Method for quantitatively evaluating retained hydrocarbon cracking gas

Abstract

The invention discloses a method for quantitatively evaluating detained hydrocarbon cracking gas, which comprises the following steps of: performing a series 1 experiment on selected samples with high organic matter abundance and low maturity by using a formation pore hot-pressing hydrocarbon generation and expulsion simulation tester, the generated gas amount is the sum of the kerogen cracking gas amount and the residual crude oil cracking gas amount; taking an oil generation peak point as a starting point, extracting residual samples after simulation at each temperature point on the basis of hydrocarbon generation and expulsion simulation of the series 1 by adopting a formation pore hot-pressing hydrocarbon generation and expulsion simulation tester, removing residual oil, and then carrying out heating simulation at the next temperature point, namely a series 2 experiment, so as to obtain a gas generation amount which is a kerogen gas generation amount; subtracting the experimental result of the series 2 from the experimental result of the series 1 to finally obtain the retained hydrocarbon cracking gas quantity. The method can guide resource evaluation, exploration direction and favorable area prediction of related natural gas, reduces exploration risks, and is of great significance to oil and gas accumulation analysis.

Description

Technical Field

[0001] The invention relates to the technical fields of petroleum geology and oil and gas geochemistry, and in particular to a method for quantitatively evaluating retained hydrocarbon cracking gas. Background Art

[0002] Pyrolysis gas can come from kerogen cracking or crude oil (including colloid and asphaltene) cracking. Residual oil cracking gas refers to the formation of natural gas when the asphalt remaining in the source rock is cracked under certain temperature conditions during the hydrocarbon expulsion process.

[0003] At the beginning of this century, when exploring the hydrocarbon generation potential of deep and highly evolved source rocks, my country's oil and gas geochemists proposed the possibility that residual asphalt in source rocks (including extractable liquid asphalt and solid primary-same layer asphalt) and residual asphalt after further evolution of reservoir destruction (including soluble reservoir asphalt and solid thermally altered asphalt) could be used as hydrocarbon sources, but no in-depth research was conducted. It was not until the successful exploration and development of shale oil and gas in North America that the oil and gas industry began to pay attention to the hydrocarbon generation and accumulation effect of residual asphalt in source rocks. Although it has been recognized that the retained asphalt generated in source rocks during the oil generation window stage has an important contribution to gas generation in the highly evolved stage, the existing research is still very weak. The contribution of retained asphalt in source rocks to gas generation is basically obtained by analyzing geological phenomena and theoretical speculation. There is no clear experimental confirmation, and no specific amount of gas generation can be given. On the one hand, the residual asphalt is in an organic-inorganic complex system, and the cracking of kerogen and residual asphalt is a dynamic process that overlaps with each other, so it is impossible to directly evaluate the gas generation potential of residual asphalt. On the other hand, there is a certain difficulty in the implementation of experimental technology.

[0004] Thermal simulation experiments are based on the principle of time-temperature compensation. They simulate the low-temperature slow evolution and hydrocarbon generation process of organic matter under geological conditions under short-term high-temperature conditions in the laboratory. It is one of the important means for studying the evolution process of organic matter, hydrocarbon generation mechanism, oil and gas yield, etc. Hydrocarbon generation simulation experiments can be divided into open systems, semi-open and semi-closed systems, and closed systems according to the openness of the experimental device. Open systems such as rock pyrolysis instrument Rock-Eval, thermogravimeter TG, pyrolysis gas chromatography PY-GC, etc. are suitable for situations with low maturity and no secondary cracking. The products are discharged as they are produced. They are mainly used to study the amount of residual hydrocarbons and their overall hydrocarbon generation potential, but they cannot simulate the cracking of residual asphalt. Closed systems include MSSV and gold tube confined systems. Their main drawback is that the kerogen cracking hydrocarbons cannot be discharged and there is a superposition of the contribution of the secondary cracking of residual asphalt, which is difficult to investigate. The evolution characteristics of organic matter in the high evolution stage and its hydrocarbon generation mechanism, and at the same time, they fail to reflect the hydrocarbon expulsion effect in the actual geological body.

