A method for recovering hydrocarbons in tight rock cores

Abstract

This invention discloses a method for recovering hydrocarbons from tight rock cores. The recovery method includes the following steps: Pyrolysis of the oil-bearing rock core after crushing to obtain the relative content of total hydrocarbons S1+S2 in the core; dissolving the oil-bearing rock core with chloroform, separating the resulting crude oil to obtain saturated hydrocarbons, aromatic hydrocarbons, non-hydrocarbons, and asphaltenes, thereby obtaining the proportion of saturated hydrocarbons in the total hydrocarbons in the core; performing full-hydrocarbon gas chromatography analysis on the dissolved crude oil to quantitatively analyze n-alkanes and isoalkanes, analyze the relative peak areas of all alkane compounds in the full-hydrocarbon chromatogram, and identify plutonium and phytane; taking crude oil from the corresponding production well of the core for full-hydrocarbon gas chromatography analysis to quantitatively analyze n-alkanes and isoalkanes, analyze the relative peak areas of all alkane compounds in the full-hydrocarbon chromatogram, and identify plutonium and phytane; obtaining the total hydrocarbon content in the core as: (S1+S2) / (1-h).

Description

Technical Field

[0001] This invention relates to a method for recovering hydrocarbons in tight rock cores, belonging to the field of oil and gas exploration technology. Background Technology

[0002] The evaluation of crude oil content in conventional or shale oil reservoirs is very important. For example, the quantitative determination of hydrocarbons determines the calculation of reserves. For example, the evaluation of the relative content of free and bound hydrocarbons in shale oil is important, as the content of free hydrocarbons determines the crude oil that can be extracted from the ground.

[0003] Rock cores extracted from underground contain abundant hydrocarbons. The lighter components of these hydrocarbons are highly volatile, leading to inaccurate hydrocarbon content measurements in experimental tests. Currently, the main methods for evaluating hydrocarbons in rock cores are dissolution and pyrolysis. Both methods have drawbacks and cannot quantitatively recover volatile lighter hydrocarbons.

[0004] Light hydrocarbons in petroleum refer to C1-C 14 These light hydrocarbons are most active in the initial migration of hydrocarbons from source rocks and in their secondary migration into migration channels and reservoirs. Current experimental analyses show that most of the light hydrocarbons are lost through chloroform extraction or rock sample pyrolysis; even with adsorption methods and light hydrocarbon recovery methods, only a portion can be recovered.

[0005] In the evaluation of shale oil, previous researchers typically used the pyrolysis parameter S1 (free hydrocarbon content) and the chloroform bitumen “A” content to characterize the residual hydrocarbon and residual oil content, respectively.

[0006] The working principle of the rock pyrolysis analysis method used to evaluate the oil content parameter S1 of shale oil is as follows: The pulverized rock sample is kept at 300℃ for 3 minutes in a pyrolysis furnace and detected by a hydrogen ion flame detector to quantitatively analyze the free hydrocarbons S1 (mg / g) in the source rock. Then, the temperature is increased from 300℃ to 850℃ at a predetermined rate, and the pyrolytic hydrocarbons S2 (mg / g) generated from the pyrolysis of kerogen in the source rock are quantitatively detected. S1 + S2 represents the total hydrocarbon content in the rock; the larger the S1 + S2 value, the higher the hydrocarbon content in the rock.

[0007] The working principle of the chloroform extraction method for evaluating the chloroform bitumen "A" content, a parameter used to evaluate the oil content of shale oil, is as follows: After crushing the rock, it is wrapped in an extraction filter paper tube, placed in the sample chamber of the extractor, and extracted with chloroform until the fluorescence of the extract dripping from the sample chamber weakens to below fluorescence level 3; the extract solution is transferred to a constant-weight weighing bottle and evaporated to dryness, and the difference between the weight of the empty weighing bottle and the weighing bottle containing chloroform bitumen is the mass of chloroform bitumen "A".

