A method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature

Abstract

This invention relates to the field of hydrate extraction technology, and particularly to a method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature. The method includes: (1) establishing a three-dimensional geological model based on the geological parameters of a natural gas hydrate reservoir, wherein the geological model includes a hydrate layer; (2) performing a dynamic simulation of depressurization extraction of the hydrate layer based on the established geological model and obtaining numerical simulation results; (3) obtaining the reservoir pressure and temperature distribution at different extraction times based on the numerical simulation results; (4) selecting observation points at different distances based on the numerical simulation results and the pressure and temperature distribution, and obtaining the dynamic evolution of pressure and temperature at different observation points; (5) selecting a pressure and temperature change standard, and determining the range of monitoring well locations based on the dynamic evolution of pressure and temperature at different observation points. The monitoring well locations determined by this method can monitor reservoir pressure and temperature changes to the greatest extent, achieving the best dynamic monitoring effect for hydrate extraction.

Description

Technical Field

[0001] This invention relates to the field of hydrate extraction technology, and in particular to a method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Natural gas hydrate (NGH) is widely distributed in marine areas and permafrost, with large reserves and high energy density, making it an important potential high-efficiency clean energy alternative to oil and gas. China's proven NGH resources are mainly concentrated in deep-sea continental slope areas. The Ministry of Land and Resources estimates that China's offshore NGH resources amount to approximately 80 billion tons of oil equivalent. If commercial exploitation of offshore NGH can be achieved, these resources will help solve China's energy shortage problem and are of great significance for ensuring energy independence and security in the country's economic development.

[0004] Hydrate reservoirs exhibit complex production characteristics, influenced by phase change, seepage, and heat transfer. The distribution and evolution of reservoir pressure and temperature are crucial to the dynamics of hydrate exploitation, determining gas production and reservoir stability, and are also important parameters for ensuring safe and efficient hydrate extraction. The propagation of pressure drop during depressurization directly affects hydrate decomposition; temperature changes and propagation influence the decomposition rate and process. The spatiotemporal evolution of pressure and temperature during hydrate reservoir exploitation is complex. Currently, the main controlling factors and influencing mechanisms of hydrate reservoir pressure and temperature are unclear. Hydrate decomposition rate, reservoir seepage capacity, and reservoir heat and heat transfer capacity are key factors affecting hydrate decomposition dynamics; however, these three factors interact and are influenced by numerous factors, necessitating clarification of the main factors controlling pressure and temperature and their influencing mechanisms. Therefore, research on the propagation patterns of reservoir pressure and temperature during hydrate reservoir exploitation is extremely important.

[0005] To better understand the dynamics of natural gas hydrate reservoir exploitation, it is necessary to continuously monitor the changes in various parameters of the reservoir during production. A well-planned layout of monitoring wells can effectively monitor pressure and temperature changes in the hydrate reservoir and understand the propagation patterns of pressure and temperature at different production stages during hydrate extraction. However, there are currently no clear standards for determining the location of monitoring wells in hydrate extraction. The few global hydrate trial productions, including Mallik 2002 and 2007, Japan 2013 and 2017, and the South China Sea 2017 and 2020, have mostly determined the location of monitoring wells based on the geological characteristics of the hydrate reservoir and experience with conventional oil and gas reservoir development. This method of monitoring well placement has the following problems in hydrate trial production: if the monitoring well is too close to the production well, it cannot monitor whether pressure and temperature changes have occurred further away from the production well, or the magnitude of those changes; conversely, if the monitoring well is too far from the production well, the monitored pressure and temperature changes may be minimal until the end of the trial, and the evolution of pressure and temperature near the production well cannot be monitored. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature. The monitoring well locations determined by this method can monitor changes in reservoir pressure and temperature to the greatest extent possible, thereby achieving the best dynamic monitoring effect for hydrate extraction.

[0007] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0008] A method for determining the location of monitoring wells for hydrate exploitation based on pressure and temperature includes: (1) establishing a three-dimensional geological model based on the geological parameters of the natural gas hydrate reservoir, wherein the geological model includes a hydrate layer; (2) performing a production dynamic simulation of depressurization exploitation of the hydrate layer based on the established geological model and obtaining numerical simulation results; (3) obtaining the reservoir pressure and temperature distribution under different exploitation times based on the numerical simulation results; (4) selecting observation points at different distances based on the numerical simulation results and the pressure and temperature distribution, and obtaining the pressure and temperature evolution dynamics at different observation points; (5) selecting a pressure and temperature change standard and determining the range of monitoring well locations based on the pressure and temperature evolution dynamics at different observation points.

