A method for rapid identification of lithology while drilling in the Upper Paleozoic strata

Abstract

The present invention discloses a method for rapidly identifying the lithology of Upper Paleozoic strata while drilling, and the steps include: collecting gas logging data of the lithology of the interpretation layer of the completed wells in the relevant area; selecting characteristic parameters and calculating the corresponding characteristic parameter values ​​according to the obtained gas logging data; establishing a linear relationship diagram for lithology identification of gas-bearing sand layers / coal seams according to the characteristic parameter values; determining the interpretation layer of the lithology to be identified; selecting and obtaining the characteristic parameters and parameter values ​​of the interpretation layer of the lithology to be identified; and determining the lithology according to the position of the curve corresponding to the characteristic parameter value of the interpretation layer of the lithology to be identified on the linear relationship diagram for lithology identification. The method for identifying the lithology of Upper Paleozoic strata while drilling provided by the present invention is simple, rapid and accurate, and can provide a reliable basis for accurately pinpointing the completed drilling layer, reducing the invalid footage by under-drilling, and selecting the test gas layer after drilling.

Description

Technical field:

[0001] The invention relates to the technical field of exploration and development of tight sandstone lithologic trap gas reservoirs, and in particular to a method for rapidly identifying the lithology of Upper Paleozoic strata while drilling. Background technology:

[0002] In the exploration process of tight sandstone lithologic gas reservoirs, gas logging is the only rapid logging technology for continuous detection of gas content in formations while drilling. The total hydrocarbon and component values ​​directly measured by gas logging can only reflect the gas content of the formation, but cannot identify which lithology contains gas. In different basins and different lithologies, the composition of oil and gas components is closely related to their geological conditions. Taking the Sulige gas field as an example, the gas field is a typical tight sandstone lithologic closed gas reservoir developed in the Upper Paleozoic clastic rock system. This type of gas reservoir generally has the "five low" characteristics of low porosity, low permeability, low pressure, low production and low abundance, which leads to an increase in development costs. The principle for completing drilling in the Sulige gas field is generally to drill through the Shanxi Formation gas-bearing sandstone for 30 meters to complete the drilling. However, when drilling to the gas-bearing sandstone of the Upper Paleozoic Shanxi Formation and the gas-bearing coal seams of the lower Taiyuan Formation, in the absence of logging curves, poor representativeness of the rock cuttings, and when the gas logging value is high but the drilling time is low, it is very difficult for the logging site staff to determine whether the sandstone or the coal seam contains gas. Especially under fast drilling conditions, the rock cuttings are fine and broken, and many pieces fall off from the upper part, resulting in highly mixed rock cuttings and poor representativeness. In addition, the sandstone is darker in color due to changes in the sedimentary environment, and cannot be effectively distinguished from the coal seam. Summary of the invention:

[0003] In view of the above problems, the purpose of the present invention is to provide a method for quickly and accurately identifying the lithology of gas-bearing layers in the Upper Paleozoic strata at the logging site, which can provide an accurate basis for accurately pinpointing the completed drilling layer, reducing the ineffective footage and selecting the gas testing layer after drilling.

[0004] The method for rapidly identifying the lithology of Upper Paleozoic strata while drilling described in the present invention specifically comprises the following steps:

[0005] 1. Collect gas logging data on the lithology of the wells interpreted in the relevant area (Upper Paleozoic strata);

[0006] 2. Select characteristic parameters and calculate corresponding characteristic parameter values ​​according to the gas measurement data obtained in step 1;

[0007] 3. Establish a linear relationship diagram for lithology identification of gas-bearing sand layers and gas-bearing coal layers according to the characteristic parameters selected in step 2 and the corresponding characteristic parameter values;

[0008] 4. Determine the lithologic interpretation layer to be identified;

[0009] 5. Select the same characteristic parameters as in step 2, and calculate the corresponding characteristic parameter values ​​according to the gas logging data of the lithology interpretation layer to be identified;

[0010] 6. Draw a corresponding curve based on the points projected on the lithology identification linear relationship diagram according to the characteristic parameter values ​​obtained in step 5, and determine the lithology of the lithology interpretation layer to be identified based on the position of the curve.

