Method for establishing formation drillability grade profile based on logging data

Abstract

The present application relates to a method for establishing a formation drillability grade profile based on logging data, which utilizes P-wave interval transit time and lithology density logging data to establish a drillability grade calculation model, and based on this, forms a continuous curve of a self-top-to-bottom profile through the wellbore. The curve can better indicate the rock drillability at different depths and horizons, and can be used to guide the selection of drill bits at the drilling site, so as to improve the drilling efficiency, reduce the tripping times of tripping in and out, save the drilling period, and thus reduce the drilling cost. The present application makes up for the deficiency that only the drillability grade of the cored well section can be obtained in the past.

Description

Technical Field

[0001] This invention relates to the field of drilling, and more specifically, to a method for establishing a formation drillability level profile based on well logging data. Background Technology

[0002] Formation drillability is a crucial basis for production planning and drill bit selection. For a long time, researchers have devoted considerable effort to obtaining accurate data on formation drillability. This research can be broadly categorized into three main types: ① obtaining data through laboratory testing methods; ② obtaining data by establishing drilling rate prediction models using engineering parameters; and ③ using models based on logging data such as acoustic waves for prediction. Each method has its advantages and disadvantages. Laboratory testing methods can be further divided into micro-drilling and rock breaking ratio methods. The former is the standard method in the petroleum industry, while the latter is mostly used in the mining industry and is only suitable for impact rock breaking, with limited application in the petroleum industry. Indoor testing methods use direct experimental measurements, offering relatively high accuracy. However, they require physical core samples, necessitating repeated testing in different regions and wells, leading to high costs. Furthermore, these tests often deviate from the actual underground temperature and pressure conditions, resulting in some distortion of the results. Additionally, the drillability grade of formations in sections without core samples cannot be determined. The drilling rate equation method uses engineering parameters such as drilling time, drilling pressure, rotational speed, and torque to build a model for prediction. Data acquisition is simple and quick, but the model is relatively complex, and the engineering parameters are influenced by human factors, resulting in some randomness and relatively insufficient accuracy. Since sonic transit time has a good correlation with formation drillability, well logging data methods often use sonic transit time data as the basis for model building and prediction. This method first obtains the drillability grade of a specific rock section indoors, then uses mathematical statistics to establish a regression equation between the grade and sonic transit time. However, rock drillability is a comprehensive manifestation of its resistance to external damage, and it is related to a variety of factors such as lithology, porosity, and the properties of the fluids contained therein. The single parameter of acoustic transit time often cannot reflect the level of rock drillability, and it also has certain limitations.

[0003] In summary, traditional methods have two major drawbacks: first, drillability ratings are mostly limited to core drilling sections; and second, the calculation methods are too complex, resulting in insufficient guidance for field drilling applications. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for establishing a formation drillability grade profile based on well logging data, which can form a continuous drillability grade profile in the longitudinal direction, which is beneficial to guiding the selection of drill bits in drilling engineering.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for constructing a formation drillability level profile based on well logging data, comprising the following steps:

[0006] S1. Collect the P-wave transit time, lithology density logging curves, and drillability grade parameters of the cored well section in the target area;

[0007] S2. Collect drilling and logging data for the entire target area to understand the vertical distribution characteristics of difficult-to-drill strata in the region;

[0008] S3. Using X=EXP(DEN*DEN / LN(AC)) as the independent variable and the drillability grade of the core sample section as the dependent variable, fit the model to obtain the drillability grade calculation model under polynomial, power function, and exponential function; where X is the joint model parameter, DEN is the lithological density, and AC is the P-wave transit time.

[0009] S4. Based on the goodness of fit, select the best model among the above models as the regional drillability level calculation model.

[0010] S5. Based on the optimal model, use geological mapping software to generate a continuous curve of the drillability grade value for a single well. Combine this with the actual drilling and logging data of wells already drilled in the area to determine the degree of agreement between the drillability grade value and the actual drilling results. If the agreement is good, use this as the calculation model for the drillability grade value of the target area. If the agreement is not good, further optimize the model until it is good.