[0005] At present, the quantitative evaluation of natural gas generation in the high and over-mature stages of source rocks using various thermal simulation experimental devices has become a research hotspot. For example, Xie Liujuan et al. (Xie Liujuan. Study on the gas generation potential and mechanism of deep hydrocarbon source in the high evolution stage [D]. Zhejiang University, 2014.) calculated the contribution of residual asphalt to cracking gas based on the thermal pressure simulation experiment of hydrocarbon generation and expulsion using the hydrogen mass balance calculation method. Zhang Li et al. (Zhang Li, Xiong Yongqiang, Chen Yuan, et al. Gas generation mechanism of typical marine organic-rich shales in China [J]. Earth Science, 2017, 42(07):1092-1106.) used the hydrocarbon generation kinetics simulation experimental method to conduct a golden tube gas generation kinetics simulation experiment, and concluded that the retained oil and kerogen continued to thermally evolve in the source rock, becoming the main source of unconventional natural gas.

[0006] However, the above research methods have the following shortcomings: the commonly used geochemical methods such as asphalt "A" and pyrolysis have become ineffective. How to effectively reconstruct the hydrocarbon generation and expulsion evolution process of high-mature source rocks during burial evolution and determine the amount of expelled hydrocarbons and retained hydrocarbons, and how to quantify kerogen cracking gas and retained oil (hydrocarbon) cracking gas in different evolutionary stages are still the current problems. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for quantitatively evaluating retained hydrocarbon cracking gas.

[0008] The present invention is achieved by adopting the following technical solutions.

[0009] A method for quantitatively evaluating retained hydrocarbon cracking gas comprises the following steps:

[0010] S1. Use pyrolysis, total organic carbon determination, vitrinite reflectance determination and microscopic component identification experiments to determine the abundance, type and maturity characteristics of organic matter in the samples, and select samples with high organic matter abundance and low maturity;

[0011] S2. The samples were subjected to a series 1 experiment using a formation pore hot pressure hydrocarbon generation and expulsion simulation tester. The series 1 experiment was a continuous hot pressure simulation experiment at 10 temperature points ranging from 300°C to 600°C. The generated gas volume was the sum of the kerogen cracking gas volume and the residual crude oil cracking gas volume. The generated gas before the oil generation peak was all kerogen cracking gas. Only after the oil generation peak was reached, a small amount of crude oil cracking gas could be generated. The retained hydrocarbons before the oil generation peak point were basically not cracked. Therefore, the generated gas volume was the sum of the kerogen cracking gas volume and the residual crude oil cracking gas volume.

[0012] S3. Taking the oil generation peak point as the starting point, the residual samples after simulation at each temperature point are extracted by using the formation pore hot pressure hydrocarbon generation and expulsion simulation test instrument on the basis of the simulation of hydrocarbon generation and expulsion in series 1, and the heating simulation at the next temperature point is performed after removing the residual oil, i.e., series 2 experiment, and the obtained gas generation amount is the kerogen gas generation amount;

[0013] S4. The kerogen cracking gas volume obtained from the series 1 hydrocarbon generation and expulsion simulation experiment and the residual crude oil cracking gas volume are subtracted from the kerogen cracking gas volume obtained from the series 2 to finally obtain the retained hydrocarbon cracking gas volume. The collected products include the expelled oil, the generated natural gas, and the residual sample after the simulation. The expelled oil is quantified, the gas components of the generated natural gas are detected by gas chromatography, and the chloroform asphalt A of the residual sample is detected.

[0014] Furthermore, in step S1, pyrolysis analysis and total organic carbon determination are performed to measure the pyrolysis parameters S1, S2, Tmax, HI and TOC of the sample to evaluate the organic matter abundance of the sample; vitrinite reflectance is measured and microscopic components are identified to evaluate the maturity of the source rock sample.

