CN111812736A - Method for evaluating gas content of compact sandstone anhydrous gas reservoir - Google Patents
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Abstract
The invention discloses a method for evaluating gas content of a compact sandstone anhydrous gas reservoir, which solves the technical problem of low evaluation precision of the gas content of the compact sandstone anhydrous gas reservoir in the prior art. The invention mainly calculates the mud content curve V in turnshEffective porosity curve phieThe gas content evaluation method comprises the following steps of obtaining a pure rock neutron curve CNL1, an apparent sandstone skeleton hydrogen content index curve CNL2 and a gas content evaluation index parameter GASFG curve, and finally carrying out gas content evaluation according to the gas content evaluation index parameter GASFG curve. The invention fully utilizes the excavation effect of natural gas on the neutron logging curve to carry out quantitative characterization of gas content index parameters, and effectively solves the technical problem that the reservoir gas content of the compact sandstone in the prior art is difficult to accurately evaluate under the condition of lacking of information such as formation water and the like through classification evaluation. Practice proves that the technology not onlyThe gas content of the compact sandstone anhydrous gas reservoir can be accurately evaluated, and the high-gamma reservoir can be effectively identified, so that an accurate exploration method is provided for oil-gas exploration.
Description
Technical Field
The invention belongs to the technical field of gas reservoir exploration and development, and particularly relates to a method for evaluating gas content of a compact sandstone anhydrous gas reservoir.
Background
In recent years, the exploration result of compact sandstone in narrow rivers in the group of the Jurashi temple in the Jurassic area in mid-autumn forest in Sichuan has shown that the source storage in the area is well configured, which is beneficial to the facies development of reservoirs. At present, the trial results of the new well and the old well in the block prove that the sand group 5, the sand group 8 and the sand group 11 of the Shaxi temple all obtain high-yield gas wells, no formation water is produced, and good exploration potential is shown. With the continuous and intensive research, some wells in the research area are found to show good reservoir characteristics on the well logging curve, but the test result is an empty layer. The exploration practice proves that the gas content evaluation and the reservoir effectiveness evaluation of the reservoir have important significance. Currently, the evaluation of air entrainment in the sand body group of the Shaxi temple in the research area is one of the efforts of oil and gas exploration researchers.
At present, a gas saturation (Sg) parameter is generally adopted as an important index for evaluating the gas content of a tight sandstone reservoir, and the parameter acquisition method mainly comprises the steps of directly measuring in a closed and cored laboratory, and carrying out gas saturation inversion and well logging data calculation based on capillary pressure data. (1) And (4) directly measuring the saturation of the gas in the closed core. The method is restricted by factors such as drilling engineering technology, coring conditions, laboratory measuring equipment and the like, and is inconvenient for widely developing application research in areas. (2) The invention is based on the principle that the invention is disclosed by the invention patent (patent number: CN201410602210.8) based on the rock-capillary model for back calculation of the gas saturation. Although the method has simple calculation principle and is easy to implement, a lot of uncertainties exist. Firstly, capillary pressure data is influenced by experimental means and experimental conditions, and the precision of the capillary pressure data is uncertain; secondly, the method needs to convert the capillary pressure under the laboratory condition into the uncertainty under the gas reservoir condition, and the uncertainty exists in the determination of parameters such as interfacial tension, wetting angle and the like; thirdly, the method is applied on the premise that the gas-water interface and the gas column height are determined, and large uncertainty exists. This method is also a relatively low accuracy method. (3) Obtaining gas saturation from well log data is the most common method. The water saturation (Sw) is typically calculated first by the saturation equation and the gas saturation is calculated using equation 1.
