Method for obtaining porosity of cuttings while drilling

Abstract

The present invention relates to the technical field of rock porosity acquisition methods, and is a method for acquiring rock cuttings porosity while drilling, comprising subjecting the rock cuttings samples while drilling to initial thermal catalysis, saturation treatment and later thermal catalysis treatment, and calculating the dry weight coefficient using the mass of the initial thermal catalysis rock cuttings sample and the mass of the later thermal catalysis rock cuttings sample; finally, using the wet weight and dry weight difference model to calculate the rock cuttings porosity of each rock cuttings sample, taking an average value of the rock cuttings porosity of all rock cuttings samples, and the average value is used as the rock cuttings porosity while drilling. The rock cuttings porosity acquisition method while drilling of the present invention can continuously analyze the rock cuttings while drilling, and only needs to select a small amount of samples, giving full play to the advantages of logging data, and can quickly evaluate reservoir physical properties on site, which is of great significance to oil and gas discovery and evaluation, thereby solving the problem that nuclear magnetic resonance requires large rock sample particle size and large amount, and provides technical guarantee for oil exploration.

Description

Technical Field

[0001] The invention relates to the technical field of rock porosity acquisition methods, in particular to a method for acquiring porosity of rock cuttings while drilling. Background Art

[0002] Porosity is a basic parameter for reservoir evaluation and the basis for quantitative evaluation of oil and gas layers by logging. In general, nuclear magnetic resonance has a good effect in measuring porosity, but it still has the following shortcomings under new drilling conditions or in special formations:

[0003] First, NMR measurement requires the selection of larger rock sample particles, with a diameter of more than 10 mm, while the rock cuttings obtained by the PDC drill bit while drilling are relatively small and cannot meet the particle size requirements of the NMR measurement for samples; second, the amount of sample required for NMR measurement is large (weighing more than 50 g), which cannot be obtained by drilling cuttings; NMR measurement has the best measurement effect on cores. If NMR is used to measure the porosity of cuttings, the error is large, and the porosity measured by drilling cuttings has no reference value for reservoir physical property evaluation and other aspects. Summary of the invention

[0004] The present invention provides a method for obtaining the porosity of drilling cuttings, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the problem that the method of measuring porosity by nuclear magnetic resonance is not suitable for measuring the porosity of drilling cuttings.

[0005] The technical solution of the present invention is achieved by the following measures: A method for obtaining porosity of cuttings while drilling, comprising:

[0006] Obtain cuttings samples: Obtain several cuttings samples while drilling in the well section;

[0007] Initial thermal catalysis: the rock cuttings sample is subjected to a first cycle and a second cycle of thermal catalysis treatment in sequence to obtain an initial thermal catalytic rock cuttings sample, the mass of which is W;

[0008] Saturation treatment: The initial thermal catalytic cuttings sample is saturated with water to obtain a saturated cuttings sample, and the mass of the saturated cuttings sample is W1;

[0009] Late thermal catalysis: After the saturated rock cuttings sample is subjected to the third cycle of thermal catalysis, a late thermal catalytic rock cuttings sample is obtained, and the mass of the late thermal catalytic rock cuttings sample is W2;

[0010] Calculate the dry weight coefficient: Calculate the dry weight coefficient C using the mass W of the initial thermal catalytic cuttings sample and the mass W2 of the later thermal catalytic cuttings sample;

[0011] Obtaining the slope: Performing a linear fit on the density of the initial thermal catalytic rock cuttings sample and the roughly calculated porosity to obtain a linear fitting formula, the slope of which is k;

[0012] Calculate the porosity of the cuttings while drilling: Calculate the porosity of each cuttings sample using the wet weight and dry weight difference model, take the average value of the porosity of all cuttings samples, and use the average value as the porosity of the cuttings while drilling. The wet weight and dry weight difference model is as follows:

[0013]

[0014] In the formula, Φ represents the rock chip porosity of the rock chip sample, N represents the number of rock chip samples; Φ s represents the porosity of drilling cuttings; W1 represents the mass of saturated cuttings sample; W2 represents the mass of later thermal catalytic cuttings sample; k represents the slope of the linear fitting formula; ρ r Indicates the rock fragment skeleton density (generally 2.6 g / cm 3 ); C represents the dry weight coefficient.

