A method for predicting gas production of a gas well in a tight gas reservoir poor gas layer

Abstract

This invention relates to a method for predicting gas production in gas wells in poorly ventilated tight gas reservoirs, belonging to the technical field of gas field development research. The method includes the following steps: establishing a correspondence between the thickness of Class I gas layers and the tested gas production in a tight gas reservoir, and establishing a relationship between the production per meter of Class I gas layer thickness and the production per meter of Class II poorly ventilated gas layer thickness; based on the established relationship, and combining the relationship between the thickness of Class II poorly ventilated gas layers and the thickness of Class I gas layers in the tight gas reservoir with the same natural gas volume, establishing a relationship between the thickness of Class II poorly ventilated gas layers and the gas production; and then predicting the gas production of Class II poorly ventilated gas layers in tight gas reservoir wells based on the thickness of the Class II poorly ventilated gas layers. This prediction method can solve the problem of not being able to effectively tap the potential of remaining undeveloped reservoirs with relatively poor gas content but high gas production potential in existing old wells, and has significant guiding significance for the potential tapping of old wells in gas fields.

Description

Technical Field

[0001] This invention relates to a method for predicting gas production in gas wells in tight gas reservoirs with poor gas content, belonging to the technical field of gas field development research. Background Technology

[0002] As development progresses and the gas field becomes increasingly developed, the geological conditions in the remaining undeveloped areas are gradually deteriorating. It is becoming more and more difficult to tap the potential of old areas through new wells. Implementing measures on old wells is an important means to maintain stable production in the gas field. However, due to the previous infiltration and adjustment of Class I gas layers with better reservoir quality, there are fewer and fewer Class I gas layers left that can be used for measures, making the measures more difficult and unable to meet the long-term stable production of the gas field. Therefore, the remaining Class II poor gas layers are the focus of the next step of measures. In the prior art, Chinese patent document CN108661631A discloses a production prediction method. This method constructs a pseudo-pressure normalized production function for the shale gas well to be analyzed based on the original formation pressure, bottom hole flowing pressure, and daily production. Based on the pseudo-pressure normalized production function, a double logarithmic plotting function is determined, and a pseudo-pressure normalized production double logarithmic plot is drawn using this function. The pseudo-pressure normalized production double logarithmic plot is fitted, and based on the fitting results, production and pressure history are fitted to determine the relevant parameters of the shale gas well to be analyzed. Based on a pre-set shale gas well production prediction model, the predicted production is determined according to the relevant parameters of the shale gas well to be analyzed. However, this method cannot achieve rapid production prediction of gas wells in tight gas reservoirs with poor gas flow, and it cannot effectively tap the potential of old wells in tight gas reservoirs with gas production potential. Summary of the Invention

[0003] The purpose of this invention is to provide a method for predicting the gas production of gas wells in tight gas reservoirs with poor gas content, which can guide the effective tapping of gas-producing reservoirs in old wells.

[0004] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0005] A method for predicting gas production in gas wells in tight gas reservoirs with poor gas flow zones includes the following steps:

[0006] 1) Based on the gas production test data of Class I gas layers in tight gas reservoirs with different gas layer thicknesses in the mine, construct the correspondence between the gas layer thickness of Class I gas layers in tight gas reservoirs and the tested gas production.

[0007] Based on field test data, the relationship between the production of Class I gas layers per meter thickness and the production of Class II poor gas layers per meter thickness in tight gas reservoirs is established; the Class I gas layers and Class II poor gas layers in tight gas reservoirs are classified into reservoirs based on well logging interpretation results.

[0008] 2) Based on the correspondence between the gas layer thickness of Class I gas layers in tight gas reservoirs and the test gas production, as well as the relationship between the production of Class I gas layers per meter of thickness and the production of Class II gas layers per meter of thickness in tight gas reservoirs, and combined with the relationship between the gas layer thickness of Class II gas layers and Class I gas layers in tight gas reservoirs with the same natural gas volume, the relationship between the gas layer thickness of Class II gas layers in tight gas reservoirs and the gas production is constructed. Then, the gas production of Class II gas layers in tight gas reservoir wells is predicted based on the thickness of the Class II gas layers in the tight gas reservoir wells.