[0008] However, rock samples used for pyrolysis analysis are often left to stand in the core library for a long time, resulting in the complete loss of C6-C9 light hydrocarbons. This is significantly more severe than the loss of light hydrocarbons in chloroform bitumen "A" due to the experimental procedures. Therefore, this invention is proposed to provide a basis for calculating oilfield reserves or exploring and developing effective layers. Summary of the Invention

[0009] The purpose of this invention is to provide a method for recovering hydrocarbons from dense rock cores, which employs rock pyrolysis, crude oil chromatography column separation, and full hydrocarbon gas chromatography to address the following shortcomings in existing technologies: pressure-holding core sampling is expensive and does not guarantee that light hydrocarbons will be lost during the experimental process.

[0010] The method for recovering hydrocarbons in tight rock cores provided by this invention includes the following steps:

[0011] S1. After the oil-bearing core is crushed, it is pyrolyzed to obtain the relative content of total hydrocarbons in the core, S1+S2 (mg / g).

[0012] S2. Dissolve the oil-bearing core with chloroform, and separate the crude oil to obtain saturated hydrocarbons, aromatic hydrocarbons, non-hydrocarbons and asphaltenes. Then, obtain the proportion of saturated hydrocarbons in the core to the total hydrocarbons, denoted as a.

[0013] S3. The crude oil obtained from the dissolution in step S2 was subjected to full hydrocarbon gas chromatography analysis to analyze and quantify n-alkanes and isoalkanes, analyze the relative peak areas of all alkane compounds in the full hydrocarbon chromatogram, and identify phytane and terane.

[0014] S4. Take crude oil from the corresponding production well for full hydrocarbon gas chromatography analysis, analyze and quantify n-alkanes and isoalkanes, analyze the relative peak areas of all alkane compounds in the full hydrocarbon chromatogram, and identify phytane and phytane.

[0015] The proportion of light hydrocarbons lost in the core is obtained from the following formula: A1 / (A1+A2);

[0016] Where A1 represents the total area of ​​alkane lost in the core, A2 represents the total area of ​​alkane measured in the core, and A3 represents the total area of ​​phytoalkane (Pr) and phytane (Ph) in the core.

[0017] S1 is obtained from the following: (A1+A2) / A3=A4 / A5;

[0018] Where A4 represents the total measured alkane area in the crude oil of the production well, and A5 represents the total area of ​​pterane (Pr) + phytane (Ph) in the crude oil of the production well;

[0019] The total hydrocarbon content in the core was obtained as follows: (S1+S2) / (1-h) mg / g;

[0020] Where h = a × A1 / (A1 + A2).

[0021] In steps S3 and S4, the conditions for the full-hydrocarbon gas chromatography analysis are as follows:

[0022] Gas chromatograph: split / splitless injection system, compatible with capillary columns; detector: flame ionization detector (FID); air compressor; hydrogen generator. Chromatographic conditions: HP-PONA column, 50m long, 0.200mm diameter, 0.50μm film thickness. Temperature program: 35℃ at 3℃ / min to 70℃, then at 4℃ / min to 310℃, held for 3min. As high-purity helium (purity not less than 99.995%), hydrogen (purity not less than 99.9%, prepared by a hydrogen generator), and air pass through the column, different compounds are separated at different rates and reach the detector for detection and quantification. The compounds detected in the total hydrocarbon gas chromatography are mainly those in saturated hydrocarbons.

[0023] In step S1, the pyrolysis conditions are as follows:

[0024] Rock pyrolysis analyzer, residual organic carbon analyzer, electronic balance (sensitivity 0.1 mg). Hydrogen (purity not less than 99.99%); helium (purity not less than 99.99%); nitrogen (purity not less than 99.99%); compressed air (dried and purified); anhydrous calcium sulfate; color-changing silica gel; carbon dioxide adsorbent; sulfur dioxide adsorbent; manganese dioxide; copper oxide; 5A molecular sieve (particle diameter 2 mm); nickel catalyst.

[0025] The programmed heating method is as follows: the initial temperature is 300℃, held for 3 minutes, and the rate is 50℃ / min. The final pyrolysis temperature is 600℃, and held for 1 minute.

[0026] The saturated hydrocarbons were separated by column chromatography.

[0027] The steps for separating saturated hydrocarbons, aromatic hydrocarbons, non-hydrocarbons, and asphaltenes are as follows:

[0028] 1. Separation of asphalt

[0029] (1) Weigh 20mg to 50mg of crude oil and place it in a 50ml stoppered triangular flask. Add about 30ml of n-hexane while shaking continuously, and let it stand for 12 to 24 hours or more to fully precipitate the asphalt.

