Daqing Oilfield Cable Controlled Intelligent Separate Injection Technology Process Optimization

The cable controlled intelligent separate injection process realizes the continuous monitoring and real-time measurement and adjustment of downhole parameters, greatly improves the measurement and adjustment efficiency, provides sufficient data for reservoir analysis, and helps to tap the potential of remaining oil in the later stage of ultra-high water cut. However, due to the multi-disciplinary application of downhole tools and complex process, it is found in the previous field test that The number of wells with more than two years of operation of cable controlled intelligent separate injection wells accounts for only 51.9%, which can not meet the needs of large-scale application. Through the fault analysis of the early test well, the key factors affecting the success rate of well completion are found. Aiming at the main problems, the flow control valve of the cable controlled intelligent water distributor, the cable sealing connection process and the well flushing valve structure through the cable packer are optimized and improved. The flow control valve of cable controlled intelligent water distributor is opened and closed smoothly under 10MPa pressure difference, and the leakage is less than 1m³/d; The connection between the cable and the cable controlled intelligent water distributor is sealed reliably, and the cable can pass through the upper and lower joints of the cable packer smoothly; Since the optimization of process technology until January 2023, 223 wells have been tested on site, and the number of wells with more than two years of operation has increased from 56.1% to 91.9%. The stability of the optimized cable controlled intelligent separate injection process has been improved, which lays a foundation for the large-scale application of this technology in the oilfield.


Introduction
With the number of subdivided wells and subdivided intervals increasing year by year, the contradiction between the large test workload and the limited test team is increasingly prominent.At the same time, in order to provide continuous and detailed data for the detailed reservoir description, Daqing Oilfield has started the exploratory research of intelligent layered water injection technology since the beginning of this century, mainly including non-contact intelligent injection separation, wave-code communication injection separation, ground intelligent injection separation, and cable-controlled intelligent injection separation, Solved the problems existing in conventional separate injection technology, and realized long-term real-time control of fine, effective and intelligent separate injection [1-8].Among them, the cable-controlled intelligent injection separation process has advantages in terms of technical maturity, testing and adjustment efficiency, testing accuracy, and scope of application.It has realized continuous monitoring and real-time testing and adjustment of downhole parameters, and the efficiency of testing and adjustment has been greatly improved, which is conducive to tapping the potential of remaining oil in the later stage of ultra-high water cut; However, because downhole tools involve multi-system combination and multidisciplinary application such as parameter acquisition system, power management system, communication system and automatic control system, and well completion operation involves cable connection and protection, the process is complex [9][10][11][12], the reliability is relatively low, and the process cost is high.From 2012 to the end of 2017, 54 wells have been tested on site, and the number of wells operated for more than 2 years accounts for only 51.9%,The process stability and reliability can not meet the needs of large-scale application.
Through the analysis of 26 fault wells, it can be seen that: (1) the main causes of the fault are the sealing failure of the connection between the cable and the intelligent water distributor, the failure of the flow control valve, and the failure of the well flushing valve through the cable packer; Among them, there are 12 wells with sealing failure at the connection between cable and intelligent water distributor, accounting for 46.2%; 7 wells with flow control valve failure, accounting for 26.9%;Four wells failed to wash well with cable packer, accounting for 15.4%;Other factors, accounting for 11.5%; (2) The time of failure is mainly concentrated in the first 6 months after the well is down; The number of failed wells in the first six months was 23, accounting for 88.5% of the total number of failed wells; From the 7th month to the 24th month, the number of wells with faults was 3, accounting for 11.5% of the total number of wells with faults.In order to further improve the cable-controlled layered water injection process technology, the flow control valve, cable packer and other tools of the cable-controlled intelligent water distributor have been optimized, the connection seal between the cable and the cable-controlled intelligent water distributor has been improved, the service life of the tool has been extended, and the reliability of the cable-controlled intelligent water injection process has been improved.

.Optimization of Flow Control Valve of Intelligent Water Distributor
The flow control valve is the actuator of the intelligent water distributor to adjust the injection volume, and is the key component to ensure the qualified rate of water injection.The preliminary test found that the main problems of the flow control valve are: (1) the injected water contains impurities and large particles, and the flow control valve is easy to block; (2) Reverse tripping occurs after the flow control valve is fully opened or fully closed; (3) When the pressure difference between the front and rear is more than 3 MPa, the transmission shaft is easy to break.
For this reason, the flow control valve is optimized as follows: (1) The outer diameter of the ceramic valve core of the flow control valve is expanded from Ø 10 mm to Ø 14 mm, which increases the maximum flow area of the valve body and reduces the blocking probability of the flow control valve; (2) The balance hole is designed at the rear end of the ceramic valve core of the flow control valve to realize the pressure balance at the front and rear ends of the ceramic valve core, reduce the resistance caused by the pressure difference during the switching process, and prevent the flow control valve from not moving.(3) Stress analysis was carried out on the connecting shaft, and the size of the transmission shaft was optimized.After the inner diameter of the valve core increased from Ø 3 mm to Ø 5 mm, the connecting thread of the transmission shaft was adjusted from M2 to M4, which improved the tensile and shear strength.The optimized flow control valve structure is shown in Figure 1.

