Maritime positive rhythm low-permeability edge water sandstone gas reservoir multi-layer three-dimensional horizontal well position optimization method

Abstract

The invention relates to a method for optimizing the well position of a multi-layer three-dimensional horizontal well of an offshore positive rhythm low-permeability edge water sandstone gas reservoir. The method comprises the following steps: dividing a low-permeability layer, a medium-permeability layer and a high-permeability layer in the longitudinal direction of a target gas reservoir; reservoir geological parameters of a low-permeability layer, a medium-permeability layer and a high-permeability layer in the target gas reservoir and engineering parameters of a horizontal well are obtained respectively; according to the reservoir geological parameters, the engineering parameters of the horizontal well and the low-permeability-medium-permeability-high-permeability three-stage composite reservoir seepage model, the toe end positions of the horizontal well in the low-permeability layer, the medium-permeability layer and the high-permeability layer are determined; a longitudinal heterogeneous large-size physical model seepage testing device is built, water is injected at the edge at a constant speed to simulate the edge water invasion process, and visual tracking of water drive front edge evolution characteristics in a multi-layer differential well mode is achieved through a transparent glass plate. Longitudinal development contradiction can be relieved, differentiation physical property resistance and gas leakage power are coordinated, uniform propulsion of a gas-water interface is promoted, and stable gas and water control of a gas well and balanced utilization of a gas reservoir in the longitudinal direction and the plane are achieved.

Description

Technical Field

[0001] The invention relates to a method for optimizing the well position of multi-layer stereoscopic horizontal wells in an offshore positive rhythm low-permeability edge-water sandstone gas reservoir, and belongs to the field of oil and gas field development. Background Art

[0002] Due to the large difference in physical properties between layers and the non-uniform distribution of sand bodies, the offshore positive rhythm low-permeability edge water gas reservoirs show uneven vertical edge water advancement and strong heterogeneity in the development process. The contradiction between the production between layers and within the layers of the gas reservoir is prominent, making it difficult to balance the production of reserves. Secondly, due to the restrictions of production platforms, the well network density is limited, the development investment is large, and the operating costs are high, resulting in heavy economic tasks for single wells. The mature drainage gas production technology and fracturing transformation technology on land are difficult to implement on a large scale at sea.

[0003] Therefore, how to effectively utilize limited wellheads to optimize well location design, coordinate the physical resistance between layers with different physical properties and the gas release dynamics, achieve the coupling of differentiated pressure gradient disturbances, and guide the balanced advancement of edge water in the vertical direction is a key issue in achieving the overall efficient utilization of offshore gas reservoirs. Summary of the invention

[0004] The purpose of the present invention is to provide a method for optimizing the well location of multi-layer stereoscopic horizontal wells in offshore positive rhythm low permeability edge water sandstone gas reservoirs in response to the problems existing in the prior art. The method is conducive to alleviating the contradiction of vertical development, coordinating differentiated physical resistance and gas leakage dynamics, promoting uniform advancement of the gas-water interface, and achieving stable gas and water control in gas wells and balanced utilization of gas reservoirs in the vertical and horizontal directions.

[0005] The technical solution provided by the present invention to solve the above technical problems is: a method for optimizing the well location of multi-layer stereoscopic horizontal wells in an offshore positive rhythm low-permeability edge-water sandstone gas reservoir, comprising the following steps: Step S10, dividing the target gas reservoir into a low permeability layer, a medium permeability layer, and a high permeability layer in the longitudinal direction; Step S20, respectively obtaining reservoir geological parameters of the low permeability layer, the medium permeability layer, and the high permeability layer in the target gas reservoir and engineering parameters of the horizontal well; Step S30, constructing a three-level composite reservoir seepage model of low permeability, medium permeability and high permeability based on the photoelectric wave propagation and reflection coupling mechanism; Step S40: Determine the length of the horizontal well in the low permeability layer, the medium permeability layer, and the high permeability layer according to the reservoir geological parameters of the low permeability layer, the medium permeability layer, and the high permeability layer, the engineering parameters of the horizontal well, and the low permeability-medium permeability-high permeability three-level composite reservoir seepage model. Step S50, construct a longitudinal heterogeneous large-scale physical model seepage test device, inject water at a constant rate at the edge to simulate the process of edge water invasion, and realize the visual tracking of the evolution characteristics of the water drive front in the multi-layer differentiated well mode through a transparent glass plate.