[0011] Those skilled in the art should understand that the relevant area in step 1) should be the area where the well is located while drilling and where the interpretation layer needs to be determined and lithology identification needs to be performed.

[0012] Furthermore, the lithology identification linear relationship diagram contains gas-bearing sand layer partitions and gas-bearing coal layer partitions, and the gas-bearing sand layer partitions and gas-bearing coal layer partitions are determined according to the characteristic parameter values ​​of the gas-bearing sand layer and the gas-bearing coal layer of the relevant area obtained in step 2).

[0013] Furthermore, in step 6, the lithology of the lithology interpretation layer to be identified is determined in the following manner: when the curve is in the gas-bearing sand layer partition, the lithology of the lithology interpretation layer to be identified is the gas-bearing sand layer; when the curve is in the gas-bearing coal layer partition, the lithology of the lithology interpretation layer to be identified is the gas-bearing coal layer.

[0014] Furthermore, the lithologic interpretation layer to be identified in step 4 is determined by: determining it based on the logging information, and as long as one of the following conditions is met, it is determined as an interpretation layer: (1) the total hydrocarbon display value of the gas logging is 2 times higher than the base value; (2) the drilling time display value is 1 to 3 minutes.

[0015] Preferably, the gas measurement data in step 1 and step 5 include: absolute contents of gas measurement components, and the gas measurement components are: methane, ethane, propane, isobutane, normal butane, isopentane and normal pentane.

[0016] Preferably, the characteristic parameters in step 2 and step 5 are: isomerization ratio, propane ratio, humidity ratio, and medium quality; the characteristic parameter values ​​are calculated by the following formula:

[0017] Isomer ratio = (iC4 + iC5) / (C1 + C2 + C3 + nC4 + nC5) × 1000

[0018] Propane ratio = C3 / ∑C×100

[0019] Humidity ratio = (C2 + C3 + iC4 + nC4 + iC5 + nC5) / ∑C × 100

[0020] Medium sum = (C2 + C3) / ∑C × 100

[0021] In the formula, C1, C2, C3, iC4, nC4, iC5, and nC5 represent the absolute contents of gas-measured components methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane, respectively; ∑C represents the total amount of hydrocarbons, which is the sum of the absolute contents of gas-measured components methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane.

[0022] Preferably, the lithology identification linear relationship diagram in step 3 is established in the following manner: a plane rectangular coordinate system is used, with the vertical axis as the parameter axis, and different height positions on the vertical axis correspond to specific characteristic parameters: isomerization ratio, propane ratio, moisture ratio and medium quality; the horizontal axis is used as the scale axis, and the numerical values ​​thereon correspond to specific characteristic parameter values, each characteristic parameter has a horizontal axis and all horizontal axes have a common scale; the division interval of each characteristic parameter regarding gas-bearing sand layers and gas-bearing coal layers is determined according to the distribution position of the characteristic parameter values ​​of multiple completed well interpretation layers on the horizontal axis; the area between the line connecting the left end point and the line connecting the right end point of each characteristic parameter regarding the gas-bearing sand layer division interval constitutes a gas-bearing sand layer partition, and the area between the line connecting the left end point and the line connecting the right end point of each characteristic parameter regarding the gas-bearing coal layer division interval constitutes a gas-bearing coal seam partition.

