinity change. The migration capacity of Sr in solution is stronger than that of Ba, as the salinity is increased, the mineralization degree of the solution is increased, ba2+ firstly reaches saturation, firstly precipitates in the form of sulfate, and then Sr2+ can precipitate as the salinity is further increased. Therefore, the Sr/Ba high value reflects that the ancient salinity is larger, whereas the ancient salinity is smaller. A Sr/Ba value >1 indicates a salty water environment; 0.5> Sr/Ba >1 indicates a brackish water environment; sr/Ba <0.5 indicates a brackish water environment.
Mg/Ca: are often used to distinguish between fresh water environments and salty water environments, thereby indicating the redox characteristics of the sedimentary environment. Typically Mg/Ca >1 indicates a high salt environment; 0.5> mg/Ca >1 indicates a salt water environment; 0.25> mg/Ca >0.50 indicates a brackish water environment; mg/Ca <0.25 indicates a brackish water environment.
V/(v+ni): the higher V/(V+Ni) ratio reflects the strong layering property of the water body, and the H 2 S reduction environment appears at the bottom. (V/(V+Ni) >1.5,1< V/(V+Ni) <1.5, V/(V+Ni) < 1) respectively indicate anoxic, and oxygen-enriched environments.
U/Th: U/Th <0.75 indicates an oxidizing environment, 0.75< U/Th <1.25 indicates an oxygen-deficient environment, and U/Th >1.25 indicates a reducing environment.
V/Cr: in a reducing environment, V precipitates as a more efficient organic complex than Cr, preferentially concentrates in the deposit, and thus V/Cr can be used as an oxygen content indicator. V/Cr <2 indicates an oxidizing environment, V/Cr >4.25 indicates a reducing environment, and 2<V/Cr <4.25 indicates an oxygen-deficient environment.
Ni/Co: ni/Co <5 indicates an oxidizing environment, 5< Ni/Co <7 indicates an oxygen-deficient environment, and Ni/Co >7 indicates a reducing environment.
And U: uranium element (U) is active in nature, exists as insoluble U 4+ under reducing conditions, can cause enrichment of U in the deposit, and exists as soluble U 6+ under oxidizing conditions to be easily migrated and lost.
U=u/0.5 (Th/3+U), U >1 generally indicates a hypoxic reducing environment.
S: elemental sulfur is effective in indicating the redox characteristics of the deposition environment, with higher levels of elemental sulfur being more reducing.
3. Ancient productivity parameters:
p: phosphorus is one of important plankton nutrition elements and can be used as a good index for indicating the ancient ocean productivity.
Ni+zn+cu: the higher the content of copper, nickel and zinc elements, the higher the biological productivity.
Si Biological material and Ba Biological material : when evaluating productivity using elemental silicon and barium, only silicon and barium of biological origin are of concern, and therefore correction of land-based debris material is required. Al and Ti can effectively reflect the influence of land debris on deposited organic matters, and are commonly used for correcting the land debris.
And (3) selecting the average components of the Australian shale (Pass) in the back-to-the-ancient universe as the standard, and calculating the enrichment coefficient and the standardization.
The enrichment factor of element X is calculated as follows:
XEF＝X Sample of -Y Sample of ·(X/Y)pass
Wherein, X EF is the enrichment factor of element X, Y is the element for chip correction, generally Al and Ti, (X/Y) pass is the average composition of the Australian shale in the after-Taigu world.
If X EF is greater than 1, this indicates that element X is enriched relative to Pass; if X EF is less than 1, this indicates that element X is deficient relative to Pass.
Si Biological material : the biogenic quartz is derived from siliceous organisms, and sometimes the biogenic quartz is dissolved and recrystallized under the condition of water rock action or diagenetic action, and autogenic quartz can be formed. The silicon content in the deposit can thus be better restored to the archaeal productivity level.
Si Biological material ＝Si Sample of -Al Sample of ·(Si/Al)pass，(Si/Al)pass＝3.11
Ba Biological material : the barium element mainly originates from barite formed in the rotten phytoplankton organic matters and barite in the biological skeleton, and part of the barium element exists in silicate and carbonate of the organic matters and biological causes. The sources of Ba are 4, but only biological sources of Ba can accurately reflect the productivity level, and the method is the basis for establishing an ancient productivity calculation model.