[0006] A further technical solution is that in step S10, through multi-level information fusion of core description, 3D seismic and rock physical logging parameters, three layers of low permeability, medium permeability and high permeability are vertically divided based on the structural, sedimentary and diagenetic evolution characteristics.

[0007] A further technical solution is that the reservoir geological parameters include effective thickness, wellbore radius, gas saturation, true gas compression factor, gas viscosity, formation temperature, formation pressure, porosity, and permeability.

[0008] A further technical solution is that the engineering parameters include a gas leakage radius and a distance between the horizontal well and a lower boundary.

[0009] A further technical solution is that the three-level composite reservoir seepage model of low permeability, medium permeability and high permeability is:

[0010] Where: Z represents the natural gas compression factor; c g Indicates the compression coefficient, MPa -1 ; Indicates the porosity of the reservoir; μ Indicates gas viscosity, mPa•s; δ represents high-speed non-Darcy characteristic parameters; P Indicates the current formation pressure, MPa; , , is the permeability; Indicates the current formation pressure of layer n, MPa; x , y , z Respectively represent the projection distances in the three directions of the coordinate axis; t Indicates time.

[0011] A further technical solution is that the process of determining the horizontal well length in step S40 is as follows: Step A, setting the lengths of the three horizontal wells in the low permeability layer, the medium permeability layer and the high permeability layer to meet the configuration principle of long at the top and short at the bottom; Step B, respectively substituting the lengths of the horizontal wells of the low permeability layer, the medium permeability layer and the high permeability layer into the low permeability-medium permeability-high permeability three-level composite reservoir seepage model to calculate the pressures of the low permeability layer, the medium permeability layer and the high permeability layer; Step C, respectively calculate the pressure gradient between the low permeability layer, the medium permeability layer, and the medium permeability layer and the high permeability layer. If the pressure gradient is greater than the maximum pressure gradient threshold between adjacent layers, the horizontal well section length of the medium permeability layer or the high permeability layer is adjusted downward, and steps A to C are repeated until the pressure gradients between the low permeability layer, the medium permeability layer, and the medium permeability layer and the high permeability layer are all less than or equal to the maximum pressure gradient threshold between adjacent layers, and then the final horizontal well lengths of the low permeability layer, the medium permeability layer, and the high permeability layer are output.

[0012] A further technical solution is that in step S50, the geometric length and position of the horizontal well and the displacement speed of the large-scale physical simulation experiment are determined based on geometric similarity, flow similarity and resistance similarity.

[0013] A further technical solution is that in step S50, the porosity and permeability of single-mesh quartz sand are calibrated by artificial one-dimensional cores to obtain reservoir properties under different confining pressure conditions and clarify the sand filling scheme under different pressures and porosity and permeability conditions during the sand filling process of the physical model.

[0014] Beneficial effects of the present invention: 1. Considering the low-permeability seepage characteristics and the non-uniform pressure response characteristics among multiple layers in the vertical direction, a three-level composite reservoir seepage model of low-permeability, medium-permeability and high-permeability was constructed based on the coupling mechanism of photoelectric wave propagation and reflection, realizing the fine characterization of the comprehensive seepage characteristics of the composite reservoir.

[0015] 2. A three-dimensional multi-layer differentiated well layout method is proposed to coordinate the physical resistance and gas leakage dynamics between different layers, promote the uniform advancement of edge water, and facilitate the uniform development of gas reservoirs.

[0016] 3. Build a large-scale physical model test device to truly reflect the vertical heterogeneity characteristics of the gas reservoir, realize the visual tracking of the water invasion front under the three-dimensional multi-layer differentiated well layout mode, and demonstrate the rationality of the well layout strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the propagation and reflection of pressure waves at interfaces of different layers in an embodiment of the present invention; Figure 2 Schematic diagram of a multi-layer stereoscopic well pattern for an offshore positive rhythm edge water gas reservoir in an embodiment of the present invention; Figure 3 It is a flow chart of the two-dimensional visualization model experiment in an embodiment of the present invention; Figure 4 It is the effect of coordinating the uniform advancement of edge water in the vertically non-uniform reservoir three-dimensional well pattern in the embodiment of the present invention. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] The present invention provides a method for optimizing the well location of multi-layer stereoscopic horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir, comprising the following steps: Step S10: on the target gas reservoir, core description, 3D seismic, and rock physical logging parameters are integrated to determine the structural model, sedimentary background, and diagenetic evolution law, revealing the development and distribution law of the "sweet spots" of the heterogeneous reservoir; taking into account the sedimentary rhythm and physical property differences, three layers of low permeability, medium permeability, and high permeability can be divided vertically; Step S20, respectively obtaining reservoir geological parameters of the low permeability layer, the medium permeability layer, and the high permeability layer in the target gas reservoir and engineering parameters of the horizontal well; The reservoir geological parameters include effective thickness, wellbore radius, gas saturation, true gas compressibility factor, gas viscosity, formation temperature, formation pressure, porosity, and permeability.

