Method for calculating density of shale gas reservoir by using element logging

Abstract

The application provides a method for calculating the density of a shale gas reservoir by using element logging, and the method comprises the following steps: according to the content of reservoir elements measured by element logging and the molecular formula of minerals in the reservoir, the mass fraction of each mineral and the density of rock framework are inversely calculated; according to the fitting curve of the content of nickel elements, the total organic carbon content in the reservoir is calculated; based on the minerals in the reservoir, the porosity of the shale gas reservoir is calculated; according to the content of illite, the water saturation and the gas saturation are calculated; and according to the calculation results, the rock density of the shale gas reservoir is calculated. The mineral component content and the rock framework density are inversely calculated by using element logging data, and then the total organic carbon content, the porosity and the water saturation and the gas saturation are sequentially calculated, so that the rock density of the reservoir is obtained, the calculation result error is small, the evaluation of the reservoir physical property is relatively accurate, and the theoretical and data support is provided for shale gas development; the method is simple in operation, reduces the difficulty of physical property parameter measurement, and is suitable for a wide range of applications.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of shale gas exploration and development, and relates to a method for calculating the density of a shale gas reservoir by using element logging. BACKGROUND

[0002] With the development of unconventional oil and gas resources, shale gas has become an important part of current oil and gas resource development, and shale reservoirs are the main areas for accumulation and storage of shale gas. Therefore, characterization of the related characteristics and parameters of shale reservoirs is the basis for shale gas development. Logging operation is a basic technology in oil and gas reservoir exploration and development activities, and is the most timely and direct technical means for discovering and evaluating oil and gas reservoirs. It has the characteristics of obtaining underground information in a timely, diverse and fast manner, and can provide reliable information service support for drilling operations. Element logging is an important type of logging technology, which is mainly used for detection and analysis of element content in rock strata to determine the mineral composition of the rock strata and facilitate the evaluation of rock strata properties, thereby providing technical support for oil and gas exploration and development.

[0003] In the process of oil and gas exploration and development, density is an important parameter for describing the reservoir capacity, and its acquisition methods include density logging and shale density logging. Due to engineering safety and cost reduction factors, a large number of horizontal wells do not carry out density logging, resulting in a lack of evaluation parameters. Therefore, shale density is currently calculated by logging. Since reservoir density is related to minerals, sedimentary environment and other factors, shale gas reservoirs are composed of rock framework, total organic carbon, formation water and shale gas, and the calculation of reservoir density needs to consider all components. The rock framework is composed of multiple minerals, and different minerals have different physical properties, which will also cause uneven density, further increasing the difficulty of shale gas reservoir density calculation and physical property evaluation.

[0004] In the article "Shale Density Calculation Model Based on Multivariate Adaptive Regression Splines" by Ouchengen et al., a method for fitting shale density is proposed by measuring single element content by element logging and using multivariate adaptive regression splines algorithm. However, the same single element can correspond to multiple minerals, and each mineral has its specific element composition and physical properties. Even if it contains the same element, its properties may differ greatly. Therefore, single element fitting is not suitable for shale gas reservoirs with multiple mineral types and multiple components. This method has poor universality.

[0005] CN 111997598A discloses a mud logging while drilling reservoir evaluation method, model establishment method, device and electronic equipment, the evaluation method comprises the following steps: obtaining element logging data in the drilling process; calculating the brittleness index, sedimentary environment and physical property parameter according to the element logging data; normalizing the brittleness index and sedimentary environment respectively; obtaining the reservoir evaluation result while drilling according to the physical property parameter, the pre-established three-parameter reservoir evaluation model and the normalized brittleness index and sedimentary environment. The method for evaluating the reservoir does not specify the specific calculation method, only gives the related parameters, the logging data required by the parameters is different from the parameters and data required for reservoir density calculation, and does not involve the calculation of reservoir density based on minerals.

[0006] In summary, for the element logging calculation of shale gas reservoir density, the mineral composition and constituent part in the reservoir need to be based on the element logging calculation of shale gas reservoir density, so as to accurately evaluate the reservoir physical property and provide data support for the exploitation of shale gas. SUMMARY

[0007] In view of the problems in the prior art, the purpose of the present application is to provide a method for calculating the density of shale gas reservoir by element logging, which inversely calculates the content of each mineral component and the rock skeleton density through the element content measured by element logging, and further calculates the porosity of the shale gas reservoir through the calculation of total organic carbon content, and then calculates the rock density of the reservoir through the calculation of water and gas saturation, the calculation result has smaller error, the evaluation of the reservoir physical property is more accurate, and the present application provides theoretical and data support for the development of shale gas.

[0008] To achieve the above purpose, the present application adopts the following technical solutions:

[0009] The present application provides a method for calculating the density of shale gas reservoir by element logging, which comprises the following steps:

[0010] (1) according to the mass fraction of the reservoir elements measured by element logging and the molecular formula of the minerals in the reservoir, inversely calculating the mass fraction of each mineral, and further calculating the density of the rock skeleton in the shale gas reservoir;

[0011] (2) according to the fitting curve of the nickel element content measured by element logging, calculating the total organic carbon content in the shale gas reservoir;

[0012] (3) according to the different total organic carbon content obtained in step (2), taking quartz, calcite, dolomite and clay in the reservoir minerals as the basis, calculating the porosity of the shale gas reservoir;

[0013] (4) according to the content of illite in the reservoir minerals calculated in step (1), calculating the water saturation of the shale gas reservoir, and further calculating the gas saturation of the shale gas reservoir;

[0014] (5) calculating the rock density of the shale gas reservoir according to the components of the shale gas reservoir and the calculation results of steps (1)-(4).