[0023] Further, when the lithology determination result of step 6 shows that the curve is not completely in a single gas-bearing sand layer partition or a gas-bearing coal layer partition, continue to execute step 7: calculate the hydrocarbon slope value of the completed well interpretation layer based on the gas logging data obtained in step 1, determine the hydrocarbon slope division interval for the gas sand layer and the gas-bearing coal layer based on the scattered distribution of the hydrocarbon slope value of the completed well interpretation layer, calculate the hydrocarbon slope value of the to-be-identified interpretation layer based on the gas logging data of the to-be-identified lithology interpretation layer, and determine the lithology of the to-be-identified lithology interpretation layer based on the hydrocarbon slope division interval where the hydrocarbon slope value of the to-be-identified interpretation layer is located.

[0024] The lithology determination process of the lithology interpretation layer to be identified by the method provided by the present invention is as follows: Figure 1 shown.

[0025] Preferably, the hydrocarbon slope values ​​of the completed well interpretation layer and the interpretation layer to be identified are calculated by the following formula:

[0026] Hydrocarbon slope = C2 / C3

[0027] Wherein, C2 and C3 represent the absolute contents of gas measurement components ethane and propane, respectively.

[0028] The method for identifying the lithology of the Upper Paleozoic strata while drilling provided by the present invention is simple, fast and accurate. In particular, when the identification is performed with the aid of a computer system, the lithology while drilling can be quickly and accurately reflected, providing a reliable basis for accurately pinpointing the completed drilling layer, reducing the ineffective footage, and selecting the gas testing layer after drilling. Description of the drawings:

[0029] Figure 1 This is a flow chart for determining the lithology of the lithology interpretation layer to be identified in the present invention.

[0030] Figure 2 The figure is a linear relationship diagram for lithology identification constructed by the method of the present invention.

[0031] Figure 3 It is a scatter plot of hydrocarbon slope obtained based on hydrocarbon slope values ​​of multiple groups of well interpretation layers.

[0032] Figure 4 The distribution positions of the curves corresponding to the characteristic parameter values ​​of interpretation layer 1 and interpretation layer 2 in the lithology identification linear relationship diagram.

[0033] Figure 5 This is the logging data diagram of S76-14-12 well (including interpretation layer 1 and interpretation layer 2). Specific implementation method:

[0034] The technical solution of the present invention is further described in detail below through embodiments.

[0035] Taking the Sulige S76-14-12 well as an example, when drilling into the Paleozoic strata, the gas logging data of the lithology of multiple well interpretation layers in the area (Upper Paleozoic strata) were first collected, including the absolute contents of methane, ethane, propane, isobutane, n-butane, isopentane and n-pentane gas logging components. The values ​​of the isomer ratio, propane proportion, moisture ratio, and the four characteristic parameters of medium quality and were calculated based on the multiple sets of gas logging data obtained. The corresponding calculation formula is:

[0036] Isomer ratio = (iC4 + iC5) / (C1 + C2 + C3 + nC4 + nC5) × 1000

[0037] Propane ratio = C3 / ∑C×100

[0038] Humidity ratio = (C2 + C3 + iC4 + nC4 + iC5 + nC5) / ∑C × 100

[0039] Medium sum = (C2 + C3) / ∑C × 100

[0040] In the formula, C1, C2, C3, iC4, nC4, iC5, and nC5 represent the absolute contents of gas-measured components methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane, respectively, and ∑C is the total amount of total hydrocarbons, that is, the sum of the absolute contents of gas-measured components.

