книги / Разработка нефтяных и газовых месторождений

Developing and wide range testing of new types of equipment makes it possible to solve efficiently old problems. Thus, OOO Universal-Service has put forward an idea of applying a MKS Mobile Test Complex for flow-after-flow testing of wells equipped with electric centrifugal pumps, and now it is widely used for selecting optimal operation conditions for electric centrifugal pumps and well development. Availability of current frequency converter in MKS Mobile Test Complex makes it possible to control submersible electric motor current frequency within wide range. And, as a result, submersible electric pump performance and well operation conditions under various drives have been improved. MKS Mobile Test Complex has been used for flow-after-flow testing in the OOO LUKOIL-PERM fields since 2006.

The accumulated experience shows that application of MKS Mobile Test Complex gives an opportunity:

•to perform flow-after-flow test of electric centrifugal pumping wells;

•to determine productivity factor changing for wells and development targets within the range when bottomhole pressure is lower than bubble point pressure; and

•to develop wells non-damaging after applying enhanced oil recovery or well work over, especially after reservoir fracturing; and

•to select optimal well operation conditions.

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Course of lectures in

PRACTICAL EXERCISES

Practical Exercise 1. Acid Formation Treatment Simulation at Well Workover Simulator (Electronic Trainer)

1. Acid Formation Treatment. General Information

Primary and secondary drilling-in under well construction and operation can adversely affect deliverability in the bottomhole formation zones. The lower rock permeability in the bottomhole formation zones, the lower fluid (oil) influx and injectivity capacity of injection wells. To maintain the given oil well flow rates under such conditions, it is necessary to reduce bottomhole pressure, but it can cause various problems in well operation and inefficient (unnecessary) use of reservoir energy for oil influx.

To restore and increase deliverability in the bottomhole formation zones, acid formation treatment is applied. For carbonate reservoirs, hydrochloric acid treatment of formation has received wide recognition. 10–20 % hydrochloric acid (HCl) aqueous solution is injected and squeezed to formation. Acid dissolves carbonate rock and particles which mud porous channels, and, as a result, reservoir permeability in the bottomhole formation zone becomes higher.

Acid solution consumption rate ranges from 0.5 up to 1.5…2.0 m3 per 1 m of net oil thickness.

2. Simulator Operations. Scope

When operating at the trainer-simulator, the acid solution formation treatment is simulated in visualization and animation mode. Operator (trainee) performs actions which provide the correct sequence of the simulated process under potential emergency conditions (acid solution absorption or backflow due to bottomhole pressure drop).

Simulation operations should be as follows:

a)Determine acid solution volume and density (i.e. HCl concentration in solution);

b)Make-up acid solution of the given density;

c)Determine bottomhole pressure for acid solution injection into borehole and reservoir;

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d)Inject the given volume of acid solution into borehole;

e)Determine density displacement fluid;

f)Inject (if necessary) displacement fluid into borehole for bringing acid solution to bottomhole; and

g)Squeeze (inject) acid solution until it is completely displaced from well.

3.Operator (Trainee) Control Panel Operations

3.1. Initial (Startup) Operations:

At the Flow Head Equipment Console:

•Close the plug valve 3 (top left);

•Close the plug valve 4 (top right);

•Close the plug valve 5 (bottom left); and

•Close the plug valve 6 (bottom right). At the Fracturing Treatment Console:

•Open the plug valve 1 or the plug valve 2;

•Stop the pumping unit motor;

•Stop the mixer (СМ) motor;

•Stop the service pump;

•Number of the pumping units –1;

•Density of acid solution in the acid mixer is 0.9 g/cm3 (solution density set

before «Start» dictates the solution density in well).

Press «Start». If the initial settings are incorrect, no Start is performed and initial settings error is recorded.

Select the volume and density of acid solution to be injected.

3.2. Stage I: Injection the required volume of acid solution into borehole by direct circulation

•Set the T-valve to position Tank 1 or 2. Select the density of acid solution at the Fracturing Treatment console, start the service pump and acid solution preparation unit (КСА) drive, and wait until the acid solution preparation process is completed. The inlet density of acid solution shall become equal to acid density in the acid preparation unit (in our case, the mixer acts as acid preparation unit (КСА);

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•At the Flow Head Equipment console (ПУА), open the plug valves 3 or 4, and 5 or 6, start the pumping unit motor and set the speed other than neutral, and motor shaft revolutions;

•Set the required bottomhole pressure by changing the speed and motor shaft revolutions, and inject the calculated volume of acid;

•When the required volume of acid is injected, stop the pumping unit motor, service pump and acid solution preparation unit (КСА), close the plug valves 3, 4, 5 and 6 at the Flow Head Equipment console.

The first stage is completed.

3.3.Stage II: Acid solution squeeze to the annulus space with displacement mud.