[0015] In the present application, the data measured by the element logging mainly includes the content of each element. However, the same element can correspond to multiple minerals, and the fitting formula established by fitting a single element has poor universality and is not accurate for evaluating the physical properties of the shale gas reservoir. Therefore, in the present application, the content of each mineral in the reservoir is calculated by inversely calculating the element content measured by the element logging, and the density of the rock skeleton can be calculated according to the mineral content. Then, the total organic carbon content in the shale gas reservoir is fitted, which is related to the calculation of porosity. Based on this, the calculation formula of porosity is fitted in combination with the content of the mineral types in the reservoir related to porosity. The calculation formula of water saturation is obtained according to the minerals related to the water saturation of the shale gas reservoir, and the gas saturation is also obtained. The calculation formula of the overall density of the shale gas reservoir is obtained by using the density of each component, and the calculation result obtained by the calculation formula has a smaller error with the logging result and high accuracy, which realizes the accurate evaluation of the physical properties of the shale gas reservoir, provides data support for the calculation of other physical parameters of the reservoir, improves the exploitation efficiency of shale gas, and reduces the exploitation difficulty.

[0016] The following is a preferred technical solution of the present application, but not as a limitation of the technical solution provided by the present application. Through the following technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0017] As a preferred technical solution of the present application, the reservoir elements in step (1) include Si, Ca, Al, Mg, K, Na, Fe, S and Ni.

[0018] Preferably, the mineral components of the shale gas reservoir include quartz, calcite, dolomite and clay.

[0019] Preferably, the mineral components of the shale gas reservoir further include any one or a combination of at least two of pyrite, gypsum or feldspar. Typical but non-limiting examples of the combination include a combination of pyrite and gypsum, a combination of gypsum and feldspar, a combination of pyrite, gypsum and feldspar, etc.

[0020] Preferably, the clay includes any one or a combination of at least two of illite, montmorillonite, kaolinite or mica. Typical but non-limiting examples of the combination include a combination of illite and montmorillonite, a combination of kaolinite and mica, a combination of illite, montmorillonite and kaolinite, a combination of illite, montmorillonite, kaolinite and mica, etc.

[0021] Preferably, the feldspar includes any one of potassium feldspar, sodium feldspar or analcite, or a combination of at least two of them, and typical but non-limiting examples of the combination include: a combination of potassium feldspar and sodium feldspar, a combination of sodium feldspar and analcite, a combination of potassium feldspar, sodium feldspar and analcite, etc.

[0022] In the present application, the shale gas reservoir is mainly located in a sedimentary rock stratum, and the mineral components involved include quartz, clay, carbonate rock, feldspar, gypsum, etc., and specifically include quartz, potassium feldspar, sodium feldspar, analcite, kaolinite, montmorillonite, illite, mica, calcite, dolomite, gypsum and pyrite, etc., and the chemical molecular formula and main elements of each mineral are shown in Table 1.

[0023] Table 1 Chemical molecular formula and main elements of each mineral in the shale gas reservoir

[0024]

[0025]

[0026] The minerals listed in the above table are not all the minerals that constitute the shale gas reservoir, but only the minerals with a larger mass fraction. Of course, not all shale reservoirs include the above-mentioned minerals, and according to the different regions and horizons, only some of the above-mentioned minerals may be included.

[0027] As a preferred technical solution of the present application, the inversion calculation of each mineral in the shale gas reservoir also needs to determine at least one coefficient representing the mass fraction ratio of two minerals according to the region and horizon where the shale gas reservoir is located.

[0028] Preferably, the two minerals corresponding to the coefficient at least contain one same element.

[0029] In the present application, in addition to the content of each element and the molecular formula of the mineral, the inversion calculation of the mineral content also needs to associate the minerals containing the same element, especially the few kinds of minerals containing only this element, so as to facilitate the simultaneous equation calculation of the content of each mineral.

[0030] Preferably, the density of the rock skeleton in step (1) is calculated by taking the inverse of the sum of the ratio of the mass fraction of each mineral to its density, and the density of the rock skeleton is denoted as ρ s-el .

[0031] In the present application, the density of the rock skeleton is calculated according to the mineral composition of the rock skeleton in the shale gas reservoir and the density of the single mineral, and for the listed minerals, the calculation formula is

[0032] ρ s-el =100 / (ω 1-el / ρ1+ω 2-el / ρ2+ω3-el / p3 + ω 4-el / p4 + ω 5-el / p5 + ω 6-el / p6 + ω 7-el / p7

[0033] Wherein, ω 1-el , ω 2-el , ω 3-el , ω 4-el , ω 5-el , ω 6-el and ω 7-el are the mass fraction of quartz, calcite, dolomite, clay, pyrite, gypsum and feldspar calculated by element logging, ρ1, ρ2, ρ3, ρ4, ρ5, ρ6 and ρ7 are the density of quartz, calcite, dolomite, clay, pyrite, gypsum and feldspar, if the reservoir does not contain a certain mineral, the item is not included in the calculation, if a certain mineral includes multiple, it is split and calculated respectively; among the above-mentioned mineral types, the quartz density is 2.5, the potassium feldspar density is 2.57, the sodium feldspar density is 2.62, the anorthite density is 2.6, the kaolinite density is 2.63, the montmorillonite density is 2.6, the illite density is 2.8, the mica density is 3.05, the calcite density is 2.71, the dolomite density is 2.87, the gypsum density is 2.4, the pyrite density is 5.2, and the density unit is g / cm 3 .

