CN113417596B - Theory for reinforcing and preventing collapse and sand in natural gas hydrate stratum layer and implementation method - Google Patents
Theory for reinforcing and preventing collapse and sand in natural gas hydrate stratum layer and implementation method Download PDFInfo
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- E21B33/00—Sealing or packing boreholes or wells
- E21B33/10—Sealing or packing boreholes or wells in the borehole
- E21B33/13—Methods or devices for cementing, for plugging holes, crevices or the like
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- E—FIXED CONSTRUCTIONS
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Abstract
The invention belongs to the field of reservoir transformation in a natural gas hydrate development process, and particularly relates to a theory and an implementation method for reinforcement, collapse prevention and sand prevention in a natural gas hydrate stratum layer. The invention combines stratum reconstruction and fracturing grouting reinforcement technology, cracks appear in the natural gas hydrate stratum through the fracturing grouting technology, and the curing liquid enters the cracks and penetrates into the stratum through the pressure difference to form a reinforcement body which has a ribbed plate structure and has certain strength and permeability, thereby playing roles of supporting, preventing collapse and preventing sand for the stratum. According to the invention, through analyzing physical parameters of a target stratum, a curing agent system is utilized to regulate a fracturing construction process and pump and inject curing liquid into the stratum in the fracturing process, the purposes of reinforcing, anti-collapse and sand prevention in a natural gas hydrate stratum layer are realized, the formed reinforcing body can be well cemented with the surrounding stratum, and accidents such as sand production caused by hydrate decomposition and borehole wall instability caused by stratum collapse are effectively avoided.
Description
Technical Field
The invention belongs to the field of reservoir transformation in a natural gas hydrate development process, and particularly relates to a theory and an implementation method for reinforcement, collapse prevention and sand prevention in a natural gas hydrate stratum layer.
Background
Natural gas hydrates, also known as "combustible ice", are ice-like crystalline substances formed by natural gas and water under high pressure and low temperature conditions, and are generally distributed in deep sea sediments or permafrost in land areas. In 2016, the inventor lists "hydrate pilot mining-hydrate commercial mining" in the national focus research and development plan of thirteen-five. And in 2017, 5, 18 and 5 months, the success of trial production of the sea area combustible ice is realized for the first time, and the gas hydrate trial production is continuously produced for nearly 8 days in the sea area of the south China sea Shenhu, so that the historical breakthrough of the development of the gas hydrate in China is realized.
Natural gas hydrates have a position that cannot be replaced by other oil and gas resources. (1) The natural gas hydrate reserves are large. Natural gas hydrateThe second largest carbon storage warehouse in the world is just second to carbonate rock, and natural gas resources stored in the second largest carbon storage warehouse have huge potential. According to conservative estimation, the total resource amount of natural gas contained in the global natural gas hydrate is (18-21) multiplied by 1015m3Its thermal equivalent is 2 times the total thermal equivalent of coal, oil and natural gas known globally. At present, natural gas hydrates in China are mainly distributed in the south China sea area, the east China sea area, the Qinghai-Tibet plateau area and the northeast China permafrost zone, and the content of the natural gas hydrates is large. The research shows that the equivalent natural gas resource reserves are respectively about (64.97 multiplied by 10)12）m3、（3.38×1012）m3、（12.5×1012）m3、（2.8×1012）m3. (2) The energy density of natural gas hydrates is extremely high. 1m in the standard state (0 ℃, 101.325kPa)3The natural gas hydrate can release about 164m after decomposition3The energy density is much higher than that of conventional natural gas. (3) And (4) cleaning the natural gas hydrate. Compared with the conventional natural gas, the natural gas hydrate has the main substances of alkane such as methane and the like, the content of other impurities is less, the required purification process is simpler, and the natural gas hydrate is energy with better cleanness. Therefore, hydrate resources are one of strategic resources with the most commercial development prospect in the 21 st century.
