A method and system for evaluating formation fluid state after gas injection in oil reservoir

Abstract

The present invention discloses a method and system for evaluating the state of formation fluid after gas injection in oil reservoirs. The method and system are based on big data analysis of historical production data of oil fields, summarize and conclude the relationship between the state of formation fluid and actual production data of oil fields, divide the formation fluid into five phase zones by dividing phase zones, and define the judgment criteria of each phase zone, so as to form an evaluation system for the state of formation fluid, and can accurately judge that the oil production wells are in different operating phase zones at different production times, so as to guide the oil wells to formulate appropriate operation plans according to the changing trends of formation fluids in different production time periods when injecting gas, and can guide other oil fields to improve their understanding of underground fluids after gas injection. In the actual gas injection process of other oil fields, the current gas injection production can be judged according to the division methods of different phase zones and the changes in underground fluid properties, so as to guide the next gas injection adjustment, thereby providing an evaluation method for improving the gas injection operations of oil fields across the country, and having important guiding significance for oil field exploitation.

Description

Technical Field

[0001] The invention relates to the technical field of gas injection effect evaluation in clastic rock oil fields, and in particular to a method and a system for evaluating the state of formation fluid after gas injection in oil reservoirs. Background Art

[0002] When exploiting clastic reservoirs, the injection of hydrocarbon gas will cause changes in parameters such as formation crude oil saturation pressure, production gas-oil ratio, water content, and crude oil composition. At present, domestic and foreign experiments are limited to analyzing the change process of formation fluid after gas injection, including indoor experiments (including PVT, long cores, and thin tubes). For details, please refer to the literature "Evaluation of the mechanism of condensation / evaporation miscible drive of hydrocarbon-rich gas injection", "New method for miscible determination in CO_2_crude oil thin tube test", "Feasibility evaluation of CO_2 miscible drive", "Research on fuzzy comprehensive screening evaluation method of CO_2 miscible drive", and "Evaluation method of gas injection miscible drive mechanism". If the state of formation fluid after gas injection can be clearly understood and evaluated, it will be of great significance to oilfield exploitation.

[0003] In the prior art, the evaluation methods for the formation fluid state after gas injection in oil reservoirs at home and abroad are only evaluated in indoor experiments, and the evaluation methods mainly include PVT method, long core method and capillary method, etc. The PVT phase experiment is fitted by PVT experiment fitting and state equation parameter adjustment, so that the fluid phase experiment data-state equation model-fluid thermodynamic parameter field meet the thermodynamic compatibility, so that the results of state equation phase simulation are consistent with the actual phase change process of oil and gas reservoir fluid; the saturation pressure change process of fluid under different gas injection conditions is calculated by PX phase diagram simulation; through multi-stage contact process phase simulation, the thermodynamic-phase equilibrium theoretical equation is used to calculate the phase change of fluid under different component contents of formation fluid; through capillary experiment simulation, the capillary experiment is the main experimental means to determine the minimum miscible pressure. The role of the capillary model is to provide a continuous contact environment for reservoir oil and injected gas in porous media, and to eliminate the influence of unfavorable mobility ratio, viscosity fingering, gravity separation, lithology heterogeneity and other factors as much as possible.

[0004] The above-mentioned methods for evaluating the state of formation fluid all have certain defects. They all evaluate the state of formation fluid after gas injection only through theoretical calculations and indoor experiments. The evaluation results are not strongly correlated with the gas injection at the actual production site of the oil field, and have little guiding significance for understanding and judging the state of formation fluid after gas injection. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method and system for evaluating the state of formation fluid after gas injection in an oil reservoir. The technical problem to be solved is to establish a standard for dividing formation phase zones after gas injection in an oil reservoir, determine the state of formation fluid through actual production data of the oil field, and adjust the oil field exploitation construction process at any time according to actual conditions, so as to make it more suitable for practical use.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for evaluating the state of formation fluid after gas injection in an oil reservoir comprises the following steps:

[0008] Step 1: Divide the formation crude oil into several phase zones from the gas injection well to the oil production well and set the standard of each phase zone;

[0009] Step 2, obtaining actual production data of the oil field; the data includes production gas-oil ratio, saturation pressure, surface crude oil density, surface crude oil viscosity, formation crude oil light components, formation crude oil intermediate hydrocarbon components, formation crude oil heavy components and whether there is asphaltene deposition in the wellbore;

[0010] Step 3: Compare the data with the standard to determine the formation fluid state.