Sg＝1-Sw (1)
As is well known, many studies have been conducted at home and abroad to calculate the water saturation by using well logging data, and the water saturation can be mainly divided into an electrical method and a non-electrical method, and the electrical method is mainly used. From the publication of Archie's formula in 1942, many electrical method saturation models exist, for example, the invention patent (patent number: CN201910760689.0) discloses a compact sandstone gas saturation calculation method based on calcium content correction. Although many models are used to calculate saturation, several parameters in common in the models are critical to the calculation result. That is the electrical parameters a, b, m and n and the formation water resistivity Rw. The rock-electricity parameters can be obtained by rock-electricity experiments under simulated formation conditions. However, similar to the situation of no formation water production in the research area, because formation water analysis data cannot be obtained, calculation can be performed only by using data or empirical parameters of the adjacent area, and the calculation result is often not practical, which brings difficulty to the evaluation of gas bearing property. The methods for determining the gas saturation by the non-electric method mainly comprise a sound wave method, a neutron method and a nuclear magnetic resonance method. For example, the invention patent (patent number: CN201811323041.9) discloses a method for identifying a gas layer by using element gamma energy spectrum logging, and the saturation of the gas in the stratum is determined according to the ratio (R) of the non-elastic gamma counting rate of fast neutrons to the thermal neutron capture gamma counting rate. The method needs to establish a response equation among gas saturation, porosity and R, the equation is influenced by too many factors, the non-elastic gamma counting rate obtained by fast neutrons is related to lithology, and the influence of the lithology is large; secondly, the thermal neutron capture gamma counting is greatly influenced by elements with strong capture capacity in the stratum; most importantly, the adaptability of this equation is not demonstrated in the field. The invention patent (patent number: CN201611263196.9) discloses a gas saturation determination method and a gas saturation determination device based on longitudinal and transverse wave logging speeds. The method obtains a gas saturation calculation formula based on experiments, and has a complex process and low practicability. Because it is difficult to extract the parameters of the first longitudinal wave time difference and the second longitudinal wave time difference in the well logging data. In addition, the nuclear magnetic resonance logging can better evaluate the gas content by determining the porosity which is independent of the lithology. However, the method is high in cost, and a research area cannot acquire a large amount of nuclear magnetic resonance logging information, so that the method is not suitable for comprehensively evaluating the gas content in the area.
In a word, the gas content evaluation method is influenced by multiple factors such as difficulty in mass sampling for coring, difficulty in experimental method, experimental conditions and data shortage, uncertainty of evaluation results is high, and evaluation precision is difficult to meet production requirements. However, for a long time, people are used to qualitatively describe the gas layer by using the excavation effect phenomenon of neutron logging, but no report on quantitative evaluation is found. The invention provides a novel gas content evaluation index and evaluation method, which can effectively solve the technical problem of low precision of evaluation results in the prior art.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method for evaluating the gas content of the compact sandstone anhydrous gas reservoir solves the technical problem that the evaluation precision of the gas content of the compact sandstone anhydrous gas reservoir is low in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
an anhydrous compact sandstone gas reservoir gas content evaluation method comprises the following steps:
step 2, calculating the effective porosity phi e, and calibrating by using the core physical property analysis data;
step 3, carrying out shale correction on the neutron logging curve by using the shale content Vsh calculated in the step 1 to obtain a neutron curve CNL1 of pure rock;
step 4, converting the pure rock neutron curve CNL1 in the step 3 into a sandstone skeleton hydrogen-containing index curve CNL 2;
step 5, calculating a gassiness evaluation index parameter GASFG curve by using the porosity phi e calculated in the step 2 and the CNL2 curve obtained in the step 4 and adopting a rock volume physical model;
and 6, evaluating the gas content by using the gas content evaluation index parameter GASFG curve calculated in the step 5.
Further, in the step 1, a natural gamma curve or a natural gamma energy spectrum curve is adopted for carrying out
Where Sh is the relative value of natural gamma, GR is the measured value of natural gammaminNatural gamma value, GR, for pure sandstonemaxNatural gamma value of pure mudstone; GCUR is the empirical coefficient associated with the age of the geology, taking 2 for old strata and 3.7 for new strata.
Further, in step 1, the natural gamma curve or the natural gamma energy spectrum curve refers to a logging curve after filtering and regional standardization.