[0015] Specifically, ① the sample was crushed and passed through a 100-mesh sieve, placed in a dryer, and dried for 24 hours. The carbonate in the sample was removed with dilute hydrochloric acid, and the total organic carbon content (TOC) was analyzed and determined using a LECO CS230 carbon-sulfur instrument according to the standard method GB / T 19145-2003 Determination of total organic carbon in sedimentary rocks. ② The core sample was crushed and passed through an 80-mesh sieve, and 80 to 100 mg of the sample was weighed for rock pyrolysis experiment. According to the national standard "Rock Pyrolysis Analysis" GB / T 18602-2012, the sample was tested at a temperature of 25°C and a humidity of 65% RH. ③ The sample was ground into a thin slice, placed under a Leica DM4500P microscope for morphological and optical characteristics observation and microscopic component identification; the reflectance was measured under a Leica DM4500P microscope with an external J&M photometer and using the double standard method, and the reflectance of the standard sample was 0.59% and 0.89%, respectively.

[0016] Further, in step S2, a first series of formation pore hot pressure simulation experiments at 300°C, 325°C, 340°C, 370°C, 390°C, 420°C, 450°C, 500°C, 550°C, and 600°C are performed, including the following steps:

[0017] a. Coarsely crush the selected samples with high organic matter abundance and low maturity, then mix and load;

[0018] b. Sampling quantity: 40-120 g of original samples at 300°C and 325°C are directly simulated, 150-200 g of original samples are loaded at 340°C, and after the simulation, the residual solid samples at 340°C are used to simulate at 370°C to 600°C;

[0019] c. Set the experimental parameters: the temperatures are 300℃, 325℃, 340℃, 370℃, 390℃, 420℃, 450℃, 500℃, 550℃, and 600℃, a total of 10 temperature points; the simulated formation pressures are set to 37, 44, 49, 58, 62, 69, 75, 83, 89, and 97Mpa, respectively; the heating rate is set to 1℃ / min; after reaching the set temperature, keep the temperature constant for 24-48h; after the constant temperature ends, cool down to 150℃ at a rate of 1℃ / min, and collect the gas generated by pyrolysis;

[0020] d. After simulating each temperature point, take out 10%-20% of the sample and then simulate the next temperature point;

[0021] e. Recover the solid samples after thermal simulation at each temperature point and store them in a sealed manner;

[0022] f. Recover the oil samples discharged at each temperature point and store them separately in a sealed container.

[0023] Further, in step S3, a second series of formation pore hot pressure simulation experiments at 340°C, 370°C, 390°C, 420°C, 450°C, 500°C, 550°C, and 600°C are performed, including the following steps:

[0024] a. Sample preparation and loading: Take the original sample, the sample loading amount is 150-200 grams;

[0025] b. Set the experimental parameters: the temperatures are 340℃, 370℃, 390℃, 420℃, 450℃, 500℃, 550℃, and 600℃, a total of 8 temperature points; the simulated formation pressures are set to 49, 58, 62, 69, 75, 83, 89, and 97Mpa, respectively; the heating rate is set to 1℃ / min; after reaching the set temperature, keep the temperature constant for 24-48h; after the constant temperature ends, cool down to 150℃ at a rate of 1℃ / min, and collect the gas generated by pyrolysis;

[0026] c. After each temperature point is completed, 10%-20% of the samples are taken out;

[0027] d. Extract the residual solid sample taken out after the simulation with chloroform, the extraction temperature is 61℃-75℃, the extraction time is not less than 24h, and then use the residual solid sample after extraction to simulate the remaining temperature points;

[0028] e. The extracted sample is dried at 60℃-75℃ for not less than 5 hours;

[0029] f. Recover the solid samples after thermal simulation at each temperature point and store them in a sealed manner;

[0030] g. Recover the oil samples discharged at each temperature point and store them separately in a sealed container.