[0011] Preferably, the phase zones in step 1 include a crude oil phase zone, a front transition zone, a mixed phase zone, a two-phase zone and a gas phase zone in sequence;

[0012] The crude oil phase zone refers to the formation crude oil in its initial state, which is not affected by the injected gas;

[0013] The front transition zone refers to the injected gas dissolved in the crude oil, and the gas dissolved in the formation crude oil close to the gas injection well reaches a saturated state;

[0014] The miscible zone is a zone formed by injecting gas to extract light components from crude oil multiple times, and carrying the light components to move continuously toward the oil producing wells, forming a miscible zone together with the crude oil in a saturated state;

[0015] The two-phase zone refers to the supersaturation of the extracted formation crude oil, which is in the form of oil and gas two phases with the injected gas;

[0016] The gas phase zone refers to the zone where the formation crude oil is completely displaced by the injected gas and only gas exists in the formation.

[0017] Preferably, the data of the crude oil phase band simultaneously meet the following standards: production gas-oil ratio <50m3 / m3, saturation pressure 6-10Mpa, no change in surface crude oil density, no change in surface crude oil viscosity, no change in light components of formation crude oil, no change in intermediate hydrocarbon components of formation crude oil, no change in heavy components of formation crude oil, and no asphaltene deposition in the wellbore.

[0018] Preferably, the data of the leading edge transition zone simultaneously meet the following standards: production gas-oil ratio of 50-300m3 / m3, saturation pressure of 10-49.95Mpa, reduced density of surface crude oil, reduced viscosity of surface crude oil, increased light components of formation crude oil, reduced intermediate hydrocarbon components of formation crude oil, reduced heavy components of formation crude oil, and no asphaltene deposition in the wellbore.

[0019] Preferably, the data of the miscible zone simultaneously meet the following standards: production gas-oil ratio of 300-400m3 / m3, saturation pressure of 10-49.95Mpa, reduced density of surface crude oil, reduced viscosity of surface crude oil, increased light components of formation crude oil, increased intermediate hydrocarbon components of formation crude oil, reduced heavy components of formation crude oil, and no asphaltene deposition in the wellbore.

[0020] Preferably, the data of the two-phase zone simultaneously meet the following standards: production gas-oil ratio of 400-1500m3 / m3, saturation pressure>49.95Mpa, increased density of surface crude oil, increased viscosity of surface crude oil, decreased light components of formation crude oil, decreased intermediate hydrocarbon components of formation crude oil, increased heavy components of formation crude oil, and the presence of asphaltene deposition in the wellbore.

[0021] Preferably, the data of the gas phase zone simultaneously meet the following standards: production gas-oil ratio>1500m3 / m3, saturation pressure>49.95Mpa, surface crude oil density increases, surface crude oil viscosity increases, light components of formation crude oil decrease, intermediate hydrocarbon components of formation crude oil decrease, heavy components of formation crude oil increase, and asphaltene deposition exists in the wellbore.

[0022] Preferably, the method further comprises the following steps:

[0023] Step 4: When the formation fluid state gradually enters the gas phase from the crude oil phase, add asphalt dispersant to the wellbore and ground pipelines, mix it with the crude oil and circulate it for production to ensure the production rate and normal production of the oil well.

[0024] A system for evaluating the state of formation fluid after gas injection in an oil reservoir, comprising:

[0025] A standard acquisition unit, used to acquire the division standard of the formation crude oil phase zones from the oil producing well to the gas injection well;

[0026] A data acquisition unit is used to acquire actual production data of the oil field; the data include production gas-oil ratio, saturation pressure, surface crude oil density, surface crude oil viscosity, formation crude oil light components, formation crude oil intermediate hydrocarbon components, formation crude oil heavy components and whether there is asphaltene deposition in the wellbore;

