CN117784278B - Prediction method and prediction system for dense sandstone gas dessert - Google Patents
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Abstract
The invention discloses a prediction method and a prediction system for a dense sandstone gas dessert, and relates to the technical field of oil-gas geological exploration. Comprising the following steps: drawing an intersection chart of cumulative gas yield, monthly gas yield and year and month of production of the tight sandstone gas well, judging the decreasing trend of the cumulative gas yield of the single well according to the intersection chart, and calculating the cumulative gas yield of the single well of the tight sandstone gas according to the decreasing trend; acquiring static control factors of compact sandstone gas, and creating an enrichment coefficient EF; and drawing a prediction intersection diagram, and obtaining a lower limit value of dense sandstone gas enrichment according to the prediction intersection diagram, wherein the lower limit value is a dense sandstone gas dessert value. According to the method, the characteristics of the tight sandstone gas reservoir are taken as a starting point, a prediction intersection chart is drawn, and the lower limit value of the enrichment of the tight sandstone gas is obtained through the prediction intersection chart, namely the value of the dessert of the tight sandstone gas, so that the method can replace the unimpeded flow of the tight sandstone gas well to reflect the enrichment degree of the tight sandstone, and the detection of the dessert of the tight sandstone gas is more accurate.
Description
Technical Field
The invention relates to the technical field of oil and gas geological exploration, in particular to a prediction method and a prediction system for tight sandstone gas desserts.
Background
Along with the continuous development of unconventional oil and gas geology theory and the progress of exploration and development technology, dense sandstone gas dessert prediction becomes a key and core in unconventional natural gas geology and is also a weak link of natural gas reservoir formation, enrichment and target prediction research.
In the prior art, the unimpeded flow of the dense sandstone gas well is calculated by utilizing the technologies of enrichment master control factors, multiple linear regression, double dessert evaluation parameters of the reservoir, earthquake attribute prediction based on machine learning and the like, so as to evaluate the dense sandstone gas dessert.
The defects of the prior art are as follows: the tight sandstone gas reservoir has the characteristics of low pore permeability, compactness and fracture transformation during development, and the unimpeded flow of the tight sandstone gas well in the general sense cannot reflect the enrichment degree of the tight sandstone, so that the evaluation of the tight sandstone gas dessert is not accurate enough.
Disclosure of Invention
Based on the above, it is necessary to provide a method and a system for predicting a dense sandstone gas dessert in order to solve the above-mentioned technical problems.
The embodiment of the invention provides a method for predicting dense sandstone gas desserts, which comprises the following steps:
drawing an intersection diagram of cumulative gas yield, monthly gas yield and year and month of production of the dense sandstone gas well,
Judging the decreasing trend of the cumulative gas yield of the single well according to the intersection graph, and calculating the cumulative gas yield of the single well of the tight sandstone gas according to the decreasing trend;
Respectively drawing a prediction intersection chart of the cumulative gas yield and the porosity phi of a single well, the thickness H of a single-layer sand body and the enrichment coefficient EF, and a prediction intersection chart of the thickness H of the single-layer sand body and the saturation S g of gas;
respectively drawing a prediction intersection graph of the cumulative gas yield and the porosity phi of a single well, the gas saturation S g and the thickness H and the enrichment coefficient EF of a single-layer sand body;
and obtaining a lower limit value of the enrichment degree of the dense sandstone gas according to all the predicted intersection graphs, wherein the lower limit value is a dense sandstone gas dessert value.
In addition, the step-down trend of the cumulative gas production of the single well is judged according to the intersection graph, and the step-down trend comprises the following steps:
When the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in a linear relation on an intersection chart, the decreasing trend of the cumulative gas yield of the single well is an exponential decrease;
when the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in a semilogarithmic straight line relationship on an intersection chart, the decreasing trend of the cumulative gas yield of the single well is in harmony decrease;
When the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in neither a straight line relation nor a semilogarithmic straight line relation on an intersection graph, the decreasing trend of the cumulative gas yield of the single well is hyperbolic decreasing.