Further, the rock core data refers to the reset rock core shale content data; preferably, the data is full-rock clay analysis data or full-rock particle size analysis data.
Further, in the step 2, calculating the effective porosity Φ e by using the acoustic wave or the density log; preferably, the effective porosity Φ e is calculated as:
ΔT＝Φe.ΔTmf+Vsh.ΔTsh+Vma.ΔTma；
Φe+Vsh+Vma＝1；
wherein, Delta T is a sound wave time difference curvemfAcoustic time difference, Δ T, for mud filtrateshIs the mudstone acoustic time difference, Δ TmaFor the acoustic time difference of the skeleton, VmaIs a sandstone stock price volume.
Further, in the step 2, the sound wave or density curve needs to be standardized; preferably, the porosity of the core needs to be subjected to deep homing treatment; further preferably, after core analysis porosity calibration, the effective porosity Φ e error obtained by logging calculation needs to be within an error range specified by a reserve specification.
Further, in step 3, the calculation formula for performing shale correction on the neutron log is as follows:
CNL1＝CNL-Vsh.ΦNsh；
wherein, CNL is neutron logging value,
is the mudstone neutron value;
preferably, phi in the above formulaNshDetermined from the GR and CNL cross plots.
Further, in the step 4, the calculation formula for converting the pure rock neutron curve CNL1 into the sandstone skeleton hydrogen index curve CNL2 is as follows:
further, in the step 5, a calculation formula for calculating the gassiness evaluation index parameter GASFG curve is:
further, in the step 6, the evaluation index for evaluating the gas inclusion property by using the gas inclusion property evaluation index parameter GASFG curve is: the GASFG is greater than 0.9 and is a gas layer, the GASFG is between 0.7 and 0.9 and is a gas-poor layer, the GASFG is between 0.5 and 0.7 and is a gas-containing layer, and the GASFG is less than 0.5 and is a dry layer or a non-reservoir layer.
Compared with the prior art, the invention has the following beneficial effects:
the method has scientific and reasonable design and wonderful conception, fully utilizes the excavation effect of natural gas on the neutron logging curve to carry out quantitative calculation of the gas content index parameters, effectively solves the technical problem that the gas content of the anhydrous compact sandstone gas reservoir in the prior art cannot be accurately evaluated under the condition of lacking of information such as formation water and the like through classification evaluation, and can effectively evaluate the gas content of the anhydrous sandstone gas reservoir and identify a high-gamma reservoir, thereby providing an accurate exploration method for oil-gas exploration.
Drawings
FIG. 1 is a flow chart of the present invention.
FIG. 2 is a diagram of the results of the present invention in evaluating the gas bearing capacity of a autumn forest 16 well.
FIG. 3 is a chart of the results of the present invention in evaluating the gas bearing capacity of a autumn forest 208 well.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation or be constructed and operated in a particular orientation, and thus, it should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; of course, mechanical connection and electrical connection are also possible; alternatively, they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
As shown in fig. 1, the method for evaluating the gas content of the anhydrous tight sandstone gas reservoir provided by the invention comprises the following steps:
further, in the step 1, a natural gamma curve or a natural gamma energy spectrum curve is adopted for carrying out
Where Sh is the relative value of natural gamma, GR is the measured value of natural gammaminNatural gamma value, GR, for pure sandstonemaxNatural gamma value of pure mudstone; GCUR is the empirical coefficient associated with the age of the geology, taking 2 for old strata and 3.7 for new strata.
The natural gamma curve or the natural gamma energy spectrum curve refers to a logging curve after filtering and regional standardization. The core data refers to the restored core mass content data; preferably, the data is full-rock clay analysis data or full-rock particle size analysis data.