With the global attention and research of natural gas hydrate, a great deal of research results are continuously generated, and the exploitation project also makes a staged breakthrough. However, due to the complex characteristics of the natural gas hydrate reservoir and the deep water shallow layer mining environment, a plurality of problems which need to be solved urgently are brought to the mining and development process, especially a series of safety problems are easily caused by hydrate decomposition in the depressurization mining process, and the problems mainly comprise: (1) the solid hydrate which plays a role in cementation or support is decomposed into gas-liquid mixed fluid in a flowing state, so that the mechanical bearing capacity of the stratum is reduced, and meanwhile, water generated by decomposition permeates the stratum, so that the water content of the stratum of the well wall is increased, the connection among particles is weakened, and the instability of the well wall is caused; (2) not only can the mechanical strength of the stratum be reduced, but also the pore pressure of the stratum can be increased, so that the consolidation strength of hydrate stratum sediments is greatly reduced, and the seabed landslide can be caused under the action of external forces such as earthquake or load increase; (3) reservoir structure is damaged, sand grains are peeled off from the skeleton sand and become loose sand, formation fluid begins to flow along with reservoir development, and drag force is generated on the sand grains by the fluid, so that sand production is caused.
Hydrate trial production and related research show that: the depressurization method is the most effective method for developing hydrate, and the pressure condition of stable existence of hydrate is destroyed by reducing the pressure of hydrate layer, and when the reservoir pressure is reduced to be lower than the equilibrium pressure of hydrate phase, the hydrate begins to decompose. However, the decrease of the hydrate formation pressure can cause the increase of the effective stress of the reservoir and the vertical deformation, meanwhile, the increase of the reservoir stress can cause the destabilization damage of the reservoir due to the poor cementation and the low strength of the marine natural gas hydrate reservoir, the hydrate plays a cementation role among reservoir sediment particles, the hydrate decomposition caused by depressurization can reduce the strength of the reservoir, and the risk of the destabilization of the reservoir is further increased. Hydrate stratum transformation is carried out in a hydraulic fracturing mode in Yanglin (the crushing process of Yanglin hydrate reservoirs under the action of high-pressure water jet and reservoir transformation yield-increasing research [ D ]; Jilin university) and the like, and experimental results show that: when the pressure reduction method or other methods are combined for mining, when the jet speed is fixed, the relatively large jet distance can reduce the crushing volume and reduce the influence on the stability of a reservoir stratum on the basis of meeting the crushing depth. Yuanyilong and the like (Yuanyilong, xutianfu, xinxin, Xianyeli, Li ice. Marine natural gas hydrate depressurization exploitation stratum borehole wall mechanical stability analysis [ J ] mechanics report, 2020, 52 (2): 544 and 555) consider that depressurization leads to increase of stratum effective stress, further causes settlement of the stratum around the well, the settlement of the stratum mainly occurs in the earlier stage of depressurization exploitation, the maximum settlement position is located around the borehole wall, and the settlement amount of the stratum extending to the inside of the reservoir is rapidly reduced; the mechanical strength of the formation around the well is reduced due to the decomposition of the hydrate, and the sedimentation of the reservoir is intensified; the wellbore depressurization causes the most obvious stress concentration on the well wall of the perforation section, thereby causing the potential risk of well wall damage, and the areas are the key areas for controlling the sand production of hydrate. CN107446560A discloses a cementing-stratum solidifying one-body fluid applied to a deep water weakly cemented stratum. Meanwhile, CN106198933A discloses a device for simulating a gradient layer of deep water weakly consolidated formation cementing strength, which can simulate and solidify the gradient layer aiming at the weakly consolidated formation. The reservoir stability is a key problem faced by hydrate exploitation and is a precondition for ensuring the safety and high efficiency of hydrate exploitation.
At present, related researches on the formation modification of the natural gas hydrate are few, and the research direction is mostly that cracks with high flow conductivity are formed around a near-well casing in a fracturing mode, so that the hydrate deposit productivity is effectively improved. The related research on hydrate formation strengthening is still in an exploration stage, and the related research at home and abroad only carries out preliminary research on formation deformation and damage in the hydrate exploitation process in a numerical simulation mode, so that an effective hydrate formation strengthening and anti-collapse method is not provided.
Disclosure of Invention
The invention aims to provide a theory and an implementation method for reinforcing and preventing collapse and sand in a natural gas hydrate stratum layer.
