Novel well completion structure of geothermal well

Abstract

A novel well completion structure of a geothermal well comprises a first well opening section A, a second well opening section B and a third well opening section C which are arranged from top to bottom and communicate with one another. A surface casing well cementation cement sheath is arranged on the outer layer of the first well opening section A, and an intermediate casing well cementation cement sheath is arranged on the outer layer of the second well opening section B; the annular space of the first opening well section A and the second opening well section B is sealed by the well cementation cement sheath, the stability of the well wall on the upper portion of the heat storage exploitation layer can be guaranteed to the maximum extent, the method is particularly suitable for stratums with poor lithology and loose cementation, the collapse risk of the well wall can be reduced, and the service life of a geothermal well is prolonged. If the well is a recharge well, when pressure is increased for recharge, the aquifer on the upper portion of the recharge layer is protected, and other aquifers cannot be damaged.

Description

Technical Field

[0001] The utility model relates to the technical field of geothermal well drilling, in particular to a new well completion structure for a geothermal well. Background Art

[0002] The development of hydrothermal geothermal resources is inseparable from geothermal well drilling. The success or failure of geothermal well completion directly determines the quality and service life of the geothermal well. The existing completion method for developing hydrothermal geothermal resources is generally casing suspension + screen completion (expansion rubber water stop). This completion method is a two-opening well body structure: the surface pump chamber section of the first opening is all sealed with cement, and the casing and screen are suspended by a hanger after the second opening is completed. The part above the screen is sealed with an expansion rubber water stop, and the second opening annulus is not sealed with cement. The existing completion method has the characteristics of simple construction, low cost, and short completion cycle.

[0003] However, the above completion methods have the following shortcomings: (1) The expansion rubber water stop is used to stop the water in the secondary opening annulus. During the long-term use of the geothermal well, due to the aging of the rubber, there is a possibility that the water stop will fail, allowing the upper low-temperature formation water to enter the lower wellbore, reducing the water temperature at the geothermal water wellhead, resulting in a decrease in the energy grade of the geothermal fluid extracted from the geothermal well. If it is a recharge well, the recharge water will be injected into non-target layers, causing damage to other aquifers. (2) If the geothermal well is used as a recharge well, the fine silt in the sand-shale interlayer is easily flushed with a large amount of liquid during the recharge process, and the fine silt in it is easy to enter the formation with the geothermal water to block the pore throat, reducing the recharge volume, and the mudstone section will block the recharge section after collapse, further reducing the recharge capacity. (3) The secondary opening section is too long, and the high-permeability sandstone thermal reservoir is soaked in drilling fluid for a long time during the drilling and completion process, which makes it easy for the drilling and completion fluid to penetrate into the formation through the pores, blocking the seepage channel, resulting in a decrease in the formation porosity and permeability, and damaging the thermal reservoir. Summary of the invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the utility model is to provide a new completion structure for a geothermal well. The water-producing stratum above the heat storage exploitation layer is sealed with cementing cement, which can maximize the stability of the well wall above the heat storage exploitation layer. It is particularly suitable for strata with poor diagenesis and loose cementation, which can reduce the risk of well wall collapse and extend the service life of the geothermal well. For the reinjection well, when the pressure is increased for reinjection, the aquifer above the reinjection layer is protected; the upper low-temperature formation water is prevented from entering the wellbore, resulting in a decrease in the water outlet temperature of the geothermal well and the heat extraction capacity of a single well; it is suitable for the drilling of geothermal wells for the development of hydrothermal geothermal resources.

[0005] In order to achieve the above objectives, the technical solution adopted by the utility model is:

[0006] A new completion structure for a geothermal well comprises a first well section A, a second well section B and a third well section C which are connected and arranged from top to bottom; the structure is characterized in that the outer layer of the first well section A is provided with a surface casing cementing cement ring 1, and the outer layer of the second well section B is provided with a technical casing cementing cement ring 3.