And 2, calculating the effective porosity phi e, and calibrating by using the core physical property analysis data. And when the effective porosity phi e is calculated, calculating the effective porosity phi e by utilizing the acoustic wave or the density logging curve. The effective porosity Φ e is calculated as:
ΔT＝Φe.ΔTmf+Vsh.ΔTsh+Vma.ΔTma；
Φe+Vsh+Vma＝1；
wherein, Delta T is a sound wave time difference curvemfAcoustic time difference, Δ T, for mud filtrateshIs the mudstone acoustic time difference, Δ TmaFor the acoustic time difference of the skeleton, VmaIs the volume of the sandstone framework.
The sound wave or density curve needs to be standardized; the porosity of the core needs to be subjected to deep homing treatment; after core analysis porosity calibration, the error of the effective porosity phi e obtained by logging calculation needs to be within the error range specified by the reserves specification.
And 3, performing argillaceous correction on the neutron logging curve by using the argillaceous content Vsh calculated in the step 1 to obtain a neutron curve CNL1 of pure rock. The calculation formula for performing the shale correction on the neutron well logging curve is as follows:
CNL1＝CNL-Vsh.ΦNsh；
wherein, CNL is neutron logging value,
is the mudstone neutron value;
preferably, phi in the above formulaNshDetermined from the GR and CNL cross plots.
And 4, converting the pure rock neutron curve CNL1 in the step 3 into a sandstone skeleton hydrogen-containing index curve CNL 2. The CNL1 neutron logging curve obtained in step 3 is actually an apparent limestone hydrogen index curve, so the apparent limestone hydrogen index curve CNL1 needs to be converted into a sandstone skeleton hydrogen index curve CNL2, and the calculation formula for converting the pure rock neutron curve CNL1 into a sandstone skeleton hydrogen index curve CNL2 is as follows:
and 5, calculating a gassiness evaluation index parameter GASFG curve by using the porosity phi e calculated in the step 2 and the CNL2 curve obtained in the step 4 and adopting a rock volume physical model. The calculation formula for calculating the gassiness evaluation index parameter GASFG curve is as follows:
and 6, evaluating the gas content by using the gas content evaluation index parameter GASFG curve calculated in the step 5. The evaluation indexes for evaluating the gas content by using the gassiness evaluation index parameter GASFG curve are as follows: the GASFG is greater than 0.9 and is a gas layer, the GASFG is between 0.7 and 0.9 and is a gas-poor layer, the GASFG is between 0.5 and 0.7 and is a gas-containing layer, and the GASFG is less than 0.5 and is a dry layer or a non-reservoir layer.
The method has scientific and reasonable design and wonderful conception, fully utilizes the excavation effect of natural gas on the neutron logging curve to carry out quantitative calculation of the gas content index parameters, effectively solves the technical problem that the gas content of the anhydrous compact sandstone gas reservoir in the prior art cannot be accurately evaluated under the condition of lacking of information such as formation water and the like through classification evaluation, and can effectively evaluate the gas content of the anhydrous sandstone gas reservoir and identify a high-gamma reservoir, thereby providing an accurate exploration method for oil-gas exploration.
In order to enable a person skilled in the art to better understand the technical scheme, the technology of the invention is described in detail by taking a autumn forest 16-well dwarashium series salxi temple group compact sandstone reservoir as an example:
1. calculating the mud content Vsh by using a natural gamma or natural gamma energy spectrum curve:
GRminnatural gamma value, GR, for pure sandstonemaxIs the natural gamma value of pure mudstone.
2. Method for calculating effective porosity phi e of reservoir by utilizing sound waves
ΔT＝Φe.ΔTmf+Vsh.ΔTsh+Vma.ΔTma；
Φe+Vsh+Vma＝1；
Δ T is the sonic time difference curve, Δ TmfMud filtrate acoustic time difference, Δ TshIs the mudstone acoustic time difference, Δ TmaIs the acoustic time difference of the skeleton.
3. Conversion of the neutron curve CNL1 in pure rock. For an anhydrous sandstone gas reservoir, the neutron log is affected by the combined action of effective porosity, shale content and excavation effect. Firstly, performing shale correction on the compensation neutron curve CNL to obtain a neutron logging curve CNL1 of pure rock.