In addition, the single well cumulative gas yield of the dense sandstone gas predicted by the decreasing trend comprises:
When the decreasing trend is the harmonic decreasing, the decreasing index n=1, there is:
Q / Qi = (D / Di )n；
When the decreasing trend is decreasing, the decreasing index The following steps are:
Q / Qi = (D / Di )n
Wherein, Q is the cumulative gas production of a single well, Q i is the initial yield in the decreasing stage, D is the yield decreasing rate, D i is the initial instantaneous decreasing rate, n is the decreasing index, and i is a positive integer;
when the decreasing trend is a hyperbolic decrease, the decreasing index n is 1 < ≡,
Q = Qi / {1 + (Di / n)×t}n
Wherein, Q is the cumulative gas production of a single well, Q i is the initial yield of the decreasing stage, D i is the initial instantaneous decreasing rate, t is the production time of the decreasing stage, n is the decreasing index, and i is a positive integer.
In addition, the static control factors specifically include:
Porosity Φ: calculating the porosity phi of the single-layer sand body by using logging combination parameters of natural gamma GR, neutron logging CNL, acoustic logging AC and density logging DEN;
gas saturation S g: calculating a water saturation model through an Archie formula, and solving for the gas saturation S g:
Sw n = abRw/RtФm
Sg = 1 - Sw
Wherein S w is water saturation, a and b are lithology coefficients, R W is formation water resistivity, R t is formation resistivity, phi is porosity, m is cementing coefficient, and n is saturation index;
thickness H of single-layer sand body: the thickness of the single-layer sand body is determined according to the porosity phi and the gas saturation S g of the single-layer sand body.
In addition, the enrichment factor EF is:
EF = H × Φ × Sg
wherein H is the thickness of a single-layer sand body, phi is the porosity, and S g is the gas saturation.
In addition, the lower limit value for obtaining dense sandstone gas enrichment comprises the following steps:
Establishing a single-layer sand thickness evaluation standard of the enrichment degree of the tight sandstone gas reservoir through intersection of the cumulative gas yield of a single well and the single-layer sand thickness H;
Establishing a dense sandstone gas enrichment porosity evaluation standard through intersection of single well cumulative gas yield and porosity phi;
Establishing a dense sandstone gas enrichment degree gas saturation evaluation standard through intersection of the single-layer sand thickness H and the gas saturation degree S g;
Establishing a dense sandstone gas enrichment degree enrichment coefficient evaluation standard through intersection of the accumulated gas yield of a single well and an enrichment coefficient EF;
And determining the lower limit value of the gas enrichment degree of the compact sandstone according to the single-layer sand thickness evaluation standard, the porosity evaluation standard, the gas saturation evaluation standard and the enrichment coefficient evaluation standard.
In addition, a system for predicting a dense sandstone gas dessert, comprising:
the drawing module is used for drawing an intersection chart of cumulative gas yield, monthly gas yield and production year and month of the tight sandstone gas well;
the judging and identifying module is used for judging the decreasing trend of the cumulative gas yield of the single well according to the intersection graph, and calculating the cumulative gas yield of the single well of the tight sandstone gas according to the decreasing trend;
the simultaneous module is used for acquiring static control factors of the tight sandstone gas, wherein the static control factors comprise: the porosity phi, the gas saturation S g and the single-layer sand thickness H are combined, and all static control factors are combined to create an enrichment coefficient EF;
The secondary drawing module is used for respectively drawing a prediction intersection chart of the cumulative gas production and the porosity phi of the single well, the thickness H of the single-layer sand body and the enrichment coefficient EF, and a prediction intersection chart of the thickness H of the single-layer sand body and the gas saturation S g;
and the inference module is used for obtaining the lower limit value of the enrichment degree of the dense sandstone gas according to all the prediction intersection graphs, wherein the lower limit value is the dessert value of the dense sandstone gas.