[0020] The engineering parameters include the gas leakage radius and the distance between the horizontal well and the lower boundary.

[0021] Step S30, constructing a three-level composite reservoir seepage model of low permeability, medium permeability and high permeability based on the photoelectric wave propagation and reflection coupling mechanism; Considering the stress sensitivity and non-Darcy seepage characteristics of the low permeability layer, the permeability can be expressed as:

[0022] Where: K represents the current reservoir permeability, K i represents the permeability of the reservoir in its original state, mD; α represents the stress sensitivity coefficient; P i represents the original formation pressure, MPa; P Indicates the current formation pressure, MPa; δ Represents high-speed non-Darcy characteristic parameters.

[0023] High-speed non-Darcy characteristic parameters δ It can be characterized by the seepage velocity and Forchheimer coefficient:

[0024] Where: β represents the Forchheimer coefficient associated with non-Darcy seepage characteristics;v represents the seepage velocity, m / d; ρ Indicates gas density, g / m 3 ; μ Indicates gas viscosity, mPa•s.

[0025] For multi-layer composite gas reservoirs, combined with the unsteady continuity equation, gas state equation, etc., the real gas seepage equation can be expressed as:

[0026] Where: Z represents the natural gas compression factor; c g Indicates the compression coefficient, MPa -1 ; Indicates the porosity of the reservoir; μ Indicates gas viscosity, mPa•s; δ represents high-speed non-Darcy characteristic parameters; P Indicates the current formation pressure, MPa; , , is the permeability; Indicates the current formation pressure of layer n, MPa; x , y , z Respectively represent the projection distances in the three directions of the coordinate axis; t Indicates time.

[0027] Dependent variable:

[0028]

[0029]

[0030]

[0031]

[0032] Where: h is the layer where the horizontal well is located, z w is the distance from the horizontal well to the lower boundary, L w is the half length of the horizontal well.

[0033] Pseudo-pressure m for:

[0034] Where: P 0 As the reference pressure, take the atmospheric pressure; The model is dimensionless through characteristic parameters such as pressure, time and wellbore radius. D ) h and time t D for:

[0035]

[0036] Where: h h is the thickness of the sub-layer where the horizontal well is located, m; T sc is the temperature under standard conditions, 273.15 K; p sc is the pressure under standard conditions, 0.101 MPa; q sc is the gas flow rate under ground conditions, m 3 ; T is temperature, K; m ini is the original pseudo pressure; m w ) h ( t ) is the pseudo pressure at the bottom of the horizontal well at any time; c t is the comprehensive compression coefficient, MPa -1 .

[0037] The dimensionless wellbore radius is r wD :

[0038] The closed formation point source Green's function is introduced to perform constant pressure boundary treatment on the top and bottom of the reservoir, and the solution is obtained in the Laplace space to obtain the differentiated response characteristics of multi-layer pressure.

[0039] Where: s is the Laplace space variable; s / k n is a dimensionless variable; Written as a partial differential equation of Green's function, the pressure of the h-th layer where the horizontal well is located is:

[0040] Where: r is the seepage radius of any point in the formation, m; G is the Green’s function; The pressures of the other n small layers are:

[0041] Given boundary conditions:

[0042] Where: r D is the dimensionless radial distance; r eD is the dimensionless supply boundary radius; Therefore, the point source solution of the h layer where the horizontal well is located is expressed as:

[0043] Where: U represents the upward propagation coefficient; D represents the downward propagation coefficient.

[0044] Finally, the dimensionless pressure (m D ) h and time t D relationship, thereby determining the relationship between pressure and output.