[0041] Then, a linear relationship diagram for lithology identification of gas sand layers / coal layers is established based on the multiple sets of characteristic parameter values ​​obtained. The specific mapping method is as follows: a plane rectangular coordinate system is used, with the vertical axis as the parameter axis, and different height positions on the vertical axis correspond to specific characteristic parameters: isomerization ratio, propane percentage, moisture ratio, and medium quality sum; the horizontal axis is used as the scale axis, and the values ​​on it correspond to specific characteristic parameter values. Each characteristic parameter has a horizontal axis and all horizontal axes have a common scale; the division interval of each characteristic parameter with respect to gas sand layers and gas coal layers is determined according to the distribution position of the characteristic parameter values ​​of multiple completed well interpretation layers on the horizontal axis. In this specific implementation, the division interval of each characteristic parameter with respect to gas-bearing coal layers is: 0≤isomerization ratio≤4, 0≤propane percentage≤2, 4≤moisture ratio≤8, 4≤medium quality sum≤8; the division interval of each characteristic parameter with respect to gas sand layers is: 4≤isomerization ratio≤8, 2≤propane percentage≤6, 8≤moisture ratio≤12, 8≤medium quality sum≤12. The linear relationship diagram for lithology identification constructed by this specific implementation is shown as follows: Figure 2 As shown, the area between the connecting line of the left end point (in order: 4, 2, 8, 8) and the connecting line of the right end point (in order: 8, 6, 12, 12) of the isomer ratio, propane proportion, moisture ratio and medium quality on the horizontal axis and the gas sand layer division interval constitutes the gas sand layer division, and the area between the connecting line of the left end point (in order: 0, 0, 4, 4) and the connecting line of the right end point (in order: 4, 2, 8, 8) on the horizontal axis constitutes the gas coal layer division. In addition, the hydrocarbon slope values ​​of multiple groups of well interpretation layers are calculated based on the gas logging data of the lithology of multiple well interpretation layers in the area, and the hydrocarbon slope division intervals for gas sand layers and gas coal layers are determined based on the scattered distribution of these hydrocarbon slope values. Among them, the calculation formula of the hydrocarbon slope value is: hydrocarbon slope = C2 / C3, where C2 and C3 represent the absolute contents of ethane and propane in the gas logging components, respectively. Figure 3 This is a hydrocarbon slope scatter plot obtained based on the hydrocarbon slope values ​​of multiple groups of well interpretation layers in this specific implementation. According to the scatter distribution, the hydrocarbon slope division interval for gas-bearing sand layers is: hydrocarbon slope ≤ 10; the hydrocarbon slope division interval for gas-bearing coal layers is: hydrocarbon slope > 10.

[0042] Then, the interpretation layer was determined based on the logging information of Well S76-14-12. The main basis for determination was the following two conditions: (1) the total hydrocarbon display value of gas logging was 2 times higher than the base value; (2) the drilling time display value was 1 to 3 minutes. As long as one of the two conditions was met, it was determined to be an interpretation layer. According to this determination method, two interpretation layers were identified in the well section 3510.0-3537.0m, namely interpretation layer 1 and interpretation layer 2 ( Figure 5As shown). According to the gas logging data of each interpretation layer, the above calculation formula is used to calculate the corresponding isomer ratio, propane percentage, moisture ratio, medium quality and hydrocarbon slope values ​​(as shown in Table 1). According to the obtained isomer ratio, propane percentage, moisture ratio, medium quality and values, a corresponding curve is drawn on the lithology identification linear relationship diagram (i.e., the numerical points on the horizontal axis). The curve is a line connecting each point in sequence. The lithology of the lithology interpretation layer to be identified is determined according to the position of the curve. The lithology determination result of this specific implementation method is shown in Figure 4 As shown: the curve of the interpretation layer 1 falls within the gas sand layer partition, and accordingly, the projection points of the four characteristic parameter values ​​also fall within the corresponding characteristic parameter division interval for the gas sand layer, thereby judging that the lithology of the interpretation layer 1 is the gas sand layer; the curve of the interpretation layer 2 falls within the gas coal layer partition, and accordingly, the projection points of the four characteristic parameter values ​​also fall within the corresponding characteristic parameter division interval for the gas coal layer, thereby judging that the lithology of the interpretation layer 2 is the gas coal layer.