[0009] In another preferred embodiment of the present invention, in step (1), the size of the three-dimensional geological model is 1500m×500m×300m.

[0010] In another preferred embodiment of the present invention, the three-dimensional geological model further includes an overlying layer, a mixed layer, a free gas layer, and an underlying layer.

[0011] In another preferred embodiment of the present invention, a production dynamic simulation of the combined depressurization mining of hydrates and free gas layers is performed in step (2).

[0012] In another preferred embodiment of the present invention, in step (2), horizontal wells are set simultaneously in the hydrate layer and the free gas layer, with the hydrate layer being a 250m horizontal well section and the free gas layer being a 300m horizontal well section.

[0013] In another preferred embodiment of the present invention, the production pressure of the horizontal well is set to 3MPa in step (2) to perform dynamic simulation of pressure reduction mining production.

[0014] In another preferred embodiment of the present invention, in step (3), pressure and temperature distribution field maps of 0 days, 15 days, 30 days, 40 days, 45 days, and 60 days are selected respectively for comparative analysis of pressure and temperature evolution and propagation laws.

[0015] In another preferred embodiment of the present invention, in step (4), a location at the same depth as the horizontal section and near the middle of the well section is selected as an observation point for dynamic analysis of the pressure and temperature evolution at the observation point.

[0016] In another preferred embodiment of the present invention, the distances of the observation points from the wellbore in step (4) are 0.25m, 1m, 2m, 4m, 8m, 16m, and 32m, respectively.

[0017] In another preferred embodiment of the present invention, in step (5), the range of locations for monitoring wells for hydrate extraction is determined using 1 MPa / 0.5℃ and 0.5 MPa / 0.25℃ as pressure and temperature change standards.

[0018] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0019] This invention, based on detailed modeling of natural gas hydrate reservoirs, analyzes in detail the spatiotemporal evolution of pressure and temperature during horizontal well depressurization production in natural gas hydrate formations. Optimal monitoring well locations are selected according to different pressure and temperature change standards to ensure that monitoring wells can detect reservoir pressure and temperature changes to the greatest extent possible, achieving optimal dynamic monitoring results for hydrate production. Continuous monitoring of the hydrate-bearing layer and its surrounding environment during development not only provides fundamental data support for the dynamic optimization of development plans but is also crucial for evaluating the environmental impact of the development process.

[0020] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. Attached Figure Description

[0022] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0023] Figure 1 This is a schematic diagram of the geological model of the hydrate reservoir and the trajectory of the production well, according to an embodiment of the present invention.

[0024] Figure 2 These are pressure distribution field diagrams of the hydrate layer at different times according to embodiments of the present invention;

[0025] Figure 3 These are free gas layer pressure distribution field diagrams at different times according to embodiments of the present invention;

[0026] Figure 4 The variation of pressure propagation distance between the hydrate layer and the free gas layer over time in an embodiment of the present invention (left: hydrate layer; right: free gas layer);

[0027] Figure 5 This is a schematic diagram of the range of observation point locations in an embodiment of the present invention (top: hydrate layer; bottom: free gas layer);

[0028] Figure 6 Pressure changes at observation points in the hydrate layer and free gas layer according to an embodiment of the present invention (left: hydrate layer; right: free gas layer);

[0029] Figure 7 Temperature changes at observation points in the hydrate layer and free gas layer according to an embodiment of the present invention (left: hydrate layer; right: free gas layer);

[0030] The distances or dimensions between parts have been exaggerated to show their positions; the diagram is for illustrative purposes only. Detailed Implementation

[0031] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is intended to include the plural form as well.

[0033] To address the problems in the existing technology, this invention proposes a method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature, comprising the following steps:

[0034] (1) Based on the geological parameters of the natural gas hydrate reservoir, a three-dimensional geological model for the joint depressurization exploitation of hydrate and free gas reservoir was established using numerical simulation software.

[0035] (2) Based on the established geological model, horizontal wells were set up simultaneously in the hydrate layer and the free gas layer to simulate the production dynamics of the joint depressurization mining of the hydrate and free gas layers.

[0036] (3) Based on the numerical simulation results, the reservoir pressure and temperature distribution under different mining times were selected to analyze the evolution law of relevant parameters.

