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CN-121994855-A - CO (carbon monoxide)2Method for quantitatively calculating blocking degree of driven asphaltene

CN121994855ACN 121994855 ACN121994855 ACN 121994855ACN-121994855-A

Abstract

A CO 2 driven asphaltene blockage degree quantitative calculation method relates to the technical field of oil and gas field development. The technical scheme includes that core in-situ condition online nuclear magnetic testing is performed, a solution for saturated cores is prepared, saturated rock samples are prepared, static pore throat nuclear magnetic T 2 spectrum is measured, nuclear magnetic T 2 spectrum in the CO 2 displacement process is measured, nuclear magnetic T 2 spectrum after CO 2 displacement is measured, the permeability injury rate and the porosity injury rate of the cores are calculated through respectively obtaining the static pore throat nuclear magnetic T 2 spectrum and the nuclear magnetic T 2 spectrum in the CO 2 displacement process of different cores, and therefore the CO 2 displacement asphaltene blockage index is obtained. The method has the beneficial effects that the on-line nuclear magnetic experiment of the core in-situ condition is adopted, the microscopic pore structure characteristics of the reservoir core are subjected to classification research, the representative real core is used for observing the microscopic dynamic process of CO 2 displacement, the asphaltene and wax blocking degree of each stage can be quantitatively analyzed, the observation is simple, the operation is low, and the method provides support for improving the recovery ratio and reducing the residual oil distribution in the later work of the oil field.

Inventors

  • LI ZHONGCHENG
  • HUANG MINGXIN
  • CHEN LI
  • LI JINLONG
  • WANG HONGXUE
  • CHEN WEI

Assignees

  • 中国石油天然气股份有限公司

Dates

Publication Date
20260508
Application Date
20241108

Claims (10)

  1. 1. A CO 2 driven asphaltene blockage degree quantitative calculation method is characterized by comprising the following steps: S1, performing core in-situ condition on-line nuclear magnetic testing; S1.1, preparing a solution for a saturated rock core; S1.2, preparing a saturated rock sample; S1.3, measuring a static pore laryngeal core magnetism T 2 spectrum; S1.4, measuring nuclear magnetism T 2 spectrum of the CO 2 displacement process; S1.3, measuring a nuclear magnetism T 2 spectrum after CO 2 is displaced; s2, calculating the permeability injury rate and the porosity injury rate of the core by respectively obtaining the static pore throat nuclear magnetism T 2 spectrum and the nuclear magnetism T 2 spectrum of the CO 2 displacement process of different cores, so as to obtain the CO 2 driven asphaltene blockage index.
  2. 2. The method for quantitatively calculating the blocking degree of CO 2 flooding asphaltenes as set forth in claim 1, wherein the step S1.1 is specifically performed by calculating the mass of solutes required for preparing a plurality of X ml solutions according to the collected requirements of formation water mineralization degree and type of a target area, drying the solutes to constant weight at 100-120 ℃, putting the solutes into a dryer to cool the solutes to 15-25 ℃ at room temperature, pouring the weighed solutes into an X ml volumetric flask, and adding the solutes into the volumetric flask The flask was shaken with milliliters of distilled water until the solute was completely dissolved, and then distilled water was added to the X milliliter scale with shaking.
  3. 3. The method for quantitatively calculating the clogging degree of CO 2 driven asphaltenes according to claim 1, wherein in the step S1.2, a saturated rock sample is prepared according to the SY/T5336 standard method.
  4. 4. The method for quantitatively calculating the clogging degree of the CO 2 driven asphaltenes according to claim 1, wherein the specific steps in the step S1.3 are as follows: S1.3.1, measuring a rock sample, namely measuring transverse relaxation time T 2 , namely packaging a prepared rock sample to be measured by a non-magnetic container without hydrogen, placing the rock sample into a measuring cavity, positioning the center of the rock sample at the center of a magnetic field, selecting a corresponding pulse sequence according to the measurement content, setting parameters of a measuring system, an echo interval, a full recovery time, the number of acquired echoes, the acquisition scanning times and the receiving gain, and starting measurement after confirming that the current parameters are accurate; S1.3.1, processing measurement results, namely measuring transverse relaxation time T 2 by adopting a CPMG pulse sequence, and then solving transverse relaxation time T 2 distribution by a processing program.
  5. 5. The method for quantitatively calculating the clogging degree of the CO 2 driven asphaltenes according to claim 1, wherein the specific steps in the step S1.4 are as follows: S1.4.1, measuring a T 2 spectrum under a saturated oil state, namely taking out, drying and vacuumizing a core after the static pore throat nuclear magnetic T 2 spectrum measurement is finished, saturating deuterium water solution under a certain pressure, displacing the core after saturating deuterium water by using crude oil of a target block, and establishing a T 2 spectrum curve of the irreducible water saturation measurement core; S1.4.2, after CO 2 displacement is finished, T 2 spectrum measurement, namely placing the core with the saturation of the built-up irreducible water into a core holder, carrying out a CO 2 oil displacement experiment at a certain displacement flow rate, and measuring a nuclear magnetic resonance T 2 spectrum curve of the core after the experiment is finished.
  6. 6. The method for quantitatively calculating the blocking degree of the CO 2 flooding asphaltenes according to claim 1, wherein the specific steps in the step S1.5 are that petroleum ether is washed and dried after the displacement is finished, the stratum water is saturated by vacuum pumping and pressurization again, nuclear magnetic scanning is carried out after the saturation is finished, and the core pore distribution characteristics after asphaltene precipitation are obtained.
  7. 7. The method for quantitatively calculating the blocking degree of the CO 2 driven asphaltenes according to any one of claims 1 to 6, wherein after the static pore-throat core magnetism T 2 spectrum of different cores and the nuclear magnetism T 2 spectrum of the CO 2 driving process are obtained, in the step S2, a nuclear magnetism characteristic map is made by the static pore-throat core magnetism T 2 spectrum of different cores and the nuclear magnetism T 2 spectrum of the CO 2 driving process, and the change of the cores in pore size distribution during saturated cores and driving is compared.
  8. 8. The method for quantitatively calculating the degree of the blockage of the CO 2 flooding asphaltenes according to claim 7, wherein the change trend of the pore throat distribution in the CO 2 flooding process is analyzed by combining an initial pore throat distribution of a core, a pore throat distribution of a saturated oil state and a pore throat radius distribution contrast chart of the end of CO 2 flooding, and the impression of the pore diameter distribution by asphaltenes and wax blockage at each stage when different cores are subjected to CO 2 flooding under the same conditions is clarified.
  9. 9. The method for quantitatively calculating the CO 2 -driven asphaltene blockage level according to claim 7, wherein the permeability injury rate and the porosity injury rate of the core are calculated, and then the ratio of the permeability injury rate to the porosity injury rate of the core, namely the CO 2 -driven asphaltene blockage index, is obtained.
  10. 10. The method for quantitatively calculating the degree of CO 2 -driven asphaltene blockage according to claim 4, wherein the non-magnetic container is a glass test tube, and the measuring cavity is a rock chamber or a sample chamber.