[0030] (2) Filter the asphalt using a funnel plugged with absorbent cotton, collect the filtrate in an Erlenmeyer flask, and wash the Erlenmeyer flask and absorbent cotton with n-hexane until the filtrate is colorless. Concentrate the filtrate to 3-5 ml using a rotary evaporator.

[0031] (3) Replace with a constant-weight weighing bottle, dissolve the asphalt on the degreased cotton in the Erlenmeyer flask and funnel with dichloromethane, wash until the filtrate is colorless, evaporate the solvent, and weigh the asphalt.

[0032] 2. Separation of saturated hydrocarbons

[0033] (1) The chromatography column should be installed in a fume hood at 10-30℃. Fill the bottom of the chromatography column with a small amount of degreased cotton, add 3g of silica gel first, then add 2g of alumina, tap the column wall lightly to make the adsorbent fill evenly, and immediately add an appropriate amount of n-hexane to wet the column.

[0034] (2) When the n-hexane liquid level that wets the column is close to the top interface of the alumina layer, transfer the concentrated solution (3-5 ml) obtained after filtration into the chromatography column, and wash the saturated hydrocarbons 6 times with 5 ml of n-hexane each time. Collect the saturated hydrocarbon fraction in a weighing bottle with constant weight.

[0035] 3. Separation of aromatic hydrocarbons

[0036] When the final 5 ml hexane eluent level is close to the top interface of the alumina layer, elute the aromatic hydrocarbons four times with a 5 ml 2:1 dichloromethane:n-hexane mixture each time. When 3 ml of the first 5 ml dichloromethane:n-hexane mixture (2 ml for crude oil sample) has flowed into the column, remove the weighing bottle that received the saturated hydrocarbons and replace it with the weighing bottle that received the aromatic hydrocarbons.

[0037] 4. Separation of non-hydrocarbons

[0038] When the surface of the final 5 ml mixture of dichloromethane and n-hexane is close to the top interface of the alumina layer, rinse the non-hydrocarbon components first with 10 ml of anhydrous ethanol, followed by 10 ml of dichloromethane. When 3 ml of anhydrous ethanol has flowed into the column, remove the weighing bottle that received the aromatic hydrocarbons and replace it with the weighing bottle that received the non-hydrocarbon components.

[0039] The background for establishing this invention is that during the process of core samples being transported from the well bottom to the surface, during the long-term storage of the core samples in the core storage facility, and during the sample crushing process before the experiment, gaseous hydrocarbons (C1-C5) and light liquid hydrocarbons (C6-C9) in shale are almost entirely lost. In the evaluation of shale oil resources, using the chloroform bitumen "A" content to represent the amount of shale oil ignores the C6-C9 hydrocarbons lost during the experimental operation. 13 Light hydrocarbons. The parameter S1 is used to represent the amount of shale oil, ignoring high-carbon hydrocarbons with boiling points below 300℃, NSO compounds, and light hydrocarbons volatilized during sample placement and preparation.

[0040] The reason why this invention does not use the difference between the saturated hydrocarbons separated from drilling crude oil and the saturated hydrocarbons dissolved in core oil to determine the loss is that if the crude oil contains a large amount of light hydrocarbons, they will be lost during the separation process. Moreover, the reagents are mixed with the light hydrocarbons during the separation process, and the light hydrocarbons will also volatilize along with the reagents during the volatilization process. Therefore, this method is inaccurate. The crude oil sample should be directly injected for testing to preserve its authenticity.

[0041] The evaluation of crude oil content in conventional or shale oil reservoirs is crucial. Accurately quantifying hydrocarbon content determines the calculation of reserves, the evaluation of exploitation value, and the design of engineering projects, which is an urgent problem to be solved in the oilfield. Attached Figure Description

[0042] Figure 1 This is a gas chromatogram of all hydrocarbons in the dissolved oil from the core.