Compared with the prior art, the method and the system for predicting the dense sandstone gas dessert provided by the embodiment of the invention have the following beneficial effects:
According to the invention, through drawing the intersection graph of cumulative gas yield, monthly gas yield and production year and month of the tight sandstone gas well, the decreasing trend of the cumulative gas yield of a single well is judged according to the intersection graph; calculating the cumulative gas yield of the single well of the compact sandstone gas through the decreasing trend; acquiring static control factors of the dense sandstone gas, wherein the static control factors comprise: the porosity phi, the gas saturation S g and the single-layer sand thickness H are combined, and all static control factors are combined to create an enrichment coefficient EF; respectively drawing a prediction intersection chart of the cumulative gas yield and the porosity phi of a single well, the thickness H of a single-layer sand body and the enrichment coefficient EF, and a prediction intersection chart of the thickness H of the single-layer sand body and the saturation S g of gas; and obtaining a lower limit value of dense sandstone gas enrichment according to the predicted intersection graph, wherein the lower limit value is the dense sandstone gas dessert value. Compared with the prior art, starting from the characteristics of a tight sandstone gas reservoir, respectively drawing a prediction intersection chart of the cumulative gas yield and the porosity phi of a single well, the thickness H of a single-layer sand body and the enrichment coefficient EF, and a prediction intersection chart of the thickness H of the single-layer sand body and the gas saturation S g; and obtaining a lower limit value of dense sandstone gas enrichment through a predicted intersection graph, wherein the lower limit value is a dense sandstone gas dessert value.
The scheme can replace unimpeded flow of the tight sandstone gas well to reflect the enrichment degree of the tight sandstone, and the detection of the tight sandstone gas dessert is more accurate.
Drawings
FIG. 1 is a flow diagram of a method for predicting a tight sandstone gas dessert, provided in one embodiment;
FIG. 2 is a graph of hyperbolic decreasing trend of a method of predicting tight sandstone gas desserts, provided in one embodiment;
fig. 3 is a prediction cross-plot of a method of predicting a tight sandstone gas dessert, provided in one embodiment.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In one embodiment, a method for predicting a dense sandstone gas dessert is provided, as shown in fig. 1, the method comprising:
1. and drawing an intersection chart of cumulative gas yield, monthly gas yield and year and month of production of the tight sandstone gas well.
2. And judging the decreasing trend of the accumulated gas yield according to the intersection graph, and calculating the accumulated gas yield of the single well of the tight sandstone gas according to the decreasing trend.
And 2.1, judging the decreasing trend of the cumulative gas yield of the single well of the tight sandstone gas well according to the intersection diagram.
(1) When the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in a linear relation on the intersection graph, the decreasing trend of the cumulative gas yield of the single well is an exponential decrease.
(2) When the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in a semilogarithmic straight line relationship on the intersection graph, the decreasing trend of the cumulative gas yield of the single well is in harmony decrease.
(3) The characteristics of the two are not obvious, and the decreasing trend of the cumulative gas production of the single well is hyperbolic decreasing.
The upper left corner of FIG. 2 is the intersection of Shan Jingda G6-7, the upper right corner of FIG. 2 is the intersection of Shan Jingda G7-8, the lower left corner of FIG. 2 is the intersection of Shan Jingda G5-4 to 4, and the lower right corner of FIG. 2 is the intersection of single wells 1-7 to 6.
2.2, Calculating the cumulative gas production value of the single well of the tight sandstone gas well according to the single well yield decreasing trend corrected by the production data;
the most common method is the yield decreasing rule equation proposed by Arps:
Q / Qi = (D / Di )n
Where q=gas production, 10 4 m3/d;Qi =initial yield in the decrementing stage, 10 4 m3/d; d = yield decline rate, 1/month; d i = initial instantaneous reduction rate; n=decreasing exponent; i is a positive integer. Wherein the initial production (Q i) and the production time (t) of the depletion phase are based on existing well test gas results including, but not limited to, gas production (Q). Further, the yield decreasing rate (D) is calculated by the gas yield (Q)/the trial production time (t), and the initial instantaneous decreasing rate (D i) is calculated by the initial yield (Q i)/the trial production time (t) in the decreasing stage.