[0031] This application has the following beneficial effects.

[0032] The present invention adopts a semi-open system, and the laboratory semi-closed and semi-open simulation experiment confirms the contribution of residual asphalt in source rocks with high organic matter abundance at a high evolution stage to gas production. According to the residual oil cracking gas generation and kerogen cracking gas generation model, the gas production contribution rate of kerogen and retained hydrocarbons in a given source rock is quantitatively simulated and calculated to solve the problem that the superposition of kerogen gas generation and retained hydrocarbon gas generation cannot be estimated. The present invention obtains the contribution ratio of kerogen cracking gas and retained hydrocarbon cracking gas by simulating the thermal evolution process of source rocks, thereby guiding the resource evaluation, exploration direction and favorable area prediction of related natural gas reservoirs, reducing exploration risks, and is of great significance to oil and gas reservoir analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a Soxhlet extraction experimental device and an extraction retained oil diagram of the present invention;

[0034] Figure 2 This is a calculation diagram of the amount of gas generated by cracking retained oil in source rocks according to the present invention. DETAILED DESCRIPTION

[0035] The present patent application is further described below in conjunction with embodiments.

[0036] Unless otherwise specified, the experimental methods used in the following preparation examples and examples are all conventional methods; the materials, reagents, etc. used in the following preparation examples and examples are all commercially available unless otherwise specified.

[0037] Example

[0038] A method for quantitatively evaluating retained hydrocarbon cracking gas, the specific implementation steps are as follows:

[0039] (1) Selection of simulated experimental samples: Through geochemical experimental analyses such as pyrolysis analysis, total organic carbon determination, and vitrinite reflectance determination, the pyrolysis parameters S1, S2, Tmax, HI, TOC, and Ro of the samples were measured to evaluate the abundance, type, and maturity of organic matter in the source rock samples.

[0040] ① The sample was crushed and passed through a 100-mesh sieve, placed in a dryer, and dried for 24 hours. The carbonate in the sample was removed with dilute hydrochloric acid. The total organic carbon content (TOC) was analyzed and determined using a LECO CS230 carbon-sulfur analyzer according to the standard method GB / T 19145-2003 for the determination of total organic carbon in sedimentary rocks.

[0041] ② After the core sample is crushed, it is passed through an 80-mesh sieve, and 100 mg of the sample is weighed for rock pyrolysis experiment. According to the national standard "Rock Pyrolysis Analysis" GB / T 18602-2012, the sample is tested at a temperature of 25°C and a humidity of 65% RH.

[0042] ③ The samples were ground into thin slices and placed under a Leica DM4500P microscope for morphological and optical characteristics observation and identification of microscopic components; the reflectance was measured under a Leica DM4500P microscope with an external J&M photometer and using the double standard method, and the reflectances of the standard samples were 0.59% and 0.89%, respectively.

[0043] (2) The first series of formation pore hot pressure simulation experiments at 300°C, 325°C, 340°C, 370°C, 390°C, 420°C, 450°C, 500°C, 550°C, and 600°C were conducted using a DK-III formation pore hot pressure simulation tester. The experiments were mainly divided into the following six steps:

[0044] ① Coarsely crush the selected samples with high organic matter abundance and low maturity, then mix and load;

[0045] ② Sampling amount: 80g of original sample was taken for direct simulation at 300℃ and 325℃, and 180g of original sample was taken for 340℃. After the simulation, the residual solid sample at 340℃ was used for simulation at 370℃ to 600℃.