[0015] The following are further optimizations and / or improvements to the above technical solutions:

[0016] The diameter of the above-mentioned cuttings sample while drilling is 1 mm±0.2 mm and the weight is 0.1 g.

[0017] The first cycle of thermal catalytic treatment specifically includes heat treatments in the initial temperature stage, the first stage, the second stage, the third stage and the fourth stage carried out successively;

[0018] The temperature in the initial stage is 90°C, and the constant temperature time is 2 minutes;

[0019] In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 200℃, and the constant temperature time is 1min;

[0020] The temperature of the first stage was programmed to the second stage, with a heating rate of 50°C / min, the temperature of the second stage was 350°C, and the constant temperature time was 1min;

[0021] The temperature of the second stage was programmed to the third stage, with a heating rate of 50°C / min, the temperature of the third stage was 450°C, and the constant temperature time was 1min;

[0022] The temperature was raised from the third stage to the fourth stage at a rate of 50°C / min. The temperature of the fourth stage was 600°C and the constant temperature time was 1 min.

[0023] The second cycle of thermal catalytic treatment specifically includes continuous initial temperature stage, first stage and second stage thermal treatment;

[0024] The temperature in the initial stage is 90°C, and the constant temperature time is 2 minutes;

[0025] In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 300℃, and the constant temperature time is 3min;

[0026] The temperature was raised from the first stage to the second stage at a rate of 50°C / min. The temperature of the second stage was 600°C and the constant temperature time was 1 min.

[0027] The above-mentioned saturation treatment specifically includes: cooling the initial thermal catalytic rock chip sample to room temperature, adding deionized water to submerge the initial thermal catalytic rock chip sample, maintaining the initial thermal catalytic rock chip sample under a pressure of 1 MPa for 30 minutes, allowing the deionized water to completely fill the internal pores of the initial thermal catalytic rock chip sample, releasing the pressure and taking it out, wiping the surface of the initial thermal catalytic rock chip sample with filter paper to obtain a saturated rock chip sample, and weighing it. This weight is set as W1.

[0028] The third cycle of thermal catalytic treatment specifically includes a continuous initial temperature stage and a first stage of thermal treatment;

[0029] The temperature in the initial stage is 100°C, and the constant temperature time is 2 minutes;

[0030] The temperature was raised from the initial temperature stage to the first stage at a rate of 50°C / min, the temperature of the first stage was 600°C, and the constant temperature time was 10 min.

[0031] The slope k of the above linear fitting formula is obtained as follows:

[0032] With the roughly calculated porosity as the x value and the density of the initial thermal catalytic rock cuttings sample as the y value, a scatter plot is established, a linear trend line is added to the scatter plot, and a linear fitting formula is generated:

[0033] ρ=ρ r -kΦ c

[0034] Where, ρ represents the density of the initial thermal catalytic rock cuttings sample; ρ r Indicates the rock fragment skeleton density (generally 2.6 g / cm 3 );Φ c represents the rough porosity; k is the slope.

[0035] The density of the above-mentioned initial thermal catalytic rock cuttings sample is calculated as follows:

[0036]

[0037] Wherein, ρ represents the density of the initial thermal catalytic rock cuttings sample; W represents the mass of the initial thermal catalytic rock cuttings sample; V represents the volume of the initial thermal catalytic rock cuttings sample;

[0038] The rough porosity is calculated as follows:

[0039] Φ c =(1-W 容 / ρ 容 )×100%

[0040] In the formula, Φ c Represents the rough porosity; W 容 Indicates the weight of rock cuttings sample per unit volume; ρ 容 Indicates the density of the rock cuttings sample.

[0041] Calculate W 容 , 容 When the cuttings are used, they are cuttings samples that have not undergone initial thermal catalytic treatment.