[0009] The method for predicting gas production in tight gas reservoirs with poor gas content can solve the problem of not being able to effectively tap the potential of undeveloped reservoirs with relatively poor gas content but high gas production potential in existing old wells. It has great guiding significance for tapping the potential of old wells in gas fields.

[0010] Furthermore, in step 2), the relationship between the thickness of the Class I gas layer in the constructed tight gas reservoir and the tested gas production is shown in Equation 1:

[0011] q g1 =A×H g1 +B (Equation 1);

[0012] In Equation 1, q g1 The test gas production of a Class I gas layer in a tight gas reservoir is 10,000 cubic meters per day; H g1 Let be the thickness of the Class I gas layer in a tight gas reservoir, in meters; A and B are constants relating to the tight gas reservoir.

[0013] Based on field test data, the relationship between the production of Class I gas layers per meter thickness and the production of Class II poor gas layers per meter thickness in tight gas reservoirs can be obtained through cross-plots, as shown in Equation 2:

[0014] q g11 =α×q g21 (Equation 2);

[0015] In Equation 2, q g11 The test gas production per meter of thickness of a Class I gas layer in a tight gas reservoir, in 10,000 cubic meters per day; q g21 α represents the test gas production per meter of thickness of the Class II differential gas layer in a tight gas reservoir, in 10,000 cubic meters per day; α is the correlation coefficient between the production of Class I gas layer per meter of thickness in a tight gas reservoir and the production of Class II differential gas layer per meter of thickness in a tight gas reservoir.

[0016] Further, in step 2), the relationship between the thickness of the Class II gas-deficient layer and the gas production of the tight gas reservoir is constructed according to Equations 1 and 2, as shown in Equation 3:

[0017]

[0018] In Equation 3, qg2 The gas production of a Class II differential gas layer in a tight gas reservoir is 10,000 cubic meters per day; H g2 φ1 represents the thickness of the Class II gas layer in a tight gas reservoir, in meters; φ1 represents the porosity of the Class I gas layer in a tight gas reservoir, in percentage points; S g1 The gas saturation of a Class I gas layer in a tight gas reservoir, in %; Porosity of the Class II differential gas layer in a tight gas reservoir, %; S g2 denoted as , where is the gas saturation of the Class II poor gas layer in a tight gas reservoir (%); A and B are constants relating to the tight gas reservoir; and α is the correlation coefficient between the production of Class I gas layers per meter thickness and the production of Class II poor gas layers per meter thickness in the same tight gas reservoir.

[0019] The gas content per unit volume of natural gas is calculated according to formula (4):

[0020] V g =A g ·H g ·φ·S g (Equation 4)

[0021] In Equation 4:

[0022] V g —Natural gas volume, m 3 ;

[0023] A g —Aeration area, m 2 ;

[0024] H g —Gas layer thickness, m;

[0025] φ—Porosity, %;

[0026] S g —Gas saturation, %;

[0027] Based on the relationship between the natural gas content per unit volume of the same area controlled by a single well in Class I gas reservoirs and Class II poor gas reservoirs, the natural gas content per unit volume of the same area controlled by a single well in Class I gas reservoirs and Class II poor gas reservoirs is calculated according to Formula 4, that is:

[0028]

[0029] In Equation 5, V g1 The volume of natural gas in a Class I gas layer of a tight gas reservoir is given by m. 3 A g1 The gas-bearing area of ​​the Class I gas layer in a tight gas reservoir, in m 2 H g1 φ1 represents the thickness of the Class I gas layer in a tight gas reservoir, in meters; φ1 represents the porosity of the Class I gas layer in a tight gas reservoir, in percentage points; S g1The gas saturation of a Class I gas layer in a tight gas reservoir, in %; V g2 The volume of natural gas in the Class II differential gas layer of a tight gas reservoir, m 3 A g1 The gas-bearing area of ​​the Type II differential gas layer in a tight gas reservoir, in m 2 H g2 φ1 represents the thickness of the Class II differential gas layer in a tight gas reservoir, in meters; φ2 represents the porosity of the Class II differential gas layer in a tight gas reservoir, in percentage (%); S g2 The gas saturation of the Type II differential gas layer in a tight gas reservoir, in %

[0030] For the same gas reservoir in the target area, the formation pressure (Pi), formation temperature (Ti), natural gas deviation factor (Zi), and gas constant (R) are all constant values. Therefore, they can be regarded as constants in the comparison of natural gas content per unit volume between Class I gas reservoirs and Class II gas reservoirs.

