Method for quantitatively predicting fluid properties by using gas logging total hydrocarbon curve

Abstract

The invention discloses a method for quantitatively predicting fluid properties by using a gas logging total hydrocarbon curve, which comprises the following steps: acquiring a gas logging total hydrocarbon value through a gas logging instrument to form a continuous gas logging total hydrocarbon curve; solving an overlying mudstone gas logging background value of the oil and gas display layer through the gas logging total hydrocarbon curve; fitting the gas logging total hydrocarbon curve of the oil and gas display layer section through a least square method to obtain a gas logging total hydrocarbon model of the oil and gas display layer; obtaining the hydrocarbon abundance of the oil and gas display layer through the gas logging total hydrocarbon model of the oil and gas display layer and the overlying mudstone gas logging background value of the oil and gas display layer; and predicting fluid properties according to the hydrocarbon-containing abundance of the oil and gas display layer. According to the method for quantitatively predicting the fluid property by using the gas logging total hydrocarbon curve, the hydrocarbon abundance can be quantitatively predicted, and compared with a conventional method, the method for judging the fluid property is lower in cost, higher in timeliness and better in continuity; according to the method, the oil-gas bearing performance of the stratum can be judged under the condition of lack of logging and core data.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum exploration and development, and particularly relates to a method for quantitatively predicting fluid properties by utilizing a gas logging total hydrocarbon curve. Background Art

[0002] Hydrocarbon saturation is an important parameter for determining fluid properties and is also an important parameter for oilfield reserve discovery and evaluation. In the past, hydrocarbon saturation calculations mainly included laboratory analysis methods and logging data acquisition methods. Laboratory analysis methods require closed cores and oil-water layers to analyze oil layers, which are often limited by the high cost of coring, long time consumption, and difficulty of experimental analysis technology, making it difficult to promote and apply them widely in oil fields. In oilfield exploration, development and production, logging data is mainly used to obtain hydrocarbon saturation parameters, and the relationship between resistivity and laboratory core measurement parameters and formation parameters is established using the Archie formula. However, it is often limited by the wellbore environment (mud invasion) and formation factors (such as low-resistivity oil layers), and it is impossible to accurately obtain hydrocarbon saturation. In addition, if logging while drilling technology is not used during drilling, hydrocarbon saturation parameters cannot be calculated while drilling, which makes it difficult for the calculation accuracy and timeliness of parameters to meet the needs of production operations.

[0003] In the existing hydrocarbon saturation calculation methods, oilfield production is mainly calculated using logging data, but without logging while drilling technology, timeliness is difficult to guarantee, which will be detrimental to the oil and gas exploration and development process. Gas logging technology is carried out during the drilling process and can directly discover oil and gas shows. It is a logging method that directly analyzes the oil and gas content in the drilling fluid and can reflect the oil and gas content in the formation. However, the method of determining fluid properties using gas logging methods has mainly used the absolute value of gas logging total hydrocarbons to judge, without considering the influence of gas logging background values, and mainly based on qualitative judgment methods, lacking quantitative evaluation methods.

[0004] Therefore, it is necessary to study and develop a new method to quantitatively predict hydrocarbon abundance during drilling. Summary of the invention

[0005] The purpose of the present invention is to provide a method for quantitatively predicting fluid properties using a gas logging total hydrocarbon curve, which can quantitatively predict hydrocarbon abundance and determine fluid properties; and can determine the oil and gas content of a formation in the absence of logging and core data.

[0006] The technical solution provided by the present invention is:

[0007] A method for quantitatively predicting fluid properties using a gas logging total hydrocarbon curve comprises the following steps:

[0008] Step 1: Obtain the total hydrocarbon value of gas logging by using a gas logging mud logger to form a continuous total hydrocarbon curve of gas logging;

[0009] Step 2: Calculate the gas logging background value of the overlying mudstone of the oil and gas showing layer through the gas logging total hydrocarbon curve; and fit the gas logging total hydrocarbon curve of the oil and gas showing layer segment through the least square method to obtain the gas logging total hydrocarbon model of the oil and gas showing layer;

[0010] Step 3, obtaining the hydrocarbon abundance of the oil and gas showing layer through the gas logging total hydrocarbon model of the oil and gas showing layer and the gas logging background value of the overlying mudstone of the oil and gas showing layer;

[0011] Step 4: predicting fluid properties based on the hydrocarbon abundance of the oil and gas display layer.