[0034] As a preferred technical scheme of the present application, the device used for element logging measurement includes an X-ray fluorescence spectrum analyzer (XRF), wherein the commonly used device model is Tianrui EDX4500H type and Tianrui EDX5500H type.

[0035] Preferably, the area of element logging measurement includes Longmaxi shale formation and Wufeng shale formation.

[0036] At present, the exploration and exploitation of shale gas mainly comes from Longmaxi shale reservoir and Wufeng shale reservoir, the former belongs to Silurian bottom layer, and the latter belongs to Ordovician stratum; the parameters collected by element logging are element types and content, wherein the main elements are Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, etc., and the trace elements are Co, Ni, Cu, Zn, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, In, Sn, W, Pb, Se, Ga, Cr, etc.

[0037] As a preferred technical scheme of the present application, step (2) needs multiple groups of data of nickel element content and total organic carbon content.

[0038] Preferably, the data of the total organic carbon content is obtained by geochemical logging analysis or laboratory analysis.

[0039] In the present application, in order to fit the calculation formula of the total organic carbon content, in addition to the content of nickel element, the point value of the total organic carbon content is also needed, which is obtained by other methods, used for fitting the curve to obtain the formula, and then the total organic carbon content under the element logging is calculated, and the data with small difference between the two calculation methods is selected.

[0040] As a preferred technical solution of the present application, the formula obtained after fitting the curve is

[0041] TOC el =(2.1228*ln(ω Ni -ω Ni-B )+14.4470)*ω0

[0042] Wherein, TOC el is the total organic carbon content calculated by element logging, ω Ni is the normalized nickel element content measured by element logging, ω Ni-B is the base value of the nickel element content of element logging, which refers to the corresponding nickel element content in the stratum with low total organic carbon content, and ω0 is the TOC correction coefficient, the value range of the correction coefficient is 0.5-2, for example, 0.5, 0.8, 1, 1.2, 1.5 or 2, etc., which is related to the regional nickel enrichment degree and the measured value of TOC.

[0043] Preferably, according to the value of TOC el , if the calculation result is less than 0, TOC el is 0.

[0044] In the present application, the content of metal nickel is selected as the calculation basis for the calculation of the total organic carbon content, mainly based on the fact that through statistical analysis, it is found that the TOC of core laboratory analysis or the TOC calculated by geochemical logging has good correlation with the content of element nickel, the correlation coefficient is 0.7563, and the corresponding goodness of fit is 0.572.

[0045] As a preferred technical solution of the present application, the total organic carbon content in step (3) is divided into two ranges, which are TOC el ≤2.5wt% and TOC el >2.5wt%.

[0046] In the present application, the two ranges of the total organic carbon content are mainly based on the empirical value obtained by parameter statistics, mainly used for distinguishing organic silicon and inorganic silicon, when TOC el>2.5wt%, the silicon in the shale gas reservoir is mainly in the form of organic silicon, and the porosity is positively correlated with the content of organic silicon; taking the Longmaxi Formation and the Wufeng Formation as examples, most of the high-silicon reservoirs in the Longmaxi Formation have the characteristics of high TOC and high porosity, and the high-silicon reservoirs in the Wufeng Formation, which is the underlying stratum of the Longmaxi Formation, have the characteristics of low TOC and low porosity.

[0047] Preferably, the calculation of the porosity is related to the mass fractions of quartz, calcite, dolomite and clay in the minerals, and the mass fractions are denoted as ω 1-el , ω 2-el , ω 3-el and ω 4-el , respectively.

[0048] As a preferred technical solution of the present application, when the total organic carbon content TOC el ≤2.5wt%, the calculation formula of the porosity of the shale gas reservoir is

[0049]

[0050] wherein, is the porosity calculated by elemental logging, and ε1 is the first shale gas reservoir coefficient.

[0051] Preferably, the first shale gas reservoir coefficient ε1 takes a value of 2-5, such as 2, 3, 4 or 5, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0052] As a preferred technical solution of the present application, when the total organic carbon content TOC el >2.5wt%, the calculation formula of the porosity of the shale gas reservoir is

[0053]

[0054] wherein, is the porosity calculated by elemental logging, and ε2 is the second shale gas reservoir coefficient.

[0055] Preferably, the second shale gas reservoir coefficient ε2 takes a value of 5-15, such as 5, 6, 8, 10, 12 or 15, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0056] In the present application, quartz, calcite, dolomite and clay are selected as the basis for calculating the porosity of the shale gas reservoir, mainly because according to previous research, the porosity of the shale gas reservoir is generally positively correlated with the content of silicon, and is negatively correlated with the content of clay and the content of carbonate rocks; in addition, under the same conditions, the thermal expansion coefficient of quartz is 5-10 times that of other most rock minerals, and quartz is more likely to produce cracks, so the porosity of the reservoir with high quartz content is higher.