[0046] ③ Set the experimental parameters, the temperatures are 300℃, 325℃, 340℃, 370℃, 390℃, 420℃, 450℃, 500℃, 550℃, 600℃, a total of 10 temperature points, the simulated formation pressure is set to 37, 44, 49, 58, 62, 69, 75, 83, 89, 97Mpa, the heating rate is set to 1℃ / min, and the temperature is kept constant for 48h after reaching the set temperature. After the constant temperature ends, the temperature is reduced at a rate of 1℃ / min to 150℃, and the gas generated by pyrolysis is collected;

[0047] ④After simulating each temperature point, take out 20 grams of sample and then simulate the next temperature point;

[0048] ⑤ Recover the solid samples after thermal simulation at each temperature point and store them in clean glass bottles;

[0049] ⑥ Recover the oil samples discharged at each temperature point and store them separately in sealed glass bottles containing n-hexane solvent.

[0050] (3) Conducting a second series of formation pore thermal pressure simulation experiments at 340°C, 370°C, 390°C, 420°C, 450°C, 500°C, 550°C, and 600°C is mainly divided into the following six steps:

[0051] ① Sample preparation and loading: Take the original sample, the sample volume is 180 grams;

[0052] ② Set the experimental parameters. The temperatures were 340℃, 370℃, 390℃, 420℃, 450℃, 500℃, 550℃, and 600℃, respectively, for a total of 8 temperature points. The simulated formation pressures were set to 49, 58, 62, 69, 75, 83, 89, and 97Mpa, respectively. The heating rate was set to 1℃ / min. After reaching the set temperature, the temperature was kept constant for 48 hours. After the constant temperature was over, the temperature was reduced at a rate of 1℃ / min to 150℃, and the gas generated by pyrolysis was collected.

[0053] ③After each temperature point is completed, take out 20 grams of sample;

[0054] ③Use chloroform to extract the residual solid sample taken out after simulation ( Figure 1 ), the water bath temperature was set to 75°C, the extraction time was 48h, and the residual solid sample after extraction was used to simulate the remaining temperature points;

[0055] ④ Dry the extracted sample in a 60℃ oven for 8 hours;

[0056] ⑤ Recover the solid samples after thermal simulation at each temperature point and store them in clean glass bottles;

[0057] ⑥ Recover the oil samples discharged at each temperature point and store them separately in sealed glass bottles containing n-hexane solvent.

[0058] (4) The collected products, including the discharged oil, the generated natural gas, and the residual sample after simulation, are quantified for the discharged oil, the generated natural gas is tested for gas components using a gas chromatograph, and the chloroform asphalt A in the residual sample is tested.

[0059] The hydrocarbon gas volumetric yield obtained from the first series of experiments was calculated and compared with the hydrocarbon gas yield of the second series to obtain the amount of retained oil cracking gas.

[0060] The source rock samples of the third member of the Shahejie Formation in the DY1 well in the Bohai Bay Basin were selected as the research objects. Through geochemical experimental analysis such as pyrolysis analysis, total organic carbon determination and vitrinite reflectance determination, the TOC of the source rock samples was measured to be 2.05%, the vitrinite reflectance was 0.60%, and the organic matter type was II. 2 The hydrocarbon generation simulation experiment was carried out on the sample, and the total gas generation and kerogen gas generation were obtained (Table 2, Figure 2 ), the calculation result is the II 2The kerogen gas generation of the source rock accounts for 88%, and the residual oil gas generation accounts for 12%.

[0061] Table 1 Results of original source rock evaluation experiment

[0062]

[0063] Table 2 Results of total gas production and kerogen gas production

[0064]

[0065]

[0066] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for quantitatively evaluating retained hydrocarbon cracking gas, characterized in that: The following steps are involved: S1. Use pyrolysis, total organic carbon determination, vitrinite reflectance determination and microscopic component identification experiments to determine the abundance, type and maturity characteristics of organic matter in the samples, and select samples with high organic matter abundance and low maturity; S2. Using a formation pore hot pressure generation and expulsion simulation tester, the sample was subjected to a series 1 experiment. The series 1 experiment was a continuous hot pressure simulation experiment at 10 temperature points ranging from 300°C to 600°C. The generated gas volume was the sum of the kerogen cracking gas volume and the residual crude oil cracking gas volume. S3. Taking the oil generation peak point as the starting point, the residual samples after simulation at each temperature point are extracted by using the formation pore hot pressure hydrocarbon generation and expulsion simulation test instrument on the basis of the simulation of hydrocarbon generation and expulsion in series 1, and the heating simulation at the next temperature point is performed after removing the residual oil, i.e., series 2 experiment, and the obtained gas generation amount is the kerogen gas generation amount; S4. The kerogen cracking gas volume obtained from the series 1 hydrocarbon generation and expulsion simulation experiment and the residual crude oil cracking gas volume are subtracted from the kerogen gas generation volume obtained from the series 2 to finally obtain the retained hydrocarbon cracking gas volume.

