A method of gas lift for a shale gas well

Abstract

The present application belongs to the technical field of oil and gas well development, and particularly relates to a shale gas well gas lift method. By adding foam displacement liquid to reduce the gas well liquid density, short annulus gas lift, reducing wellhead back pressure, balancing casing pressure to reduce static column height, and alternating positive and negative lift, the gas lift pressure is significantly reduced to 40-60%, the method can speed up the gas well production progress, improve the gas lift effect, and reduce the production cost. In the process of deep shale gas well lifting, the existing gas lifting equipment can be optimized to realize the gas well lifting, and the success rate of the technology is as high as 80%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas well development, and particularly relates to a shale gas well gas lift lift-through method. BACKGROUND

[0002] Gas lift is one of the effective means for liquid discharge and production recovery of deep shale gas water flooded or channeling gas wells. Through the injection of pressure gas (nitrogen / gas) into the oil / casing of the wellbore, the bottom hole pressure is increased to lift the accumulated liquid in the gas well. When the gas lift reaches the lift-through pressure, the injected pressure gas is lifted to the ground along with the gas and liquid produced by the gas well, thereby achieving the effect of liquid discharge and production recovery of the channeling / water flooded well.

[0003] Currently, the following situations often occur during gas lift liquid discharge:

[0004] The wellbore of the deep shale gas well is greater than 3500m, and the accumulated liquid after water flooding exerts a back pressure of 20-35MPa on the bottom of the gas well, making it difficult to lift and effectively discharge liquid for production recovery. For water flooded and shut-in gas wells, continuous gas lift liquid discharge is required for effective production recovery.

[0005] The existing gas lift equipment is usually of two levels, 30MPa and 50MPa. When a 35MPa gas lift equipment is selected, it cannot achieve the purpose of production recovery of water flooded wells for gas wells with a lift-through pressure higher than 35MPa. When a 50MPa gas lift equipment is selected, the cost is 1.5 times higher than that of a 35MPa equipment, which is not economical and does not meet the long-term liquid discharge requirement.

[0006] In the case of high lift-through pressure, higher level pressure pipelines and other supporting equipment need to be used, which increases the construction cost and cannot be effectively promoted. Moreover, the gas lift equipment has the defect of insufficient running stability, which easily causes equipment damage and results in high equipment maintenance cost.

[0007] Based on the above-mentioned practical problems, the cost of production recovery of deep shale gas water flooded / channelling wells is high. Therefore, how to effectively reduce the gas well lift-through pressure will be conducive to reducing the production recovery cost of deep shale gas water flooded / channelling wells and improving the production recovery efficiency of gas wells.

[0008] The existing gas lift technology mainly reduces the start-up pressure during gas lift by optimizing the pipe string to increase the gas lift valve and closed gas lift, which can reduce the gas lift lift-through pressure to a certain extent. However, for deep shale gas wells with a wellbore depth of more than 3500m, the pressure loss is 30-35MPa, and the downhole temperature is above 130℃. In addition, there is a problem of corrosion in the wellbore due to the return of proppants such as gas well fracturing sand. The adaptability of downhole tools such as gas lift valve and closed gas lift is weak, and the failure of these tools will affect the gas lift effect, resulting in limited effect of the existing technical solutions on reducing the gas lift lift-through pressure, and causing complex downhole conditions and high maintenance cost. SUMMARY

[0009] The present application aims at: aiming at the technical defects of high gas lift lift-through pressure of deep shale gas watered-out well and channeling well, the need for higher gas lift equipment matching, and high cost, providing a method for reducing the gas lift lift-through pressure of deep shale gas well at low cost, aiming at solving the problem of high cost of gas lift re-production of deep shale gas well.