The decreasing trend is divided into 3 types: decreasing the index, decreasing the hyperbolic and blending the decrease;
when the decreasing trend is that the index decreases, the monthly yield and the accumulated yield are in a linear relation on a common coordinate system, and the decreasing index is n-infinity;
when the decreasing trend is the harmony decreasing trend, the monthly yield and the cumulative yield are in a semilogarithmic linear relationship, and the decreasing index n=1;
when the decreasing trend is a hyperbolic decrease, 1 < progressively decreases index n < ++:
Q = Qi / {1 + (Di / n)×t}n
Wherein q=gas production, 10 4 m3/d;Qi =initial yield in the decrementing stage, 10 4 m3/d;Di =initial instantaneous rate of decline, 1/month; t is the production time of the decreasing stage; n=decreasing exponent; i is a positive integer.
TABLE 1 comparison of typical Shan Jingdi year cumulative gas yield prediction and actual production of certain block of tight sandstone gas
And calculating the cumulative gas yield in the 7 th year by applying a hyperbolic decreasing rule. As shown in table 1, a typical well with longer production time in the da ning-ji county block is used for verification, and the consistency of the accumulated gas yield predicted by the hyperbolic decrease and the actual production data is found to be high, so that the fact that the dense gas decrease of the ancient kingdom on the research area accords with the hyperbolic decrease rule is further verified, and the decrease rule accords with the dynamic trend of the dense gas production of the research area.
3. Acquiring static control factors of the dense sandstone gas, wherein the static control factors comprise: the porosity Φ, the gas saturation S g and the single layer sand thickness H, all of the static control factors in combination create the enrichment factor EF.
3.1, Preferably, the static control factors of the tight sandstone gas, such as the thickness (H) of the single-layer sand body, the porosity (phi) and the gas saturation (S g), and the like.
(1) Porosity phi
The well logging data are used for calculating the porosity of the reservoir, and the well logging method mainly depends on 3 kinds of porosities of neutrons, density and sound waves. The 3 porosity logging methods of the homogeneous clastic rock stratum reflect the stratum porosity without essential difference, and the porosity value reflected by a single factor can be influenced by considering that the heterogeneity of the tight sandstone in the longitudinal direction and the transverse direction is strong, so that the porosity is calculated by selecting a logging parameter combination of a natural gamma logging parameter GR, a neutron logging parameter CNL, an acoustic logging parameter AC and a density logging parameter DEN. Based on the test result constraint of single well 1000m 3 and 3000m 3 output, respectively reading single-layer sand interpretation combination parameters of the Daning-Ji county block box 8+mountain 2+Benxi drilling gas layer. According to statistical analysis results, natural gamma logging parameters GR, neutron logging parameters CNL, acoustic logging parameters AC and density logging parameters DEN corresponding to the yields of 1000m 3 and 3000m 3 are selected, and models of natural gamma logging parameters GR, neutron logging parameters CNL, acoustic logging parameters AC, density logging parameters DEN logging combination parameters and porosity phi are established.
And fully developing explanation of the single-layer sand porosity of the research area according to the model: the well logging data are used for calculating the porosity of the reservoir, and the well logging method mainly depends on 3 kinds of porosities of neutrons, density and sound waves. The 3 porosity logging methods of the homogeneous clastic rock stratum reflect the formation porosity without essential difference, and the porosity value reflected by a single factor can be influenced by considering that the heterogeneity of the compact sandstone in the longitudinal direction and the transverse direction is strong, so that the sandstone is evaluated based on the natural gamma logging parameter GR and the neutron logging parameter CNL, and then the porosity is calculated through the combination of the acoustic logging parameter AC and the density logging parameter DEN logging parameter. Taking the average value of the two calculated values as the calculated porosity value of the set of sandstone.