CNL1＝CNL-Vsh.ΦNsh；
In the formula phiNshIt should be determined from the GR and CNL cross-plots.
4. Apparent sandstone hydrogen index curve (CNL 2). According to the rock volume physical model, the apparent limestone hydrogen index curve CNL1 of pure rock is used for calculating to obtain the apparent sandstone skeleton hydrogen index curve CNL 2.
To obtain
5. Calculating a gassiness evaluation index parameter curve GASFG, wherein the calculation formula is as follows:
6. and performing gas-containing classification evaluation by using a gas-containing evaluation index parameter curve GASFG, wherein a gas layer is formed when the GASFG is more than 0.9, a gas layer is formed when the GASFG is between 0.7 and 0.9, a gas layer is formed when the GASFG is between 0.5 and 0.7, and a dry layer or a non-reservoir layer is formed when the GASFG is less than 0.5. The results of the qilin 16 well gas bearing evaluation are shown in fig. 2.
Taking autumn forest 16 wells and autumn forest 208 wells as examples, the gas bearing results evaluated by the technology of the invention have good evaluation effects, the evaluation results are shown in fig. 2 and 3, the evaluation results are consistent with the test conditions of the two wells, the water saturation recognition results are superior to the water saturation recognition results calculated by a conventional electrical method, and the high gamma reservoir recognition can be effectively carried out.
The method has scientific and reasonable design and wonderful conception, fully utilizes the excavation effect of natural gas on the neutron logging curve to carry out quantitative calculation of the gas content index parameters, and effectively solves the technical problem that the accurate gas content evaluation can not be carried out under the condition that the anhydrous compact sandstone gas is hidden in the lack of the formation water and other data in the prior art through classification evaluation. The method of the invention obtains good effect by applying the anhydrous compact sandstone gas reservoir in the Jurassic series Shaxi temple group in the autumn forest area. By utilizing the method, the gas content of the anhydrous sandstone gas reservoir can be effectively evaluated and the high-gamma reservoir can be effectively identified, so that the aim of better providing service for oil and gas exploration is fulfilled.
The invention provides an evaluation index of gas content of an anhydrous compact sandstone gas reservoir by utilizing the principle of the excavation effect of natural gas on neutron logging, and performs classified evaluation of the gas content on the basis. Practice proves that the index not only can accurately evaluate the gas content, but also can effectively identify the high-gamma reservoir of the research area. The method for calculating the gas content evaluation index comprises the following steps: calculating the argillaceous content Vsh; calculating the effective porosity phi of the reservoir; performing mud correction according to a hydrogen index curve of limestone; converting the hydrogen-containing index curve of the pure rock visual sandstone; quantitatively calculating the gas content evaluation index; and (4) classified evaluation of air inclusion. The method can effectively solve the technical problem that the prior art is limited by multiple factors such as difficulty in mass sampling, experimental method, experimental conditions, lack of data and the like, so that the evaluation result is low in precision.
Finally, it should be noted that: the above embodiments are only preferred embodiments of the present invention to illustrate the technical solutions of the present invention, but not to limit the technical solutions, and certainly not to limit the patent scope of the present invention; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention; that is, the technical problems to be solved by the present invention, which are not substantially changed or supplemented by the spirit and the concept of the main body of the present invention, are still consistent with the present invention and shall be included in the scope of the present invention; in addition, the technical scheme of the invention is directly or indirectly applied to other related technical fields, and the technical scheme is included in the patent protection scope of the invention.