[0045] Step S40, determining the length of the horizontal well in the low permeability layer, the medium permeability layer, and the high permeability layer respectively according to the reservoir geological parameters of the low permeability layer, the medium permeability layer, and the high permeability layer, the engineering parameters of the horizontal well, and the low permeability-medium permeability-high permeability three-level composite reservoir seepage model; like Figure 1 As shown, for the pressure disturbance between different layers, the pressure wave will experience changes in propagation at each layer boundary. By analogy with the reflection principle of waves at the interface in optoelectronics, local reflection and propagation coefficients are established to solve the pressure response characteristics between different layers.

[0046] For gas reservoirs with different permeability layers, the effects of different horizontal well lengths, vertical positions within the layer and other factors on the productivity are calculated based on the productivity formula, and the reasonable range of factors such as horizontal well length is preliminarily determined.

[0047] Since the low-permeability sand body distribution in the target area presents a discontinuous and non-uniform distribution pattern, based on the development and distribution pattern of the "sweet spots" of its heterogeneous reservoir, long horizontal wells that can cross multiple periods of "sweet spots" are preferred for development, and the target position at the foot of the upper low-permeability reservoir is preferentially determined to realize the release of the low-permeability reservoir production capacity.

[0048] By analogy with the propagation and reflection of pressure at the interface of different layers, the non-uniform distribution characteristics of the pressure in the low permeability layer and other layers in the vertical direction are obtained. Subsequently, the redistributed pressure is substituted into the seepage equation of the medium permeability layer as an input parameter to update the pressure response under the influence of reservoir properties, horizontal well parameters, and production in the medium permeability layer. On this basis, the overall pressure disturbance and redistribution caused by the deployment of horizontal wells in the high permeability layer are further calculated.

[0049] Due to the different seepage resistances caused by the vertical physical property differences, in order to coordinate the difference in gas discharge dynamics, the length of the horizontal wells is gradually reduced from the low permeability to the high permeability layer during the setting of the horizontal well length to balance the scale of the pressure field disturbance in different small layers. The length relationship of the three-layer horizontal wells in the upper low permeability layer, the middle medium permeability layer and the lower high permeability layer is initially set to meet the configuration principle of "long on top and short on bottom". The initial settings are 1600 m, 1000 m and 800 m respectively. Secondly, for the reasonable selection of the well location, the pressure gradient of each layer is calculated by obtaining the pressure difference between the bottom hole pressure and the edge water position, and the scale of the pressure field disturbance in different small layers is coordinated from the top low permeability layer to the bottom high permeability layer. From top to bottom, the length of the horizontal wells is gradually reduced, and the toe becomes farther away from the edge water, forming a reasonable well location. Figure 2 The “three-layer” three-dimensional horizontal well distribution pattern shown.

[0050] The process of determining the horizontal well length is: Step A, setting the lengths of the three horizontal wells in the low permeability layer, the medium permeability layer and the high permeability layer to meet the configuration principle of long at the top and short at the bottom; Step B, respectively substituting the lengths of the horizontal wells of the low permeability layer, the medium permeability layer and the high permeability layer into the low permeability-medium permeability-high permeability three-level composite reservoir seepage model to calculate the pressures of the low permeability layer, the medium permeability layer and the high permeability layer; Step C, respectively calculate the pressure gradient between the low permeability layer, the medium permeability layer, and the medium permeability layer and the high permeability layer. If the pressure gradient is greater than the maximum pressure gradient threshold between adjacent layers, the length of the horizontal well section of the medium permeability layer or the high permeability layer is decreased (the adjustment step is 50 m). Repeat steps A to C until the pressure gradients between the low permeability layer, the medium permeability layer, and the medium permeability layer and the high permeability layer are less than or equal to the maximum pressure gradient threshold between adjacent layers. Then, the final output is that the upper low permeability layer horizontal section is 1200 m long, the medium permeability layer horizontal section is 700 m long, and the high permeability layer horizontal section is 400 m long.

[0051] Step S50: construct a longitudinal inhomogeneous large-scale physical model seepage test device (such as Figure 3 As shown in the figure, water is injected at a constant rate at the edge to simulate the process of edge water invasion, and the transparent glass plate is used to realize the visualization tracking of the evolution characteristics of the water flooding front in the multi-layer differentiated well mode.

