Method for exploiting hydrate based on multilateral well
Technical Field
The invention relates to a method for jointly exploiting a high-temperature high-pressure gas reservoir and a hydrate reservoir, which is applied to the field of natural gas hydrate exploitation.
Background
Geothermal energy and hydrates have attracted extensive attention from various countries as clean energy sources with abundant reserves. The geothermal energy refers to the energy released by the earth, and can be divided into hydrothermal type, enhanced type and shallow geothermal energy resources according to the property of a heat storage body. Hydrates are currently distributed in deep sea sediments or permafrost in land areas, and natural gas and water form ice-like crystalline substances under high pressure and low temperature conditions. Currently, the exploitation assumed by the marine natural gas hydrate mainly comprises a thermal shock exploitation method, a depressurization exploitation method, a chemical agent injection method and the like. But the thermal shock method has large heat loss and low utilization efficiency; the depressurization exploitation method is only economically feasible for oil extraction when the hydrate reservoir is positioned near a temperature-pressure balance boundary, but has larger risk of stratum destruction; the chemical injection method has a slow effect on hydrate reservoirs and is very costly. Therefore, a method for exploiting the hydrate reservoir with high efficiency, no pollution and good economic benefit is urgently needed. At present, the multilateral well exploitation method is widely applied to oil and gas exploitation, but the single exploitation of high-temperature and high-pressure water-containing natural gas reservoirs or hydrate reservoirs has limitations, and the rapid and large-scale exploitation of the hydrate reservoirs is difficult to realize effectively.
Disclosure of Invention
In order to solve the technical problems mentioned in the background technology, the invention provides a well group structure and a method for developing hydrate reservoirs by using high-temperature high-pressure hot water and assisting in exploiting natural gas hydrate reservoirs. The invention adopts the separation same-well injection-production exploitation method to exploit the hydrate reservoir, can accelerate the exploitation speed of the hydrate, enables the hydrate to be exploited in large quantity, and can solve the problems of low thermal excitation utilization rate and high development cost in the traditional exploitation mode.
The technical scheme of the invention is as follows: the method for exploiting the hydrate based on the multilateral well comprises the following steps:
the method comprises the steps that firstly, a vertical well is deployed in a target measure area, an upper horizontal well is deployed at the upper third of a natural gas hydrate reservoir, and a lower horizontal well is deployed at the lower third of the natural gas hydrate reservoir; the upper horizontal well and the lower horizontal well are parallel to each other and are both connected with the vertical well; deploying an oil pipe in the vertical well;
secondly, installing a gas-water separation device and a pump at the junction of a lower horizontal well and a vertical well which are positioned at one third of the lower part of the natural gas hydrate reservoir; the gas-water separation device is positioned in the vertical well, and a liquid flow outlet of the gas-water separation device is positioned in the lower horizontal well;
thirdly, the bottom of the vertical well is arranged at the top of the high-temperature high-pressure water-containing natural gas reservoir, and a bottom flow horizontal well is arranged at the bottom of the vertical well;
fourthly, perforating the upper horizontal well, the lower horizontal well and the bottom flow horizontal well, and opening the high-temperature high-pressure water-containing natural gas reservoir and the natural gas hydrate reservoir;
fifthly, carrying out mining operation, separating the mined gas-water mixture into natural gas and high-temperature water through a gas-water separation device, and conveying the natural gas and the high-temperature water according to the following mode, namely lifting the natural gas to the ground along an oil pipe in the vertical well, and pumping the high-temperature water into a lower horizontal well in the natural gas hydrate reservoir through a pump;
and sixthly, raising the temperature of a hydrate reservoir in the natural gas hydrate reservoir after the high-temperature water is pumped, conveying the generated methane gas to the vertical well through the upper horizontal well, and lifting the produced methane gas to the ground along the wall of the vertical well.
In the second step, preferably, a layer of shaft insulation layer is added on the outer wall of the vertical shaft and outside the vertical shaft section below the gas-water separation device to reduce heat loss in the fluid transportation process, and the shaft insulation layer is made of polyvinyl chloride.
The invention has the following beneficial effects: according to the extraction method provided by the invention, two horizontal wells are established in the hydrate reservoir, wherein one horizontal well is used for heating the hydrate reservoir, and the other horizontal well is used for extracting decomposed methane gas. A high-temperature high-pressure water-containing natural gas reservoir is opened through a bottom perforation of the vertical well, a gas-water separation device and a pump are installed at the junction of the vertical well and a horizontal well at the lower part of the natural gas hydrate reservoir, gas-water mixture produced from the bottom is separated by the gas-water separation device, high-temperature water is injected into the horizontal well at the lower part of the natural gas hydrate reservoir through the pump, and natural gas is lifted upwards to the ground through a well wall. The invention applies the principle of injection and production in the same well and the multi-branch well, the method for injection and production of hydrate in more wells is more economical and practical, saves the cost, fully utilizes the advantages of the multi-branch well and accelerates the exploitation of the hydrate reservoir. The added gas-water separation device can well utilize high-temperature water in a natural gas reservoir and fully utilize geothermal resources, so that the exploitation of the hydrate can be accelerated while the natural gas is exploited, and the exploitation efficiency of the hydrate is improved.