[0012] Preferably, the step 1 further comprises:

[0013] If the depth of the abnormal section of the total hydrocarbon detected by gas logging cannot completely match the depth of the fluorescent display layer section of the lithological section, the depth of the abnormal section of the total hydrocarbon detected by gas logging is relocated and matched with the fluorescent display layer; and

[0014] Eliminate thin interlayer display segments in the gas logging total hydrocarbon curve, display segments with oil-water interface or gas-water interface in the same display layer, and false oil and gas display segments with non-formation gas in the display segment;

[0015] If the gas logging total hydrocarbon value of a certain section in the gas logging total hydrocarbon curve is greater than 3 times the total hydrocarbon value of the background gas curve, then the section is judged as a gas logging total hydrocarbon abnormal section.

[0016] Preferably, in the step 2, obtaining the gas detection background value of the overlying mudstone of the oil and gas showing layer comprises the following steps:

[0017] Step 1: Select the overlying mudstone layer for calculating the overlying mudstone gas measurement background value:

[0018] If the thickness of the overlying mudstone adjacent to the oil and gas showing layer is greater than 5 meters, the overlying mudstone adjacent to the oil and gas showing layer is selected as the overlying mudstone layer for calculating the overlying mudstone gas measurement background value;

[0019] If the thickness of the overlying mudstone adjacent to the oil and gas display layer is less than 5 meters, the search will continue upward until the thickness of the overlying mudstone is greater than 5 meters. The overlying mudstone with a current thickness greater than 5 meters will be selected as the overlying mudstone layer for calculating the overlying mudstone gas measurement background value;

[0020] Step 2: Calculate the average value of the total hydrocarbon value of the gas logging at each depth point of the selected overlying mudstone layer, and use the average value as the overlying mudstone gas logging background value of the oil and gas showing layer.

[0021] Preferably, in step 2, the gas logging total hydrocarbon model of the oil and gas display layer obtained by least squares fitting is:

[0022]

[0023] in, is a set of linearly independent functions, a k is the coefficient to be determined, k = 1, 2, ..., m; k represents the number of terms of the coefficient to be determined;

[0024] The fitting criterion is to make the observed value y of the total hydrocarbon value of the gas measurement i (i=1,2,…,n) and f(x i ) is the smallest distance square sum; m and n are the maximum number of unknown coefficients and the maximum number of observed values, respectively, m<n.

[0025] Preferably, in step 3, the calculation formula for the hydrocarbon abundance of the oil and gas display layer is:

[0026]

[0027] Among them, S N is the background gas baseline value for all hydrocarbons in the overlying mudstone gas, S S is the integrated area of ​​the gas logging full hydrocarbon model of the oil and gas display layer, and d is the thickness of the oil and gas display layer.

[0028] Preferably, the integral area of ​​the gas logging full hydrocarbon model of the oil and gas display layer is calculated as follows:

[0029] S s =∫0 d f(x)dx;

[0030] Among them, f(x) is the gas logging total hydrocarbon model of the oil and gas display layer, and d is the thickness of the oil and gas display layer.

[0031] Preferably, the calculation formula for the background gas baseline value of the overlying mudstone gas for total hydrocarbon measurement is:

[0032]

[0033] in, is the gas measurement background value of the overlying mudstone of the oil and gas showing layer, and d is the thickness of the oil and gas showing layer.

[0034] The beneficial effects of the present invention are:

[0035] The method provided by the present invention for quantitatively predicting fluid properties using the gas logging total hydrocarbon curve can quantitatively predict hydrocarbon abundance and judge fluid properties with lower cost, higher timeliness and better continuity than previous methods; the method can judge the oil and gas content of the formation in the absence of logging and core data, providing a more reliable basis for oil and gas exploration and development. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1This is a flow chart of the present invention for quantitatively predicting fluid properties using a gas-measured total hydrocarbon curve.

[0037] Figure 2 This is a gas logging total hydrocarbon curve diagram in an embodiment of the present invention.

[0038] Figure 3 This is a correlation diagram between the hydrocarbon abundance calculated using the least squares method and the hydrocarbon saturation calculated by well logging in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0040] like Figure 1 As shown, the present invention provides a method for quantitatively predicting fluid properties using a gas-measured total hydrocarbon curve, and the specific implementation process is as follows.