[0031] The average porosity and average gas saturation of Class I gas layers and Class II poor gas layers in tight gas reservoirs were statistically analyzed separately. The average porosity of each type of gas layer was taken as the porosity value of the corresponding type of gas layer, and the average gas saturation of each type of gas layer was taken as the gas saturation of the corresponding type of gas layer.

[0032] In a unit volume of the same area, the natural gas content of a Class I gas reservoir is k times that of a Class II gas-poor reservoir. If the natural gas content of a Class II gas-poor reservoir is the same as that of a Class I gas reservoir, then in the same gas reservoir, the porosity φ and gas saturation S of the Class I and Class II gas-poor reservoirs are... g In a given gas reservoir, this is a fixed value. Since the area is the same, the volume of natural gas corresponding to a 1-meter thickness of Class I gas layer is equal to the volume of natural gas corresponding to a k-meter thickness of Class II gas layer. That is, the thickness of the Class II gas layer is k times the thickness of the Class I gas layer.

[0033]

[0034] Based on Equations 6, 2, and 1, the relationship between the production and thickness of Class II gas-deficient reservoirs is obtained, namely:

[0035]

[0036] In equations 6 and 7 above, H g1 The thickness of a Class I gas layer in a tight gas reservoir is given in meters (m); q g2 The gas production of a Class II differential gas layer in a tight gas reservoir is 10,000 cubic meters per day; H g2 φ1 represents the thickness of the Class II gas layer in a tight gas reservoir, in meters; φ1 represents the porosity of the Class I gas layer in a tight gas reservoir, in percentage points; S g1 φ1 represents the gas saturation of the Type I gas layer in a tight gas reservoir, in %; φ2 represents the porosity of the Type II poor gas layer in a tight gas reservoir, in %; Sg2 denoted as , where is the gas saturation of the Class II differential gas layer in a tight gas reservoir, in %; A and B are constants relating to the tight gas reservoir; α is the correlation coefficient between the production of Class I gas layers per meter thickness and the production of Class II differential gas layers per meter thickness in the same stratigraphic position; and k is the ratio of the natural gas content of Class I gas layers to that of Class II differential gas layers per unit volume.

[0037] Furthermore, the Class I gas layer and Class II poor gas layer of the tight gas reservoir are classified according to the gas saturation and porosity of the same gas reservoir as interpreted by well logging.

[0038] Furthermore, the porosity of the Class I gas layer in the tight gas reservoir is ≥8%, and the gas saturation is ≥50%; the porosity of the Class II poor gas layer is ≥6% and <8%, and the gas saturation is ≥35% and <50%. Attached Figure Description

[0039] Figure 1 This is a quantitative relationship diagram of porosity and gas saturation for Class I gas layers and Class II poor gas layers in the embodiments;

[0040] Figure 2 This is a graph showing the relationship between the thickness of the Class I gas layer and the tested gas production rate established in the example.

[0041] Figure 3 The graph shows the relationship between the production rate of a Class I gas layer per meter of thickness and the production rate of a Class II poor gas layer per meter of thickness, as established in the example. Detailed Implementation

[0042] Taking the Tai-2 gas reservoir in the Tai-2 gas field as an example, the technical solution of this invention is further explained below by classifying the gas-bearing layers into Class I, Class II, and Class III gas-bearing layers based on the gas saturation and porosity conclusions interpreted from well logging, combined with specific implementation methods. The Tai-2 gas reservoir is a tight gas reservoir that has already undergone large-scale development. Early development focused on Class I gas layers and localized Class II poor-quality gas layers, resulting in a high degree of reserve utilization. However, large-scale reserve utilization remains challenging, necessitating further exploration of the remaining Class II poor-quality gas layers. The formation pressure (Pi), formation temperature (Ti), natural gas deviation factor (Zi), and gas constant (R) of the Tai-2 gas reservoir are all constant values.