[0010] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0011] A method for reducing the gas lift lift-through pressure of deep shale gas well at low cost, comprising the following steps:

[0012] Step 1, first inject a foaming agent into the tubing and casing of the target gas well, respectively, the foaming agent is used to reduce the accumulation liquid density of the gas well; use ρ 液 to represent the back pressure caused by accumulation liquid, use △P w to represent; observe the gas well energy index, when the shut-in pressure recovery of the gas well energy is greater than 2MPa / d; directly proceed to step 3, if the shut-in pressure recovery of the gas well energy cannot be recovered to 2MPa / d; then proceed to step 2;

[0013] Step 2, before formal gas lift operation, according to the casing pressure, short-time gas lift supplemental pressure is carried out in the tubing-casing annulus, to avoid the reverse extrusion of wellbore accumulation liquid into the formation during gas lift, causing reservoir water lock and reducing the gas well productivity; the time of short-time gas lift is not more than 30min;

[0014] Step 3, air lift operation is carried out, which is used to reduce the wellhead back pressure P yy , during the air lift process, the injection pressure (P 注 ) and the lift-through condition of the gas well are observed; it is judged whether the gas lift pressure value (P 注 ) is higher than the rated pressure of the gas lift equipment (P 额定 ), when the injection pressure is equal to the rated pressure of the gas lift equipment (P 注 =P 额定 ), the gas well has not been lifted through (P 注 P jt ), step 4 is continued;

[0015] Step 4, the oil casing pressure is balanced to reduce the water column liquid level difference △H of the tubing-casing, the purpose is to reduce the wellbore static column back pressure △P w , the gas lift condition of the gas well is continuously observed, when the gas lift pressure value is equal to the highest level of the equipment rated pressure (P 注 =P 额定 ), the gas well has not been lifted through (P 注 P jt ), step 5 is continued;

[0016] Step 5, take the alternating positive and negative air lift way to carry out the excited wellbore liquid level, overcome the self weight and slip loss of liquid column; observe the gas well lifting condition, if the gas well is still not lifted (P 注 <P jt ), return to step 2 operation link repeats N cycles until the gas well is put into production.

[0017] In the technical scheme of the application, an operation method for realizing low-cost deep shale gas well lifting is provided, in which the lifting pressure is reduced by changing the gas well liquid density and the liquid accumulation state, which can effectively reduce the requirement for gas lifting equipment. According to the calculation formula of the gas lifting lifting pressure, the wellhead pressure P yy , the pressure △P w caused by liquid accumulation (i.e. pressure loss) and the reduction of the lifting pressure P jt by changing the wellbore liquid accumulation state through process switching are reduced respectively. According to the above steps in the order, the final lifting pressure P jt can be reduced.

[0018] Preferably, the calculation formula of the gas lifting lifting pressure is as follows:

[0019] P jt =P yy +△P w +P f -P ty ,

[0020] △P w =ρ 液 g△H,

[0021] △H=H y -H t ,

[0022] Wherein, P jt is the gas lifting lifting pressure, P yy is the wellhead pressure, △P w is the pressure caused by liquid accumulation, g is the acceleration of gravity, ρ 液 is the density of the liquid accumulation, △H is the oil casing liquid level difference, H y is the liquid level height in the oil pipe, H t is the liquid level height in the casing, P f is the fluid friction loss, and P ty is the casing pressure.

[0023] Preferably, the selection of the foaming agent is selected by the comprehensive foaming effect between the ground simulation gas well flowback liquid and the foaming agent. The foaming agent with the highest foaming performance, the best foam stability performance and the best use concentration of the foaming agent can further improve the degree of reduction of the gas lifting lifting pressure.

[0024] The foaming agent is a surface active substance which mainly reduces the interfacial tension on the air-water interface, and the molecular structure is composed of lipophilic groups and hydrophilic groups to form so-called "amphiphilic structure" molecules with both hydrophilic and lipophilic properties. When the foaming agent is added to water, the hydrophilic groups are inserted into the water phase, while the lipophilic groups are inserted into the oil phase or stand in the air, forming directional arrangement on the interfacial layer or surface, thereby reducing the interfacial tension or surface tension.

[0025] Further preferably, according to the composition of the gas well fluid, a foaming agent of the type of salt resistance, oil resistance, etc. is preferably selected, and the foaming agent is added in an amount of 0.5% according to the gas well accumulation condition.

[0026] Further preferably, the selection of the foaming agent can be further subjected to compatibility test with other well fluids to avoid the formation of colloid and other precipitates due to incompatibility of the downhole fluid, thereby improving the accumulation density p 液 .