[0011] According to the above scheme, step S3 includes the following steps:

[0012] S301. Take the logarithm of the acoustic time difference, and record the result as X1, i.e., X1 = LN(AC);

[0013] S302. The lithological density is squared and the result is denoted as X2, i.e., X2 = DEN * DEN;

[0014] S303. Further processing of the above parameters X1 and X2 yields the joint model parameter X, i.e., X = (DEN*DEN) / LN(AC);

[0015] S304. Using the joint model parameter X as the explanatory variable and the drillability level value as the dependent variable, perform fitting of various types of functions such as linear, quadratic, cubic, and power functions. Based on the goodness of fit, select the best-fitting model.

[0016] According to the above scheme, the formation drillability rating is positively correlated with lithological density.

[0017] According to the above scheme, the formation drillability rating is negatively correlated with the acoustic transit time.

[0018] According to the above scheme, the drilling and logging data in step S2 are P-wave transit time and lithology density logging data, as well as the core drillability rating test results of the core section.

[0019] The method for establishing formation drillability level profiles based on well logging data according to the present invention has the following beneficial effects:

[0020] 1. The basic data required for this invention are P-wave transit time and lithology density logging data, as well as the core drillability rating test results of the core section, which are relatively easy to obtain and inexpensive.

[0021] 2. This invention can form a continuous curve running through the wellbore profile, which facilitates a visual and intuitive comparison of the drillability ratings of different layers;

[0022] 3. The calculation results obtained by the model in this invention can be used as a qualitative judgment basis for the drillability of regional formations, and can be applied to guide drilling to optimize the selection of drill bits for formations with different drillability. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0024] Figure 1 It is a comprehensive logging diagram;

[0025] Figure 2 This is a schematic diagram of the drillability level value fitting surface under different function types;

[0026] Figure 3 This is a graph showing the correlation between drillability grade and acoustic transit time.

[0027] Figure 4 This is a graph showing the correlation between drillability rating and lithological density;

[0028] Figure 5 This is the comprehensive well drillability diagram in Example 1;

[0029] Figure 6 This is the comprehensive well drillability diagram in Example 2; Detailed Implementation

[0030] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0031] The present invention provides a method for establishing formation drillability level profiles based on well logging data, comprising the following steps:

[0032] S1. Collect the P-wave transit time, lithology density logging curves, and drillability grade parameters of the cored well section in the target area;

[0033] S2. Collect drilling and logging data for the entire target area to understand the vertical distribution characteristics of difficult-to-drill formations in the region; a comprehensive logging map is shown below. Figure 1 As shown;

[0034] S3. Using X=EXP(DEN*DEN / LN(AC)) as the independent variable and the drillability grade of the core sample section as the dependent variable, fit the model to obtain the drillability grade calculation model under polynomial, power function, and exponential function; where X is the joint model parameter, DEN is the lithological density, and AC is the P-wave transit time.

[0035] S4. Based on the goodness of fit, select the best model among the above models as the regional drillability level calculation model.

[0036] S5. Based on the optimal model, use geological mapping software to generate a continuous curve of the drillability grade for a single well, such as... Figure 2 As shown, and in conjunction with the actual drilling and logging data of the wells already drilled in the area, the degree of agreement between the drillability grade value and the actual drilling results is determined. If the agreement is good, it is used as the calculation model for the drillability grade value of the target area. If the agreement is not good, the model is further optimized until it agrees.

[0037] The principle of this invention is as follows:

[0038] The research results show that there is a certain correlation between sonic transit time, lithological density, and drillability rating. Generally, as the burial depth increases, the degree of compaction gradually increases, sonic transit time decreases, and it has a negative correlation with the drillability rating. Lithological density, on the other hand, shows the opposite trend. Figure 3 , Figure 4 As shown.