Mudstone porosity was calculated using the acoustic moveout equation of Wyllie (Wyllie et al, 1956):
ΦAC = (Δt-Δtma) / (Δtf -Δtma) (1)
Where Δt is the sonic travel time, Δ f is the pore fluid sonic travel time, Δt ma is the matrix (or particle) sonic travel time, Φ AC represents the sandstone porosity at the depth z.
The density log calculated mudstone porosity was determined by the following formula (Dasgupta et al, 2016):
ΦDEN = (ρma -ρb) / (ρma-ρf) (2)
where ρ ma is the sandstone matrix density, ρ b is the sandstone bulk density obtained in the density log, and ρ f is the pore fluid density.
(2) Saturation of gas S g
Aiming at a low-permeability sandstone gas reservoir, rock Archie parameter characteristics are analyzed through rock resistivity experiments, and a water saturation model is established by using an Archie formula on the basis. The reliability of the water saturation is verified by combining a high-pressure mercury-pressing experiment and a nuclear magnetic resonance experiment with the actual reservoir geological background of the dense gas in the research area.
Rock resistivity experiments refer to the standard of SY T5385-2007 rock resistivity parameter laboratory measurement and calculation methods. Formation factor (F), resistivity (I), cementation index (m) and saturation index (n) were calculated sequentially using the Archie formula, respectively. And (3) drawing an intersection graph of stratum factors (F) and porosity (phi) and an intersection graph of resistivity increase rate (I) and water saturation (S w) on a plurality of rock samples from the same layer group under a double-logarithmic coordinate. And fitting a stratum factor (F) and porosity (phi) curve, a resistivity increase rate (I) and water saturation (S w) curve by using a power function to obtain lithology coefficients (a and b), a cementation index (m) and a saturation index (n). The Archie formula is:
Wherein S w is water saturation, a and b are lithology coefficients, R W is formation water resistivity, R t is formation resistivity, phi is porosity, m is cementing coefficient, and n is saturation index.
(3) Thickness H of single-layer sand body
The thickness of the single-layer sand body is determined according to the porosity phi and the gas saturation S g of the single-layer sand body, and the method specifically comprises the following steps: based on the gas layer interpretation under the yield constraint of single wells 1000m 3 and 3000m 3, preferably, the combined parameter values of the Daning-Ji county block box 8+mountain 2+Benxi gas layer single layer sand body interpretation are natural gamma logging parameters GR, neutron logging parameters CNL, acoustic logging parameters AC, density logging parameters DEN, porosity phi and gas saturation S g, and the interpretation of the thickness of the single layer sand body is carried out according to the logging combined parameters. Based on the test results of the existing drilling, namely according to the actual measurement constraint of the yields of 1000m 3 and 3000m 3 of a single well, single-layer sand interpretation combination parameters of the drilling gas layer of Daning-Ji county block box 8+mountain 2+Benxi are respectively read. According to the statistical analysis result, natural gamma logging parameters GR, neutron logging parameters CNL, acoustic logging parameters AC, density logging parameters DEN, porosity phi and lower limit values of gas saturation S g logging parameters corresponding to the production of 1000m 3 and 3000m 3 are selected, natural gamma logging parameters GR, neutron logging parameters CNL, acoustic logging parameters AC, density logging parameters DEN, porosity phi and gas saturation S g logging combination parameter models are established, and explanation of the single-layer sand gas layer thickness of the investigation region is carried out as in the embodiment 1.
Example 1
Single-layer sand body interpretation combination parameter selection of Daning-Ji county block box 8+mountain 2+Benxi air layer
Single well daily production is 1000m 3: the acoustic logging parameter AC is more than or equal to 195 mu s/M, the resistivity value M2RX is more than or equal to 70 omega.m, the neutron logging parameter CNL is less than or equal to 18.0%, the density logging parameter DEN is less than or equal to 2.67g/cm 3, and the natural gamma logging parameter GR is less than or equal to 92API.
