Disclosure of Invention
One of the technical problems to be solved by the invention is to provide a horizontal well development method of natural gas hydrate for preventing formation collapse.
In order to solve the above technical problems, an embodiment of the present application provides a method for developing a horizontal well of a natural gas hydrate, including: drilling a horizontal well in an upper portion of a natural gas hydrate reservoir, the horizontal section of the horizontal well being tracked a distance from the reservoir that approximates each other but does not cause disturbance of the reservoir; windowing two sides of a horizontal section of the horizontal well, drilling a preset number of lateral radial wells, pouring concrete into the lateral radial wells, and forming an artificial framework loaded on a lower interlayer of the reservoir after the concrete is solidified; windowing the lower part of the horizontal well, and drilling a vertical radial well to drill through the whole reservoir; and backfilling the production area after the development of the natural gas hydrate in the production area is completed.
In one embodiment, a lateral radial well is drilled using a hydraulic jet technique, with the initial jet position being set at a laterally horizontal downward angle to ensure that the hydraulic jet drill bit remains drilling in a diagonally downward direction.
In one embodiment, in the process of drilling the lateral radial well, assuming that the reservoir thickness is h, drilling of the lateral radial well is completed when the hydraulic jet drill bit penetration reaches Acos-1 alpha x h, wherein A is a redundancy multiple and alpha is a set angle of the jet initial position.
In one embodiment, the set angle α of the initial position of the jet is 45 ° and the redundancy is 1.5 times.
In one embodiment, the well spacing of lateral radial wells drilled in the horizontal section is determined based on the degree of stability of the reservoir.
In one embodiment, if the reservoir rock formation skeleton is high in strength and high in stability, increasing the well spacing of the radial wells; if the reservoir bed skeleton is low in strength or has no bed skeleton at all, the stability is poor, and the well spacing of the radial wells is reduced.
In one embodiment, the radial wells have a well spacing in the range of 50m to 100m when the reservoir rock matrix is strong and stable.
In one embodiment, the radial wells have a well spacing in the range of 10m to 20m when the reservoir skeleton is low in strength or completely free of the formation skeleton and poor in stability.
In one embodiment, when well group development is employed, the well group is laid out in a well row or nine-point layout such that the artificial skeletons formed by the lateral radial wells of each individual well are intersected.
In one embodiment, the horizontal trajectory of the horizontal well is in the range of 10m to 20m from the reservoir.
One or more embodiments of the above-described solution may have the following advantages or benefits compared to the prior art:
based on the defects of the prior art, the embodiment of the invention provides a systematic method integrating reservoir pretreatment, exploitation and backfill after exploitation, which increases the strength of a reservoir rock frame by forming an artificial skeleton in the reservoir, and meanwhile, the disturbance of the process of forming the artificial skeleton on the reservoir is small and the risk is low. When the well group is adopted for large-scale development, the artificial skeleton forms an artificial support system of the system, so that the effective development of the reservoir is realized, and the collapse risk of the reservoir is effectively reduced.
Additional features and advantages 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. The objectives and other advantages of the invention may be realized and attained by the structure and/or process particularly pointed out in the written description and claims hereof as well as the appended drawings.
Detailed Description
The following will describe embodiments of the present invention in detail with reference to the drawings and examples, thereby solving the technical problems by applying technical means to the present invention, and realizing the corresponding technical effects can be fully understood and implemented accordingly. The embodiments and the features in the embodiments can be combined with each other under the condition of no conflict, and the formed technical schemes are all within the protection scope of the invention.
The inventors of the present application have studied the prior art to find that: at present, the technical schemes such as various development methods or devices aiming at natural gas hydrate are mainly focused on specific development modes, and are still specific process modes of main stream ideas such as a pressure reduction mode, a temperature rising mode, a replacement mode, a solid crushing mode and the like, wherein only one mode of backfilling formation defect caused by exploitation is adopted, and the operability of the method is yet to be demonstrated. For example, in the first prior art, the stability of a near-well zone reservoir is improved by forming foam mortar jet grouting piles around the well, and the efficacy thereof is focused on the stability of the well wall for a single well; in the second existing technical scheme, three fluids are sequentially introduced through an injection well group, so that the replacement of natural gas in a reservoir is realized, and simultaneously, the defect formed by the production of the natural gas is backfilled in real time; in the third prior art, the vertical well is used as the core, the radial well is drilled on the upper and lower parts of the reservoir respectively, the displacement and the replacement circulation exploitation of the radial well on the upper and lower parts of the reservoir in the same vertical well are realized through two loops of an oil pipe and a sleeve, and meanwhile, the stability of the well wall is realized by means of a concrete well cementation process; in the fourth prior art, the exploitation and backfilling are sequentially carried out according to the preset working procedures in a mode of cooperative production of well groups, so that the utilization of the reservoir is realized, and meanwhile, the stability of the reservoir is ensured; in the fifth prior art, foam cement is sprayed in the lateral direction to form a honeycomb structure after a horizontal well is drilled in a reservoir to provide support for the horizontal well and a stratum, so that well wall stability is realized; in the sixth technical scheme, the small well hole is drilled in the lateral direction of the vertical well to obtain larger reservoir contact area, and meanwhile, the sand screen is carried into the small well hole to realize sand prevention, so that the development effect is effectively improved. However, in a reservoir with insufficient strength of a non-diagenetic reservoir or a rock mass frame, the method of mining first and then backfilling cannot effectively reduce the risk of reservoir collapse and is not feasible, and geological phenomena such as landslide caused by stratum collapse can have serious consequences no matter in a marine or frozen soil environment.