[0027] As a preferred scheme of the present application, in step 2, the pressure of the annular pressure supplement is selected as follows: according to the flow stability and the flow pressure test results, the bottom hole pressure condition and the accumulation condition are determined, and the gas lift pressure should be lower than the bottom hole flow pressure when the annular pressure is supplemented.

[0028] Further preferably, the time of the annular pressure supplement is selected as follows: when the casing pressure is less than or equal to 5 MPa, the short-time gas lift is 1-2 h; when the casing pressure is greater than 5 MPa and less than or equal to 10 MPa, the short-time gas lift is 3-4 h; and when the casing pressure is greater than 10 MPa, the short-time gas lift is not needed.

[0029] As a preferred scheme of the present application, in step 3, the air lift specifically includes the following steps: if the reverse lift is selected, the tubing is connected to the blowout pit process, the casing gas injection valve is opened with the opening degree of the wellhead throttle needle valve being 1 / 4-1 / 2 (adjusted according to the pressure after throttling), and the gas lift is started; if the positive lift is selected, the casing is connected to the blowout pit process, the tubing gas injection valve is opened with the opening degree of the throttle pry throttle needle valve being 1 / 4-1 / 2 (adjusted according to the pressure after throttling), and the gas lift is started.

[0030] As a preferred technical scheme of the present application, in step 4, the balance of the oil casing pressure specifically includes the following steps: if the positive lift is in the external transport process, the casing valve is opened and the oil casing pressure of the wellbore is balanced under the condition that the gas lift equipment is stopped, the casing valve is closed after the pressure balance is indicated by the pressure gauge, and the gas lift is restored; if the reverse lift is in the external transport process, the tubing production gate is opened and the oil casing pressure of the wellbore is balanced under the condition that the gas lift equipment is stopped, the tubing production gate is closed after the pressure balance is indicated by the pressure gauge, and the gas lift is restored.

[0031] As described above, due to the adoption of the above technical scheme, the present application has the following beneficial effects:

[0032] In the technical scheme of the present application, by comprehensively adopting the methods of reducing the gas well liquid loading density by injecting foam, reducing the wellhead back pressure by air lifting, balancing the oil casing pressure to reduce the static liquid column height, etc., the air lifting lift-through pressure is obviously reduced to 40-60%, the method can accelerate the gas well production recovery progress, improve the air lifting effect, and reduce the production recovery cost.

[0033] In the technical scheme of the present application, in the process of lifting the deep shale gas well, the gas well lift-through can be realized by optimizing the operation steps of the existing gas lifting equipment, and the technical method can realize effective gas lifting with a success rate of up to 80% in the face of different factors such as high temperature and high pressure, wellbore corrosion, sand production, etc. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a flow chart of the operation method of the present application. DETAILED DESCRIPTION

[0035] The present application will be described in detail below with reference to the accompanying drawings.

[0036] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0037] Example 1

[0038] A low-cost method for reducing the gas lifting lift-through pressure of a deep shale gas well, comprising the following steps:

[0039] Step 1, before the gas lifting operation, foam agent is injected into the tubing and casing respectively to reduce the gas well liquid loading density and reduce the influence of liquid column back pressure; the gas well energy index is observed, and when the gas well energy shut-in pressure is restored to more than 2MPa / d, step 3 is directly performed, and when the gas well energy shut-in pressure is restored to not more than 2MPa / d, step 2 is performed; specifically, the selection of the foam agent is selected by the comprehensive foaming effect between the ground simulation gas well flowback fluid and the foam agent; the foam agent with high foaming performance, good foam stability performance, and optimal use concentration of the foam agent can further improve the degree of reduction of the gas lifting lift-through pressure; according to the composition of the gas well fluid, the foam agent of the types of salt resistance and oil resistance is preferred, and the foam agent injection amount is injected according to the proportion of 0.5% according to the gas well liquid loading condition;

[0040] Step 2, before formal gas lift operation, according to casing pressure, short time gas lift supplement pressure is carried out to oil casing annulus, to avoid wellbore fluid reverse extrusion into formation during gas lift, causing reservoir water lock, reducing gas well productivity; annulus pressure selection: according to the flow steady flow pressure test results, the bottom hole pressure and fluid accumulation situation is clear, when annulus pressure, gas lift pressure should be lower than the bottom hole flowing pressure.