The daily yield of a single well is 3000m 3: the acoustic logging parameter AC is more than or equal to 195 mu s/M, the resistivity value M2RX is more than or equal to 70 omega.m, the neutron logging parameter CNL is less than or equal to 16.0%, the density logging parameter DEN is less than or equal to 2.64g/cm 3, and the natural gamma logging parameter GR is less than or equal to 90API.
The 2-segment electrical value constraint of the two-fold system Shanxi mountain on the Daning-Ji county block by the daily gas production of a single well for 90 days is as follows:
Single well daily production is 1000m 3: the gas saturation S g is more than or equal to 66%, the logging calculation porosity phi is more than or equal to 4.1%, the acoustic logging parameter AC is more than or equal to 195 mu S/m, and the neutron logging parameter CNL is less than or equal to 19.5%.
The daily yield of a single well is 3000m 3: the gas saturation S g is more than or equal to 75%, the logging calculation porosity phi is more than or equal to 5.5%, the acoustic logging parameter AC is more than or equal to 195 mu S/m, and the neutron logging parameter CNL is less than or equal to 19.5%.
3.2, In combination with the above static parameters, an Enrichment Factor (EF), i.e. ef=h×Φ×s g, was created for evaluating tight sandstone gas desserts.
4. And respectively drawing a predicted intersection graph of the cumulative gas yield and the porosity phi of the single well, the gas saturation S g and the enrichment coefficient EF, and an intersection graph of the thickness H of the single-layer sand body and the gas saturation S g.
Obtaining a lower limit value of dense sandstone gas enrichment according to the predicted intersection graph, wherein the lower limit value is a dense sandstone gas dessert value, as shown in fig. 3:
4.1, establishing a single-layer sand thickness evaluation standard of the enrichment degree of the tight sandstone gas reservoir (shown in fig. 3 (a)) through intersection of the cumulative gas production of a single well and the single-layer sand thickness (H);
4.2, establishing a dense sandstone gas enrichment degree gas saturation evaluation standard (shown in fig. 3 (b)) through intersection of the single-layer sand thickness (H) and the gas saturation degree (S g);
4.3, establishing a dense sandstone gas reservoir enrichment porosity evaluation standard (shown in fig. 3 (c)) through intersection of the cumulative gas production of a single well and the porosity (phi);
4.4, establishing a dense sandstone gas reservoir enrichment degree enrichment coefficient evaluation standard (shown in fig. 3 (d)) through intersection of the single well accumulated gas yield and the enrichment coefficient (EF).
4.5, Obtaining a lower limit value of the enrichment degree of the dense sandstone gas according to all the prediction intersection graphs, wherein the lower limit value is a dense sandstone gas dessert value, and the values are shown in table 2. In the table, the I type is 0.077X10 8m3 of accumulated gas produced in 7 years, which is equivalent to 3000m 3 of daily production of single well in 7 years, the II type is 0.026X10 8m3 of accumulated gas produced in 7 years, which is equivalent to 1000m 3 of daily production of single well in 7 years, and the above is the lower limit of industrial scale gas layer of a certain block of medium petroleum.
TABLE 2 evaluation criteria for dense sandstone gas key horizon desserts of a block of the Erdos basin
In one embodiment, a system for predicting a dense sandstone gas dessert is provided, comprising:
And the drawing module is used for drawing an intersection chart of cumulative gas yield, monthly gas yield and production year and month of the tight sandstone gas well.
And the judging and identifying module is used for judging the decreasing trend of the cumulative gas yield of the single well according to the intersection graph, and calculating the cumulative gas yield of the single well of the tight sandstone gas through the decreasing trend.
And the simultaneous module is used for acquiring static control factors of the tight sandstone gas, and creating an enrichment coefficient EF by combining all the static control factors.