[0027] The comparison and judgment unit is used to compare the data with the standard to determine the state of the formation fluid.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] The method for evaluating the state of formation fluid after gas injection in an oil reservoir proposed in the present invention is based on big data analysis of historical production data of an oil field, summarizes and concludes the relationship between the state of formation fluid and the actual production data of an oil field, divides the formation fluid into five phase zones by dividing phase zones, and defines the judgment criteria of each phase zone, thereby forming an evaluation system for the state of formation fluid, which can accurately judge that an oil well is in different operating phase zones at different production times, thereby guiding the oil well to formulate a suitable operation plan according to the change trend of formation fluid in different production time periods when injecting gas, and can guide other oil fields to improve their understanding of underground fluid after gas injection. In the actual gas injection process of other oil fields, the current stage of gas injection production can be judged according to the division method of different phase zones and the change of underground fluid properties, so as to guide the next gas injection adjustment, thereby providing an evaluation method for improving gas injection operations in oil fields across the country, and having important guiding significance for oil field exploitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the formation fluid state of Well DH1-13 in Donghe Oilfield according to an embodiment of the present invention;

[0031] Figure 2 Schematic diagram of the production gas-oil ratio variation trend of the formation fluid according to the embodiment of the present invention;

[0032] Figure 3 is a schematic diagram of the saturation pressure variation trend of the formation fluid in an embodiment of the present invention;

[0033] Figure 4 is a schematic diagram of the surface crude oil density variation trend of the formation fluid in an embodiment of the present invention;

[0034] Figure 5 is a schematic diagram of the variation trend of the surface crude oil viscosity of the formation fluid in an embodiment of the present invention;

[0035] Figure 6 It is a schematic diagram of the component change trend of the formation crude oil of the formation fluid in the embodiment of the present invention;

[0036] Figure 7 It is a schematic diagram of the change trend of the well opening rate of Donghe Oilfield in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below in conjunction with the accompanying drawings, which are intended to explain the present invention rather than to limit it.

[0038] The present invention provides a method for evaluating the state of formation fluid after gas injection in an oil reservoir, which comprises the following steps:

[0039] Step 1: From oil producing wells to gas injection wells, the formation crude oil is divided into several phase zones and the standards of each phase zone are set;

[0040] As attached Figure 1 As shown, from the oil producing well to the gas injection well, several phase zones include the crude oil phase zone, the front transition zone, the mixed phase zone, the two-phase zone and the gas phase zone.

[0041] The crude oil phase zone refers to the initial state of the formation crude oil, which is not affected by the injected gas.

[0042] The front transition zone refers to the area where the injected gas dissolves in the crude oil and the gas dissolved in the formation crude oil close to the gas injection well reaches a saturated state.

[0043] A miscible zone refers to a zone where gas is injected multiple times to extract light components from crude oil, and the light components are carried continuously toward the oil producing wells, forming a miscible zone together with the saturated crude oil.

[0044] The two-phase zone refers to the supersaturation of the extracted formation crude oil, which is in the form of oil and gas two phases with the injected gas.

[0045] The gas phase zone refers to the situation where the formation crude oil is completely displaced by the injected gas and only gas exists in the formation.

[0046] Crude oil phase zone standards: production gas-oil ratio <50m3 / m3, saturation pressure 6-10Mpa, no change in surface crude oil density, no change in surface crude oil viscosity, no change in light components of formation crude oil, no change in intermediate hydrocarbon components of formation crude oil, no change in heavy components of formation crude oil, and no asphaltene deposition in the wellbore.

[0047] Standards for the front transition zone: production gas-oil ratio of 50-300m3 / m3, saturation pressure of 10-49.95Mpa, reduced surface crude oil density, reduced surface crude oil viscosity, increased light components of formation crude oil, reduced intermediate hydrocarbon components of formation crude oil, reduced heavy components of formation crude oil, and no asphaltene deposition in the wellbore.

[0048] Standards for the miscible zone: production gas-oil ratio of 300-400m3 / m3, saturation pressure of 10-49.95Mpa, reduced density of surface crude oil, reduced viscosity of surface crude oil, increased light components of formation crude oil, increased intermediate hydrocarbon components of formation crude oil, reduced heavy components of formation crude oil, and no asphaltene deposition in the wellbore.

[0049] Standards for the two-phase zone: production gas-oil ratio of 400-1500m3 / m3, saturation pressure >49.95Mpa, increased density of surface crude oil, increased viscosity of surface crude oil, decreased light components of formation crude oil, decreased intermediate hydrocarbon components of formation crude oil, increased heavy components of formation crude oil, and asphaltene deposition in the wellbore.