The hydraulic fracturing is to inject fracturing fluid into the stratum to generate fracturing cracks or expand natural cracks in the stratum, and improve the permeability and the heat and mass transfer efficiency, thereby achieving the purpose of increasing the yield. Hydraulic fracturing techniques have been relatively well established in conventional hydrocarbon reservoir formations. For the natural gas hydrate stratum, the main components of the sediment are silt and clay, and the sediment is in a weakly cemented or unconsolidated state, so that the difficulty of hydraulic fracturing is increased. However, the hydrate exists near the contact point of the particles in the form of cement or exists in the sediment in the form of pore filling, so that the cementing property of the hydrate layer is greatly improved, and the hydraulic fracturing is favorably carried out. On the basis of fracturing, curing liquid is injected into a stratum fracture, certain pump injection pressure is maintained, the fracture is prevented from being closed, the curing liquid is prevented from being extruded out, and meanwhile, the curing liquid is retained in the fracture and cured to form a reinforcing body with a rib plate structure and certain strength. The reinforcing body and the surrounding stratum have good cementing performance, and after the hydrate is decomposed, the stratum can be effectively supported, collapse is prevented, and the sand prevention effect is taken into consideration. Based on the thought, the invention provides a theory of reinforcement, collapse prevention and sand prevention in a natural gas hydrate stratum layer.
The method takes the fracturing crack generated by natural gas hydrate fracturing and the surrounding stratum as research areas, adopts a fracturing grouting mode to form a series of reinforcing bodies in the hydrate stratum, simultaneously, the curing liquid permeates the stratum and is well cemented with the hydrate stratum, the curing effect is improved, the problems of stratum collapse, sand production and the like caused by hydrate decomposition are effectively avoided, an innovative solution is provided for improving the stability of the natural gas hydrate stratum, and important guarantee is provided for the safety and the high efficiency of natural gas hydrate development.
The method for realizing reinforcement, collapse prevention and sand prevention in the natural gas hydrate stratum layer is realized by the following steps:
(1) collecting a natural gas hydrate stratum sample or determining temperature and pressure environment parameters of a target stratum based on existing field data;
(2) analyzing the physical property parameters of the target stratum, and determining a simulated stratum formula by adopting a solidified granular material with better mechanical property and proper grain size according to the physical property parameters of the target stratum and the occurrence mode of the physical property parameters; controlling the hydrate saturation in a water quantification and gas excess mode, and monitoring the hydrate stability according to the conditions of the temperature and the pressure of a target stratum; maintaining the simulated stratum under the conditions of temperature and pressure of the target stratum, testing physical parameters of the simulated stratum, comparing the parameters of the target stratum, and adjusting test design parameters until the physical parameters of the simulated stratum and the physical parameters of the target stratum are the same or similar;
(3) solidifying and implementing the solidification liquid system in a simulated stratum by adopting a fracturing mode to form a reinforcing body for in-layer reinforcement; the reinforcing body has reasonable permeability and strength;
(4) according to the required reinforcement range of the target stratum, the fracturing grouting construction process is regulated and controlled by combining the characteristics of a reinforcement body, and the fracturing grouting construction process comprises the following steps: and (4) performing slotting parameters and curing liquid injection parameters of the grouting pipe column until the requirement of stratum curing is met.
The physical parameters in the step (2) include but are not limited to density, porosity, permeability, particle size distribution, hydrate saturation and virgin formation strength.
Furthermore, the curing liquid has good permeability and can penetrate into a certain depth through a crack and a stratum; the curing liquid is suitable for the conditions of temperature and pressure of the natural gas hydrate stratum, has smaller consistency before being pumped into the stratum, and ensures the flowing characteristic of the curing liquid in the construction process; the solidified reinforced body and the target stratum have good cementation, reasonable permeability and strength performance.
Further, the implantation parameters include: injection pressure differential and injection flow rate; the grouting pipe column slotting parameters comprise: the shape of the slot and the shape parameters thereof; the reinforcement body characteristics include: the depth of the reinforcement, the cross-sectional shape, the number of reinforcement and the strength of the reinforcement itself.
Furthermore, a stratum fracturing method is adopted for the reinforcement in the hydrate stratum layer, and fracturing parameters are determined according to physical parameters and mechanical parameters of the hydrate stratum; the indoor simulation can be implemented and monitored by adopting the existing hydrate reservoir stratum internal consolidation simulation device.
Furthermore, in the process of forming a reinforcing body by waiting for setting, the curing liquid system needs to maintain a pumping pressure for a certain time under the condition of target formation temperature so as to prevent the crack from being closed and prevent the curing liquid from being extruded out; the magnitude of the pump pressure can be determined from the injection pressure difference: the time for maintaining the pump pressure may be determined based on the setting fluid gelation characteristics.