The secondary drawing module is used for respectively drawing a prediction intersection chart of the cumulative gas production and the porosity phi of the single well, the thickness H of the single-layer sand body and the enrichment coefficient EF, and a prediction intersection chart of the thickness H of the single-layer sand body and the gas saturation S g.
And the inference module is used for obtaining the lower limit value of the enrichment degree of the dense sandstone gas according to all the prediction intersection graphs, wherein the lower limit value is the dessert value of the dense sandstone gas.
The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (5)
1. A method for predicting a dense sandstone gas dessert, comprising:
drawing an intersection diagram of cumulative gas yield, monthly gas yield and year and month of production of the dense sandstone gas well,
Judging the decreasing trend of the cumulative gas yield of the single well according to the intersection graph, and calculating the cumulative gas yield of the single well of the tight sandstone gas according to the decreasing trend;
acquiring static control factors of the dense sandstone gas, wherein the static control factors comprise: the porosity phi, the gas saturation S g and the single-layer sand thickness H are combined, and all static control factors are combined to create an enrichment coefficient EF;
Respectively drawing a prediction intersection chart of the cumulative gas yield and the porosity phi of a single well, the thickness H of a single-layer sand body and the enrichment coefficient EF, and a prediction intersection chart of the thickness H of the single-layer sand body and the saturation S g of gas;
Obtaining a lower limit value of the enrichment degree of the dense sandstone gas according to all the predicted intersection graphs, wherein the lower limit value is a dense sandstone gas dessert value;
wherein,
The step-down trend of the cumulative gas production of the single well is judged according to the intersection diagram, and the step-down trend comprises the following steps:
When the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in a linear relation on an intersection chart, the decreasing trend of the cumulative gas yield of the single well is an exponential decrease;
when the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in a semilogarithmic straight line relationship on an intersection chart, the decreasing trend of the cumulative gas yield of the single well is in harmony decrease;
When the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in neither a straight line relation nor a semilogarithmic straight line relation on an intersection graph, the decreasing trend of the cumulative gas yield of the single well is hyperbolic decreasing;
The single well cumulative gas yield of the compact sandstone gas is calculated through the decreasing trend, and the method comprises the following steps:
when the decreasing trend is the harmonic decreasing, the decreasing index n=1, there is:
Q/Qi＝(D/Di)n
When the decreasing trend is decreasing, the decreasing index n → infinity is:
Q/Qi＝(D/Di)n
Wherein, Q is the cumulative gas production of a single well, Q i is the initial yield in the decreasing stage, D is the yield decreasing rate, D i is the initial instantaneous decreasing rate, n is the decreasing index, and i is a positive integer;
When the decreasing trend is a hyperbolic decrease, the decreasing index n < ++1 is:
Q＝Qi/{1+(Di/n)×t}n
wherein, Q is the cumulative gas production of a single well, Q i is the initial yield of the decreasing stage, D i is the initial instantaneous decreasing rate, t is the production time of the decreasing stage, n is the decreasing index, and i is a positive integer.
2. The method for predicting a dense sandstone gas dessert of claim 1, wherein said static control factors specifically comprise:
porosity Φ: calculating the porosity phi of the single-layer sand body by using a logging combination parameter natural gamma parameter GR, a neutron logging parameter CNL, an acoustic logging parameter AC and a density logging parameter DEN;
gas saturation S g: calculating a water saturation model through an Archie formula, and solving for the gas saturation S g:
Sw n＝abRw/RtФm
Sg＝1-Sw
Wherein S w is water saturation, a and b are lithology coefficients, R W is formation water resistivity, R t is formation resistivity, phi is porosity, m is cementing coefficient, and n is saturation index;
thickness H of single-layer sand body: the thickness of the single-layer sand body is determined according to the porosity phi and the gas saturation S g of the single-layer sand body.
3. The method of claim 2, wherein the enrichment factor EF is:
EF＝H×Φ×Sg
wherein H is the thickness of a single-layer sand body, phi is the porosity, and S g is the gas saturation.