Ba Biological material ＝Ba Sample of -Ti Sample of ·(Ba/Ti)pass，(Ba/Ti)pass＝0.11。
Compared with the prior art, the invention has the beneficial effects that:
It is first proposed to characterize shale deposition environment characteristics for simultaneous shale formation classification and dessert identification. Firstly, testing the total organic carbon and free hydrocarbon content to perform shale oiliness characterization, then optimizing out an element combination sensitive to shale oiliness through correlation analysis according to an element content measurement experiment result, performing shale sedimentary environment characterization from various dimensions by utilizing the parameters, including paleoclimatic conditions, paleoredox environment and paleoproductivity characteristics, constructing a sedimentary environment factor I E by combining the parameters, and finally completing shale oil geological stratification according to the rotation characteristics of I E. The traditional method mainly adopts natural Gamma (GR) and resistivity curves (RLLD, RT and the like) to divide the shale reservoir into strata, and has the problems of low stratum identification precision and incapability of effectively dividing the strata. The shale stratum dividing method provided by the invention can effectively improve stratum identification precision.
Drawings
FIG. 1 is a diagram of the technical scheme of the present invention
FIG. 2 is a graph showing the correlation analysis of OSI and 6 deposition environment related parameters in example 1 of the present invention
FIG. 3 is a graph showing the variation of GR, RLLD and IE with depth in example 1 of the present invention
FIG. 4 is a graph showing the correlation analysis of OSI and 6 deposition environment related parameters in example 2 of the present invention
FIG. 5 is a graph showing the variation of GR, RLLD and IE with depth in example 2 of the present invention
Detailed Description
The present invention is described in detail below by way of specific examples, but the scope of the present invention is not limited thereto. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and all experimental equipment, materials, reagents, etc. used can be obtained from commercial sources.
Example 1
A shale stratum partitioning method based on a sedimentary environment comprises the following steps:
step 1: system sampling target shale intervals
Taking the sample of the Songliao basin south Qingshan port group shale as an example, the sample of the shale of the embodiment 1 is taken from a D86 well, 40 samples are taken in total, the depth range of the sample is 1971.48m to 2062.55m, the sample interval is 0.65-6.95m, the average sample interval is 2.34m, and the system sampling is carried out through the long well section of a single well, so that the characteristics of the shale deposition environment can be comprehensively represented.
Step 2: performing a total organic carbon and rock pyrolysis experiment on a shale sample to obtain Total Organic Carbon (TOC) and free hydrocarbon (S 1) contents, and calculating an OSI (OSI=S 1/TOC.100) value;
step 3: performing element analysis experiments on shale samples to obtain the main quantity, trace quantity and rare earth element content of the shale samples; the analytical results are shown in Table 1, wherein the content of the principal element is in wt%. Trace element content is in ppm (parts per million). The rare earth element content is in ppm (parts per million).
Table 1: d86 well shale sample TOC, rock pyrolysis and element content meter
Step 4: and performing correlation analysis on elements and OSIs, and preferably selecting an element combination sensitive to the OSIs to respectively characterize paleoclimatic conditions, paleoredox conditions and paleoproductivity characteristics of shale sediments.
As shown in FIG. 2, OSI is analyzed with respect to C-value, sr/Cu, V/Cr, & U, P, ni +Zn+Cu.
The correlation analysis results show that: OSI positively correlates with C-value, & U, P, ni +Zn+Cu (R 2 is 0.81, 0.69, 0.73 and 0.81, respectively) and negatively correlates with Sr/Cu and V/Cr (R 2 is 0.79 and 0.78, respectively).
Thus, the above preferred combination of elements may be involved in constructing the deposition environment factor.
The depositional environment factor may be represented by equation 1:
As shown in fig. 3, GR and RLLD logs have no significant change in characteristics with increasing depth, so the formation cannot be effectively partitioned using conventional GR and RLLD logs.
The method provided by the invention has the advantages that the I E curve obviously shows 3-segment spiral characteristics, and the stratum can be divided into 3 segments according to the layering boundary line 1 and the layering boundary line 2.
Example 2
A shale stratum partitioning method based on a sedimentary environment comprises the following steps:
step 1: system sampling target shale intervals
Taking the sample of the southern Qingshan port group shale of the Songliao basin as an example, the sample of the shale of the example 2 is taken from a TY well, 22 samples are taken in total, the depth range of the sample is 2257.8m to 2370.0m, the sample interval is 1.0-15.0m, the average sample interval is 5.34m, and the system sampling is carried out through the long well section of a single well, so that the characteristics of the shale deposition environment can be comprehensively represented.