[0057] As a preferred technical solution of the present application, the illite in step (4) belongs to one of the clays, and the mass fraction thereof is calculated from step (1) and denoted as ω 41-el .

[0058] Preferably, the calculation formula of the water saturation in step (4) is

[0059] S w-el = 19.2828 x POWER (ω 41-el , 1 / 2) - 3.6675

[0060] wherein S w-el is the water saturation calculated by element logging.

[0061] Preferably, according to the calculation result of S w-el , if the value thereof is less than 0, S w-el is taken as 0, and if the value thereof is greater than 100, S w-el is taken as 100.

[0062] In the present application, the water saturation calculation formula is obtained in addition to the point value of the mass fraction of illite calculated by element logging, and the value of the water saturation, which is obtained through core laboratory analysis or logging calculation; wherein the calculation of the water saturation is based on the content of illite, mainly because the water saturation has a good correlation with the content of illite, and the correlation coefficient between the water saturation and the square root of the content of illite is 0.7426, and the corresponding goodness of fit is 0.5515.

[0063] Preferably, the gas saturation S g-el of the shale gas reservoir is 100-S w-el .

[0064] Preferably, if the reservoir is a shale oil reservoir, the corresponding oil saturation S o-el is 100-S w-el .

[0065] In the present application, when the formation is a shale gas reservoir, the gas saturation is calculated from the water saturation, and when it is a shale oil reservoir, the oil saturation is calculated from the water saturation.

[0066] As a preferred technical solution of the present application, the shale gas reservoir in step (5) is composed of a rock skeleton, total organic carbon, formation gas and formation water.

[0067] Preferably, the calculation formula of the rock density in step (5) is

[0068]

[0069] wherein ρb-el ρ is the rock density calculated by elemental logging s-el ρ is the rock skeleton density calculated by elemental logging g ρ is the formation gas density fw ρ is the formation water density TOC ρ is the organic matter density; among the above densities, the formation gas density is taken as 1.5, the salt water density is taken as 1.05, and the organic matter density is taken as 1.5; if it contains oil phase, the shale oil density is taken as 1.0, and the unit is g / cm 3 .

[0070] In the present application, the rock density of the shale gas reservoir is determined by the relationship between each component and the overall density. In the above formula, the shale gas reservoir is composed of rock skeleton, formation water, formation gas and organic matter. The rock density is calculated according to the rock volume model and the conversion relationship of the volume fraction, mass fraction and density of each part.

[0071] As a preferred technical solution of the present application, the method comprises the following steps:

[0072] (1) According to the mass fraction of the reservoir elements measured by elemental logging and the molecular formula of the minerals in the reservoir, the mass fraction of each mineral is inversely calculated, wherein the reservoir elements include Si, Ca, Al, Mg, K, Na, Fe, S and Ni, and the mineral components of the reservoir include quartz, calcite, dolomite and clay, and any one or combination of at least two of pyrite, gypsum or feldspar; at least one coefficient representing the mass fraction ratio of two minerals is determined according to the region and layer where the shale gas reservoir is located, and the two minerals corresponding to the coefficient contain at least one same element; and then the density of the rock skeleton in the shale gas reservoir is calculated, which is obtained by taking the inverse of the sum of the ratio of the mass fraction of each mineral to its own density.

[0073] (2) A fitting curve is obtained according to the nickel element content measured by elemental logging, wherein the fitting curve needs multiple sets of nickel element content and total organic carbon content data, the total organic carbon content data is obtained by geochemical logging analysis or laboratory analysis, and the formula obtained after the fitting curve is TOC el =(2.1228*ln(ω Ni -ω Ni-B )+14.4470)*ω0, the total organic carbon content in the shale gas reservoir is calculated, and if the calculation result is less than 0, TOC el is taken as 0.

[0074] (3) According to the different total organic carbon content obtained in step (2), the total organic carbon content is divided into two ranges, which are TOC el ≤2.5wt% and TOC el>2.5wt%, based on the mass fraction of quartz, calcite, dolomite and clay in the reservoir mineral, total organic carbon content TOC el When ≤2.5wt%, the calculation formula of the shale gas reservoir porosity is Total organic carbon content TOC el When >2.5wt%, the calculation formula of the shale gas reservoir porosity is The porosity of the shale gas reservoir is calculated.

[0075] (4) The mass fraction ω of illite in the reservoir mineral is calculated according to step (1) 41-el The water saturation of the shale gas reservoir is calculated, and the calculation formula of the water saturation is S w-el = 19.2828*POWER(ω 41-el , 1 / 2) - 3.6675, and the gas saturation S g-el = 100 - S w-el of the shale gas reservoir is further calculated.