Fig. 7 is a flow chart of a method of horizontal well development of natural gas hydrate according to an embodiment of the present invention. The steps of the embodiments of the present application are described below with reference to fig. 7.
As shown in fig. 7, in step S110, a horizontal well is drilled in an upper portion of the natural gas hydrate reservoir, wherein a trajectory of a horizontal section of the horizontal well is brought close to the reservoir in distance from each other, but does not cause disturbance of the reservoir.
FIG. 1 is a schematic diagram of a horizontal well drilled in an upper portion of a reservoir according to an embodiment of the present application. As shown in fig. 1, a horizontal well (5) is drilled in the upper part of the natural gas hydrate reservoir (3), the horizontal well (5) penetrating the surface layer (1) (sea or earth-float layer) into the upper cover layer (2) of the reservoir, the horizontal section track of the horizontal well being as close as possible to the reservoir (3) but not causing disturbance of the reservoir (3), preferably the horizontal track of the horizontal well is at a distance in the range of 10m to 20m from the reservoir.
In step S120, windows are opened on both sides of the horizontal section of the horizontal well, a preset number of lateral radial wells are drilled, concrete is poured into the lateral radial wells, and after the concrete is solidified, an artificial skeleton carried on the interlayer at the lower part of the reservoir is formed. In one embodiment, a lateral radial well is drilled using a hydraulic jet technique, with the initial jet position being set at a laterally horizontal downward angle to ensure that the hydraulic jet drill bit remains drilling in a diagonally downward direction.
In the process of drilling a lateral radial well, assuming that the reservoir thickness is h, when the hydraulic jet drill bit penetration reaches Acos-1 And drilling the lateral radial well is completed at alpha×h, wherein A is a redundancy factor, and alpha is a set angle of the initial position of the jet. For example, in the above example, when the set angle α downhole in the lateral horizontal direction is 45 °, then when the hydraulic jet drill head penetration reaches cos-1 At 45 DEG x h the bit is considered to reach the bottom compartment, considering 1.5 times redundancy, when the bit penetration reaches 1.5 x cos-1 Drilling of radial wells is completed at 45 ° x h, i.e., l=2.12 x h.
Because of the circulating pressure existing in the drilling process of the drill bit, the natural gas hydrate cannot change in phase state, so that effective support can be formed for the drilled radial well bore. When the radial well drilling is finished, the hydraulic jet drill bit is retracted and concrete can be injected through the jet drill bit, so that the radial well drilled by the hydraulic jet drill bit is filled with concrete after the hydraulic jet drill bit is successfully retracted. And plugging the layer in the horizontal well, lifting the working tool to drill the upper radial well, and sequentially circulating until the whole section of the horizontal well finishes the drilling and concrete filling of the lateral radial well, and waiting for the concrete to be completely solidified. The reason that the radial well construction is carried out on a certain layer is that the layer needs to be plugged is as follows: the horizontal section of the horizontal well is divided into a plurality of layer sections from the toe end to the heel end, only a single layer section can be constructed at a time, and the construction is sequentially carried out according to the construction sequence from the toe end to the heel end, and the working tool is gradually lifted. After lifting, the constructed interval is required to be plugged and isolated because the radial well exists, otherwise, the construction of the upper interval is easy to release pressure, so that the progress cannot be smoothly progressed, and the plugging and isolation of the constructed interval is generally realized by carrying a bottom packer through a continuous oil pipe.
The well spacing of the lateral radial wells drilled in the horizontal section is determined by the stability of the reservoir. If the reservoir stratum skeleton has higher strength and higher stability, the well spacing of the radial wells can be properly increased, for example, the well spacing range is set to be 50-100 m; if the reservoir stratum skeleton strength is lower or the stratum skeleton is not present at all and the stability is poor, the well spacing of the radial well is properly reduced, for example, the well spacing range is set to be 10-20 m. It will be readily appreciated that the well spacing of the lateral radial wells may be designed according to the circumstances and is not limited to the two examples described above.