[0050] Standards for the gas phase zone: production gas-oil ratio > 1500m3 / m3, saturation pressure > 49.95Mpa, increased density of surface crude oil, increased viscosity of surface crude oil, decreased light components of formation crude oil, decreased intermediate hydrocarbon components of formation crude oil, increased heavy components of formation crude oil, and asphaltene deposition in the wellbore.

[0051] Step 2, obtaining actual production data of the oil field; the data include production gas-oil ratio, saturation pressure, surface crude oil density, surface crude oil viscosity, formation crude oil light components, formation crude oil intermediate hydrocarbon components, formation crude oil heavy components and whether there is asphaltene deposition in the wellbore.

[0052] Specifically, the production gas-oil ratio refers to the ratio of the daily gas production to the daily oil production of a single well. At the production site, the daily gas production and daily oil production of the well can be obtained based on the measurement of the metering separator.

[0053] The saturation pressure refers to the pressure point when the first bubble appears in the formation crude oil. The saturation pressure of the formation crude oil can be determined by sampling at the production site and performing PVT experiments indoors.

[0054] The surface crude oil density refers to the mass of formation crude oil per unit volume. Formation crude oil samples can be taken from the wellhead at the production site and the results can be tested using an indoor density meter.

[0055] The surface crude oil viscosity refers to the measure of the internal friction of the formation crude oil when it flows under the action of gravity. The formation crude oil sample can be taken from the wellhead of the production site and its viscosity can be tested using an indoor viscosity tester.

[0056] The light components, intermediate hydrocarbon components and heavy components of the formation crude oil: the content of C1, C2, C3... in the crude oil can be measured by taking a formation crude oil sample from the wellhead at the production site and testing the crude oil components using a chromatographic analyzer, wherein the light components are components of C1 to C6, the intermediate hydrocarbon components are components of C7 to C15, and the heavy components are components greater than or equal to C16.

[0057] Step 3: Compare the actual production data obtained in step 2 with the standard established in step 1 to determine the state of the formation fluid and regulate the production process of the oil well according to the state of the formation fluid.

[0058] Step 4: As gas injection continues, the state of the formation fluid gradually moves from the crude oil phase to the gas phase. The asphaltene in the crude oil in the gas phase is easy to precipitate. It is necessary to add asphalt dispersant to the wellbore and ground pipeline, mix it with the crude oil and circulate it for production to ensure the production rate and normal production of the oil well.

[0059] Example

[0060] The phase belt evaluation method of the present invention is described in detail below based on the actual production data of the DH1-13 oil well in the Donghe Oilfield of the Tarim Oilfield Branch.

[0061] As the gas injection development progressed, the gas-oil ratio and saturation pressure of the oil well gradually increased, resulting in the incompatibility of the mechanical recovery method and affecting the well opening rate of mechanical recovery. Figure 2 To Attachment Figure 3 The point where the curve is interrupted is the time when the oil field is shut in.

[0062] Through the technical solution of the present invention, the phase belt is recognized, and it is confirmed that the crude oil is in the front transition zone at this time. The production gas-oil ratio and saturation pressure rise rapidly, so the development mode is quickly changed, and the well opening rate of the oil field is improved. The well opening rate = the number of oil wells opened / the total number of oil wells, as shown in the attached figure. Figure 7 shown.

[0063] As attached Figure 4 To Attachment Figure 6 As shown in Table 1, as the gas injection development progresses, the light components and intermediate hydrocarbon components of the formation crude oil are extracted, and the density, viscosity and components become heavier, resulting in asphaltene blocking the wellbore and affecting production. There are currently 7 wells with asphaltene precipitation in the Donghe Oilfield, resulting in a 161-day drop in production time and a cumulative reduction of 6,183 tons of oil. The statistics of asphaltene affecting the production of the Donghe Oilfield are shown in Table 1.

[0064] Table 1

[0065]

[0066] Through the phase zone evaluation of the technical solution of the present invention, the increase of heavy components of crude oil is located in the two-phase zone and the gas phase zone. If measures can be taken in advance to adjust the construction process of oilfield exploitation before the crude oil enters the gas phase zone, it is estimated that the oil production can be increased by 6,183 tons.