2. The method for quantitatively evaluating the retained hydrocarbon cracking gas according to claim 1, characterized in that: In step S1, pyrolysis analysis and total organic carbon determination are performed to measure the pyrolysis parameters S1, S2, Tmax, HI and TOC of the sample and evaluate the organic matter abundance of the sample; vitrinite reflectance is measured and microscopic components are identified to evaluate the maturity of the source rock sample.

3. The method for quantitatively evaluating the retained hydrocarbon cracking gas according to claim 1, characterized in that: In step S2, a first series of formation pore hot pressure simulation experiments at 300°C, 325°C, 340°C, 370°C, 390°C, 420°C, 450°C, 500°C, 550°C, and 600°C are performed, including the following steps: a. Coarsely crush the selected samples with high organic matter abundance and low maturity, then mix and load; b. Sampling quantity: 40-120 g of original samples at 300°C and 325°C are directly simulated, 150-200 g of original samples are loaded at 340°C, and after the simulation, the residual solid samples at 340°C are used to simulate at 370°C to 600°C; c. Set the experimental parameters: the temperatures are 300℃, 325℃, 340℃, 370℃, 390℃, 420℃, 450℃, 500℃, 550℃, and 600℃, a total of 10 temperature points; the simulated formation pressures are set to 37, 44, 49, 58, 62, 69, 75, 83, 89, and 97Mpa, respectively; the heating rate is set to 1℃ / min; after reaching the set temperature, keep the temperature constant for 24-48h; after the constant temperature ends, cool down to 150℃ at a rate of 1℃ / min, and collect the gas generated by pyrolysis; d. After simulating each temperature point, take out 10%-20% of the sample and then simulate the next temperature point; e. Recover the solid samples after thermal simulation at each temperature point and store them in a sealed manner; f. Recover the oil samples discharged at each temperature point and store them separately in a sealed container.

4. The method for quantitatively evaluating the retained hydrocarbon cracking gas according to claim 1, characterized in that: In step S3, a second series of formation pore hot pressure simulation experiments at 340°C, 370°C, 390°C, 420°C, 450°C, 500°C, 550°C, and 600°C are performed, including the following steps: a. Sample preparation and loading: Take the original sample, the sample loading amount is 150-200 grams; b. Set the experimental parameters: the temperatures are 340℃, 370℃, 390℃, 420℃, 450℃, 500℃, 550℃, and 600℃, a total of 8 temperature points; the simulated formation pressures are set to 49, 58, 62, 69, 75, 83, 89, and 97Mpa, respectively; the heating rate is set to 1℃ / min; after reaching the set temperature, keep the temperature constant for 24-48h; after the constant temperature ends, cool down to 150℃ at a rate of 1℃ / min, and collect the gas generated by pyrolysis; c. After each temperature point is completed, 10%-20% of the samples are taken out; d. Extract the residual solid sample taken out after the simulation with chloroform, the extraction temperature is 61℃-75℃, the extraction time is not less than 24h, and then use the residual solid sample after extraction to simulate the remaining temperature points; e. The extracted sample is dried at 60℃-75℃ for not less than 5 hours; f. Recover the solid samples after thermal simulation at each temperature point and store them in a sealed manner; g. Recover the oil samples discharged at each temperature point and store them separately in a sealed container.

Images