Fig. 2 is a schematic diagram of drilling a radial well on both sides of a horizontal section of a horizontal well according to an embodiment of the present application, wherein fig. 2 (a) on the left side is a front view, and fig. 2 (b) on the right side is a side view. As shown in fig. 2 (a), a plurality of lateral radial wells (6) are drilled on both sides of the horizontal section, the radial wells being spaced apart in the horizontal direction, the lateral radial wells (6) penetrating the natural gas hydrate reservoir (3) and entering the barrier (4) in the lower part of the reservoir. From the side view of fig. 2 (b), after the concrete has been fully set, an artificial skeleton (supporting structure) consisting of lateral radial wells (6) is formed in the reservoir, which can effectively support the reservoir above, and a safe production zone (8) is formed below the artificial skeleton.
In step S130, a vertical radial well is drilled to drill through the entire reservoir by windowing the lower portion of the horizontal well.
As shown in fig. 3 (a), a vertical radial well (7) is drilled in the lower part of the horizontal well (e.g. the lower part of the horizontal section), and the vertical radial well (7) is drilled through the whole reservoir (3) and into the barrier (4) in the lower part of the reservoir. At the moment, the horizontal well (5) is communicated with the production area (8) through the vertical radial well (7), so that natural gas hydrate can be produced. The end result of drilling a radial well at the bottom of a horizontal well may also be referred to as the top view shown in fig. 3 (b).
In step S140, after the development of the natural gas hydrate of the production zone is completed, the production zone is backfilled.
Specifically, after the development of the mining area is finished, backfilling is carried out on the mining area, so that collapse caused by failure of the later-stage artificial framework is avoided.
In addition, the steps S110 to S140 are directed to development of a single well, and in other embodiments, well group layout may be performed based on development of a single well.
As shown in fig. 4, which shows a side view of a well group of a plurality of individual wells, each individual well has a horizontal section drilled with a plurality of lateral radial wells, and the artificial skeletons of these lateral radial wells intersect. According to research, when the artificial frameworks formed by the lateral radial wells are crossed, the supporting effect of the whole reservoir is improved, and the risk of stratum collapse is further reduced. In a preferred example, a well-array layout as shown in fig. 5 in plan view can be selected when well-array layout is performed, and this well-array layout method can improve the utilization degree of the reservoir, namely, the recovery rate, on the one hand, and can form good support for the whole reservoir through the cross-type layout of the well array on the other hand. Further, a nine-point layout may be provided as shown in fig. 6 in a plan view, and as shown in fig. 6, eight additional wells may be uniformly distributed around the circumference of the nine-point layout when any single well is used as a center well. Nine-point methods are more compact than well string type well placement. Through the layout, the whole cross type support of the reservoir can be realized, and meanwhile, the recovery ratio or the exploitation effect can be ensured.
In summary, the embodiment of the invention can bring the following technical effects: (1) The traditional well drilling is stopped at the cover layer at the upper part of the reservoir, meanwhile, the water jet technology is adopted at the bottom of the well to drill obliquely downwards, the whole reservoir is drilled, compared with the traditional well drilling, the method has the advantages that the disturbance to the reservoir is small, the probability of unstable reservoir is small, and the overall construction risk is low; (2) The radial well drilled through the reservoir is filled with concrete while the hydraulic jet drill bit is recovered, and after the radial well is solidified, a frame structure borne on a lower interlayer of the reservoir, namely an artificial skeleton is formed, so that on one hand, the integral strength of the reservoir is improved, the collapse risk of the reservoir is reduced, on the other hand, a safe production area is formed at the lower part covered by the artificial skeleton, the defect formed by the lower production area is supported by the artificial skeleton, and meanwhile, the supported load is transferred to the lower interlayer, so that time is created for backfilling after production; (3) When the well group is used for development, the artificial frameworks formed by the single wells are staggered, so that the overall stability of the reservoir is further improved, the range of a safe production area is enlarged, and the production degree and economic benefit are improved.
It is to be understood that the disclosed embodiments are not limited to the specific structures, process steps, etc. disclosed herein, but are intended to extend to equivalents of these features as would be understood by one of ordinary skill in the relevant arts. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase "one embodiment" or "an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.
Although the embodiments of the present invention are disclosed above, the embodiments are only used for the convenience of understanding the present invention, and are not intended to limit the present invention. Any person skilled in the art can make any modification and variation in form and detail without departing from the spirit and scope of the present disclosure, but the scope of the present disclosure is still subject to the scope of the appended claims.