[0076] (5) The rock density of the shale gas reservoir is calculated according to the composition of the shale gas reservoir and the calculation results of steps (1)-(4), and the calculation formula of the rock density is

[0077] Compared with the prior art, the present application has the following beneficial effects:

[0078] (1) The method of the present application calculates the content of each mineral component and the rock framework density through the element content measured by element logging, and further calculates the porosity of the shale gas reservoir through the calculation of the total organic carbon content, and then calculates the rock density of the reservoir through the calculation of the water and gas saturations. The error of the calculation result compared with the logging result is small, and the average error of the two is only -0.44%, and the overall average error is -0.35%. The evaluation of the reservoir properties is more accurate, which provides theoretical and data support for the development of shale gas.

[0079] (2) The method of the present application is simple to operate, and the acquisition of the fitting formula reduces the difficulty of measuring the physical property parameters of the shale gas reservoir, and has a wide range of application. BRIEF DESCRIPTION OF DRAWINGS

[0080] Figure 1 is the element logging density calculation and logging density comparison chart provided by the embodiment of the present application. DETAILED DESCRIPTION

[0081] In order to better illustrate the present application, facilitate understanding of the technical solutions of the present application, the present application is further described in detail below. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims.

[0082] The specific embodiment part of the present application provides a method for calculating the density of a shale gas reservoir by using element logging, and the method comprises the following steps:

[0083] (1) According to the mass fraction of reservoir elements measured by element logging and the molecular formula of minerals in the reservoir, the mass fraction of each mineral is inversely calculated, and then the density of the rock framework in the shale gas reservoir is calculated;

[0084] (2) According to the fitting curve of the nickel element content measured by element logging, the total organic carbon content in the shale gas reservoir is calculated;

[0085] (3) According to the different total organic carbon contents obtained in step (2), the quartz, calcite, dolomite and clay in the reservoir minerals are taken as the basis to calculate the porosity of the shale gas reservoir;

[0086] (4) According to the content of illite in the reservoir minerals calculated in step (1), the water saturation of the shale gas reservoir is calculated, and then the gas saturation of the shale gas reservoir is calculated;

[0087] (5) According to the composition of the shale gas reservoir and the calculation results of steps (1)-(4), the rock density of the shale gas reservoir is calculated.

[0088] The following are typical but non-limiting examples of the present application:

[0089] Example 1:

[0090] The present embodiment provides a method for calculating the density of a shale gas reservoir by using element logging, taking a shale gas horizontal well in Luzhou area of Sichuan Basin as an example, and the method comprises the following steps:

[0091] (1) According to the mass fraction of reservoir elements measured by element logging and the molecular formula of minerals in the reservoir, the mass fraction of each mineral is inversely calculated, and then the density of the rock framework in the shale gas reservoir is calculated;

[0092] Within the well section with a depth of 3900–5992 m, elemental logging measurements and analysis were performed on the samples. Taking the 5000 m depth point as an example, based on the inversion calculation of the content of each element, the mass fractions of the above minerals are as follows: quartz 49.03%, calcite 23.12%, dolomite 10.31%, clay 10.64%, pyrite 2.80%, and albite 4.10%. Among them, the clay is divided into illite 0.00%, montmorillonite 0.95%, kaolinite 1.30%, and mica 8.39%.

[0093] Combining the density values ​​of each mineral, the corresponding density of the rock skeleton is ρ. s-el =100 / (49.03 / 2.5+4.1 / 2.62+8.39 / 3.05+0.95 / 2.6+1.30 / 2.63+0.00 / 2.8+23.12 / 2.71+10.31 / 2.87+2.8 / 5.2)=2.67g / cm 3 ;

[0094] (2) A fitting curve is obtained based on the nickel content measured by elemental logging. This fitting curve requires multiple sets of data on nickel content and total organic carbon (TOC). The TOC data is obtained from geochemical logging analysis. The formula obtained after fitting the curve is TOC. el =(2.1228×ln(ω) Ni -ω Ni-B )+14.4470)×ω0, calculate the total organic carbon content in the shale gas reservoir;

[0095] At a well depth of 5000m, elemental logging showed a nickel content of 196 ppm, with a corresponding ω Ni It is 0.0196%, ω Ni-B The value is 0.00%, and the ω0 correction factor is 0.8. Substituting these values ​​into the formula, we obtain the TOC. el It is 4.88 wt%;

[0096] (3) Based on the total organic carbon content obtained in step (2), since TOC el >2.5wt%, based on the mass fractions of quartz, calcite, dolomite, and clay in the reservoir minerals, the formula for calculating shale gas reservoir porosity is as follows: Where ε2 is 10, the porosity of the shale gas reservoir is calculated. It was 4.73%;

[0097] (4) The mass fraction ω of illite in the reservoir minerals calculated according to step (1) 41-el Calculate the water saturation of the shale gas reservoir and substitute it into the calculation formula S. w-el =19.2828×POWER(ω 41-el,1 / 2)-3.6675, the calculation result is less than 0, then the water saturation S w-el Take 0.00%, and then use the formula S g-el = 100-S w-el Calculate the gas saturation S of the shale gas reservoir g-el is 100%;

[0098] (5) According to the shale gas reservoir composed of rock skeleton, total organic carbon, formation gas and formation water, plus the calculation results of steps (1)-(4), the rock density of the shale gas reservoir is calculated, and the calculation formula is Combined with the values of ρ g , ρ fw , ρ TOC , the rock density of the shale gas reservoir is 2.52 g / cm 3 .