[0067] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating the state of formation fluid after gas injection in an oil reservoir, characterized in that: It includes the following steps: Step 1: Divide the formation crude oil into several phase zones from the gas injection well to the oil production well and set the standard of each phase zone; Step 2, obtaining actual production data of the oil field; the data includes production gas-oil ratio, saturation pressure, surface crude oil density, surface crude oil viscosity, formation crude oil light components, formation crude oil intermediate hydrocarbon components, formation crude oil heavy components and whether there is asphaltene deposition in the wellbore; The phase zones include crude oil phase zone, front transition zone, mixed phase zone, two-phase zone and gas phase zone in sequence; The crude oil phase zone refers to the formation crude oil in its initial state, which is not affected by the injected gas; The front transition zone refers to the injected gas dissolved in the crude oil, and the gas dissolved in the formation crude oil close to the gas injection well reaches a saturated state; The miscible zone refers to the injection of gas to extract the light components in the crude oil multiple times, and carry the light components to move continuously toward the oil producing wells, forming a miscible zone together with the crude oil in a saturated state; The two-phase zone refers to the supersaturation of the extracted formation crude oil, which is in the form of oil and gas two phases with the injected gas; The gas phase zone refers to the formation where the crude oil is completely displaced by the injected gas and only gas exists in the formation; The data of the crude oil phase zone simultaneously meet the following standards: production gas-oil ratio <50m3 / m3, saturation pressure 6-10Mpa, no change in surface crude oil density, no change in surface crude oil viscosity, no change in formation crude oil light components, no change in formation crude oil intermediate hydrocarbon components, no change in formation crude oil heavy components, no asphaltene deposition in the wellbore; The data of the front transition zone simultaneously meet the following standards: production gas-oil ratio of 50-300m3 / m3, saturation pressure of 10-49.95Mpa, reduced surface crude oil density, reduced surface crude oil viscosity, increased light components of formation crude oil, reduced intermediate hydrocarbon components of formation crude oil, reduced heavy components of formation crude oil, and no asphaltene deposition in the wellbore; The data of the miscible zone simultaneously meet the following standards: production gas-oil ratio of 300-400m3 / m3, saturation pressure of 10-49.95Mpa, reduced surface crude oil density, reduced surface crude oil viscosity, increased light components of formation crude oil, increased intermediate hydrocarbon components of formation crude oil, reduced heavy components of formation crude oil, and no asphaltene deposition in the wellbore; The data of the two-phase zone simultaneously meet the following standards: production gas-oil ratio of 400-1500m3 / m3, saturation pressure>49.95Mpa, surface crude oil density increased, surface crude oil viscosity increased, light components of formation crude oil decreased, intermediate hydrocarbon components of formation crude oil decreased, heavy components of formation crude oil increased, and asphaltene deposition exists in the wellbore; The data of the gas phase zone simultaneously meet the following standards: production gas-oil ratio>1500m3 / m3, saturation pressure>49.95Mpa, surface crude oil density increased, surface crude oil viscosity increased, light components of formation crude oil decreased, intermediate hydrocarbon components of formation crude oil decreased, heavy components of formation crude oil increased, and asphaltene deposition exists in the wellbore; Step 3: Compare the data with the standard to determine the formation fluid state.

2. A method for evaluating the state of formation fluid after gas injection in an oil reservoir according to claim 1, characterized in that: The following steps are also included: Step 4: When the formation fluid state gradually enters the gas phase from the crude oil phase, add asphalt dispersant to the wellbore and ground pipelines, mix it with the crude oil and circulate it for production to ensure the production rate and normal production of the oil well.

3. A system for executing the method for evaluating the state of formation fluid after gas injection in an oil reservoir as claimed in any one of claims 1 to 2, characterized in that: include, A standard acquisition unit, used to acquire the division standard of the formation crude oil phase zones from the oil producing well to the gas injection well; A data acquisition unit is used to acquire actual production data of the oil field; the data include production gas-oil ratio, saturation pressure, surface crude oil density, surface crude oil viscosity, formation crude oil light components, formation crude oil intermediate hydrocarbon components, formation crude oil heavy components and whether there is asphaltene deposition in the wellbore; The comparison and judgment unit is used to compare the data with the standard to determine the state of the formation fluid.

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