[0042] The above dry weight coefficient C is calculated as follows:

[0043] C=1-W(W-W2)

[0044] Where C represents the dry weight coefficient; W represents the mass of the initial thermal catalytic cuttings sample; W2 represents the mass of the later thermal catalytic cuttings sample.

[0045] The method for obtaining porosity of drilling cuttings described in the present invention can continuously analyze the drilling cuttings, only needs to select a small amount of samples, and fully utilizes the advantages of logging data. It can quickly evaluate reservoir physical properties on site, which is of great significance to oil and gas discovery and evaluation, thereby solving the difficult problems of nuclear magnetic resonance requiring large rock sample size and large amount, and providing technical guarantee for oil exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Attached Figure 1 A scatter plot.

[0047] Attached Figure 2 This is the cuttings porosity curve for well H2014H, with the well section being from 1123.00m to 1135.00m.

[0048] Attached Figure 3 This is the cuttings porosity curve for well M76, with the well section being from 1870.00m to 1878.00m. DETAILED DESCRIPTION

[0049] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0050] The present invention will be further described below in conjunction with embodiments:

[0051] Embodiment 1: A method for obtaining porosity of rock cuttings while drilling, comprising:

[0052] Obtain cuttings samples: Obtain several cuttings samples while drilling in the well section.

[0053] Since the clastic reservoir is highly heterogeneous, the selection of representative samples is the key to subsequent thermal catalysis. The cuttings samples in the same layer or the same well section should be analyzed multiple times, and the average of the analysis results should be taken, which is more representative. Therefore, several cuttings samples while drilling are selected here.

[0054] At the same time, the cuttings samples must be cleaned and, if necessary, cleaned again to reduce the contamination of drilling fluid. Sampling should be timely to ensure that the pores of the cuttings samples are filled with fluid.

[0055] Initial thermal catalysis: The rock cuttings sample is subjected to a first cycle and a second cycle of thermal catalysis treatment in sequence to obtain an initial thermal catalytic rock cuttings sample, the mass of which is W.

[0056] Saturation treatment: The initial thermal catalytic rock cuttings sample is subjected to water saturation treatment to obtain a saturated rock cuttings sample, and the mass of the saturated rock cuttings sample is W1.

[0057] Late thermal catalysis: After the saturated rock cuttings sample is subjected to the third cycle of thermal catalysis, a late thermal catalytic rock cuttings sample is obtained, and the mass of the late thermal catalytic rock cuttings sample is W2. W2 is equivalent to the mass of the rock cuttings skeleton.

[0058] Calculate the dry weight coefficient: Calculate the dry weight coefficient C using the mass W of the initial thermal catalytic cuttings sample and the mass W2 of the later thermal catalytic cuttings sample.

[0059] Obtaining the slope: Performing a linear fit on the density and roughly calculated porosity of the initial thermal catalytic rock cuttings sample to obtain a linear fitting formula, the slope of which is k.

[0060] Calculate the porosity of the cuttings while drilling: Calculate the porosity of each cuttings sample using the wet weight and dry weight difference model, take the average value of the porosity of all cuttings samples, and use the average value as the porosity of the cuttings while drilling. The wet weight and dry weight difference model is as follows:

[0061]

[0062] In the formula, Φ represents the rock chip porosity of the rock chip sample, N represents the number of rock chip samples; Φ s represents the porosity of drilling cuttings; W1 represents the mass of saturated cuttings sample; W2 represents the mass of later thermal catalytic cuttings sample; k represents the slope of the linear fitting formula; ρ r Indicates the rock fragment skeleton density (generally 2.6 g / cm 3 ); C represents the dry weight coefficient.

[0063] The reservoir pores are mainly occupied by oil and pore water. Oil is mainly composed of various hydrocarbons, colloids and asphaltene. Since colloids, asphaltene and kerogen with different hydrocarbon components, molecular weights and molecular structures have different boiling points, the rocks undergo a programmed temperature pyrolysis process, so that these organic substances and pore water are resolved from the rocks by thermal evaporation, thermal cracking and other methods, achieving the goal of no fluid inside the pores. Then, deionized water is invaded and pressurized to fill the pores. The deionized water inside the porosity is evaporated by thermal catalysis, forming the wet weight (i.e., the mass of the saturated rock cuttings sample W1) and dry weight (i.e., the mass of the later thermally catalyzed rock cuttings sample W2).