[0099] In this embodiment, the logging density of the shale gas well at the same depth and position is 2.59 g / cm 3 , and the error between the element logging calculated density and the logging density is-2.56%.

[0100] Example 2:

[0101] The embodiment provides a method for calculating the density of a shale gas reservoir by using element logging, taking a shale gas horizontal well in Luzhou area of Sichuan Basin as an example, and the method comprises the following steps:

[0102] (1) According to the mass fraction of reservoir elements measured by element logging and the molecular formula of minerals in the reservoir, the reservoir elements include Si, Ca, Al, Mg, K, Na, Fe, S and Ni, the mineral components of the reservoir include quartz, calcite, dolomite, clay, pyrite and albite, the clay includes illite, montmorillonite, kaolinite and mica, the mass fraction of each mineral is inversely calculated, and four coefficients representing the mass fraction ratio of two minerals are determined according to the area and layer of the shale gas reservoir, the two minerals corresponding to the coefficients contain the same elements; and then the density of the rock skeleton in the shale gas reservoir is calculated, and the density of the rock skeleton is calculated by taking the reciprocal of the sum of the mass fraction of each mineral and the density of each mineral.

[0103] In the well section with the depth of 3900-5992 m, element logging measurement and sample analysis are carried out, and taking the well depth point of 5600 m as an example, the mass fractions of the above minerals are respectively 50.77% for quartz, 18.30% for calcite, 13.90% for dolomite, 9.84% for clay, 2.30% for pyrite and 4.89% for albite according to the inversion calculation based on the content of each element, wherein the clay is divided into illite 0.00%, montmorillonite 1.28%, kaolinite 0.67% and mica 7.89%;

[0104] In combination with the density values of each mineral, the density of the corresponding rock skeleton is ρ s-el = 2.66 g / cm 3 ;

[0105] (2) A fitting curve of the nickel element content according to element logging measurement is obtained, a plurality of groups of nickel element content and total organic carbon content data are required for the fitting curve, the total organic carbon content data are obtained by laboratory analysis, and a formula obtained after the fitting curve is TOC el = (2.1228 x ln(ω Ni - ω Ni-B ) + 14.4470) x ω0, the total organic carbon content in the shale gas reservoir is calculated;

[0106] The nickel element content measured by element logging at the well depth point of 5600 m is 219 ppm, the corresponding ω Ni is 0.0219%, ω Ni-B is 0.00%, the ω0 correction coefficient is 0.8, and the formula is substituted to obtain TOC el of 5.07 wt%;

[0107] (3) According to the total organic carbon content obtained in step (2), since TOC el > 2.5 wt%, the mass fraction of quartz, calcite, dolomite and clay in the reservoir mineral is taken as the basis, and the calculation formula of the porosity of the shale gas reservoir is wherein ε2 is 10, and the porosity of the shale gas reservoir is calculated as 5.00%;

[0108] (4) According to the mass fraction ω 41-el of illite in the reservoir mineral calculated in step (1), the water saturation of the shale gas reservoir is calculated, and the calculation formula is S w-el = 19.2828 x POWER(ω 41-el ​,1 / 2)-3.6675, the calculation result is less than 0, then the water saturation S w-el Take 0.00%, and then use the formula S g-el = 100 - S w-el The gas saturation S of the shale gas reservoir is calculated g-el is 100%;

[0109] (5) According to the shale gas reservoir composed of rock skeleton, total organic carbon, formation gas and formation water, plus the calculation results of steps (1)-(4), the rock density of the shale gas reservoir is calculated, and the calculation formula is Combined with the values of ρ g , ρ fw , ρ TOC , the rock density of the shale gas reservoir is 2.51 g / cm 3 .

[0110] In this embodiment, the logging density of the shale gas well at the same depth and position is 2.59 g / cm 3 , and the error between the element logging calculated density and the logging density is -3.33%.

[0111] Example 3

[0112] The embodiment provides a method for calculating the density of a shale gas reservoir by element logging, taking a shale gas horizontal well in Luzhou area of Sichuan Basin as an example, and the method comprises the following steps:

[0113] (1) According to the mass fraction of reservoir elements measured by element logging and the molecular formula of minerals in the reservoir, the reservoir elements include Si, Ca, Al, Mg, K, Na, Fe, S and Ni, the mineral components of the reservoir include quartz, calcite, dolomite, clay, pyrite and albite, the clay includes illite, montmorillonite, kaolinite and mica, the mass fraction of each mineral is inversely calculated, and four coefficients representing the mass fraction ratio of two minerals are determined according to the area and layer of the shale gas reservoir, and the two minerals corresponding to the coefficients contain the same elements; and then the density of the rock skeleton in the shale gas reservoir is calculated, and the density of the rock skeleton is calculated by taking the inverse of the sum of the mass fraction of each mineral and the density of each mineral.

[0114] Within the well section with a depth of 3900–5992 m, elemental logging measurements and analysis were performed on the samples. Taking the well depth of 5848 m as an example, based on the inversion calculation of the content of each element, the mass fractions of the above minerals are as follows: quartz 55.32%, calcite 26.10%, dolomite 2.68%, clay 11.95%, pyrite 3.95%, and albite 0.00%. The clay is further divided into illite 2.11%, montmorillonite 0.36%, kaolinite 3.17%, and mica 6.31%.