[0052] In order to further verify the effectiveness of the established three-dimensional horizontal well pattern in delaying the problem of local water inrush, a Figure 4 The large-scale physical model test device shown has a three-dimensional effective space size of 50×50×2 cm 3 According to geometric similarity, flow similarity, resistance similarity, etc., the basic experimental parameters such as the geometric length and position of the horizontal well and the displacement velocity of the large-scale physical simulation experiment are determined.

[0053] Based on the artificial one-dimensional core, the porosity and permeability of single mesh quartz sand were calibrated. The selected quartz sands were 200~230, 300~330, 400~430, and 500~530. The physical properties of the small lithologies made with 10 proportions were tested under different confining pressure conditions. The permeability was mainly between 1~160 mD, and the porosity was mainly between 10%~18%. The sand filling scheme of the physical model under different pressure and porosity conditions was clarified. The permeability distribution range of the block in the embodiment is mainly 10~120 mD.

[0054] The wet filling method was used to fill the sand into the two-dimensional visualization model. In order to ensure that the model was evenly stressed, 16 sets of high-pressure hydraulic devices were used to change the overburden pressure of the model to simulate the reservoir environment. After the model was pressed, it was necessary to cast and seal it with epoxy resin. The pressed model was placed in a custom mold, and after the epoxy resin was melted, it was poured into the mold to cast and seal the model. The two-dimensional flat plate model was erected, and water was injected into the model from the bottom valve until water came out of the top valve and the sand body inside the model was observed to be filled with water. After the model was left to stand for 24 hours, gas was injected from the top valve to establish the original gas saturation.

[0055] While the well is being produced horizontally, water is injected at a constant rate at the edge to simulate the process of edge water invasion, and the evolution characteristics of the water flooding front in the multi-layer differentiated well mode are visualized and tracked through a transparent glass plate. Figure 4 As shown in the figure, the length of the horizontal section of the horizontal well decreases from the top to the bottom, and the toe becomes farther away from the edge water. Through the differentiated horizontal well deployment in the vertical direction, the gas-water interface area in the three layers of low permeability, medium permeability and high permeability in the two-dimensional model is relatively flat, which proves the rationality of the partial well strategy.

[0056] The water content at the wellhead is calculated by the metering device, and 99% is used as the critical condition for shutting down the gas well. The recovery rate calculation results show that through the arrangement of the vertical three-dimensional well pattern, the edge water at the three layers in the vertical direction tends to advance synchronously, basically achieving balanced development of the gas reservoir, and effectively alleviating the contradiction between the layers and within the layers.

[0057] Table 1 Recovery degree of each sub-layer in the vertical direction of the gas reservoir

[0058] The present invention provides a multi-layer stereoscopic horizontal well location optimization method for offshore positive rhythm low-permeability edge water sandstone gas reservoirs. Based on the structural-sedimentation-diagenetic evolution characteristics, the method takes into account the sedimentary rhythm and physical property differences, and finely divides the low-permeability-medium-permeability-high-permeability layers in the vertical direction; considers the low-permeability seepage characteristics and the non-uniform pressure response characteristics between multiple layers in the vertical direction, and constructs a composite reservoir seepage model of layered interface pressure propagation and reflection coupling mechanism; preferentially determines the toe position of the upper low-permeability reservoir, and optimizes the toe position step by step from top to bottom to form a "three-layer" stereoscopic well network, coordinates the pressure field disturbances of different small layers, and promotes the uniform advancement of edge water. By building a longitudinal heterogeneous large-scale physical model seepage test device, the visual tracking of the edge water invasion front under the multi-layer differentiated well layout mode is realized, and the rationality of the well layout strategy is demonstrated.

[0059] The present invention helps to effectively utilize the limited wellheads of offshore platforms to optimize well location design, coordinate the physical resistance between layers with different physical properties and the gas release power, realize the coupling of differentiated pressure gradient disturbances, and can solve the interlayer contradictions in the edge water drive development mode of offshore positive rhythm reservoirs, lead the uniform advancement of the edge water front in the vertical direction, and realize stable gas and water control and balanced utilization of gas reservoirs in the vertical and horizontal directions.