[0043] Table 1 Gas logging data, characteristic parameters and lithology comparison between interpretation layer 1 and interpretation layer 2

[0044]

[0045]

[0046] Because the curves of interpretation layer 1 and interpretation layer 2 completely fall within the gas-bearing sand layer partition and the gas-bearing coal layer partition, respectively, there is no need to determine the lithology based on the hydrocarbon slope. On the contrary, if the curves of interpretation layer 1 and / or interpretation layer 2 do not completely fall within any partition, it is necessary to determine the lithology based on the hydrocarbon slope division interval in which the hydrocarbon slope value of the interpretation layer is located. Taking interpretation layer 1 as an example, in this specific embodiment, if the hydrocarbon slope value of interpretation layer 1 is ≤10, it is within the hydrocarbon slope division interval of the gas-bearing sand layer, and thus the lithology of interpretation layer 1 is judged to be a gas-bearing sand layer; if the hydrocarbon slope value of interpretation layer 1 is >10, it is within the hydrocarbon slope division interval of the gas-bearing coal layer, and thus the lithology of interpretation layer 1 is judged to be a gas-bearing coal layer.

[0047] Lithology identification result verification: The principle of drilling completion in Sulige gas field is to drill through the bottom boundary of the gas-bearing sand layer of the target layer and complete the drilling, and no gas layer should be left in the pocket. After drilling into interpretation layer 1, the lithology identification method of the present invention determined that the lithology of S76-14-12 well was a gas-bearing sand layer. After drilling into interpretation layer 2, the lithology identification method of the present invention determined that the lithology was a gas-bearing coal seam. According to the principle of drilling completion, the drilling was completed at a depth of 3550m after drilling through the bottom boundary of interpretation layer 1 by 30m. If interpretation layer 2 was mistakenly identified as a gas-bearing sand layer, the drilling would be completed at 3564m. Therefore, relying on the lithology determination result of the present invention, 14m of drilling footage was finally saved. After gas testing, interpretation layer 1 produced 2.5736×10 4 m 3 , based on the daily production of 1×104 m 3 / d's industrial gas flow standard, the oil test result is an industrial gas flow well, and the interpretation layer 2 is determined to be a coal seam according to the lithology identification method of the present invention. Most coal seams in this area are aquifers and are prone to collapse, so there is no need to continue drilling or conduct gas testing verification. This shows that the method of the present invention accurately pinpoints the completed drilling layer according to the completion drilling principle after judging the gas-bearing lithology, and selects the gas-bearing sandstone layer suitable for exploitation in this area for gas testing to obtain high-yield industrial gas flow after drilling, indicating that this method has high accuracy and practicality for lithology identification of the Upper Paleozoic strata.

Claims

1. A method for rapidly identifying the lithology of Upper Paleozoic strata while drilling, characterized in that The following steps are involved: 1) Collect gas logging data on the lithology of the wells in the relevant area; 2) selecting characteristic parameters and calculating corresponding characteristic parameter values ​​according to the gas measurement data obtained in step 1); 3) establishing a linear relationship diagram for lithology identification of gas-bearing sand layers and gas-bearing coal layers according to the characteristic parameters selected in step 2) and the corresponding characteristic parameter values; 4) Determine the lithologic interpretation layer to be identified; 5) Select the same characteristic parameters as in step 2), and calculate the corresponding characteristic parameter values ​​according to the gas logging data of the lithology interpretation layer to be identified; 6) Drawing a corresponding curve based on the projected points of the characteristic parameter values ​​obtained in step 5) on the lithology identification linear relationship diagram, and determining the lithology of the lithology interpretation layer to be identified based on the position of the curve; Wherein, the gas measurement data in step 1) and step 5) include: the absolute content of gas measurement components, the gas measurement components are: methane, ethane, propane, isobutane, normal butane, isopentane and normal pentane; The characteristic parameters in step 2) and step 5) are: isomerization ratio, propane ratio, humidity ratio, and medium quality; the characteristic parameter values ​​are calculated by the following formula: Isomeric ratio = (iC4+iC5) / (C1+C2+C3+nC4+nC5)×1000 Propane ratio = C3 / ∑C×100 Humidity ratio = (C2 + C3 + iC4 + nC4 + iC5 + nC5) / ∑C × 100 Medium sum = (C2 + C3) / ∑C × 100 In the formula, C1, C2, C3, iC4, nC4, iC5, and nC5 represent the absolute contents of gas-measured components methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane, respectively; ∑C represents the total amount of hydrocarbons, which is the sum of the absolute contents of gas-measured components methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane.