[0007] The top of the surface casing cementing cement ring 1 of the well opening section A is returned to the ground, and the surface casing 2 is arranged inside the cementing cement ring 1 of the well opening section A.

[0008] The top of the technical casing cementing cement ring 3 of the second well section B returns to the casing shoe 4 of the surface casing 2, and a technical casing 5 is arranged inside the technical casing cementing cement ring 3 of the second well section B. The technical casing 5 is suspended at the bottom of the surface casing 2 through a first hanger 6.

[0009] The third well section C includes a production casing 7 , the top of which is suspended on the bottom of the technical casing 5 via a second hanger 8 .

[0010] The production casing 7 is a petroleum casing 9 or a screen tube 10 or the petroleum casing 9 and the screen tube 10 are connected in series.

[0011] The oil casing 9 is used in mudstone layers with low water production, and the screen 10 is used in sandstone layers with high water production.

[0012] The outer surface of the screen pipe 10 is treated by a wire-wrapped mesh sand prevention process.

[0013] Compared with the prior art, the utility model has the following technical effects:

[0014] (1) During the reinjection process of a geothermal well, the upper mudstone section of the wellbore is prone to collapse and block the reinjection section, and fine silt easily enters the formation and blocks the pore throat. The annulus of the first opening well section A and the second opening well section B of the utility model is sealed with cementing cement, which can maximize the stability of the well wall above the thermal reservoir production layer. It is particularly suitable for formations with poor lithology and loose cementation, which can reduce the risk of well wall collapse and extend the service life of the geothermal well. If it is a reinjection well, when the pressure is increased for reinjection, the aquifer above the reinjection layer is protected and no damage is caused to other aquifers.

[0015] (2) The utility model adopts cementing ring to seal the water-producing strata above the heat storage exploitation layer (the first well section A and the second well section B). The sealing effect is better than that of the expansion rubber water stop, which can prevent the expansion rubber water stop from failing easily and causing the upper low-temperature formation water to enter the wellbore, thereby reducing the water outlet temperature of the geothermal well and the heat extraction capacity of a single well, resulting in the problem of low grade of geothermal fluid produced by a single well.

[0016] (3) The utility model adopts a three-opening wellbore structure, so the length of the three-opening well section C is relatively short. In the well that drills the same target layer section but adopts a two-opening wellbore structure, the two-opening well section is longer. Relatively speaking, the drilling construction period of the three-opening well section C is short, which can reduce the time for the drilling and completion fluid to soak the thermal reservoir, reduce the impact on the porosity and permeability of the thermal reservoir, and alleviate the damage to the thermal reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the utility model.

[0018] Figure 2 This is a schematic diagram of the wellbore structure of the conventional completion method for geothermal wells before improvement.

[0019] Among them: 1. Surface casing cementing cement ring, 2. Surface casing, 3. Technical casing cementing cement ring, 4. Casing shoe, 5. Technical casing, 6. First hanger, 7. Production casing, 8. Second hanger, 9. Oil casing, 10. Screen. DETAILED DESCRIPTION

[0020] The technical solution of the utility model will be clearly and completely described below in conjunction with the accompanying drawings.

[0021] See also Figure 1 A new type of geothermal well completion structure includes a first well section A, a second well section B and a third well section C connected from top to bottom; the outer layer of the first well section A is provided with a surface casing cementing cement ring 1, and the outer layer of the second well section B is provided with a second (technical casing) cementing cement ring 3.

[0022] The top of the technical casing cementing cement ring 1 of the well opening section A is returned to the ground, and the surface casing 2 is arranged inside the cementing cement ring 1 of the well opening section A.

[0023] The top of the technical casing cementing cement ring 3 of the second well section B returns to the casing shoe 4 of the surface casing 2, and a technical casing 5 is arranged inside the technical casing cementing cement ring 3 of the second well section B. The technical casing 5 is suspended at the bottom of the surface casing 2 through a first hanger 6.