[0064] The difference between wet weight and dry weight is positively linearly correlated with the porosity of the rock, that is, the greater the "difference between wet weight and dry weight", the greater the porosity, and vice versa. Through this relationship, a wet weight and dry weight difference model is established to calculate the porosity of drilling cuttings.

[0065] Embodiment 2: As an optimization of the above embodiment, the first cycle of thermal catalytic treatment specifically includes heat treatments in the initial temperature stage, the first stage, the second stage, the third stage and the fourth stage carried out continuously;

[0066] The temperature in the initial stage is 90°C, and the constant temperature time is 2 minutes;

[0067] In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 200℃, and the constant temperature time is 1min;

[0068] The temperature of the first stage was programmed to the second stage, with a heating rate of 50°C / min, the temperature of the second stage was 350°C, and the constant temperature time was 1min;

[0069] The temperature of the second stage was programmed to the third stage, with a heating rate of 50°C / min, the temperature of the third stage was 450°C, and the constant temperature time was 1min;

[0070] The temperature was raised from the third stage to the fourth stage at a rate of 50°C / min. The temperature of the fourth stage was 600°C and the constant temperature time was 1 min.

[0071] Embodiment 3: As an optimization of the above embodiment, the second cycle of thermal catalytic treatment specifically includes the initial temperature stage, the first stage and the second stage of thermal treatment performed continuously;

[0072] The temperature in the initial stage is 90°C, and the constant temperature time is 2 minutes;

[0073] In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 300℃, and the constant temperature time is 3min;

[0074] The temperature was raised from the first stage to the second stage at a rate of 50°C / min. The temperature of the second stage was 600°C and the constant temperature time was 1 min.

[0075] Example 4: As an optimization of the above example, water saturation treatment specifically includes: cooling the initial thermal catalytic rock chip sample to room temperature, adding deionized water to submerge the initial thermal catalytic rock chip sample, keeping the initial thermal catalytic rock chip sample under a pressure of 1 MPa for 30 minutes, allowing the deionized water to completely fill the internal pores of the initial thermal catalytic rock chip sample, releasing the pressure and taking it out, wiping the surface of the initial thermal catalytic rock chip sample with filter paper to obtain a saturated rock chip sample, and weighing it. This weight is set as W1.

[0076] Embodiment 5: As an optimization of the above embodiment, the third cycle of thermal catalytic treatment specifically includes a continuous initial temperature stage and a stage of heat treatment;

[0077] The temperature in the initial stage is 100°C, and the constant temperature time is 2 minutes;

[0078] The temperature was raised from the initial temperature stage to the first stage at a rate of 50°C / min, the temperature of the first stage was 600°C, and the constant temperature time was 10 min.

[0079] Embodiment 6: As an optimization of the above embodiment, the slope k of the linear fitting formula is obtained as follows:

[0080] With the roughly calculated porosity as the x value and the density of the initial thermal catalytic rock cuttings sample as the y value, a scatter plot is established, a linear trend line is added to the scatter plot, and a linear fitting formula is generated:

[0081] ρ=ρ r -kΦ c

[0082] Where, ρ represents the density of the initial thermal catalytic rock cuttings sample; ρ r Indicates the rock fragment skeleton density (generally 2.6 g / cm 3 );Φ c represents the rough porosity, and k represents the slope.

[0083] Example 7: As an optimization of the above Example 6, the density of the initial thermal catalytic rock cuttings sample is calculated as follows:

[0084]

[0085] Wherein, ρ represents the density of the initial thermal catalytic rock cuttings sample; W represents the mass of the initial thermal catalytic rock cuttings sample; V represents the volume of the initial thermal catalytic rock cuttings sample;

[0086] The rough porosity is calculated as follows:

[0087] Φ c=(1-W 容 / ρ 容 )×100%

[0088] In the formula, Φ c Represents the rough porosity; W 容 Indicates the weight of rock cuttings sample per unit volume; ρ 容 Indicates the density of the rock cuttings sample.