[0115] Combining the density values ​​of each mineral, the corresponding density of the rock skeleton is ρ. s-el =100 / (55.32 / 2.5+0.00 / 2.62+6.31 / 3.05+0.36 / 2.6+3.17 / 2.63+2.11 / 2.8+26.10 / 2.71+2.68 / 2.87+3.95 / 5.2)=2.66g / cm 3 ;

[0116] (2) A fitting curve is obtained based on the nickel content measured by elemental logging. This fitting curve requires multiple sets of nickel content and total organic carbon (TOC) data. The TOC data is obtained through laboratory analysis. The formula derived from the fitting curve is TOC. el =(2.1228×ln(ω) Ni -ω Ni-B )+14.4470)×ω0, calculate the total organic carbon content in the shale gas reservoir;

[0117] At a well depth of 5848m, elemental logging measurements showed a nickel content of 225 ppm, with a corresponding ω... Ni It is 0.0225%, ω Ni-B The value is 0.00%, and the ω0 correction factor is 0.8. Substituting these values ​​into the formula, we obtain the TOC. el It is 5.12 wt%;

[0118] (3) Based on the total organic carbon content obtained in step (2), since TOC el >2.5wt%, based on the mass fractions of quartz, calcite, dolomite, and clay in the reservoir minerals, the formula for calculating shale gas reservoir porosity is as follows: Where ε2 is 10, the porosity of the shale gas reservoir is calculated. It is 5.51%;

[0119] (4) The mass fraction ω of illite in the reservoir minerals calculated according to step (1) 41-el To calculate the water saturation of a shale gas reservoir, substitute the values ​​into the formula to obtain S. w-el =19.2828×POWER(ω 41-el,1 / 2)-3.6675, the calculation result is 24.36%, and then the formula S g-el = 100-S w-el The gas saturation S of the shale gas reservoir is calculated g-el 75.64%;

[0120] (5) According to the shale gas reservoir composed of rock skeleton, total organic carbon, formation gas and formation water, and the calculation results of steps (1)-(4), the rock density of the shale gas reservoir is calculated, and the calculation formula is Combined with the values of p g , p fw , p TOC , the rock density of the shale gas reservoir is 2.49 g / cm 3 .

[0121] In this embodiment, the logging density of the shale gas well at the same depth and position is 2.55 g / cm 3 , and the error between the element logging calculated density and the logging density is-2.44%.

[0122] In the well section with a shale gas depth of 3900-5992 m, the density of the shale gas reservoir is calculated by element logging, and the logging density is given, and the comparison chart of the two is shown in Figure 1 , and the statistical results are shown in Table 2.

[0123] Table 2 Statistical results of element logging calculated density and logging density

[0124]

[0125]

[0126]

[0127]

[0128]

[0129] From Figure 1 and Table 2, in the above well section, the minimum value of the element logging calculated density is 2.42 g / cm 3 , the maximum value is 2.66 g / cm 3 , and the average value is 2.53 g / cm 3 ; and the minimum value of the logging density is 2.38 g / cm 3 , the maximum value is 2.74 g / cm 3 , and the average value is 2.54 g / cm 3The error between the average values of both is-0.44%; the average positive error is 1.53%, the average negative error is-1.92%, and the overall average error is-0.35%, the error between both is small, and the overall change trend is consistent.

[0130] It can be seen from the above examples that the method calculates the content of each mineral component and the rock skeleton density through the element content measured by element logging, and further calculates the porosity of the shale gas reservoir through the calculation of the total organic carbon content, and then calculates the rock density of the reservoir through the calculation of the water and gas saturation, the error of the calculation result compared with the logging result is small, the error between the average values of both is only-0.44%, the overall average error is-0.35%, the evaluation of the reservoir physical property is more accurate, and the method provides theoretical and data support for the development of shale gas; the method is simple to operate, the acquisition of the fitting formula reduces the difficulty of the measurement of the physical property parameters of the shale gas reservoir, and is suitable for a wide range of applications.

[0131] The detailed method of the present application is illustrated by the above examples, but the present application is not limited to the above detailed method, that is, it does not mean that the present application must rely on the above detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the method of the present application, addition of auxiliary steps, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for calculating shale gas reservoir density using elemental logging, characterized in that, The method includes the following steps: (1) Based on the mass fraction of reservoir elements measured by element logging and the molecular formula of minerals in the reservoir, the mass fraction of each mineral is calculated by inversion, and then the density of the rock skeleton in the shale gas reservoir is calculated. (2) Calculate the total organic carbon content in the shale gas reservoir based on the nickel content fitting curve obtained from elemental logging measurements; (3) Based on the different total organic carbon contents obtained in step (2), calculate the porosity of the shale gas reservoir using quartz, calcite, dolomite and clay in the reservoir minerals as the basis; (4) Calculate the water saturation of the shale gas reservoir based on the illite content in the reservoir minerals calculated in step (1), and then calculate the gas saturation of the shale gas reservoir. (5) Calculate the rock density of the shale gas reservoir based on the composition of the shale gas reservoir and the calculation results of steps (1)-(4); The fitting curve described in step (2) requires multiple sets of data on nickel content and total organic carbon content; The total organic carbon content data were obtained from geochemical logging analysis or laboratory analysis; The formula obtained after fitting the curve is: TOC el =(2.1228×ln(ω Ni -oh Ni-B )+14.4470)×ω0 Among them, TOC el The total organic carbon content calculated from elemental logging, ω Ni The normalized nickel content from elemental logging measurements, ω Ni-B ω0 is the baseline value of nickel content in elemental logging, and ω0 is the TOC correction coefficient; According to TOC el The numerical value, if its calculation result is less than 0, then TOC el Take 0.