Description

Method for quantitatively calculating blocking degree of CO 2 driven asphaltene Technical Field The invention relates to the technical field of oil and gas field development, in particular to a method for monitoring T 2 spectrum of fluid in a core in an online nuclear magnetic resonance technology of a CO 2 displacement physical simulation experiment, quantitatively analyzing and evaluating asphaltene and wax blocking degree of the core in each stage of CO 2 displacement, and evaluating adaptability of different cores to CO 2 displacement. Background The CO 2 oil displacement technology is a key technology for improving the recovery ratio of crude oil in a low-permeability oil reservoir. By injecting CO 2 into the oil reservoir, the recovery ratio of crude oil can be effectively improved, geological sequestration of CO 2 can be realized, and the dual benefits make the CO 2 oil displacement technology an economic and environment-friendly solution. The technology not only solves the requirement of energy exploitation, but also promotes environmental protection, and truly realizes win-win effect. For example, chinese patent application publication No. CN117552758A discloses a chemical system and a method for controlling channeling and blocking of carbon dioxide flooding of low-permeability oil reservoirs. The CO 2 oil displacement technology is widely applied to conventional oil reservoirs, but is not fully researched and applied in the field of unconventional oil reservoirs. At present, most researches are mainly focused on the yield increasing effect of the CO 2 oil displacement technology, and the understanding of key scientific problems such as specific flow mechanism of CO 2 in reservoir pores, oil-gas phase change characteristics, asphaltene precipitation rules and the like is still relatively vague. Asphaltene precipitation is a non-negligible problem in the CO 2 flooding process, as it can have a serious impact on well operations and even result in significant decreases in reservoir permeability. To understand this problem in depth, behbahani et al, advanced computed tomography (CT scanning) techniques were employed to visually analyze the plugging of reservoir pores by asphaltene precipitation. Their findings indicate that asphaltene precipitation is one of the major factors that lead to a reduction in reservoir permeability. Therefore, when the CO 2 oil displacement technology is popularized and applied to unconventional oil reservoirs in the future, the research on the flow rule, the oil-gas phase change, the asphaltene precipitation mechanism and the like of CO 2 in the oil reservoirs needs to be further enhanced so as to better control and manage the problems, improve the oil reservoir recovery ratio and reduce the environmental impact. Asphaltene particles and carbonate minerals may become trapped at the throat during displacement or adsorbed on the pore walls, a phenomenon that is particularly pronounced in low permeability reservoirs where pore throat structures are fine. The accumulation of these deposits gradually plugs the pores and throat, resulting in a significant decrease in the permeability of the reservoir, thereby affecting the flow and recovery of oil and gas. In addition, the different permeability reservoirs differ significantly in the distribution of fluids during displacement due to the inter-layer heterogeneity that the reservoirs exist. This difference, coupled with different displacement patterns, such as CO 2 drives, water drives, etc., can further increase the complexity of predicting residual oil distribution and reservoir damage. The prediction of reservoir damage and remaining oil distribution is an important task for reservoir management during displacement. However, these predictions become exceptionally difficult due to the many complications mentioned above. Therefore, a calculation method for the blocking degree of the asphaltene in the CO 2 flooding is needed to be found, so that the adaptability of different areas to the CO 2 flooding is evaluated, and a theoretical basis is provided for optimization of the on-site CO 2 flooding and recovery improvement mode. So as to more accurately predict and manage reservoir damage, optimize displacement strategy and improve oil and gas recovery ratio. Disclosure of Invention The invention aims to solve the technical problems in the prior art, and provides a blocking degree quantitative evaluation method based on asphaltene precipitation, so that the problem that the damage degree of different cores in the CO 2 displacement process is not fully considered in the prior art is solved, and a basis is provided for the adjustment of a next development strategy. In order to achieve the above purpose, the present invention provides the following technical solutions: A CO 2 driven asphaltene blockage degree quantitative calculation method comprises the following steps: S1, performing core in-situ condition on-line nuclear magnetic test