[0041] Specifically, the time selection of annulus pressure: when casing pressure is less than 5MPa, short time gas lift 1-2h; when casing pressure is greater than 5MPa and less than 10MPa, short time gas lift is 3-4h; when casing pressure is greater than 10MPa, no need to carry out short time gas lift.

[0042] Step 3, air lift operation is carried out, for reducing wellhead back pressure P yy , during air lift, observation of injection pressure (P 注 ), and gas well lift through situation; determine whether the gas lift pressure value (P 注 ) is higher than the rated pressure of gas lift equipment (P 额定 ), when the injection pressure is equal to the rated pressure of gas lift equipment (P 注 =P 额定 ), gas well has not been lifted (P 注 P jt ), continue to step 4; in detail, step 3, the specific air lift includes the following steps: if the reverse lift is selected, the oil pipe is connected to the blowout pool process, the wellhead throttle needle valve opening is 1 / 4-1 / 2, the casing injection valve is opened, and the gas lift is started; if the positive lift is selected, the casing is connected to the blowout pool process, the throttle pry throttle needle valve opening is 1 / 4-1 / 2, the oil pipe injection valve is opened, and the gas lift is started.

[0043] Further, the calculation formula of the gas lift lift pressure is:

[0044] P jt =P yy +△P w +P f -P ty ,

[0045] △P w =ρ 液 g△H,

[0046] △H=H y -H t ,

[0047] Wherein, P jt is the gas lift lift pressure, P yy is the wellhead pressure, △P w is the pressure caused by fluid accumulation, g is the acceleration of gravity, ρ 液is the density of the liquid, ΔH is the casing head differential, H y is the liquid level in the tubing, H t is the liquid level in the casing, P f is the fluid friction loss, P ty is the casing pressure. In this scheme, the gas lift pressure is reduced by changing the density of the liquid and the liquid state of the gas well, which can effectively reduce the requirements for gas lift equipment. According to the calculation formula of the gas lift pressure, the wellhead pressure P yy , the pressure ΔP w caused by the liquid (i.e. pressure loss) and the change of the liquid state in the wellbore by switching the process to reduce the lift pressure P jt are reduced. Among them, according to the order of the above steps, the final lift pressure P jt can be reduced.

[0048] Step 4, the oil casing pressure is balanced to reduce the liquid level difference ΔH of the oil casing, the purpose is to reduce the wellbore static liquid column back pressure ΔP w , continue to observe the gas lift situation of the gas well, when the gas lift pressure value is equal to the highest level of the rated pressure of the equipment (P 注 =P 额定 ), the gas well is still not lifted (P 注 P jt ), continue to step 5;

[0049] Specifically, balancing the oil casing pressure specifically includes the following steps: if it is in a positive lift state and in an external flow process, then in the case of gas lift equipment shutdown, the gas production tree external gate is closed, the casing valve is opened, and the wellbore oil casing pressure is balanced through the oil casing communication pipeline. When the pressure gauge indicates that the pressure is balanced, the casing valve is closed and the gas lift is restored. If it is in a reverse lift state, then in the case of gas lift equipment shutdown, the tubing production gate is opened, the wellbore oil casing pressure is balanced, and when the pressure gauge indicates that the pressure is balanced, the tubing production gate is closed until the gas lift is restored.

[0050] Step 5, the alternating positive and reverse gas lift method is used to agitate the wellbore liquid level to overcome the liquid column weight and slip loss; observe the gas lift situation of the gas well, if the gas well is still not lifted (P 注 P jt ), return to step 2 to repeat the operation link for N cycles until the gas well is put into production.