2. The method according to claim 1, characterized in that, The shale gas reservoir elements mentioned in step (1) include Si, Ca, Al, Mg, K, Na, Fe, S and Ni.

3. The method according to claim 1, characterized in that, The mineral composition of the shale gas reservoir includes quartz, calcite, dolomite, and clay.

4. The method according to claim 1, characterized in that, The mineral composition of the shale gas reservoir also includes any one or a combination of at least two of pyrite, gypsum, or feldspar.

5. The method according to claim 3, characterized in that, The clay includes any one or a combination of at least two of illite, montmorillonite, kaolinite, or mica.

6. The method according to claim 4, characterized in that, The feldspar includes potassium feldspar or sodium feldspar.

7. The method according to claim 1, characterized in that, The inversion calculation of each mineral in the shale gas reservoir also requires determining at least one coefficient that characterizes the ratio of the two mineral quantities, based on the region and stratigraphic position of the shale gas reservoir.

8. The method according to claim 7, characterized in that, The coefficients correspond to two minerals that contain at least one of the same elements.

9. The method according to claim 1, characterized in that, The density of the rock skeleton in step (1) is calculated by summing the ratios of the mass fraction of each mineral to its density and taking the reciprocal. The density of the rock skeleton is denoted as ρ. s-el .

10. The method according to claim 1, characterized in that, The equipment used for elemental logging measurements includes an X-ray fluorescence spectrometer.

11. The method according to claim 1, characterized in that, The area measured by the elemental logging includes the Longmaxi Formation shale formation and the Wufeng Formation shale formation.

12. The method according to claim 1, characterized in that, The total organic carbon content mentioned in step (3) is divided into two ranges, namely TOC. el ≤2.5wt% and TOC el >2.5wt%.

13. The method according to claim 1, characterized in that, The calculation of porosity is related to the mass fractions of quartz, calcite, dolomite, and clay in the mineral, and their mass fractions are denoted as ω. 1-el ω 2-el ω 3-el and ω 4-el .

14. The method according to claim 13, characterized in that, The total organic carbon content (TOC) el When the content is ≤2.5wt%, the formula for calculating the porosity of shale gas reservoirs is as follows: f el =(sin(ω 1-el +30)) 2 ×ε1×e (-(ω 2-el +ω 3-el ) / 100) ×e (-ω 4-el / 100) Where, φ el ε1 represents the porosity calculated from elemental logging, and ε1 is the first shale gas reservoir coefficient.

15. The method according to claim 14, characterized in that, The first shale gas reservoir coefficient ε1 is 2 to 5.

16. The method according to claim 13, characterized in that, The total organic carbon content (TOC) el When the porosity is >2.5wt%, the formula for calculating the porosity of shale gas reservoirs is as follows: f el =(sin(ω 1-el +10)) 2 ×ε2×e (-(ω 2-el +ω 3-el ) / 100) ×e (-ω 4-el / 100) Where, φ el ε1 represents the porosity calculated from elemental logging, and ε2 represents the second shale gas reservoir coefficient.

17. The method according to claim 16, characterized in that, The second shale gas reservoir coefficient ε2 is 5~15.

18. The method according to claim 17, characterized in that, The illite mentioned in step (4) is a type of clay, and its mass fraction is calculated from step (1) and denoted as ω. 41-el .

19. The method according to claim 18, characterized in that, The formula for calculating the water saturation in step (4) is as follows: S w-el =19.2828×POWER(ω 41-el ,1 / 2) -3.6675 Among them, S w-el Water saturation calculated from element logging.

20. The method according to claim 19, characterized in that, According to S w-el If the calculated result is less than 0, then S w-el If the value is 0, then S is greater than 100. w-el Take 100.

21. The method according to claim 19, characterized in that, The gas saturation S of the shale gas reservoir g-el =100-S w-el .

22. The method according to claim 19, characterized in that, If the reservoir is a shale oil reservoir, then the corresponding oil saturation S is... o-el =100-S w-el .

23. The method according to claim 22, characterized in that, The shale gas reservoir described in step (5) consists of a rock skeleton, total organic carbon, formation gas and formation water.

24. The method according to claim 23, characterized in that, The formula for calculating the rock density in step (5) is as follows: r b-el =(ρ s-el ×(1-φ el / 100)+r g ×φ el ×S g-el / 10000+r fw ×φ el ×S w-el / 10000) / (1+ρ s-el / r TOC ×TOC el / 100-TOC el / 100) Where, ρ b-el The rock density calculated for elemental logging, ρ s-el The density of the rock skeleton calculated for elemental logging, ρ g ρ is the density of the formation gas. fw ρ is the density of formation water. TOC This represents the density of organic matter.

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