[0043] Figure 2 This is a gas chromatogram of all hydrocarbons from the crude oil produced in the well. Detailed Implementation

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0045] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0046] This invention employs rock pyrolysis technology, total hydrocarbon chromatography technology, and crude oil group separation technology to quickly and effectively recover total hydrocarbons from rock cores. Taking the rock core and crude oil from well J10025 in the Jimsar Depression of the Junggar Basin in Xinjiang Uygur Autonomous Region as an example, the specific steps are as follows:

[0047] (1) Rock pyrolysis experiment: The oil-bearing rock core was crushed into 100 mesh and the relative content of total hydrocarbons S1+S2 (mg / g) in the rock was measured using a rock pyrolysis instrument. The measured total hydrocarbon content does not include the lost hydrocarbons.

[0048] The pyrolysis conditions are as follows: rock pyrolysis analyzer, residual organic carbon analyzer, electronic balance (sensitivity 0.1 mg). Hydrogen (purity not less than 99.99%); helium (purity not less than 99.99%); nitrogen (purity not less than 99.99%); compressed air (dried and purified); anhydrous calcium sulfate; color-changing silica gel; carbon dioxide adsorbent; sulfur dioxide adsorbent; manganese dioxide; copper oxide; 5A molecular sieve (particle diameter 2 mm); nickel catalyst. The programmed temperature rise method is: initial temperature 300℃, hold for 3 min, rate 50℃ / min; final pyrolysis temperature 600℃, hold for 1 min.

[0049] (2) Dissolution experiment: Take m2 g of oil-bearing core and dissolve it with chloroform reagent for 24 hours to dissolve m3 g of hydrocarbons in the core. m3 / m2 (mg / g) represents the hydrocarbon content that can be dissolved in the core. m3 / m2 is less than S1+S2 (mg / g) because some organic matter in the core cannot be completely dissolved.

[0050] (3) Separation experiment: Take the crude oil dissolved in the dissolution experiment and carry out the separation experiment. The separation steps are as follows: saturated hydrocarbons, aromatic hydrocarbons, non-hydrocarbons and asphaltenes are separated, with the proportions being a, b, c and d respectively, and a+b+c+d=1.

[0051] 1. Separation of asphalt

[0052] Principle: Asphaltene is a macromolecular compound that is insoluble in n-hexane, while saturated hydrocarbons, aromatic hydrocarbons, and non-hydrocarbons can dissolve n-hexane.

[0053] 1) Weigh 20mg to 50mg of crude oil and place it in a 50ml stoppered Erlenmeyer flask. Add about 30ml of n-hexane while shaking continuously, and let it stand for 12 to 24 hours or more to allow the asphalt to settle.

[0054] 2) Filter the asphalt using a funnel plugged with absorbent cotton. Collect the filtrate in an Erlenmeyer flask and wash the flask and absorbent cotton with n-hexane until the filtrate is colorless. Concentrate the filtrate to 3-5 ml using a rotary evaporator.

[0055] 3) Replace with a constant-weight weighing bottle, dissolve the asphalt on the degreased cotton in the Erlenmeyer flask and funnel with dichloromethane, wash until the filtrate is colorless, evaporate the solvent, and weigh the asphalt.

[0056] 2. Separation of saturated hydrocarbons

[0057] 1) The chromatography column should be installed in a fume hood at 10-30℃. Pack a small amount of degreased cotton at the bottom of the chromatography column, add 3g of silica gel first, then add 2g of alumina, tap the column wall lightly to make the adsorbent fill evenly, and immediately add an appropriate amount of n-hexane to wet the column.

[0058] 2) When the hexane liquid level that wets the column is close to the top interface of the alumina layer, transfer the concentrated solution (3-5 ml) obtained after filtration into the chromatography column, and wash the saturated hydrocarbons 6 times with 5 ml of hexane each time. Collect the saturated hydrocarbon fraction in a weighing bottle with constant weight.

[0059] 3. Separation of aromatic hydrocarbons

[0060] When the final 5 ml hexane eluent level is close to the top interface of the alumina layer, elute the aromatic hydrocarbons four times with a 5 ml 2:1 dichloromethane:n-hexane mixture each time. When 3 ml of the first 5 ml dichloromethane:n-hexane mixture (2 ml for crude oil sample) has flowed into the column, remove the weighing bottle that received the saturated hydrocarbons and replace it with the weighing bottle that received the aromatic hydrocarbons.