[0051] Example 2

[0052] The experimental object of this embodiment is gas well #1, and the basic information of gas well #1 is: the vertical depth of the gas well is 3830m, the oil pressure is 2.09MPa, the casing pressure is 18.6MPa, and the water flooding stops production;

[0053] The low-cost reduction of the gas lift lift-through pressure of the gas well #1 specifically includes the following steps:

[0054] Step 1, sampling the water sample of the gas well #1, performing the ground simulation experiment of the gas well flowback fluid and the foaming agent to determine the foaming agent with high foaming performance, good foam stability performance and optimal use concentration, injecting the foaming agent 20 Kg into the tubing and the casing respectively to reduce the gas well shaft liquid density; observing the gas well energy index, the wellhead casing pressure of the gas well #1 is greater than 10 MPa, and the short-time pressure compensation is not needed, and the operation of step 3 is directly performed;

[0055] Step 3, selecting the gas lift equipment pressure as 30 MPa, guiding the gas lift process into the open flow process for gas lift, after the gas lift for 6 hours, the oil pressure is 0 MPa, the casing pressure is 27.4 MPa, which is close to the rated pressure of the gas lift equipment; the lift-through is still not achieved; the operation of step 4 is continuously performed;

[0056] Step 4, balancing the oil casing pressure, after the balancing, the oil / casing pressure is 18.8 MPa, after the gas lift for 6 hours, the oil pressure is 1.5 MPa, the casing pressure is 26.3 MPa, the wellhead has a large amount of flowback fluid, and after the cumulative flowback fluid of 27 cubic meters is discharged, the lift-through and production are restored, the instantaneous liquid production is 93 cubic meters per day, and the instantaneous gas production is 121,000 cubic meters per day;

[0057] Step 5, successfully restoring the production, and guiding the gas well #1 into the production process.

[0058] Example 3

[0059] The experimental object of this example is the gas well #2; the basic information of the gas well #2 is that the gas well vertical depth is 3650 m, the oil pressure is 1.5 MPa, the casing pressure is 4.5 MPa, the gas well cannot produce liquid, and the oil casing pressure difference continuously expands, and the water-out trend is judged;

[0060] The low-cost reduction of the gas lift lift-through pressure of the gas well #2 specifically includes the following steps:

[0061] Step 1, sampling the water sample of the gas well #2, performing the ground simulation experiment of the gas well flowback fluid and the foaming agent to determine the foaming agent with high foaming performance, good foam stability performance and optimal use concentration, injecting the foaming agent 20 Kg into the tubing and the casing respectively to reduce the gas well shaft liquid density; observing the gas well energy index,

[0062] Step 2, because the wellhead casing pressure is less than 5 MPa, the short-time pressure compensation is performed for 2 hours, the oil pressure is 3.6 MPa, and the casing pressure is 7.8 MPa;

[0063] Step 3, selecting the gas lift equipment pressure as 30 MPa, guiding the gas lift process into the open flow process for gas lift (the oil pressure is 0 MPa, and the casing pressure is 6.5 MPa), after the gas lift for 5 hours, the wellhead has a large amount of flowback fluid (the oil pressure is 1.2 MPa, and the casing pressure is 10.5), the instantaneous gas production is 52,000 cubic meters per day, and the instantaneous liquid production is 25 cubic meters per day;

[0064] Step 4, successful production, gas well #2 into the production process.

[0065] Example 4

[0066] The experimental object of this embodiment is gas well #3, and the basic information of gas well #3 is: gas well vertical depth 3710m, oil pressure 1.0MPa, casing pressure 24.6MPa, gas well water flooding shutdown

[0067] Step 1, sampling the gas well #1 water sample, carrying out the ground simulation experiment of gas well flowback fluid and foaming agent to determine the foaming agent with high foaming performance, good foam stability and optimal use concentration of foaming agent, injecting 20kg of foaming agent into the tubing and casing to reduce the density of gas well borehole fluid; observing the energy index of the gas well, the wellhead casing pressure of gas well #1 is greater than 10MPa, which can be directly operated in step 3 without short-term pressure compensation;

[0068] Step 3, selecting the gas lift device pressure as 30MPa, guiding the gas lift process to the open flow process for gas lift, after 6h of gas lift, the oil pressure is 0MPa, the casing pressure is 26.7MPa, which is close to the rated pressure of the gas lift device, and it is still not lifted through; continue to operate step 4;

[0069] Step 4, balance the oil casing pressure, after balancing, the oil / casing pressure is 16.4MPa, after 6h of gas lift, the oil pressure is 0MPa, the casing pressure is 27.4MPa, and the wellhead intermittently returns fluid;

[0070] Step 5, switching the process to alternate positive and negative gas lift, alternating gas lift 2 times, the wellhead oil pressure is 1.2MPa, the casing pressure is 26.5MPa, the wellhead continuously returns fluid, after 1h, the wellhead oil pressure is 12.8MPa, the casing pressure is 19.4MPa, the instantaneous gas production is 98,000m3 / day, the instantaneous liquid production is 158m3 / day, and the cumulative liquid discharge is 40m3; successful production, guide into the production process.