[0037] (4) Based on the numerical simulation results and pressure and temperature distribution, select observation points at different distances and different target layers within a certain range, and analyze the dynamic evolution of pressure and temperature at different observation points in turn.

[0038] (5) Select certain pressure and temperature change standards, and combine them with the parameter analysis results of different observation points to select a suitable range of monitoring well locations.

[0039] Based on the detailed modeling of natural gas hydrate reservoirs, this invention analyzes in detail the spatiotemporal evolution of pressure and temperature during the joint depressurization and exploitation of natural gas hydrates and free gas layers using horizontal wells. According to different pressure and temperature change standards, the optimal monitoring well locations are selected to ensure that the monitoring wells can monitor the changes in reservoir pressure and temperature to the greatest extent, thereby achieving the best dynamic monitoring effect for hydrate exploitation.

[0040] Specifically, the steps include:

[0041] (1) Establishment of a detailed geological model

[0042] The established three-dimensional geological model is 1500m (x-direction) × 500m (y-direction) × 300m (z-direction) in size, with numerical grids of 282 × 72 × 100 in the x, y, and z directions, for a total of 2.04 million grids. Figure 1 The geological model shown is vertically divided into an overlying layer, a hydrate layer, a mixed layer, a free gas layer, and an underlying layer.

[0043] (2) Numerical simulation of hydrate depressurization mining

[0044] like Figure 1 As shown, the model is equipped with two horizontal wells, including a 250m horizontal well section with the target layer being a hydrate layer and a 300m horizontal well section with the target layer being a free gas layer.

[0045] The production well was set at a constant pressure of 3 MPa for combined exploitation of hydrate and free gas layers. The simulated 30-day production yielded a cumulative gas production of 849,100 cubic meters, with an average daily production rate of 28,300 cubic meters per day. The simulated 60-day production yielded a cumulative gas production of 1,577,900 cubic meters, with an average daily production rate of 26,300 cubic meters per day.

[0046] (3) Analysis of pressure evolution during mining process

[0047] The pressure field diagrams for 0 days, 15 days, 30 days, 40 days, 45 days, and 60 days in the simulation calculation results were selected for comparative analysis.

[0048] Pressure evolution on the plane of the hydrate layer horizontal well at different times is as follows: Figure 2 As shown, due to the homogeneity of the plane, the pressure changes near the horizontal wellbore are symmetrically distributed. As production progresses, a stable pressure drop region gradually forms, with the pressure drop at the horizontal wellbore being the largest.

[0049] Pressure evolution on the plane of the free gas layer horizontal well at different times is as follows: Figure 3 As shown, the pressure distribution pattern on the free gas layer plane is similar to that of the hydrate layer, but due to the pressure reduction and expansion effect of the gas, the maximum pressure drop at the center of the horizontal well in the free gas layer is much smaller than that in the hydrate layer.

[0050] like Figure 4 As shown, under combined production conditions, the pressure propagation in the hydrate layer is relatively rapid in the early stages, with pressure fluctuations observable at a maximum distance of 32m over 60 days. The overall pressure propagation pattern of the free gas layer is similar to that of the hydrate layer, but the propagation range is wider, with pressure fluctuations observable at a maximum distance of 74.5m. Therefore, observation points should be selected based on the hydrate layer, which has a smaller range of variation, to better reflect the dynamic pressure changes during the extraction of both the hydrate and free gas layers.

[0051] (4) Dynamic analysis of observation point parameters

[0052] To more accurately describe the reservoir pressure distribution during depressurization, a portion of the grid near the middle of the well section at the same depth as the horizontal section was selected as observation points. Pressure and temperature variations at different observation points from the horizontal well were analyzed. A schematic diagram of the observation point locations is shown below. Figure 5 As shown.

[0053] like Figure 6 As shown, in the hydrate layer, at a distance r = 0.25m from the wellbore, the pressure exhibits a rapid decrease, a slight rebound, and then a continuous decrease. As the distance from the wellbore increases, the pressure decrease at the observation point gradually flattens. In the free gas layer, the pressure change trend is similar to that in the hydrate layer, but due to the easily expandable nature of the gas itself, the pressure drop is smaller than that in the hydrate layer.