[0043] Example 1

[0044] The method for predicting gas production in tight gas reservoirs with poor gas layer conditions, as described in this embodiment, specifically includes the following steps:

[0045] 1) Based on the gas saturation and porosity conclusions interpreted from well logging, the Tai-2 gas reservoir is divided into three types: Class I gas-bearing layers, Class II poor gas-bearing layers, and Class III gas-bearing layers. Quantitative relationships between porosity and gas saturation are established for Class I and Class II poor gas-bearing layers, respectively. (See...) Figure 1 Among them, Class I gas-bearing layers have a porosity ≥8% and a gas saturation ≥50%; Class II poor gas-bearing layers have a porosity ≥6% and <8% and a gas saturation ≥35% and <50%; and Class III gas-bearing layers have a porosity <6% and a gas saturation <35%.

[0046] 2) Based on step 1), the porosity and gas saturation of the Type I gas layer and the Type II poor gas layer in the Tai 2 gas reservoir are statistically analyzed, and the average porosity and gas saturation of each type of gas layer are calculated. The average porosity of the Type I gas layer is 9.3% and the average gas saturation is 60.6%; the average porosity of the Type II poor gas layer is 6.8% and the average gas saturation is 41.3%.

[0047] 3) Based on step 2), using Formula 5, which relates the natural gas content per unit volume of Class I gas reservoirs and Class II poor gas reservoirs, the proportional relationship of natural gas content per unit volume between Class I gas reservoirs and Class II poor gas reservoirs can be obtained, as shown in Formula 8:

[0048]

[0049] In equation 8 above, V g1 The gas-bearing volume of a Class I gas reservoir is given in m. 3 A g1 The gas-bearing area of ​​a Class I gas layer, in m 2 H g1 φ1 represents the thickness of a Class I gas layer, in meters; φ1 represents the porosity of a Class I gas layer, in percentages; S g1 The gas saturation of a Class I gas layer, in %; V g2 The gas-bearing volume of a Class II gas-depleted reservoir, in m 3 A g2 The gas-bearing area of ​​a Class II gas-depleted layer, in m 2 H g2 φ2 represents the thickness of the Class II poor gas layer, in meters; φ2 represents the porosity of the Class II poor gas layer, in percentages; S g2 The gas saturation of a Class II poor-quality gas layer, %.

[0050] Based on Equation 6, the thickness relationship between Class I gas layers and Class II poor gas layers with the same natural gas volume is obtained. Since the controlled area of ​​a single vertical well in the target gas reservoir is the same, the gas-bearing area A of the Class I gas layer is... g1 Gas-bearing area A of the Class II gas-differential layer g2 Same, i.e., A g1 =A g2Therefore, the thickness relationship between Class I gas layers and Class II poor gas layers can be obtained as shown in Equation 9:

[0051]

[0052] In equation 9 above, H g1 φ1 represents the thickness of a Class I gas layer, in meters; φ1 represents the porosity of a Class I gas layer, in percentages; S g1 The gas saturation of a Class I gas layer, in %; H g2 φ2 represents the thickness of the Class II poor gas layer, in meters; φ2 represents the porosity of the Class II poor gas layer, in percentages; S g2 The gas saturation of a Class II poor-quality gas layer, %.

[0053] Therefore, the gas-bearing volume of a 1m Class I gas layer is equal to the gas-bearing volume of a 1.98m Class II poor gas layer.

[0054] 4) Establish the correlation between the thickness of Class I gas layers and the tested gas production using gas production test data of Class I gas layers with different thicknesses in the mine, such as... Figure 2 As shown, that is:

[0055] q g1 =0.2402×H g1 +0.1161 (Equation 10);

[0056] In Equation 12, q g1 Gas production of a Class I gas reservoir, 10,000 cubic meters per day; H g1 The thickness of a Class I gas layer is in meters (m).

[0057] Based on field test data, the relationship between the production per meter of Class I gas layer and the production per meter of Class II poor gas layer can be obtained through cross-plotting. (See...) Figure 3 ,Right now:

[0058] q g11 =2.7198q g21 (Equation 11);

[0059] In Equation 11, q g11 The gas production rate per meter of Class I gas layer thickness, in ten thousand cubic meters per day; q g21 The gas production per meter of thickness in a Class II gas-deficient layer is expressed in tens of thousands of cubic meters per day.