[0060] The above description is not intended to limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for optimizing the well location of multi-layered horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir, characterized in that: The following steps are involved: Step S10, dividing the target gas reservoir into a low permeability layer, a medium permeability layer, and a high permeability layer in the longitudinal direction; Step S20, respectively obtaining reservoir geological parameters of the low permeability layer, the medium permeability layer, and the high permeability layer in the target gas reservoir and engineering parameters of the horizontal well; Step S30, constructing a three-level composite reservoir seepage model of low permeability, medium permeability and high permeability based on the photoelectric wave propagation and reflection coupling mechanism; Step S40, determining the length of the horizontal well in the low permeability layer, the medium permeability layer, and the high permeability layer respectively according to the reservoir geological parameters of the low permeability layer, the medium permeability layer, and the high permeability layer, the engineering parameters of the horizontal well, and the low permeability-medium permeability-high permeability three-level composite reservoir seepage model; Step S50, construct a longitudinal heterogeneous large-scale physical model seepage test device, inject water at a constant rate at the edge to simulate the process of edge water invasion, and realize the visual tracking of the evolution characteristics of the water drive front in the multi-layer differentiated well mode through a transparent glass plate.

2. The method for optimizing the well location of multi-layer horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir according to claim 1, characterized in that: In step S10, by fusion of multi-level information of core description, 3D seismic and rock physical logging parameters, three layers of low permeability, medium permeability and high permeability are vertically divided based on the structural, sedimentary and diagenetic evolution characteristics.

3. The method for optimizing the well location of multi-layer horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir according to claim 1, characterized in that: The reservoir geological parameters include effective thickness, wellbore radius, gas saturation, true gas compressibility factor, gas viscosity, formation temperature, formation pressure, porosity, and permeability.

4. The method for optimizing the well location of multi-layered horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir according to claim 1, characterized in that: The engineering parameters include the gas leakage radius and the distance between the horizontal well and the lower boundary.

5. The method for optimizing the well location of multi-layered horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir according to claim 1, characterized in that: The three-level composite reservoir seepage model of low permeability, medium permeability and high permeability is: Where: Z represents the natural gas compression factor; c g Indicates the compression coefficient, MPa -1 ; Indicates the porosity of the reservoir; μ Indicates gas viscosity, mPa•s; δ represents high-speed non-Darcy characteristic parameters; P Indicates the current formation pressure, MPa; , , is the permeability; Indicates the current formation pressure of layer n, MPa; x , y , z Respectively represent the projection distances in the three directions of the coordinate axis; t Indicates time.

6. The method for optimizing the well location of multi-layered horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir according to claim 1, characterized in that: The process of determining the horizontal well length in step S40 is as follows: Step A, setting the lengths of the three horizontal wells in the low permeability layer, the medium permeability layer and the high permeability layer to meet the configuration principle of long at the top and short at the bottom; Step B, respectively substituting the lengths of the horizontal wells of the low permeability layer, the medium permeability layer and the high permeability layer into the low permeability-medium permeability-high permeability three-level composite reservoir seepage model to calculate the pressures of the low permeability layer, the medium permeability layer and the high permeability layer; Step C, respectively calculate the pressure gradient between the low permeability layer, the medium permeability layer, and the medium permeability layer and the high permeability layer. If the pressure gradient is greater than the maximum pressure gradient threshold between adjacent layers, the horizontal well section length of the medium permeability layer or the high permeability layer is adjusted downward, and steps A to C are repeated until the pressure gradients between the low permeability layer, the medium permeability layer, and the medium permeability layer and the high permeability layer are all less than or equal to the maximum pressure gradient threshold between adjacent layers, and then the final horizontal well lengths of the low permeability layer, the medium permeability layer, and the high permeability layer are output.

7. The method for optimizing the well location of multi-layered horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir according to claim 1, characterized in that: In the step S50, the geometric length and position of the horizontal well and the displacement speed of the large-scale physical simulation experiment are determined based on geometric similarity, flow similarity and resistance similarity.

8. The method for optimizing the well location of multi-layered horizontal wells in an offshore positive rhythm low permeability edge water sandstone gas reservoir according to claim 1, characterized in that: In step S50, the porosity and permeability of single-mesh quartz sand are calibrated by artificial one-dimensional cores to obtain reservoir properties under different confining pressure conditions and clarify the sand filling scheme under different pressures and porosity and permeability conditions during the sand filling process of the physical model.

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