In conclusion, after the method is applied, the hydrate reservoir can be developed by locally utilizing the heat energy of the high-temperature high-pressure water-containing gas reservoir at the deep part of land or ocean, the heat injection cost in the exploitation process can be greatly reduced, the recovery ratio is greatly improved, and the multi-dimensional exploitation is realized. The method is convenient to operate and simple in equipment, and opens up a new way for the development of hydrate reserves. The invention can efficiently raise the temperature and reduce the pressure to exploit the natural gas hydrate reservoir, realizes the cyclic utilization of stratum energy, reduces the treatment of underground water by the ground, and has low development cost and obvious environmental and economic benefits. The method can be used for large-scale exploitation of underground natural gas hydrate reservoirs on land and sea and natural gas hydrate reservoirs, and provides guidance for implementation of yield increasing measures of the hydrate reservoirs.
Description of the drawings:
fig. 1 is a schematic view of the working principle of the mining method according to the present invention.
FIG. 1-overburden; 2-natural gas hydrate reservoir; 3-interlayer; 4-high temperature high pressure water-containing natural gas reservoir; 5-upper horizontal well; 6-lower horizontal well; 7-underflow horizontal well; 8-hydrate decomposition gas; 9-perforation; 10-a motor unit; 11-heat preservation and insulation layer; 12-gas-water separation device; 13-oil pipe; 14-multilateral wells.
The specific implementation mode is as follows:
the practice of the invention is further illustrated with reference to the accompanying drawings in which:
according to the geological structure condition, the measure area is a stratum with a hydrate reservoir and a sea area or a land area with a high-temperature and high-pressure natural gas reservoir developed at the lower part of the hydrate reservoir, wherein the thickness of the stratum of the hydrate reservoir is not less than 20 m, and the high-temperature and high-pressure natural gas reservoir contains bottom water.
Establishing a multilateral well, determining a target measure area, wherein a vertical well penetrates through an overlying rock stratum and a covering layer, and two horizontal wells are arranged at the upper third and the lower third of a natural gas hydrate reservoir. The upper horizontal well and the lower horizontal well of the natural gas hydrate reservoir are parallel to each other, the included angle of the horizontal wells of the same layer system of the natural gas hydrate reservoir is 180 degrees, the length of the four sections of horizontal wells is 800-1000 m, the horizontal wells are perforated, and the distance between every two perforation points is 5-10 m.
And a gas-water separation device and a pump are arranged at the joint of the vertical well and the lower horizontal well of the natural gas hydrate reservoir and are used for separating a gas-liquid mixture and pumping high-temperature hot water.
And (3) deploying the bottom of the vertical well to the bottom of the high-temperature high-pressure water-containing natural gas reservoir, opening the high-temperature high-pressure water-containing natural gas reservoir through a perforation, and exploiting the high-temperature high-pressure water-containing natural gas reservoir.
And separating the produced gas-water mixture into natural gas and high-temperature water after passing through a gas-water separation device, wherein the natural gas is lifted to the ground along the wall of the vertical well, and the high-temperature water is pumped into a lower horizontal well in the natural gas hydrate reservoir through a pump.
And the lower horizontal well 6 positioned at the lower third of the natural gas hydrate reservoir heats the natural gas hydrate reservoir, the upper horizontal well at the upper third of the natural gas hydrate reservoir mines the natural gas hydrate reservoir, and the mined methane gas is lifted to the ground along the wall of the vertical well to form a horizontal well group for injecting the high-temperature water-mining hydrate reservoir.
As shown in fig. 1, depending on the geological conditions, land or sea where a natural gas hydrate reservoir 2 exists and a high-temperature high-pressure aqueous natural gas reservoir develops below the hydrate reservoir is selected as a measure region in the geological conditions. An overlying stratum 1 and a cover layer are arranged above the hydrate reservoir, and an interlayer 3 and a high-temperature high-pressure water-containing natural gas reservoir 4 are sequentially arranged below the hydrate reservoir. Wherein the thickness of the stratum of the natural gas hydrate reservoir 2 is not less than 20 m, and the high-temperature high-pressure water-containing natural gas reservoir contains bottom water. As shown in fig. 1, a multi-branch vertical well 1 is established, a target measure area is determined, the vertical well penetrates through an overburden 1 and a cover layer, an upper horizontal well 5 is deployed in the upper third of a natural gas hydrate reservoir 2, and a lower horizontal well 6 is deployed in the lower third of the natural gas hydrate reservoir. The upper horizontal well and the lower horizontal well of the natural gas hydrate reservoir 2 are parallel to each other, the included angle of the horizontal wells of the same layer system of the natural gas hydrate reservoir 2 is 180 degrees, the length of the four sections of horizontal wells is 800-1000 m, the horizontal wells are perforated, and the distance between every two perforated points is 5-10 m.
Fig. 1 is a schematic view of the working principle of the mining method according to the present invention. As shown in the figure, a gas-water separation device 12 and a pump are arranged at the joint of the vertical well and the horizontal well at the lower part of the natural gas hydrate reservoir 2, and are used for separating gas-liquid mixture and pumping high-temperature hot water.
And (3) deploying the bottom of the vertical well 7 to the top of the high-temperature high-pressure water-containing natural gas reservoir, opening the high-temperature high-pressure water-containing natural gas reservoir 4 through perforation, and exploiting the high-temperature high-pressure water-containing natural gas reservoir.
The produced gas-water mixture is separated into natural gas and high-temperature water through a gas-water separation device 12, wherein the natural gas is lifted to the ground along the wall of the vertical shaft, and the high-temperature water is pumped into a lower horizontal shaft 6 positioned in a natural gas hydrate reservoir through a pump.
And a lower horizontal well heating hydrate reservoir located at the lower third of the natural gas hydrate reservoir, an upper horizontal well 5 located at the upper third of the natural gas hydrate reservoir is used for exploiting the hydrate reservoir, and the exploited methane gas is lifted to the ground along the wall of the vertical well to form a horizontal well group for injecting the high-temperature water to exploit the hydrate reservoir.