Step 2: performing a total organic carbon and rock pyrolysis experiment on a shale sample to obtain Total Organic Carbon (TOC) and free hydrocarbon (S 1) contents, and calculating an OSI (OSI=S 1/TOC.100) value;
Step 3: performing element analysis experiments on shale samples to obtain the main quantity, trace quantity and rare earth element content of the shale samples; the analytical experimental results are shown in Table 2; wherein the content unit of the principal element is wt%. Trace element content is in ppm (parts per million). The rare earth element content is in ppm (parts per million).
Table 2: TY well shale sample TOC, rock pyrolysis and element content meter
Step 4: and performing correlation analysis on elements and OSIs, and preferably selecting an element combination sensitive to the OSIs to respectively characterize paleoclimatic conditions, paleoredox conditions and paleoproductivity characteristics of shale sediments.
As shown in FIG. 4, OSI is analyzed with respect to C-value, sr/Cu, V/Cr, S, P, ni +Zn+Cu.
The correlation analysis results show that: OSI correlates positively with C-value, S, P, ni +Zn+Cu (R 2 is 0.84, 0.81, 0.87 and 0.82, respectively) and negatively with Sr/Cu and V/Cr (R 2 is 0.75 and 0.74, respectively).
Thus, the above preferred combination of elements may be involved in constructing the deposition environment factor.
The depositional environment factor may be represented by equation 2:
as shown in fig. 5, GR and RLLD logs have no significant change characteristics with increasing depth, so the formation cannot be effectively partitioned using conventional GR and RLLD logs.
The method provided by the invention has the advantages that the I E curve obviously shows 2-section gyratory characteristics, and the stratum can be divided into 2 sections according to the layering boundary line.
The above-described embodiments are only preferred embodiments of the invention, and not all embodiments of the invention are possible. Any obvious modifications thereof, which would be apparent to those skilled in the art without departing from the principles and spirit of the present invention, should be considered to be included within the scope of the appended claims.
Claims (8)
1. A shale stratum partitioning method based on a sedimentary environment is characterized by comprising the following steps:
step 1: performing system sampling on the target shale interval;
Step 2: carrying out a total organic carbon and rock pyrolysis experiment on a shale sample to obtain total organic carbon and free hydrocarbon content, and calculating an OSI value;
step 3: performing element analysis experiments on shale samples to obtain the main quantity, trace quantity and rare earth element content of the shale samples;
Step 4: performing related analysis on elements and OSI, screening out an element combination sensitive to OSI, and respectively representing paleoclimatic conditions, paleoredox conditions and paleoproductivity characteristics of shale deposition;
Step 5: calculating and obtaining a deposition environment factor I E based on the screened element combination;
Step 6: and drawing a graph by using a deposition environment factor I E, determining a stratum dividing limit according to the rotation characteristic of the graph I E, wherein a curve turning point is a layering mark.
2. The method for dividing shale formations based on a sedimentary environment according to claim 1, wherein in the step (1), the shale samples are systematically sampled, namely, the shale core samples are uniformly drilled according to a section of continuous shale cores, the length L of the cores and the number x of the cores designed to be sampled, and the interval is L/x.
3. The method for partitioning shale formations based on a sedimentary environment according to claim 2, wherein in the step (2), the sample is subjected to pretreatment before the sample is subjected to the pyrolysis experiment of total organic carbon and rock; the sample was ground to 80-100 mesh powder using a quartz mortar.
4. A shale formation separation method based on a sedimentary environment according to claim 3, wherein in the step (3), the sample is ground to 200 mesh powder using a quartz mortar before the element measurement experiment.
5. The method of shale formation classification based on sedimentary environment of claim 4, wherein the elemental content determination includes, but is not limited to ：SiO2,Al2O3,Fe2O3,CaO,MgO,K2O,BaO,Cr2O3,MnO,Na2O,P2O5,SrO,TiO2, units in wt%.
6. The method of shale formation classification based on sedimentary environment of claim 5, wherein trace element content determination includes, but is not limited to ：Li,Be,B,Sc,V,Cr,Co,Ni,Cu,Zn,Ga,Ge,As,Se,Rb,Sr,Zr,Nb,Mo,Ag,Cd,Sn,Sb,Te,Cs,Ba,Hf,Ta,W,Au,Tl,Pb,Bi,Th,U, units in ppm (parts per million).
7. The method of shale formation classification based on sedimentary environment of claim 6, wherein rare earth element content determination includes, but is not limited to: la, ce, pr, nd, sm, eu, gd, tb, dy, Y, ho, er, tm, yb, lu in ppm (parts per million).
8. Use of a shale formation partitioning method based on a sedimentary environment as claimed in any of claims 1-7.
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