[0041] S1. Data collection and processing.

[0042] (1) During the drilling process, the gas after degassing of the drilling fluid is analyzed using a gas logging instrument to obtain the gas logging parameter gas logging total hydrocarbon Tg, and then a continuous gas logging total hydrocarbon Tg curve is formed.

[0043] (2) Due to the influence of factors such as the gas logging delay time, the depth of the fluorescence display layer section of the lithological section and the depth of the gas logging total hydrocarbon abnormal section sometimes cannot be completely matched; if the depth of the fluorescence display layer section of the lithological section and the depth of the gas logging total hydrocarbon abnormal section sometimes cannot be completely matched, the depth of the gas logging total hydrocarbon abnormal section is reset (the depth of the gas logging total hydrocarbon abnormal section is adjusted to the same as the depth of the lithological section fluorescence display layer) and then matched with the lithological section fluorescence display layer.

[0044] (3) The selected oil and gas display segments are processed to eliminate thin interlayer display segments (the specific thickness depends on the drilling speed and the analysis cycle of the gas logging instrument), display segments with oil-water interface or gas-water interface in the same display layer, and false oil and gas display segments with non-formation gas (such as single gas, circulating gas, etc.) in the display segment.

[0045] S2. Use the gas logging total hydrocarbon curve to obtain the gas logging background value of the mudstone overlying the oil and gas showing layer.

[0046] (1) First, select the overlying mudstone segment. If the thickness of the overlying mudstone adjacent to the oil and gas display segment is greater than 5 meters, the background gas value of this mudstone segment is selected to calculate the overlying mudstone gas measurement background value; if the thickness of the overlying mudstone adjacent to the oil and gas display segment is less than 5 meters, continue to search upward until the selected overlying mudstone thickness is greater than 5 meters, and calculate the overlying mudstone gas measurement background value based on the currently selected overlying mudstone segment.

[0047] (2) Calculation of gas logging background value of overlying mudstone. Calculate the average value of gas logging total hydrocarbon value Tg at each depth point of the mudstone layer selected above. The average value As the background value of overlying mudstone gas measurement.

[0048] S3. Fitting the gas logging total hydrocarbon curve of the oil and gas showing layer segment by using the least square method to obtain the gas logging total hydrocarbon model of the oil and gas showing layer.

[0049] The least squares method is used to fit the gas logging total hydrocarbon curve of the oil and gas display layer to obtain the fitting function f(x), the specific formula of which is as follows:

[0050]

[0051] in, is a set of linearly independent functions, which are unknown coefficients, k = 1, 2, ..., m; k represents the number of unknown coefficients. The fitting criterion is that the observed value of the total hydrocarbon value of the gas test makes y i (i=1,2,…,n) and f(x i ) is the smallest; m and n are the maximum number of undetermined coefficients and the maximum number of observed values, respectively, and m<n. The fitting function f(x) is the gas logging full hydrocarbon model of the oil and gas display layer.

[0052] S4. The gas logging total hydrocarbon model of the oil and gas showing layer and the gas logging background value of the overlying mudstone are used to calculate the gas logging total hydrocarbon abnormal area, that is, the hydrocarbon abundance of the oil and gas showing layer.

[0053] (1) The integral area Ss of the gas logging full hydrocarbon model of the oil and gas display layer is calculated using the fitting function f(x). The specific formula is as follows:

[0054] S s =∫0 d f(x)dx;

[0055] Among them, f(x) is the gas logging total hydrocarbon model of the oil and gas display layer, and d is the thickness of the oil and gas display layer.

[0056] (2) Calculate the background gas baseline S of the overlying mudstone gas for full hydrocarbon measurement N , the specific formula is as follows:

[0057]

[0058] in, is the gas measurement background value of the overlying mudstone of the oil and gas showing layer, and d is the thickness of the oil and gas showing layer.

[0059] (3) Calculation of hydrocarbon-bearing area (hydrocarbon abundance) Tg of a single oil and gas display layer f , the specific formula is as follows:

[0060]

[0061] S5. By using the correlation between the hydrocarbon abundance of the oil and gas display layer calculated based on the least squares method and the hydrocarbon saturation calculated by well logging, it is confirmed that the hydrocarbon-bearing area using the least squares method can quantitatively predict the hydrocarbon abundance.