[0089] Embodiment 8: As an optimization of the above embodiment, the dry weight coefficient C is calculated as follows:

[0090] C=1-W(W-W2)

[0091] Where C represents the dry weight coefficient; W represents the mass of the initial thermal catalytic cuttings sample; W2 represents the mass of the later thermal catalytic cuttings sample.

[0092] Embodiment 9: A method for obtaining porosity of rock cuttings while drilling, comprising:

[0093] Obtain cuttings samples: Obtain several cuttings samples while drilling in the well section;

[0094] Initial thermal catalysis: The rock cuttings sample is subjected to a first cycle and a second cycle of thermal catalysis treatment in sequence to obtain an initial thermal catalytic rock cuttings sample, the mass of which is W.

[0095] The first cycle of thermal catalytic treatment specifically includes the initial temperature stage, the first stage, the second stage, the third stage and the fourth stage of thermal treatment which are carried out successively;

[0096] The temperature in the initial stage is 90°C, and the constant temperature time is 2 minutes;

[0097] In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 200℃, and the constant temperature time is 1min;

[0098] The temperature of the first stage was programmed to the second stage, with a heating rate of 50°C / min, the temperature of the second stage was 350°C, and the constant temperature time was 1min;

[0099] The temperature of the second stage was programmed to the third stage, with a heating rate of 50°C / min, the temperature of the third stage was 450°C, and the constant temperature time was 1min;

[0100] The temperature was raised from the third stage to the fourth stage at a rate of 50°C / min. The temperature of the fourth stage was 600°C and the constant temperature time was 1 min.

[0101] The second cycle of thermal catalytic treatment specifically includes the initial temperature stage, the first stage and the second stage of thermal treatment carried out continuously;

[0102] The temperature in the initial stage is 90°C, and the constant temperature time is 2 minutes;

[0103] In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 300℃, and the constant temperature time is 3min;

[0104] The temperature was raised from the first stage to the second stage at a rate of 50°C / min. The temperature of the second stage was 600°C and the constant temperature time was 1 min.

[0105] Saturation treatment: The initial thermal catalytic rock cuttings sample is subjected to water saturation treatment to obtain a saturated rock cuttings sample, and the mass of the saturated rock cuttings sample is W1.

[0106] The saturation treatment specifically includes: cooling the initial thermal catalytic rock chip sample to room temperature, adding deionized water to submerge the initial thermal catalytic rock chip sample, maintaining the initial thermal catalytic rock chip sample under a pressure of 1 MPa for 30 minutes, allowing the deionized water to completely fill the internal pores of the initial thermal catalytic rock chip sample, releasing the pressure and taking it out, wiping the surface of the initial thermal catalytic rock chip sample with filter paper to obtain a saturated rock chip sample, and weighing it. This weight is set as W1.

[0107] Late thermal catalysis: After the saturated rock cuttings sample is subjected to the third cycle of thermal catalysis treatment, a late thermal catalytic rock cuttings sample is obtained, and the mass of the late thermal catalytic rock cuttings sample is W2.

[0108] The third cycle of thermal catalytic treatment specifically includes a continuous initial temperature stage and a stage of heat treatment;

[0109] The temperature in the initial stage is 100°C, and the constant temperature time is 2 minutes;

[0110] The temperature was raised from the initial temperature stage to the first stage at a rate of 50°C / min, the temperature of the first stage was 600°C, and the constant temperature time was 10 min.

[0111] Calculate the dry weight coefficient: Calculate the dry weight coefficient C using the mass W of the initial thermal catalytic cuttings sample and the mass W2 of the later thermal catalytic cuttings sample.

