CN115808500A - Quantitative determination method for free gas in silt shale - Google Patents
Quantitative determination method for free gas in silt shale Download PDFInfo
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- CN115808500A CN115808500A CN202111071182.8A CN202111071182A CN115808500A CN 115808500 A CN115808500 A CN 115808500A CN 202111071182 A CN202111071182 A CN 202111071182A CN 115808500 A CN115808500 A CN 115808500A
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Abstract
The invention discloses the field of shale gas content detection, and particularly relates to a quantitative determination method for free gas in silt shale. In the technical scheme of the invention, the idea of recovering lost gas by using desorbed gas is changed into a pore structure analysis method for representing free gas and adsorbed gas. Selecting a well with complete core data as a sample well to carry out sampling experiment analysis, carrying out a plurality of groups of low-temperature nitrogen adsorption experiments and helium-method porosity experiments after silt shale at different layers is sampled, representing gas-bearing characteristics by combining gas logging parameters and density curves, establishing a linear correlation relationship between gas logging total hydrocarbons and free gas, and obtaining quantitative data of the free gas in the silt shale through the linear correlation relationship.
Description
Technical Field
The invention relates to the field of shale gas content detection, in particular to a quantitative determination method for free gas in silty shale.
Background
The gas content of the shale gas is always a core parameter in the exploration and evaluation process of the shale gas, the shale gas has two occurrence states, namely free gas and adsorbed gas, and the occurrence states and the adsorption and dissociation ratios change along with the change of temperature and pressure. At present, the total gas content of a shale field gas content experiment can be divided into analysis gas, loss gas and residual gas according to different coring stages. Residual gas needs to be broken by the core to allow gas in dead pores to escape, the gas quantity of the residual gas is small, and reading errors of the residual gas quantity are large due to a thermal expansion effect in a breaking process, so that most of the residual gas is classified into analytic gas and lost gas.
The process of desorption of adsorbed gas is commonly used to predict lost gas recovery, and currently, the method commonly comprises the USBM method, the curve method, the Smith-Williams method and the like. The methods have good adaptability to testing rocks with good adsorbability, such as organic shale-rich reservoirs, coal rock reservoirs and the like. In the reservoirs rich in organic shale and coal rock, the specific gravity of free gas is small, and the specific gravity of adsorbed gas is large, so that the error generated by reversely deducing the free gas quantity through a curve obtained by an adsorbed gas desorption experiment is small.
However, for the rock with weak adsorbability, such as silty shale, the content of free gas is higher than that of adsorbed gas, and the analytic gas obtained through an experimental method is lower, so that the recovered gas content is not matched with the parameters of gas-logging total hydrocarbon obtained in the logging process, the experimental error is larger, and the gas content of a reservoir cannot be objectively evaluated; therefore, the gas mechanism of the silty shale needs to be analyzed, a new quantitative determination method is formed, and strong evidence is provided for guiding shale reservoir evaluation and reserve calculation.
Disclosure of Invention
The invention aims to overcome the defects that the existing method for recovering the lost gas in the shale in the prior art is not suitable for calculating the gas content of the silt shale and has larger errors, and provides a method for quantitatively determining the free gas in the silt shale.
In order to achieve the above object, the present invention provides the following technical solutions:
a method for quantitatively measuring free gas in silty shale comprises the following steps:
In the technical scheme of the invention, the idea of recovering lost gas by using desorbed gas is changed into a pore structure analysis method for representing free gas and adsorbed gas. Selecting a well with complete core data as a sample well to carry out sampling experiment analysis, carrying out a plurality of groups of low-temperature nitrogen adsorption experiments and helium-method porosity experiments after silt shale at different layers is sampled, representing gas-bearing characteristics by combining gas logging parameters and density curves, establishing linear correlation between gas logging total hydrocarbon and free gas, and obtaining quantitative data of the free gas in the silt shale through the linear correlation.
The BET model is the physical adsorption of a rock surface at low temperatures and is currently recognized as a standard method for measuring specific solid surfaces. It is assumed that physical adsorption is performed in a multilayer manner, and when adsorption is in equilibrium, equilibrium adsorption pressure and adsorption gas amount are measured. The surface area measured by the adsorption method is essentially the sum of the surface areas of the rocks that the adsorbate molecules can reach.
As a preferred technical scheme of the invention, the BET adsorption isotherm equation is as follows:
wherein, V m : the saturated adsorption capacity of the monomolecular layer adsorbs air;
v: the volume of gas adsorbed;
P 0 : the saturated vapor pressure of the adsorbate;
p: adsorbate pressure;
c is a constant related to the heat of vaporization of the adsorbate.