[0062] S6. Establish the limit values ​​of hydrocarbon abundance of different fluid properties to quantitatively predict the fluid properties.

[0063] Example

[0064] The application of this embodiment in actual drilling of sand and mudstone is shown in the attached figure. Figure 1 .

[0065] like Figure 2 As shown, the gas-tested total hydrocarbon Tg value measured during the drilling process is used to form a continuous gas-tested total hydrocarbon Tg curve. The specific implementation process is as follows:

[0066] S1. Data collection and processing. In this example, the depth of the lithological section fluorescence display layer is well matched with the gas logging full hydrocarbon abnormal section, and no relocation is required; the display layer is thick, and there is no obvious gas logging reduction in the layer, that is, there is no oil (gas) water interface, so there is no need to remove the abnormal section.

[0067] S2. Use the gas logging total hydrocarbon curve to obtain the gas logging background value of the mudstone overlying the oil and gas showing layer.

[0068] (1) The sandstone gas logging abnormal layer section is adjacent to the overlying mudstone (2874-2877m) with a thickness of less than 5 meters. The search is continued upward and the mudstone at 2861-2871m is selected to calculate the overlying mudstone gas logging background value.

[0069] (2) Calculation of average value of mudstone background gas. The average value of the total hydrocarbon value Tg value [2.5294, 2.6996, 2.8397, 2.8914, 2.8784, 2.5423, 2.2967, 2.2091, 2.1035, 1.9484, 0.7251] of the gas measurement at each depth point of the mudstone layer selected above is calculated. is 2.3330545454545457.

[0070] S3. Use the least square method to fit the gas logging total hydrocarbon curve and construct a gas logging total hydrocarbon model for the oil and gas display layer.

[0071] The least square method is used to fit the gas logging total hydrocarbon curve of the oil and gas display layer to obtain the fitting curve f(x), and its specific formula is as follows:

[0072] f(x)=0.004367529295383088x 3+0.29038779295368x 2 +4.995008358703139x+6.224694395086002;

[0073] S4. Calculate the gas logging total hydrocarbon abnormal area, i.e., the hydrocarbon-bearing area (hydrocarbon abundance) of the oil and gas showing layer based on the least square method, by using the gas logging total hydrocarbon model of the oil and gas showing layer and the gas logging background value of the overlying mudstone.

[0074] (1) Using the above fitting function (gas logging full hydrocarbon model), calculate the integral area S of the gas logging full hydrocarbon curve of the oil and gas display layer S is 562.205717503495, and the specific formula is as follows:

[0075] S s =∫0 d f(x)dx;

[0076] (2) Calculate the background gas baseline S of the overlying mudstone gas for full hydrocarbon measurement N It is 48.99414545454546. The specific formula is as follows:

[0077]

[0078] (3) Calculation of hydrocarbon-bearing area (hydrocarbon abundance) Tg of a single oil and gas display layer f is 23.327798729497704, and the specific formula is as follows:

[0079]

[0080] S5. Use the least squares method to calculate the hydrocarbon abundance and the hydrocarbon saturation calculated by logging to establish a correlation, such as Figure 3 As shown, the correlation is 0.87, which is a good correlation, proving that the hydrocarbon-bearing area using the least squares method can quantitatively predict the hydrocarbon abundance.

[0081] S6. Establish the limit value of hydrocarbon abundance of different fluid properties to quantitatively predict fluid properties. According to the sampled test layers in the study area, for layers with gas properties, the hydrocarbon abundance calculated by the least square method is greater than 7 for gas layers, the hydrocarbon abundance between 2 and 7 for gas-bearing water layers, and the hydrocarbon abundance less than 2 for water layers. The hydrocarbon abundance Tg calculated in this example is f It is 23.327798729497704, and the hydrocarbon abundance is greater than 7, so it is predicted that this layer is a gas layer.