[0054] like Figure 7 As shown, since hydrates only begin to decompose and absorb heat when the pressure drops to the phase equilibrium pressure, the temperature propagation range in the hydrate layer is smaller than the pressure propagation range. At r = 0.25 m, the temperature first decreases rapidly, then slowly; as the distance from the wellbore increases, the temperature change trend gradually flattens. In the gas layer, the temperature change trend is similar to that in the hydrate layer, but because there is no endothermic reaction, the temperature decrease is much smaller than in the hydrate layer.

[0055] (5) Determining the location of monitoring wells

[0056] In summary, after comparing and analyzing the observation point parameters, if the variation range of 1 MPa and 0.5℃ is used as the standard for the pressure and temperature propagation range, and assuming a simulated production time of 60 days, the pressure propagation range of the hydrate layer is 8m, and the temperature propagation range is 2m; the pressure propagation range of the free gas layer is 32m, and the temperature propagation range is 16m. Therefore, when focusing on monitoring the extraction of hydrates, it is better to place monitoring wells within a range of 2–8m from the production well; when focusing on monitoring the extraction of free gas, it is better to place monitoring wells within a range of 16–32m from the production well.

[0057] If the variation range of 0.5 MPa and 0.25 °C is used as the standard for the pressure and temperature propagation range, and assuming a simulated production time of 60 days, the pressure propagation range of the hydrate layer is 16 m, and the temperature propagation range is 4 m; the pressure propagation range of the free gas layer is 42 m, and the temperature propagation range is 37 m. Therefore, when focusing on monitoring the extraction of hydrates, it is better to place monitoring wells within a range of 4–16 m from the production well; when focusing on monitoring the extraction of free gas, it is better to place monitoring wells within a range of 37–42 m from the production well.

[0058] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

[0059] Finally, it should be noted that, unless otherwise specified, the embodiments of the present invention and the various features thereof can be combined with each other, all of which are within the protection scope of the present invention. Furthermore, all or part of the steps in the above methods can be executed in a computer system such as a set of computer-executable instructions, and although the steps are listed in the order 1, 2, 3…, in some cases, the steps shown or described may be performed in a different order than that shown here.

Claims

1. A method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature, characterized in that, include: (1) A three-dimensional geological model is established based on the geological parameters of the natural gas hydrate reservoir, wherein the geological model includes the hydrate layer; (2) Based on the established geological model, conduct a production dynamic simulation of the depressurization mining of the hydrate layer and obtain numerical simulation results; (3) Based on the numerical simulation results, obtain the reservoir pressure and temperature distribution under different mining times; (4) Based on the numerical simulation results and the pressure and temperature distribution, select observation points at different distances to obtain the dynamic evolution of pressure and temperature at different observation points; (5) Select pressure and temperature change standards, and determine the range of monitoring well locations based on the dynamic evolution of pressure and temperature at different observation points; In step (4), a location at the same depth as the horizontal section and near the middle of the well section is selected as the observation point for dynamic analysis of pressure and temperature evolution at the observation point.

2. The method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature as described in claim 1, characterized in that, In step (1), the size of the three-dimensional geological model is 1500m×500m×300m.

3. The method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature as described in claim 1, characterized in that, The three-dimensional geological model also includes the overlying layer, the mixed layer, the free gas layer, and the underlying layer.

4. The method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature as described in claim 3, characterized in that, In step (2), a production dynamic simulation of the combined depressurization mining of hydrates and free gas layers is carried out.

5. The method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature as described in claim 4, characterized in that, In step (2), horizontal wells are set up simultaneously in the hydrate layer and the free gas layer, with the hydrate layer having a 250m horizontal well section and the free gas layer having a 300m horizontal well section.

6. The method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature as described in claim 5, characterized in that, In step (2), the production pressure of the horizontal well is set to 3MPa, and dynamic simulation of depressurized mining production is carried out.

7. The method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature as described in claim 1, characterized in that, In step (3), pressure and temperature distribution field maps for 0 days, 15 days, 30 days, 40 days, 45 days, and 60 days are selected respectively for comparative analysis of pressure and temperature evolution and propagation laws.

8. The method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature as described in claim 1, characterized in that, In step (4), the distances of the observation points from the wellbore are 0.25m, 1m, 2m, 4m, 8m, 16m, and 32m, respectively.

9. The method for determining the location of monitoring wells for hydrate extraction based on pressure and temperature as described in claim 1, characterized in that, In step (5), the range of monitoring well locations for hydrate extraction is determined using 1MPa / 0.5℃ and 0.5MPa / 0.25℃ as pressure and temperature change standards.

Images