[0112] The dry weight coefficient C is calculated as follows:

[0113] C=1-W(W-W2)

[0114] Where C represents the dry weight coefficient; W represents the mass of the initial thermal catalytic cuttings sample; W2 represents the mass of the later thermal catalytic cuttings sample.

[0115] Obtaining the slope: Performing a linear fit on the density and roughly calculated porosity of the initial thermal catalytic rock cuttings sample to obtain a linear fitting formula, the slope of which is k.

[0116] The density of the initial thermal catalytic rock cuttings sample is calculated as follows:

[0117]

[0118] Wherein, ρ represents the density of the initial thermal catalytic rock cuttings sample; W represents the mass of the initial thermal catalytic rock cuttings sample; V represents the volume of the initial thermal catalytic rock cuttings sample;

[0119] The rough porosity is calculated as follows:

[0120] Φ c =(1-W 容 / ρ 容 )×100%

[0121] In the formula, Φ c Represents the rough porosity; W 容 Indicates the weight of rock cuttings sample per unit volume; ρ 容 Indicates the density of the rock cuttings sample.

[0122] The slope k of the linear fitting formula is obtained as follows:

[0123] With the roughly calculated porosity as the x value and the density of the initial thermal catalytic rock cuttings sample as the y value, a scatter plot is established, a linear trend line is added to the scatter plot, and a linear fitting formula is generated:

[0124] ρ=ρ r -kΦ c

[0125] Where, ρ represents the density of the initial thermal catalytic rock cuttings sample; ρ r Indicates the density of the rock fragment skeleton (generally 2.6 g / cm 3 );Φ c Indicates the rough porosity.

[0126] The linear fitting formula can be obtained as follows:

[0127] Take the roughly calculated porosity as the x value and the density of the initial thermal catalytic rock cuttings sample as the y value, use Excel to draw a scatter plot, select the data in the scatter plot, right-click the mouse, select "Add trend line", and select "Linear" in the "Trend line options" displayed on the right side of Excel. At the same time, in the "Trend prediction options", select: "Show formula", and the formula displayed is the linear fitting formula. For example, the style of a scatter plot can be seen Figure 1 . Figure 1 In, ρ r =2.687, k=1.97.

[0128] Calculate the porosity of the cuttings while drilling: Calculate the porosity of each cuttings sample using the wet weight and dry weight difference model, take the average value of the porosity of all cuttings samples, and use the average value as the porosity of the cuttings while drilling. The wet weight and dry weight difference model is as follows:

[0129]

[0130] In the formula, Φ represents the rock chip porosity of the rock chip sample, N represents the number of rock chip samples; Φ s represents the porosity of drilling cuttings; W1 represents the mass of saturated cuttings sample; W2 represents the mass of later thermal catalytic cuttings sample; k represents the slope of the linear fitting formula; ρ r Indicates the rock fragment skeleton density (generally 2.6 g / cm 3 ); C represents the dry weight coefficient.

[0131] Example 10: The method for obtaining porosity of drilling cuttings described in Example 9 is implemented.

[0132] Well H2014H is an evaluation well (directional well) deployed in the STH basin. The well section is from 1124.00m to 1135.00m. The lithology is gray fluorescent sandstone. The wet fluorescence is light yellow. Oil-bearing cuttings account for 2% of the cuttings and 3% of the same type of cuttings. The dripping light is light yellow ring. The soaking liquid is colorless and the fluorescence is light milky white. The series comparison is level 7. After 24 hours, the dry fluorescence is light yellow and the dripping light is light yellow ring.

[0133] The well section (1124.00m to 1135.00m) has a shale content of 29% and a carbonate content of 2.3%. Due to the strong heterogeneity of reservoir properties, 3 rock cuttings samples were taken per meter. The rock cuttings samples were processed according to the method for obtaining the porosity of rock cuttings while drilling described in Example 9. The calculated rock cuttings porosity was 9.8% to 14.1% (Table 1 and Table 2). Figure 2 ), the porosity of the drilling cuttings in this section is 11.6%, which is close to the porosity interpreted by well logging (12.5%).