[0082] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for quantitatively predicting fluid properties using a gas logging total hydrocarbon curve, characterized in that: The steps include: Step 1: Obtain the total hydrocarbon value of gas logging by using a gas logging mud logger to form a continuous total hydrocarbon curve of gas logging; Step 2: Calculate the gas logging background value of the overlying mudstone of the oil and gas showing layer through the gas logging total hydrocarbon curve; and fit the gas logging total hydrocarbon curve of the oil and gas showing layer segment through the least square method to obtain the gas logging total hydrocarbon model of the oil and gas showing layer; Step 3, obtaining the hydrocarbon abundance of the oil and gas showing layer through the gas logging total hydrocarbon model of the oil and gas showing layer and the gas logging background value of the overlying mudstone of the oil and gas showing layer; Step 4: predicting fluid properties based on the hydrocarbon abundance of the oil and gas display layer.

2. The method for quantitatively predicting fluid properties using a gas-measured total hydrocarbon curve according to claim 1, characterized in that: The step one also includes: If the depth of the abnormal section of the total hydrocarbon detected by gas logging cannot completely match the depth of the fluorescent display layer section of the lithological section, the depth of the abnormal section of the total hydrocarbon detected by gas logging is relocated and matched with the fluorescent display layer; and Eliminate thin interlayer display segments in the gas logging total hydrocarbon curve, display segments with oil-water interface or gas-water interface in the same display layer, and false oil and gas display segments with non-formation gas in the display segment; If the gas logging total hydrocarbon value of a certain section in the gas logging total hydrocarbon curve is greater than 3 times the total hydrocarbon value of the background gas curve, then the section is judged as a gas logging total hydrocarbon abnormal section.

3. The method for quantitatively predicting fluid properties using a gas-tested total hydrocarbon curve according to claim 2, characterized in that: In the step 2, obtaining the gas detection background value of the overlying mudstone of the oil and gas showing layer includes the following steps: Step 1: Select the overlying mudstone layer for calculating the overlying mudstone gas measurement background value: If the thickness of the overlying mudstone adjacent to the oil and gas showing layer is greater than 5 meters, the overlying mudstone adjacent to the oil and gas showing layer is selected as the overlying mudstone layer for calculating the overlying mudstone gas measurement background value; If the thickness of the overlying mudstone adjacent to the oil and gas display layer is less than 5 meters, the search will continue upward until the thickness of the overlying mudstone is greater than 5 meters. The overlying mudstone with a current thickness greater than 5 meters will be selected as the overlying mudstone layer for calculating the overlying mudstone gas measurement background value; Step 2: Calculate the average value of the total hydrocarbon value of the gas logging at each depth point of the selected overlying mudstone layer, and use the average value as the overlying mudstone gas logging background value of the oil and gas showing layer.

4. The method for quantitatively predicting fluid properties using a gas-measured total hydrocarbon curve according to claim 2 or 3, characterized in that: In the step 2, the gas logging total hydrocarbon model of the oil and gas display layer obtained by least squares fitting is: in, is a set of linearly independent functions, a k is the coefficient to be determined, k = 1, 2, ..., m; k represents the number of terms of the coefficient to be determined; The fitting criterion is to make the observed value y of the total hydrocarbon value of the gas measurement i (i=1,2,…,n) and f(x i ) is the smallest distance square sum; m and n are the maximum number of unknown coefficients and the maximum number of observed values, respectively, m<n.

5. The method for quantitatively predicting fluid properties using a gas-tested total hydrocarbon curve according to claim 4, characterized in that: In the step 3, the calculation formula for the hydrocarbon abundance of the oil and gas display layer is: Among them, S N is the background gas baseline value for all hydrocarbons in the overlying mudstone gas, S S is the integrated area of ​​the gas logging full hydrocarbon model of the oil and gas display layer, and d is the thickness of the oil and gas display layer.

6. The method for quantitatively predicting fluid properties using a gas-tested total hydrocarbon curve according to claim 5, characterized in that: The calculation formula for the integral area of ​​the gas logging full hydrocarbon model of the oil and gas display layer is: S S =∫0 d f(x)dx; Among them, f(x) is the gas logging total hydrocarbon model of the oil and gas display layer, and d is the thickness of the oil and gas display layer.

7. The method for quantitatively predicting fluid properties using a gas-measured total hydrocarbon curve according to claim 6, characterized in that: The calculation formula for the background gas baseline value of the overlying mudstone gas for total hydrocarbon measurement is: in, is the gas measurement background value of the overlying mudstone of the oil and gas showing layer, and d is the thickness of the oil and gas showing layer.

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