•If the calculated acid volume is less than the total volume of tubing string and annulus space from the shoe to the top of pay, the borehole is pumped down with displacement mud to displace acid from the tubing string to the annulus space so that it fills the annulus space from the shoe to the top of pay;

•For this purpose, it is necessary to select the density of displacement mud at the Fracturing Treatment Console, start the service pump and wait until displacement mud preparation process is completed; the inlet density of displacement mud shall become equal to the density in the mixer;

•At the Flow Head Equipment Console, open the plug valves 3 or 4, and 5 or 6, start the pumping unit motor and set the speed other than neutral, and motor shaft revolutions;

•Set the required bottomhole pressure by changing the speed and motor shaft revolutions, and inject the required volume of displacement mud so that acid fills the borehole from the shoe to the top of pay;

•When the required volume of acid is injected, stop the pumping unit motor and service pump, close the plug valves 3, 4, 5 and 6 at the Flow Head Equipment

console.

The second stage is completed.

3.4.Stage III: Acid solution squeeze to the reservoir

•If the acid volume injected at the I stage filled the entire tubing string and borehole from the shoe to the top of pay, and such volume is still less than the

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calculated acid volume, it is necessary to squeeze acid to the reservoir by further acid injection until sufficient amount of acid solution is in borehole. For this purpose, without changing density setting at the Fracturing Treatment Console, open the plug valve 3 or 4, start the service pump and pumping unit motor, set the 1st speed and motor shaft revolutions. When the calculated volume is injected, stop the pumping unit drive and service pump, and close the plug valves 3 and 4;

•If the acid volume injected at the I stage filled the entire tubing string and borehole from the shoe to the top of pay, and such volume is equal to the calculated acid volume, acid should be further squeezed to the reservoir with displacement mud. For this purpose, select the density of displacement mud at the Flow Head Equipment Console, start the service pump and wait until the displacement mud preparation process is completed. The inlet density of displacement mud shall become equal to the density of displacement mud in the mixer. At the Flow Head Equipment Console, open the plug valve 3 or 4, start the pumping unit motor, set the 1st speed and motor shaft revolutions. If acid was squeezed with displacement mud at the previous (second) stage from the tubing string to the borehole to the top of pay, it should be squeezed to the reservoir with the same displacement mud. For this purpose, open the plug valve 3 or 4 at the Flow Head Equipment Console, start the pumping unit motor, set the 1st speed and motor shaft revolutions;

•Squeeze acid to the reservoir until complete displacement from the tubing string and borehole, and from the annulus space to the reservoir by changing the motor speed for setting bottomhole pressure. Stop the pumping unit motor and close the plug valve 3 or 4 at the Flow Head Equipment Console.

The acid treatment is completed. Well should be hold for some time for acid and rock interaction.

3.5. Control and Identification of Emergencies

In operating the WELL WORKOVER SIMULATOR for acid treatment simulation, erroneous actions of operator (trainee) are possible, and they could cause equipment or well failures. The WELL WORKOVER SIMULATOR response to such wrong actions is as follows:

• Error Alarm – red light in the top left corner of display;

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•If error changes the process parameters, such parameters are reflected in the on-line information forms;

•Error and time penalty are recorded in the log (task execution history) of trainee.

The list of possible operating errors, description of response to such operating errors and error correction ways, unless they cause irreversible effects (for the Well Workover Simulator conditions), are given below. For acid solution and displacement mud injection, it is recommended to maintain bottomhole pressure within the range: Рr < Рbh < Рlpp,

where Рr is reservoir pressure, MPa; Рbh is bottomhole pressure, MPa; and Рlpp is loss point pressure, MPa. Failure to maintain such pressure range will cause emergencies..

Emergency «MUD-LOSS» at Рbh > Рlpp. In case of such emergency, arrows in the bottomhole zone animation show penetration of mud into the reservoir. For response it is necessary to reduce bottomhole pressure by flow rate control.

Emergency «INGRESS» at Рbh < Рr. In case of such emergency, arrows in the bottomhole zone animation show fluid ingress from the reservoir to borehole. For response it is necessary to increase bottomhole pressure by flow rate control.

Emergency «OUTLET PLUG VALVE IS OPEN».

If, in the course of displacement mud injection, the bottom of displacement mud reaches the end of the tubing string, and acid squeezing to the reservoir is not yet commenced, or during acid squeezing the plug valve 5 or 6 was opened, emergency occurs. For response it is necessary to close the plug valves 5 and 6.

Emergency «PUMPING UNIT OVERLOADED»

If, in the course of pumping unit operation, pump inlet pressure at the given speed exceeds the maximum allowable pressure for such speed (to be specified in the simulation procedure), the pumping unit is overloaded. At that, pump pressure is set equal to the maximum allowable pressure at the given speed, and flow rate at inlet is set to zero. For simulating the pumping unit repair, it is necessary to stop the pumping unit motor and then restart it.

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Emergency «PUMPING UNIT INTERLOCKED» – if in the course of pumping unit operation, the T-valve is set to position «Tank 0» (closed). For response it is necessary to open the T-valve.

FATAL EMERGENCIES.

If, in the course of simulation, the system does not response to control, it means that fatal emergency occurred, and it has no sense to go on operation. In such case it is recommended to quit. The system identifies the following emergencies: «Reservoir Fracturing» and «Parted Final Casing String».

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