4. A method of predicting a dense sandstone gas dessert as claimed in claim 3, wherein said obtaining a lower limit of dense sandstone gas enrichment comprises:
establishing a single-layer sand thickness evaluation standard of the dense sandstone gas enrichment degree through intersection of the single-well cumulative gas yield and the single-layer sand thickness H;
Establishing a dense sandstone gas enrichment porosity evaluation standard through intersection of single well cumulative gas yield and porosity phi;
Establishing a dense sandstone gas enrichment degree gas saturation evaluation standard through intersection of the single-layer sand thickness H and the gas saturation degree S g;
Establishing a dense sandstone gas enrichment degree enrichment coefficient evaluation standard through intersection of the accumulated gas yield of a single well and an enrichment coefficient EF;
And determining the lower limit value of the gas enrichment degree of the compact sandstone according to the single-layer sand thickness evaluation standard, the porosity evaluation standard, the gas saturation evaluation standard and the enrichment coefficient evaluation standard.
5. A system for predicting a dense sandstone gas dessert, comprising:
the drawing module is used for drawing an intersection chart of cumulative gas yield, monthly gas yield and production year and month of the tight sandstone gas well;
the judging and identifying module is used for judging the decreasing trend of the cumulative gas yield of the single well according to the intersection graph, and calculating the cumulative gas yield of the single well of the tight sandstone gas according to the decreasing trend;
the simultaneous module is used for acquiring static control factors of the tight sandstone gas, wherein the static control factors comprise: the porosity phi, the gas saturation S g and the single-layer sand thickness H are combined, and all static control factors are combined to create an enrichment coefficient EF;
The secondary drawing module is used for respectively drawing a prediction intersection chart of the cumulative gas production and the porosity phi of the single well, the thickness H of the single-layer sand body and the enrichment coefficient EF, and a prediction intersection chart of the thickness H of the single-layer sand body and the gas saturation S g;
The inference module is used for obtaining a lower limit value of the enrichment degree of the dense sandstone gas according to all the prediction intersection graphs, wherein the lower limit value is a dense sandstone gas dessert value;
wherein,
The step-down trend of the cumulative gas production of the single well is judged according to the intersection diagram, and the step-down trend comprises the following steps:
When the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in a linear relation on an intersection chart, the decreasing trend of the cumulative gas yield of the single well is an exponential decrease;
when the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in a semilogarithmic straight line relationship on an intersection chart, the decreasing trend of the cumulative gas yield of the single well is in harmony decrease;
When the cumulative gas yield of the compact sandstone gas well and the monthly gas yield are in neither a straight line relation nor a semilogarithmic straight line relation on an intersection graph, the decreasing trend of the cumulative gas yield of the single well is hyperbolic decreasing;
The single well cumulative gas yield of the compact sandstone gas is calculated through the decreasing trend, and the method comprises the following steps:
when the decreasing trend is the harmonic decreasing, the decreasing index n=1, there is:
Q/Qi＝(D/Di)n
When the decreasing trend is decreasing, the decreasing index n → infinity is:
Q/Qi＝(D/Di)n
Wherein, Q is the cumulative gas production of a single well, Q i is the initial yield in the decreasing stage, D is the yield decreasing rate, D i is the initial instantaneous decreasing rate, n is the decreasing index, and i is a positive integer;
When the decreasing trend is a hyperbolic decrease, the decreasing index n < ++1 is:
Q＝Qi/{1+(Di/n)×t}n
wherein, Q is the cumulative gas production of a single well, Q i is the initial yield of the decreasing stage, D i is the initial instantaneous decreasing rate, t is the production time of the decreasing stage, n is the decreasing index, and i is a positive integer.
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| CN116402225A (en) * | 2023-04-13 | 2023-07-07 | 西南石油大学 | Method for predicting gas yield of tight sandstone gas reservoir |
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| AU2020103953A4 (en) * | 2020-12-08 | 2021-02-11 | Southwest Petroleum University | Method and system for predicting production of fractured horizontal well in shale gas reservoir |
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