Compared with the prior art, the invention has the following advantages:
(1) aiming at the problems of sand production, stratum collapse and the like caused by hydrate decomposition in the hydrate stratum development process, the strengthening theory in the hydrate stratum fracturing grouting layer is put forward for the first time, and the solidification liquid is injected into the cracks to form a strengthening body with certain strength while fracturing modification, so that the stratum stability is effectively improved, and important guidance is provided for safe and efficient development of the natural gas hydrate;
(2) the reinforced body and the surrounding stratum have good cementing property, and the problems of sand falling, sand production and the like can be effectively prevented after the hydrate is decomposed;
(3) the reinforcing body has good permeability, and effectively avoids the circulation of hydrate decomposition gas in the hydrate exploitation process;
(4) the hydrate formation fracturing and the injection of the curing liquid are carried out simultaneously, and the curing liquid forms a reinforcing body after the pressure is maintained for a certain time according to the target formation environmental condition, so that the method avoids secondary damage to the formation.
Drawings
FIG. 1 is a schematic diagram of the consolidation in a hydrate formation fracturing grouting layer according to the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the following embodiments. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention.
The method for realizing the reinforcement, collapse prevention and sand prevention in the natural gas hydrate stratum layer is realized by the following steps:
(1) collecting a natural gas hydrate stratum sample or determining temperature and pressure environment parameters of a target stratum based on existing field data;
(2) analyzing the physical property parameters of the target stratum, and determining a simulated stratum formula according to the physical property parameters of the target stratum; controlling the hydrate saturation in a water quantitative and gas excess mode; maintaining the simulated stratum under the conditions of temperature and pressure of the target stratum, testing physical parameters of the simulated stratum, comparing the parameters of the target stratum, and adjusting test design parameters until the physical parameters of the simulated stratum and the physical parameters of the target stratum are the same or similar; the physical property parameters include, but are not limited to, density, porosity, permeability, particle size distribution, hydrate saturation, virgin formation strength;
(3) solidifying and implementing the solidification liquid system in a simulated stratum by adopting a fracturing mode to form a reinforcing body for in-layer reinforcement; the reinforcing body has reasonable permeability and strength;
(4) according to the required reinforcement range of the target stratum, the fracturing grouting construction process is regulated and controlled by combining the characteristics of a reinforcement body, and the fracturing grouting construction process comprises the following steps: the slotting parameters and the curing liquid injection parameters of the grouting pipe column are carried out until the requirement of stratum curing is met; the characteristics of the reinforcing body include the depth of the reinforcing body, the sectional shape, the number of the reinforcing bodies, and the strength of the reinforcing body itself.
The step (3) further comprises:
and (3-1) analyzing a solidifying liquid system suitable for the hydrate formation. The solidified liquid system mainly comprises a hardenable material, emulsion, permeable microspheres, a permeation enhancer and a rheology modifier, is suitable for low-temperature and high-pressure deep water shallow environment, and has better fluidity and permeability; the cured product has high permeability and strength, and can be well cemented with surrounding stratum;
and (3-2) adopting the curing fluid as a fracturing working fluid to perform fracturing treatment on the simulated stratum. On the basis of the existing hydrate stratum fracturing construction process, grouting pipe column slotting parameters (slotting shape and the shape parameters) and curing liquid injection parameters (injection pressure difference, injection flow, injection direction angle and the like) are designed, the influence rule of the grouting pipe column slotting parameters on the extension depth, width and thickness of a fracturing fracture is analyzed, and the parameters are regulated and controlled on the basis, so that the hydrate stratum reinforcing range requirement is met.
The step (4) further comprises:
and (4-1) after the solidification liquid is injected into the simulated stratum, maintaining the pressure for a certain time according to the environment condition of the target stratum, and enabling the solidification liquid to be retained in the fracture and solidified to form a reinforced body. Changing the temperature and pressure after the reinforcing body is formed, decomposing the hydrate in an instable way, collecting and weighing the fallen soft soil to obtain the proportion of the reinforcing body to the consolidated soft soil, and analyzing the sand prevention effect of the fracturing grouting stratum reconstruction; comparing the difference between the shape of the reinforcement body and the shape of the crack, adjusting the slotting parameters and the injection parameters of the grouting pipe column for fracturing grouting, and establishing a regulation and control method for the characteristics of the reinforcement body;
(4-2) testing the compression strength and the shear strength of the solidified simulated hydrate stratum, analyzing the reinforcing effect, and establishing a hydrate stratum in-layer reinforcing regulation and control method based on the analysis of the reinforcing body shape and the influence of the reinforcing body strength on the reinforcing effect.