2. The method for rapid identification of lithology of Upper Paleozoic strata while drilling according to claim 1, characterized in that: The lithology identification linear relationship diagram contains gas-bearing sand layer partitions and gas-bearing coal layer partitions, and the gas-bearing sand layer partitions and gas-bearing coal layer partitions are respectively determined according to the characteristic parameter values ​​of the gas-bearing sand layer and the gas-bearing coal layer in the relevant area obtained in step 2).

3. The method for rapid identification of lithology of Upper Paleozoic strata while drilling according to claim 2, characterized in that: Step 6) The method of determining the lithology of the lithology interpretation layer to be identified is: when the curve is in the gas-bearing sand layer partition, the lithology of the lithology interpretation layer to be identified is the gas-bearing sand layer; when the curve is in the gas-bearing coal layer partition, the lithology of the lithology interpretation layer to be identified is the gas-bearing coal layer.

4. The method for rapid identification of lithology of Upper Paleozoic strata while drilling according to any one of claims 1 to 3, characterized in that: The method for determining the lithologic interpretation layer to be identified in step 4) is as follows: determining it based on the logging information. As long as one of the following conditions is met, it is determined as an interpretation layer: (1) the total hydrocarbon display value of the gas logging is 2 times higher than the base value; (2) the drilling time display value is 1 to 3 minutes.

5. The method for rapid identification of lithology of Upper Paleozoic strata while drilling according to claim 4, characterized in that: In step 3), the linear relationship diagram of lithology identification is established as follows: a plane rectangular coordinate system is used, the vertical axis is used as the parameter axis, and different height positions on the vertical axis correspond to specific characteristic parameters: isomerization ratio, propane ratio, humidity ratio and medium quality; the horizontal axis is used as the scale axis, and the values ​​on it correspond to specific characteristic parameter values, each characteristic parameter has a horizontal axis and all horizontal axes have a common scale; the division interval of each characteristic parameter with respect to gas-bearing sand layer and gas-bearing coal layer is determined according to the distribution position of the characteristic parameter values ​​of multiple completed well interpretation layers on the horizontal axis; The area between the left end point and the right end point of each characteristic parameter's gas sand layer division interval constitutes a gas sand layer partition, and the area between the left end point and the right end point of each characteristic parameter's gas coal layer division interval constitutes a gas coal layer partition.

6. The method for rapid identification of lithology of Upper Paleozoic strata while drilling according to claim 5, characterized in that: When the lithology determination result of step 6) shows that the curve is not completely in a single gas-bearing sand layer partition or a gas-bearing coal layer partition, continue to execute step 7): calculate the hydrocarbon slope value of the completed well interpretation layer according to the gas logging data obtained in step 1), determine the hydrocarbon slope division interval for the gas-bearing sand layer and the gas-bearing coal layer according to the scattered distribution of the hydrocarbon slope value of the completed well interpretation layer, and then calculate the hydrocarbon slope value of the interpretation layer to be identified according to the gas logging data of the lithology interpretation layer to be identified, and determine the lithology of the lithology interpretation layer to be identified according to the hydrocarbon slope division interval where the hydrocarbon slope value of the interpretation layer to be identified is located.

7. The method for rapid identification of lithology of Upper Paleozoic strata while drilling according to claim 6, characterized in that: In step 7), the hydrocarbon slope values ​​of the interpretation layer and the interpretation layer to be identified after drilling are calculated by the following formula: Hydrocarbon slope = C2 / C3 Wherein, C2 and C3 represent the absolute contents of gas measurement components ethane and propane, respectively.

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