Claims (10)
1. The method for evaluating the gas content of the compact sandstone anhydrous gas reservoir is characterized by comprising the following steps of:
step 1, calculating the argillaceous content VshCalibrating the rock core whole rock analysis data or the granularity analysis data;
step 2, calculating the effective porosity phieAnd calibrating by using the physical property analysis data of the rock core;
step 3, utilizing the calculated argillaceous content V in the step 1shPerforming shale correction on the neutron log to obtain a neutron curve CNL1 of pure rock;
step 4, converting the pure rock neutron curve CNL1 in the step 3 into a sandstone skeleton hydrogen-containing index curve CNL 2;
step 5, utilizing the porosity phi calculated in the step 2eCalculating a gassiness evaluation index parameter GASFG curve by adopting a rock volume physical model together with the CNL2 curve obtained in the step 4;
and 6, evaluating the gas content by using the gas content evaluation index parameter GASFG curve calculated in the step 5.
2. The method for evaluating the gas content of the tight sandstone anhydrous gas reservoir according to claim 1, wherein in the step 1, a natural gamma curve or a natural gamma energy spectrum curve is adopted to calculate the shale content Vsh; preferably, the calculation formula of the argillaceous content Vsh is:
where Sh is the relative value of natural gamma, GR is the measured value of natural gammaminNatural gamma value, GR, for pure sandstonemaxNatural gamma value of pure mudstone; GCUR is the empirical coefficient associated with the age of the geology, taking 2 for old strata and 3.7 for new strata.
3. The method for evaluating the gas content of the tight sandstone anhydrous gas reservoir of claim 1, wherein in the step 1, the natural gamma curve or the natural gamma energy spectrum curve refers to a logging curve after filtering and regional standardization.
4. The method for evaluating the gas content of the tight sandstone anhydrous gas reservoir according to claim 1, wherein the core data is the restored core shale content data; preferably, the data is obtained by whole-rock clay analysis data or whole-rock particle size analysis.
5. The tight sandstone anhydrous gas reservoir gas content evaluation method of claim 1, wherein in the step 2, the effective porosity Φ e is calculated by using a sound wave or a density log; preferably, the effective porosity Φ e is calculated as:
ΔT＝Φe.ΔTmf+Vsh.ΔTsh+Vma.ΔTma；
Φe+Vsh+Vma＝1；
wherein, Delta T is a sound wave time difference curvemfAcoustic time difference, Δ T, for mud filtrateshIs the mudstone acoustic time difference, Δ TmaFor sandstone frameworks acoustic time difference, VmaIs the volume of the sandstone framework.
6. The method for evaluating the gas content of the tight sandstone anhydrous gas reservoir according to claim 1, wherein in the step 2, the sound wave or the density curve needs to be subjected to standardization treatment; preferably, the porosity of the core needs to be subjected to deep homing treatment; further preferably, after core analysis porosity calibration, effective porosity phi obtained by logging calculationeThe error is required to be within the error range specified by the reserve specification.
7. The tight sandstone anhydrous gas reservoir gas content evaluation method of claim 1, wherein in the step 3, the calculation formula for performing the shale correction on the neutron logging curve is as follows:
CNL1＝CNL-Vsh.ΦNsh；
wherein, CNL is neutron logging value,
is the mudstone neutron value;
preferably, phi in the above formulaNshDetermined from the GR and CNL cross plots.
8. The tight sandstone anhydrous gas reservoir gas content evaluation method of claim 1, wherein in the step 4, the calculation formula for converting the pure rock neutron curve CNL1 into the sandstone skeleton hydrogen-containing index curve CNL2 is as follows:
9. the method for evaluating the gas content of the tight sandstone anhydrous gas reservoir according to claim 1, wherein in the step 5, a calculation formula for calculating a gassiness evaluation index parameter GASFG curve is as follows:
10. the method for evaluating the gas content of the tight sandstone anhydrous gas reservoir according to claim 1, wherein in the step 6, the evaluation indexes of the gas content evaluation by using a gas content evaluation index parameter GASFG curve are as follows: the GASFG is greater than 0.9 and is a gas layer, the GASFG is between 0.7 and 0.9 and is a gas-poor layer, the GASFG is between 0.5 and 0.7 and is a gas-containing layer, and the GASFG is less than 0.5 and is a dry layer or a non-reservoir layer.
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