As a preferred technical scheme of the invention, the nitrogen adsorption experiment data in the step 1 are screened to obtain effective V m Data, the screening conditionsThe method comprises the following steps:
C>0; the relative pressure of the point taking range is controlled to be between 0.05 and 0.35, and must be in a range that V (1-P/P0) is increased along with P/P0; adsorption capacity V for saturation of single-layer adsorption m The corresponding pressure points are counted into a point selection range. As a preferred embodiment of the present invention, the porosity is
With rock density p r The relationship between them is:
ρ r ＝1/V rock ；
Therefore, it is
Gas logging of total hydrocarbons (T) G ) The total gas volume in the drilling fluid during the drilling process is measured by the curve, and the unit is "%". The gas logging total hydrocarbon value is mainly influenced by geological factors, drilling conditions, a degassing device and a gas logging instrument, under the condition of ensuring that the degassing efficiency, the gas logging instrument calibration and the drilling mud density are consistent, abnormal values such as single gas connection, drilling gas tripping and the like are eliminated, and the drilling gas, namely gas released by broken rocks, is identified to form gas display.
Same rock sample, too high in drilling time (Rop), slower in rock breaking, T G The value decreases, so a decreases; too high a time of drilling (Rop), faster rock breaking, T G The value decreases, a increases; when the fluctuation range is large, the gas measurement total hydrocarbon value also fluctuates, and a linear correlation with free gas is difficult to obtain. As a preferred technical scheme of the invention, the gas measurement total hydrocarbon data and V of 20-50min/m are screened when drilling free The calculated values establish a linear correlation. In the linear correlation equation, T G The bit size and the mud density corresponding to the value-taking point are consistent, the fluctuation is kept within 30-40min/m during drilling, and the variation of the gas measurement background value is relatively small.
And passing the free gas content and gasMeasuring the linear correlation of the total hydrocarbon and correcting the content of the free hydrocarbon to obtain a linear formula: v free ＝a*T G + b; wherein b = f (Rop, R) 2 -r 2 )，b<0；a＝—f(Rop，R 2 -r 2 ) Background value of/TG a>0。
Rop is drilling time, min/m;
r is the outer diameter of the drill bit m;
r is the inner diameter of the drill bit, m;
T G background value: when the mud is invaded by some gas in the overburden stratum during the drilling process, the total hydrocarbon curve has little change and is a relatively stable measured value.
As a preferred technical scheme of the invention, the porosity phi and the rock density rho are respectively obtained through a helium porosity experiment and a density logging test.
Compared with the prior art, the invention has the beneficial effects that:
the method is more consistent with the actual gas content in the rock sample and the gas-logging total hydrocarbon by providing a new testing thought, and a linear formula is obtained. The degassing efficiency is consistent, the density of drilling mud is consistent, the content of free gas in silt shale can be effectively calculated in real time when drilling is carried out for 20-50min/m, the experimental cost of on-site gas content can be saved, and the method has popularization significance in the work area.
Description of the drawings:
FIG. 1 shows the V of well A in example 1 free -T G The fitted curve graph of (1);
Detailed Description
The present invention will be described in further detail with reference to test examples and specific embodiments. It should be understood that the scope of the above-described subject matter is not limited to the following examples, and any techniques implemented based on the disclosure of the present invention are within the scope of the present invention.
Example 1
The technical scheme of the invention is explained in detail by embodiment 1, and a silt shale section sample obtained from a well near 300 cores of a well A in a certain well research area is taken, wherein the rock sample has completed the processes of drilling, logging, experimental analysis and the like, such as a drilling time curve, gas logging parameters, density logging, field gas content, helium method porosity, low-temperature nitrogen adsorption and the like.
The sample was then subjected to step 1: preparing rock into a crushed rock sample with the particle size of 3mm, weighing about 1g of the crushed rock sample, putting the crushed rock sample into a clean and dry sample tube, drying and degassing the sample tube at 90 ℃ for 8h, then putting the sample tube into liquid nitrogen at the temperature of 77K, testing the adsorption amount of nitrogen under different pressures, and drawing an adsorption isotherm. Selecting at least 5 BET equation pressure points to ensure C>0; the relative pressure of the point taking range is controlled to be between 0.05 and 0.35, and the point taking range must be selected in a range that V (1-P/P0) is increased along with P/P0. Adsorption capacity V for saturation of single-layer adsorption m The corresponding pressure points are counted into a point selection range.
Using the formula:
vm (saturated adsorption amount of monolayer) was calculated.
Helium can be injected into pores with the pore diameter of less than 0.1nm, and is the most accurate method for measuring the porosity at present. Phi is injected into a sample by a helium method, and the temperature and pressure change is monitored based on Boyle's law, so that the volume V of the rock skeleton is obtained Skeleton And obtaining V from the total volume of the rock by a three-dimensional scanning method Rock ，
The density of rock (rho) is determined by measuring the intensity of gamma rays which are absorbed by gamma rays due to the Compton effect when the gamma rays penetrate the stratum, and the intensity of the absorption of gamma rays by the stratum is determined by the number of electrons contained in a unit volume of the rock, namely the density of electrons which is related to the density of the stratum r )。
Determining the total gas quantity and the free gas V in the step 2 by using a gas-measuring total hydrocarbon curve free Establishing a linear correlation relationship according to V free -T G The gas content of the free gas can be obtained by the relational expression.