[0039] Due to the influence of multiple factors such as formation porosity, fracture development, and the presence of fluids in the formation, using a single-factor model to fit the formation drillability rating often leads to insufficient model accuracy. Therefore, this paper proposes a joint drillability rating acquisition method based on sonic transit time and lithological density. As mentioned earlier, the formation drillability rating is positively and negatively correlated with lithological density and sonic transit time, respectively. Directly using a simple binary linear fitting method results in a certain degree of multicollinearity. To preserve the binary nature of the fitting parameters while eliminating multicollinearity, the optimal solution is found among multiple models, and the following mathematical processing is performed:

[0040] 1. Take the logarithm of the sound wave time difference, and record the result as X1, i.e., X1 = LN(AC) (AC - sound wave time difference, μs / ft);

[0041] 2. Square the lithological density, and denote the result as X2, i.e., X2 = DEN * DEN (DEN - lithological density, g / cm³) 3 );

[0042] 3. Further processing of the above parameters X1 and X2 yields the joint model parameter X, i.e., X = (DEN*DEN) / LN(AC);

[0043] 4. Using the joint model parameter X as the explanatory variable and the drillability level value as the dependent variable, various types of functions such as linear, quadratic, cubic, and power functions were fitted. Based on the goodness of fit, the best-fitting model was selected. The fitting results under different modes are compared in Table 1.

[0044] Table 1 Comparison of Fitting Results under Different Modes

[0045]

[0046] Example 1

[0047] Well XX is an appraisal well in the XX block. Actual drilling data shows that the Dalong Formation, Xiayao Formation, Maokou Formation, Qixia Formation, and Yuntaiguan Formation in this area have poor drillability and low mechanical drilling rates, severely impacting drilling efficiency. Using the methods described above, a drillability rating profile for this well was established. The results show that the theoretical calculations agree well with the actual drilling data. Figure 5 As shown.

[0048] Example 2

[0049] Well XX is an exploratory well in the XX block, where the drillability of the bottom of the Changxing Formation and the first section of the Wujiaping Formation is poor. Using the same method, a drillability rating profile for this well was established. The results show that the theoretical calculations agree well with the actual drilling results. Figure 6 As shown.

[0050] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for establishing a formation drillability level profile based on well logging data, characterized in that, Includes the following steps: S1. Collect the P-wave transit time, lithology density logging curves, and drillability grade parameters of the cored well section in the target area; S2. Collect drilling and logging data for the entire target area to understand the vertical distribution characteristics of difficult-to-drill strata in the region; S3, with X=EXP(DEN) Using DEN / LN(AC) as the independent variable and the drillability grade of the core sample section as the dependent variable, the drillability grade calculation models under polynomial, power function, and exponential function are obtained; where X is the joint model parameter, DEN is the lithological density, and AC is the P-wave transit time. S4. Based on the goodness of fit, select the best model among the above models as the regional drillability level calculation model. S5. Based on the optimal model, use geological mapping software to generate a continuous curve of the drillability grade value for a single well. Combine this with the actual drilling and logging data of wells already drilled in the area to determine the degree of agreement between the drillability grade value and the actual drilling results. If the agreement is good, use this as the calculation model for the drillability grade value of the target area. If the agreement is not good, further optimize the model until it is good. Step S3 includes the following steps: S301. Take the logarithm of the acoustic time difference, and denot the result as X1, i.e., X1 = LN(AC); S302. The lithological density is squared, and the result is denoted as X2, i.e., X2 = DEN. DEN; S303. Further processing of the above parameters X1 and X2 yields the joint model parameter X, i.e., X = EXP(DEN). DEN / LN(AC)); S304. Using the joint model parameter X as the explanatory variable and the drillability level value as the dependent variable, perform fitting of various types of functions such as linear, quadratic, cubic, and power functions. Based on the goodness of fit, select the best-fitting model.

2. The method for establishing a formation drillability level profile based on well logging data according to claim 1, characterized in that, The drillability rating of a formation is positively correlated with lithological density.

3. The method for establishing a formation drillability level profile based on well logging data according to claim 1, characterized in that, The formation drillability rating is negatively correlated with the acoustic transit time.

4. The method for establishing a formation drillability level profile based on well logging data according to claim 1, characterized in that, The drilling and logging data in step S2 include P-wave transit time and lithology density logging data, as well as the core drillability rating test results of the core section.

Images