[0024] The third well section C includes a production casing 7 , the top of which is suspended on the bottom of the technical casing 5 via a second hanger 8 .

[0025] The production casing 7 is a petroleum casing 9 or a screen tube 10 or the petroleum casing 9 and the screen tube 10 are connected in series.

[0026] The oil casing 9 is used in mudstone layers with low water production, and the screen 10 is used in sandstone layers with high water production.

[0027] The outer surface of the screen pipe 10 is processed by a wire wrapping process to achieve the purpose of sand prevention.

[0028] The working principle of the utility model is:

[0029] A three-opening wellbore structure is adopted, 1) an opening well section A: the opening well section is used as the pump room section of the geothermal well, and the surface casing is lowered into the cement ring 1 of the outer surface casing; the surface casing cementing cement ring 1 seals the well wall, and the cement returns to the ground, which can firstly provide a pumping space for pumping or reinjection of the geothermal well; secondly, it can isolate the loose surface strata to avoid well wall collapse; thirdly, it can isolate shallow groundwater to avoid pollution of shallow groundwater during drilling construction.

[0030] 2) The technical casing 5 is lowered into the second well section B, and the technical casing 5 is suspended on the upper surface casing 2 by the first hanger 6. Cement is used for cementing in this well section, and the cement returns to the casing shoe of the surface casing 2; the second well section B can firstly seal and insulate the easily collapsed strata above the thermal reservoir section; secondly, it can seal and insulate the groundwater layer above the thermal reservoir section to prevent the groundwater above the thermal reservoir section from entering the wellbore and affecting the exploitation and reinjection of the geothermal well; thirdly, it can provide a diversion channel for the lower geothermal fluid production layer section.

[0031] 3) Three-well section C: The production casing 7 is lowered into the three-well section C, and the production casing 7 is suspended on the upper technical casing 5 by the second hanger 8; the production casing 7 is a combination of ordinary oil casing 9 and screen 10, and the lowering order and combination method are determined according to the results of the electrical logging display at the construction site. In principle, the screen 10 is used in the sandstone layer with a large water production, and the ordinary oil casing 9 is used in the mudstone layer with a small water production; in order to prevent sand plugging of the wellbore, the screen 10 is wrapped with wire mesh technology; the three-well section C can firstly establish a diversion channel for the thermal reservoir fluid to enter the wellbore; secondly, it can protect the wellbore wall of the thermal reservoir section.

[0032] Although the embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A new type of geothermal well completion structure, comprising a first well section A, a second well section B and a third well section C which are connected from top to bottom; characterized in that: The outer layer of the first well section A is provided with a surface casing cementing cement ring (1), and the outer layer of the second well section B is provided with a technical casing cementing cement ring (3); the top of the surface casing cementing cement ring (1) of the first well section A is returned to the ground, and the surface casing (2) is provided inside the cementing cement ring (1) of the first well section A; the top of the technical casing cementing cement ring (3) of the second well section B is returned to the casing shoe (4) of the surface casing (2), and the technical casing (5) is provided inside the technical casing cementing cement ring (3) of the second well section B, and the technical casing (5) is suspended at the bottom of the surface casing (2) through a first hanger (6); the third well section C includes a production casing (7), and the top of the production casing (7) is suspended at the bottom of the technical casing (5) through a second hanger (8).

2. A new geothermal well completion structure according to claim 1, characterized in that: The production casing (7) is a petroleum casing (9) or a screen tube (10) or the petroleum casing (9) and the screen tube (10) are connected in series.

3. A new geothermal well completion structure according to claim 2, characterized in that: The oil casing (9) is used in mudstone layers with low water production, and the screen (10) is used in sandstone layers with high water production.

4. A new geothermal well completion structure according to claim 2 or 3, characterized in that: The outer surface of the screen pipe (10) is treated by a wire-wrapped mesh sand prevention process.

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