[0061] 4. Separation of non-hydrocarbons

[0062] When the surface of the final 5 ml mixture of dichloromethane and n-hexane is close to the top interface of the alumina layer, rinse the non-hydrocarbon components first with 10 ml of anhydrous ethanol, followed by 10 ml of dichloromethane. When 3 ml of anhydrous ethanol has flowed into the column, remove the weighing bottle that received the aromatic hydrocarbons and replace it with the weighing bottle that received the non-hydrocarbon components.

[0063] 5. Weighing

[0064] The reagent is dried by blowing it with nitrogen or by letting it evaporate naturally. What remains is crude oil separated into four components, and finally the weight of each component is weighed.

[0065] 1) Gas Chromatography Experiment of Whole Hydrocarbons in Core Dissolution Oil: The crude oil dissolved in the dissolution experiment was analyzed and quantified using gas chromatography to determine the composition of n-alkanes and isoalkanes. The relative peak areas of all alkane compounds in the whole hydrocarbon chromatogram were analyzed to identify p-alkane (pr) and phytane (ph), such as... Figure 1 As shown.

[0066] 2) Gas Chromatography Experiment of Crude Oil from Production Wells: Crude oil from production wells (well-preserved and sealed, delivered for testing within one week) extracted from the aforementioned core section was used. Gas chromatography was employed to analyze and quantify n-alkanes and isoalkanes. The relative peak areas of all alkane compounds in the total hydrocarbon chromatogram were analyzed to identify p-alkane (pr) and phytane (ph), such as... Figure 2 As shown.

[0067] The gas chromatography conditions are as follows: Gas chromatograph: split / splitless injection system, compatible with capillary column; detector: flame ionization detector (FID); air compressor; hydrogen generator. Chromatographic conditions: HP-PONA column, 50 m long, 0.200 mm diameter, 0.50 μm film thickness. Temperature program: 35 °C at 3 °C / min to 70 °C, then at 4 °C / min to 310 °C, held for 3 min. As high-purity helium (purity not less than 99.995%), hydrogen (purity not less than 99.9%, prepared by hydrogen generator), and air pass through the column, different compounds are separated at different rates and reach the detector for detection and quantification. The compounds detected in the total hydrocarbon gas chromatography are mainly those in saturated hydrocarbons.

[0068] To restore hydrocarbons, follow these steps:

[0069] (1) The compounds detected in the full hydrocarbon chromatography were mainly compounds in saturated hydrocarbons. A comparison of the full hydrocarbon gas chromatography chromatograms of crude oil from production wells and the full hydrocarbon gas chromatography chromatograms of dissolved oil from cores showed that ( Figure 1 and Figure 2 In the core sample, light hydrocarbons below C15 were almost entirely lost, while compounds above C15 remained largely unaffected and consistent. Therefore, the stable compound Pr+Ph was selected as a reference to calculate the relative proportion of light hydrocarbon loss in the organic matter within the core sample.

[0070] (A1+A2) / A3=A4 / A5

[0071] A1: Total area of ​​alkane peaks lost in the core;

[0072] A2: Total area of ​​alkane peaks measured in the core sample;

[0073] A3: Sum of Pr+Ph peak areas in the core sample;

[0074] A4: Total measured alkane peak area in crude oil from production wells;

[0075] A5: The total area of ​​Pr+Ph peaks in crude oil from production wells;

[0076] Based on the above, A1 is obtained, and the proportion of alkane lost in the core is calculated as: A1 / (A1+A2);

[0077] (2) The compounds detected in the full hydrocarbon chromatography are mainly those in saturated hydrocarbons. Aromatic hydrocarbons, non-hydrocarbons, and asphaltenes cannot be displayed in the full hydrocarbon chromatography. Moreover, the macromolecular compounds aromatic hydrocarbons, non-hydrocarbons, and asphaltenes in the core are basically not lost. a represents the proportion of saturated hydrocarbons in the core of the total hydrocarbons. The proportion of light hydrocarbons lost from the core dissolved oil is h = a × A1 / (A1 + A2).

[0078] (3) The hydrocarbon content measured in the rock core is missing light hydrocarbon content and needs to be multiplied by the recovery coefficient to recover the hydrocarbon content in the underground rock core. The recovery coefficient is 1 / (1-h). Therefore, the relative content of total hydrocarbons S1+S2 (mg / g) in the rock needs to be multiplied by the recovery coefficient 1 / (1-h) to truly reflect the hydrocarbon content in the underground rock core, that is: (S1+S2) / (1-h)(mg / g).