[0060] 5) Based on Equations 10 and 11, and through the thickness relationship between Type I gas layers and Type II poor gas layers (Equation 7), the relationship between the thickness of Type II poor gas layers and gas production is established, namely:

[0061]

[0062] In Equation 12, q g2 Gas production of a Class II gas-prone reservoir: 10,000 cubic meters per day; Hg2 The thickness of the gas layer in the Class II poor gas layer, in meters;

[0063] The thickness of the Class II poor gas layer in the Tai 2 gas reservoir at well Z21 is 8m. The production rate, calculated according to Equation 14, is: q g2 =0.0883×H g2 +0.0845=0.0883×8+0.0845=0.7909 million cubic meters / day. Through the implementation of measures on the Class II poor gas layer of the Tai 2 gas reservoir in well Z21, the actual production of the measures operation was 0.74 million cubic meters / day, and the error was less than 10%, which met the production requirements of the mine.

Claims

1. A method for predicting gas production rate of a gas well in a poor gas zone of a tight gas reservoir, characterized in that: Includes the following steps: 1) Based on the gas production test data of Class I gas layers in tight gas reservoirs with different gas layer thicknesses in the mine, construct the correspondence between the gas layer thickness of Class I gas layers in tight gas reservoirs and the tested gas production. Based on field test data, a relationship is established between the production of Class I gas layers per meter thickness and the production of Class II poor gas layers per meter thickness in tight gas reservoirs; the Class I gas layers and Class II poor gas layers in tight gas reservoirs are obtained by classifying the reservoirs of tight gas reservoirs according to well logging interpretation results. 2) Based on the correspondence between the gas layer thickness of Class I gas layers in tight gas reservoirs and the test gas production, as well as the relationship between the production of Class I gas layers per meter of thickness and the production of Class II gas layers per meter of thickness in tight gas reservoirs, and combined with the relationship between the gas layer thickness of Class II gas layers and Class I gas layers in tight gas reservoirs with the same natural gas volume, the relationship between the gas layer thickness of Class II gas layers in tight gas reservoirs and the gas production is constructed. Then, the gas production of Class II gas layers in tight gas reservoir wells is predicted based on the thickness of the Class II gas layers in the tight gas reservoir wells.

2. The method of claim 1, wherein: In step 2), the relationship between the thickness of the Class I gas layer in the constructed tight gas reservoir and the tested gas production is shown in Equation 1: q g1 = A x H g1 + B (Equation 1); In formula 1, q g1 is the tested gas production of the Class I gas layer of the tight gas reservoir, 104m3 / d; H g1 is the gas layer thickness of the Class I gas layer of the tight gas reservoir, m; A and B are constants related to the tight gas reservoir.

3. The method of claim 2, wherein: Based on field test data, the relationship between the production of Class I gas layers per meter thickness and the production of Class II poor gas layers per meter thickness in tight gas reservoirs can be obtained through cross-plots, as shown in Equation 2: q g11 = a x q g21 (Formula 2); In formula 2, q g11 is the test gas production of the Class I gas layer per meter thickness of the tight gas reservoir, 104m3 / d; q g21 is the test gas production of the Class II poor gas layer per meter thickness of the tight gas reservoir, 104m3 / d; and α is the correlation coefficient of the production of the Class I gas layer per meter thickness of the tight gas reservoir and the production of the Class II poor gas layer per meter thickness of the tight gas reservoir.

4. The method of claim 3, wherein: In step 2), the relationship between the thickness of the Type II gas-deficient layer and the gas production of the constructed tight gas reservoir is shown in Equation 3: In formula 3, q g2 is the gas production of the II poor gas layer of the tight gas reservoir, ten thousand cubic meters per day; H g2 is the gas layer thickness of the II poor gas layer of the tight gas reservoir, m; is the porosity of the I gas layer of the tight gas reservoir, %; S g1 is the gas saturation of the I gas layer of the tight gas reservoir, %; is the porosity of the II poor gas layer of the tight gas reservoir, %; S g2 is the gas saturation of the II poor gas layer of the tight gas reservoir, %; A and B are constants related to the tight gas reservoir, and a is the correlation coefficient of the production per meter thickness of the I gas layer of the tight gas reservoir and the production per meter thickness of the II poor gas layer of the tight gas reservoir.

5. The method of claim 1, wherein: The tight gas reservoir has a Class I gas layer with a porosity ≥8% and a gas saturation ≥50%; and a Class II poor gas layer with a porosity ≥6% and <8% and a gas saturation ≥35% and <50%.

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