V free ＝a*T G +b；
Wherein b = f (Rop, R) 2 -r 2 )；b<0；a＝—f(Rop，R 2 -r 2 )/T G background value ，a>0。
Sampling at different depths of the same well according to the method to obtain a data summary table shown in table 1;
table 1 is a summary table of sample data from A well in a certain area
The linear correlation between the TG and the 13 sets of data in table 1 is obtained, and the relationship shown in fig. 1 is obtained: y =0.6306x-0.0469 2 0.8378, as can be seen from the linear correlation diagram in fig. 1, there is a certain linear correlation relationship between the qualitative gas logging total hydrocarbon and the quantitative free gas product, according to the linear correlation relationship, when a new well is performed, the content of the adsorbed gas of the silt shale type is small, the data of the free gas recovery performed through expensive experiments is not representative, and much experiment time and experiment cost are consumed. In this method, vm,
The parameters such as rho r and the like can be obtained through experiments, and finally the obtained V free Is credibleThe degree is also higher, passing through a series of V free The linear correlation relationship established with TG is also more accurate.
The empirical formula obtained using the a103 well may be applied to other wells in the work area. The method comprises the steps of obtaining an empirical formula of linear correlation relation by adjusting the size of a drill bit, screening the drilling time (Rop) and measuring the background value with gas, and calculating the free gas content V of other wells in the same region and the same deposition environment according to the empirical formula on other wells applied by the method free And the gas content evaluation parameters can be enriched, and the gas content experiment cost is saved.
The foregoing is illustrative of the preferred embodiments of the present invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and is not to be construed as limited to the exclusion of other embodiments, and that various other combinations, modifications, and environments may be used and modifications may be made within the scope of the concepts described herein, either by the above teachings or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (8)
1. A method for quantitatively determining free gas in silt shale is characterized by comprising the following steps:
step 1, sampling samples obtained by coring rocks aiming at silty shale of a plurality of layers, and obtaining a monolayer saturated adsorption gas volume V on the rock surface of the samples through a nitrogen adsorption experiment and a BET model m Experimental values;
step 2, passing the porosity of the rock sample
Rock density ρ r Obtaining the free gas V free Product formula:
step 3, measuring gasAll-hydrocarbon T G The total gas quantity measured by the curve and the free gas V in the step 2 free Establishing a linear correlation relationship according to V free -T G And obtaining the gas content of the free gas according to the relational expression.
2. The method for quantitatively determining the free gas in the silty shale according to claim 1, wherein in a BET model, a BET adsorption isotherm equation is as follows:
wherein, V m : the saturated adsorption capacity of the monomolecular layer adsorbs air;
v: the volume of adsorbed gas;
P 0 : the saturated vapor pressure of the adsorbate;
p: the adsorbate pressure;
c is a constant related to the heat of vaporization of the adsorbate.
3. The method for quantitatively determining the free gas in the silt shale according to claim 2, wherein the nitrogen adsorption experimental data in the step 1 are screened to obtain the effective V m Data, the screening conditions comprising:
1)、C>0；
2) The point taking range is as follows: the relative pressure is between 0.05 and 0.35, V (1-P/P) 0 ) Following P/P 0 (ii) an increased range;
3) The adsorption amount V for saturation of single-layer adsorption m The corresponding pressure points are counted into a point selection range.
4. The method of claim 1, wherein the porosity of the shale is determined by the amount of free gas in the shale
With rock density p r The relationship between them is specifically:
5. the method for quantitatively determining free gas in silty shale according to claim 1, wherein the gas logging total hydrocarbon data and V with the drilling time of 20-50min/m are screened free The calculated values establish a linear correlation.
6. The method for quantitatively determining the free gas in the silty shale according to claim 5, characterized in that the free gas content V is determined by free The linear correlation with the gas logging total hydrocarbon data corrects the free hydrocarbon content to obtain a linear formula as follows:
V free ＝a*T G +b。
wherein b = f (Rop, R) 2 -r 2 )，b<0；a＝-f(Rop，R 2 -r 2 )/T G Background value, a>0；
7. The method of claim 5, wherein all T in the linear equation is determined by the method of determining the amount of free gas in the silt shale G The bit size and the mud density corresponding to the value-taking point are consistent, the fluctuation is kept within 30-40min/m during drilling, and the variation of the gas measurement background value is relatively small.
8. The method of claim 1, wherein the porosity is determined quantitatively by measuring the amount of free gas in the silt shale
Rock density ρ r Respectively passing through helium method poresAnd testing by a degree experiment and a density logging experiment.
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| CN117074231A (en) * | 2023-07-17 | 2023-11-17 | 山东国材益新建筑科技有限公司 | Rapid detection method for solid content of wastewater slurry in green building construction |
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| CN117074231A (en) * | 2023-07-17 | 2023-11-17 | 山东国材益新建筑科技有限公司 | Rapid detection method for solid content of wastewater slurry in green building construction |
| CN117074231B (en) * | 2023-07-17 | 2024-02-13 | 山东国材益新建筑科技有限公司 | Rapid detection method for solid content of wastewater slurry in green building construction |
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