The consolidation in the fracturing grouting layer improves the overall strength of a weakly consolidated hydrate stratum, effectively supports the stratum, avoids stratum collapse caused by hydrate decomposition in the development process, simultaneously strengthens the good consolidation of a body and the stratum and a network structure formed between the strengthening bodies, can effectively reduce the dropping amount of soft soil, avoids the problems of sand production and the like, and provides important guarantee for the safety and the high efficiency of hydrate development.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, improvement, equivalent replacement, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the claims, or the equivalents of such scope and boundaries.
Claims (6)
1. The method for realizing reinforcement, collapse prevention and sand prevention in the natural gas hydrate stratum layer is characterized by comprising the following specific steps of:
(1) collecting a natural gas hydrate stratum sample or determining temperature and pressure environment parameters of a target stratum based on existing field data;
(2) analyzing the physical property parameters of the target stratum, and determining a simulated stratum formula according to the physical property parameters of the target stratum; controlling the hydrate saturation in a water quantitative and gas excess mode; maintaining the simulated stratum under the conditions of temperature and pressure of the target stratum, testing physical parameters of the simulated stratum, comparing the parameters of the target stratum, and adjusting test design parameters until the physical parameters of the simulated stratum and the physical parameters of the target stratum are the same or similar;
(3) solidifying and implementing the solidification liquid system in a simulated stratum by adopting a fracturing mode to form a reinforcing body for in-layer reinforcement; the reinforcing body has reasonable permeability and strength;
(4) according to the required reinforcement range of the target stratum, the fracturing grouting construction process is regulated and controlled by combining the characteristics of a reinforcement body, and the fracturing grouting construction process comprises the following steps: and (4) performing slotting parameters and curing liquid injection parameters of the grouting pipe column until the requirement of stratum curing is met.
2. The method for realizing reinforcement and anti-collapse and sand control in the natural gas hydrate formation layer according to claim 1, wherein the physical parameters in the step (2) comprise but are not limited to density, porosity, permeability, particle size distribution, hydrate saturation and original formation strength.
3. The method for realizing reinforcement, collapse prevention and sand prevention in the natural gas hydrate formation layer according to claim 1, wherein the curing liquid has good permeability and can penetrate into the formation to a certain depth through a crack; the curing liquid is suitable for the conditions of temperature and pressure of the natural gas hydrate stratum, has smaller consistency before being pumped into the stratum, and ensures the flowing characteristic of the curing liquid in the construction process; the solidified reinforcing body and the target stratum have good cementation, reasonable permeability and strength performance.
4. The method for achieving reinforcement and anti-collapse and anti-sand in the natural gas hydrate formation layer according to claim 1, wherein the injection parameters comprise injection pressure difference and injection flow rate; the grouting pipe column slotting parameters comprise slotting shape and shape parameters thereof; the characteristics of the reinforcing body include the depth of the reinforcing body, the sectional shape, the number of the reinforcing bodies, and the strength of the reinforcing body itself.
5. The method for realizing reinforcement, anti-collapse and anti-sand in the natural gas hydrate stratum layer according to claim 1, wherein a reservoir fracturing method is adopted for reinforcement in the hydrate stratum layer, and fracturing parameters are determined according to physical parameters and mechanical parameters of the hydrate stratum layer; and the indoor simulation is implemented and monitored by a hydrate reservoir stratum internal consolidation simulation device.
6. The method for realizing reinforcement, anti-collapse and anti-sand in the natural gas hydrate formation layer according to claim 1, wherein in the process of forming the reinforcement body by setting, the solidified liquid system needs to maintain a certain pumping pressure for a certain time under the condition of target formation temperature so as to prevent the fracture from closing and prevent the solidified liquid from being extruded out; the pumping pressure is determined according to the injection pressure difference: the time for maintaining the pump pressure is determined according to the setting-up characteristics of the curing fluid.
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| US17/727,691 US11905812B2 (en) | 2021-08-24 | 2022-04-22 | Intra-layer reinforcement method, and consolidation and reconstruction simulation experiment system and evaluation method for gas hydrate formation |
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