[0079] Taking core sample J-51 and crude oil sample JHW60-11 as examples, the saturated hydrocarbon ratio a was found to be 57.88% according to the group component analysis experiment. Core pyrolysis experiments showed S1 to be 24.13 mg / g and S2 to be 15.02 mg / g. Total hydrocarbon gas chromatography experiments showed that the total measured alkane peak area A2 in the core was 97.6 (pA*min), and the total Pr+Ph peak area A3 was 7.14 (pA*min). The total measured alkane peak area A4 in the crude oil from the production well was... The peak area of ​​Pr+Ph in the crude oil from the production well is 658.7 (pA*min). The total peak area of ​​Pr+Ph in the production well is A5, which is 16.75 (pA*min). According to the formula (A1+A2) / A3=A4 / A5, A1 is calculated to be 183.18 (pA*min). According to the formula A1 / (A1+A2), the volatility ratio is calculated to be 65.24%. Based on this, the recovery coefficient is calculated to be 1.61. Finally, it is reflected that the true hydrocarbon content (S1+S2) / (1-h) in the core is 62.90 mg / g.

[0080] Table 1 Core reconstruction analysis of the Lucao Gou Formation in the Jimsar Depression

[0081]

[0082] The evaluation of crude oil content in conventional or shale oil reservoirs is crucial. Accurately quantifying hydrocarbon content determines the calculation of reserves, the evaluation of exploitation value, engineering design, and so on. The method of this invention has also been recognized by oilfield experts and is a problem that urgently needs to be solved in oilfields.

Claims

1. A method for recovering hydrocarbons in tight rock cores, comprising the following steps: S1. After the oil-bearing core is crushed, it is pyrolyzed to obtain the relative content of total hydrocarbons in the core, S1+S2. S2. Dissolve the oil-bearing core with chloroform, and separate the crude oil to obtain saturated hydrocarbons, aromatic hydrocarbons, non-hydrocarbons and asphaltenes. Then, obtain the proportion of saturated hydrocarbons in the core to the total hydrocarbons, denoted as a. S3. The crude oil obtained from the dissolution in step S2 was subjected to full hydrocarbon gas chromatography analysis to analyze and quantify n-alkanes and isoalkanes, analyze the relative peak areas of all alkane compounds in the full hydrocarbon chromatogram, and identify phytane and terane. S4. Take crude oil from the corresponding production well for full hydrocarbon gas chromatography analysis, analyze and quantify n-alkanes and isoalkanes, analyze the relative peak areas of all alkane compounds in the full hydrocarbon chromatogram, and identify phytane and phytane. The proportion of light hydrocarbons lost in the core is obtained from the following formula: A1 / (A1+A2); in, A1 represents the total area of ​​alkanes lost in the core, A2 represents the total area of ​​alkanes measured in the core, and A3 represents the total area of ​​phytoalkane (Pr) and phytane (Ph) in the core. A1 is obtained from the following: (A1+A2) / A3=A4 / A5; Where A4 represents the total measured alkane area in the crude oil of the production well, and A5 represents the total area of ​​pterane (Pr) + phytane (Ph) in the crude oil of the production well; The total hydrocarbon content in the core was obtained from the following: (S1+S2) / (1-h); Where h = a × A1 / (A1 + A2).

2. The recovery method according to claim 1, characterized in that: In steps S3 and S4, the conditions for the full-hydrocarbon gas chromatography analysis are as follows: Gas chromatograph: split / splitless injection system, can be connected to capillary column, detector is flame ionization detector; air compressor, hydrogen generator; Chromatographic conditions: HP-PONA column, 50m long, 0.200mm in diameter, and 0.50μm thick film; The temperature rise program is as follows: from 35℃ to 70℃ at 3℃ / min, then to 310℃ at 4℃ / min, and hold for 3 minutes.

3. The recovery method according to claim 1 or 2, characterized in that: In step S1, the pyrolysis conditions are as follows: The programmed heating method is as follows: the initial temperature is 300℃, the holding time is 3 min, the rate is 50℃ / min, the final pyrolysis temperature is 600℃, and the holding time is 1 min.

4. The recovery method according to claim 1 or 2, characterized in that: The saturated hydrocarbons were separated by column chromatography.

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