[0071] In the technical scheme of the present application, by comprehensively adopting the methods of injecting foam to reduce the density of gas well fluid, reducing the wellhead back pressure of air lift, balancing the oil casing pressure to reduce the static liquid column height, the gas lift lift-through pressure is obviously reduced to 40-60%, and the method can accelerate the production progress of the gas well, improve the gas lift effect, and reduce the production cost.

[0072] In the technical scheme of the present application, in the process of lifting the deep shale gas well, the gas well can be lifted through by optimizing the operation steps of the existing gas lift device, and the technical method can realize effective gas lift with a success rate of up to 80% in the face of different factors such as high temperature and high pressure, wellbore corrosion and sand production of deep shale gas well.

[0073] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for gas lift and circulation in shale gas wells, characterized in that, Includes the following steps: Step 1: First, inject foaming agent into the tubing and casing of the target gas well. The foaming agent is used to reduce the density of the gas well fluid. Observe the gas well energy index. When the gas well shut-in pressure recovers to more than 2 MPa / d, proceed directly to step 3. If the gas well energy pressure recovery rate is less than 2 MPa / d, proceed to step 2. Step 2: Based on the flow stability and pressure test results, perform a short-term gas lift on the annulus at a pressure lower than the bottom hole pressure to replenish the bottom hole pressure. The annulus pressure replenishment time is selected according to the casing pressure: when the casing pressure ≤ 5MPa, gas lift for 1-2 hours; when 5MPa < casing pressure ≤ 10MPa, gas lift for 3-4 hours; when the casing pressure > 10MPa, skip this step; then proceed to Step 3. Step 3: Perform an air lift operation to reduce the wellhead back pressure. The air lift operation is as follows: if reverse lift is selected, connect the tubing to the blowout pool, adjust the opening of the wellhead throttle needle valve to 1 / 4-1 / 2, open the casing air injection valve, and start the air lift. If forward lift is selected, connect the casing to the blowout pool, adjust the throttle needle valve opening to 1 / 4-1 / 2, open the tubing air injection valve, and start the air lift. During the air lift process, observe the air lift pressure value of the air lift equipment and the lift status of the gas well; determine whether the air injection pressure has reached the rated pressure P of the air lift equipment. 额定 When P 注 = P 额定 If the gas well has not yet been connected, proceed to step 4; Step 4: Reduce the water column height difference in the casing and tubing by balancing the oil and casing pressure, and reduce the back pressure of the common cylinder hydrostatic column. The oil and casing pressure balancing operation is as follows: If the gas lift is in the positive lift state, close the gas tree export valve and open the casing valve when the gas lift equipment is stopped. Balance the wellbore oil and casing pressure through the oil and casing connection pipeline. After the pressure is balanced, close the casing valve and resume gas lift. If in reverse lift mode, with the gas lift equipment shut down, open the tubing production valve to balance the wellbore and casing pressure. After pressure balance, close the tubing production valve to resume gas lift; when P 注 Reaching P again 额定 If the gas well is still not operational, proceed to step 5. Step 5: Use alternating forward and reverse gas lift methods to stimulate the liquid level in the cylinder, overcoming the weight of the liquid column and slippage losses; observe the gas well lifting status. If the gas well is still not lifted, return to the operation step 2 and repeat N cycles until the gas well resumes production.

2. The shale gas well gas lift and circulation method according to claim 1, characterized in that, The foaming agent was selected based on the foaming effect between the simulated gas and the return liquid on the ground, with the foaming agent exhibiting the best effect being selected.

3. The shale gas well gas lift and circulation method according to claim 2, characterized in that, The foaming agent includes salt-resistant and oil-resistant foaming agents.

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