[0134] Example 11: The method for obtaining porosity of drilling cuttings described in Example 9 is implemented.

[0135] Well m76 is a pre-exploration well deployed in the TH basin, with a well section of 1870.00m to 1878.00m. The lithology is gray-white fluorescent fine sandstone and gray fluorescent conglomerate. The fluorescence wet and dry images are light yellow. Oil-bearing cuttings account for 3% to 5% of the cuttings, accounting for 5% to 10% of similar cuttings. The drip image is light yellow ring, the soaking liquid is colorless, the fluorescence is light milky white, the series comparison is 7 levels, and the oil-bearing level is fluorescent level. After 24 hours, the cuttings are light yellow in dry light and light yellow ring in drip light.

[0136] The well section (1870.00m to 1878.00m) has a shale content of 8% and a carbonate content of 1.2%. One rock cutting sample is taken every meter. The rock cutting sample is processed according to the method for obtaining the porosity of rock cuttings while drilling described in Example 9. The rock cutting porosity calculated using the wet weight and dry weight difference model is 5.2% to 11.8% ( Figure 3 ), the porosity of the drilling cuttings in this section is 8.3%, which is close to the porosity interpreted by well logging (9.1%).

[0137] In summary, in PDC drilling or exploration and development without coring, when the rock cuttings samples cannot meet the minimum detection requirements of nuclear magnetic resonance, the present invention first uses a thermal catalytic method to perform initial thermal catalysis on the drilling cuttings, and then continues to perform a later thermal catalytic treatment on the saturated rock cuttings samples after saturated water treatment, so that the saturated rock cuttings samples are quickly dried to obtain later thermally catalyzed rock cuttings samples.

[0138] The parameters of the cuttings samples after initial thermal catalysis and later thermal catalysis (such as the mass W of the cuttings samples after initial thermal catalysis and the mass W2 of the cuttings samples after later thermal catalysis) are used to calculate the dry weight coefficient, the density of the cuttings samples after initial thermal catalysis, the slope k of the linear fitting formula, etc. Finally, the mass W1 of the saturated cuttings sample, the mass W2 of the cuttings sample after later thermal catalysis, the slope k of the linear fitting formula, the dry weight coefficient C, etc. are integrated to calculate the porosity of the cuttings while drilling with the help of the wet weight and dry weight difference model. The calculated porosity of the cuttings while drilling is similar to the logging interpretation result.

[0139] Therefore, the method for obtaining porosity of drilling cuttings described in the present invention can be used to continuously analyze the drilling cuttings. Only a small amount of samples need to be selected, and the advantages of logging data can be fully utilized. Reservoir physical property evaluation can be quickly carried out on site, which is of great significance to oil and gas discovery and evaluation. It solves the problem that nuclear magnetic resonance requires large rock sample particle size and large amount, and provides technical guarantee for oil exploration.

[0140] The above technical features respectively constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

[0141] Table 1

[0142] .

Claims

1. A method for obtaining porosity of cuttings while drilling, characterized in that: include: Obtain cuttings samples: Obtain several cuttings samples while drilling in the well section; Initial thermal catalysis: the rock cuttings sample is subjected to a first cycle and a second cycle of thermal catalysis treatment in sequence to obtain an initial thermal catalytic rock cuttings sample, the mass of which is W; Saturation treatment: The initial thermal catalytic cuttings sample is saturated with water to obtain a saturated cuttings sample, and the mass of the saturated cuttings sample is W1; Late thermal catalysis: After the saturated rock cuttings sample is subjected to the third cycle of thermal catalysis, a late thermal catalytic rock cuttings sample is obtained, and the mass of the late thermal catalytic rock cuttings sample is W2; Calculate the dry weight coefficient: Calculate the dry weight coefficient C using the mass W of the initial thermal catalytic cuttings sample and the mass W2 of the later thermal catalytic cuttings sample; Obtaining the slope: Performing a linear fit on the density of the initial thermal catalytic rock cuttings sample and the roughly calculated porosity to obtain a linear fitting formula, the slope of which is k; Calculate the porosity of the cuttings while drilling: Calculate the porosity of each cuttings sample using the wet weight and dry weight difference model, take the average value of the porosity of all cuttings samples, and use the average value as the porosity of the cuttings while drilling. The wet weight and dry weight difference model is as follows: In the formula, Φ represents the rock chip porosity of the rock chip sample, N represents the number of rock chip samples; Φ s represents the porosity of drilling cuttings; W1 represents the mass of saturated cuttings sample; W2 represents the mass of later thermal catalytic cuttings sample; k represents the slope of the linear fitting formula; ρ r represents the rock fragment skeleton density; C represents the dry weight coefficient; The first cycle of thermal catalytic treatment specifically includes the initial temperature stage, the first stage, the second stage, the third stage and the fourth stage of thermal treatment performed continuously; The temperature in the initial stage is 90°C, and the constant temperature time is 2 minutes; In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 200℃, and the constant temperature time is 1min; The temperature of the first stage was programmed to the second stage, with a heating rate of 50°C / min, the temperature of the second stage was 350°C, and the constant temperature time was 1min; The temperature of the second stage was programmed to the third stage, with a heating rate of 50°C / min, the temperature of the third stage was 450°C, and the constant temperature time was 1min; The temperature was raised from the third stage to the fourth stage at a rate of 50°C / min, the temperature of the fourth stage was 600°C, and the constant temperature time was 1min; Saturation treatment specifically includes: cooling the initial thermal catalytic rock chip sample to room temperature, adding deionized water to submerge the initial thermal catalytic rock chip sample, keeping the initial thermal catalytic rock chip sample under a pressure of 1 MPa for 30 minutes, allowing the deionized water to completely fill the internal pores of the initial thermal catalytic rock chip sample, unloading the pressure and taking it out, wiping the surface of the initial thermal catalytic rock chip sample dry, obtaining a saturated rock chip sample, and weighing it, and this weight is set to W1; The second cycle of thermal catalytic treatment specifically includes the initial temperature stage, the first stage and the second stage of thermal treatment carried out continuously; The temperature in the initial stage is 90°C, and the constant temperature time is 2 minutes; In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 300℃, and the constant temperature time is 3min; The temperature of the first stage was programmed to the second stage, with a heating rate of 50°C / min, the temperature of the second stage was 600°C, and the constant temperature time was 1min; The third cycle of thermal catalytic treatment specifically includes a continuous initial temperature stage and a stage of heat treatment; The temperature in the initial stage is 100°C, and the constant temperature time is 2 minutes; In the initial temperature stage, the temperature is programmed to the first stage, the heating rate is 50℃ / min, the temperature of the first stage is 600℃, and the constant temperature time is 10min; The slope k of the linear fitting formula is obtained as follows: With the roughly calculated porosity as the x value and the density of the initial thermal catalytic rock cuttings sample as the y value, a scatter plot is established, a linear trend line is added to the scatter plot, and a linear fitting formula is generated: p=p r -kΦ c Where, ρ represents the density of the initial thermal catalytic rock cuttings sample; ρ r represents the rock fragment skeleton density; Φ c represents the rough porosity; k is the slope; The density of the initial thermal catalytic rock cuttings sample is calculated as follows: Wherein, ρ represents the density of the initial thermal catalytic rock cuttings sample; W represents the mass of the initial thermal catalytic rock cuttings sample; V represents the volume of the initial thermal catalytic rock cuttings sample; The rough porosity is calculated as follows: F c =(1-W 容 / r 容 )×100% In the formula, Φ c Represents the rough porosity; W 容 Indicates the weight of rock cuttings sample per unit volume; ρ 容 Indicates the density of the rock cuttings sample; The dry weight coefficient C is calculated as follows: C=1-W(W-W2) Where, C represents the dry weight coefficient; W represents the mass of the initial thermal catalytic cuttings sample; W2 represents the mass of the later thermal catalytic cuttings sample; The diameter of the cuttings sample while drilling is 1 mm ± 0.2 mm and the weight is 0.1 g.

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