.Optimization of Cable Connection Process
A section of cable is reserved at both ends of the original cable-controlled intelligent water distributor.During site construction, the cable connector is used to connect the reserved cable with the cable on the pipe column.The cables reserved outside the water distributor may be damaged during storage and transportation; During site construction, two sections of cables need to be sealed with cable connectors.For example, 9 cable connectors need to be used as cable sealing joints in the section well of 5 layers, which increases the process cost and risks sealing failure.Any seal failure will lead to the failure of the whole process.For this reason, the connection mode of the intelligent water distributor and the cable is optimized and optimized: (1) The design of the reserved cable outside the water distributor is canceled, and the wiring base is designed outside the water distributor.During site construction, the cable is directly locked on the wiring base, avoiding the risk of cable damage outside the water distributor; (2) Swagelok type cable connector is designed with rubber cap, and the outer armor and insulation layer of the cable are sealed at the same time to realize double protection.The optimized cable connection process is shown in Figure 2.

Optimization of Cable Packer
During the construction of the cable-controlled intelligent injection separation process, a cable channel is reserved through the inner liner of the cable packer, and the cable passes through the multi-stage packer without occupying the main channel, so as to avoid affecting the water injection profile and other test processes [13-15].The early test found that the problems of the wireline packer include: (1) when the well flushing pressure is high or the injection is stopped, the well flushing valve will automatically open, and when the water injection condition is restored, the well flushing valve will not automatically close, resulting in the connection between the upper and lower layers, and the packer seal failure; (2) For the complex process string, such as the string between the two packers with bare pipes, in order to reduce the use of cable connectors, it is the best choice to pass the cable through the packer, which requires that the cable packer can pass through the cable from both the upper connector and the lower connector.For this reason, the following optimization design is carried out for the cable packer.
(1) The well flushing valve structure is optimized.The well flushing valve is a device used to control the opening or closing of the well flushing channel.The original well flushing valve is an integral structure, and the optimized well flushing valve is a split structure.The well flushing channel can be opened only when the two structures act simultaneously.When the upper casing pressure is higher than the lower casing pressure, two parts of the valve act together to open the well flushing channel; When the lower casing pressure is higher than the upper casing pressure, only the upper half of the split structure acts, the lower half remains in the closed position, and the well flushing channel remains closed, thus avoiding the failure of the first stage packer caused by the high formation pressure when the injection is stopped.
The cable crossing mode is optimized.In order to make the cable pass through the packer, it is necessary to design the cable channel on the packer, which is composed of the guide channel on the upper and lower joints of the packer and the channel body on the inner liner.In the original design, the cable can only pass through the packer from the upper end to the lower end.When there is a plugging layer in the construction design, there will be no water distributor in the two-stage packer and only ordinary oil pipe.It is required that the upper and lower ends of the packer can pass through the cable.Therefore, by reducing the angle of the guide channel, adding a 15 ° chamfer at the end of the guide channel, expanding the design of the main diameter of the cable channel, and optimizing the size structure of each component (as shown in Figure 3), the cable can not only pass through the packer from the upper end to the lower end of the packer, but also pass through the packer from the lower end to the upper end of the packer, thus improving the adaptability of the packer to the intelligent water distributor and the pipe string.

.Field Application
From December 2018 to April 2022, 223 wells were tested in the field with the optimized cable-controlled intelligent injection separation process.According to the statistics of the field construction and test and adjustment test records, the number of wells operating for more than two years increased from 56.1% to 91.9%.The average operation time of 59 wells put into production in the early stage is 1150 days; The 164 wells put into production in the later stage have an average operation time of 749 days.Compared with that before optimization, the process reliability and tool service life have been greatly improved.At present, the technology is being further popularized and applied.

.Performance Analysis After Optimization
The 223 wells tested in the field have a total of more than 900 layers.During the survey and adjustment, the flow control valve of the cable-controlled intelligent water distributor did not break the shaft.After optimization, the connecting shaft strength and motor torque of the flow control valve can meet the requirements of downhole working conditions.
Up to now, the average operation time of the cable-controlled intelligent water distributor in more than 900 layers has reached 855 days.According to the analysis of the relationship between the number of failed wells and the operation time, this data will be further increased, which is 42.5% higher than the 600 days before optimization.
During the construction process, when the cable passes through the packer, it can go out from the upper joint to the lower joint, or from the lower joint to the upper head.The optimized cable packer can meet the requirements of complex process string construction; At the same time, the well flushing valve does not open when the injection is stopped or the downpressure is high, and there is no overflow at the wellhead after setting.The design of the split structure of the well flushing valve is effective in solving the problem that the well flushing valve does not automatically return.

Application Effect Analysis
After optimization, the wireline controlled intelligent separate injection process is stable, the downhole equipment operates normally, and the qualified rate of water injection is maintained at more than 90% for a long time.Through the precise control of water injection in the high permeability layer, the oil production of the connected oil wells is basically unchanged, the water cut rise rate and the natural decline rate are effectively controlled, and the low degree of production in the thin and poor layers is improved.The water absorption thickness of the sandstone is increased by 4.3 percentage points, and the water absorption thickness of the off-surface reservoir is increased by 5.8 percentage points, The cumulative oil increase is 40300 tons.See Table 2 for the change data of oil reservoir water absorption in the field test block.

Conclusion and Prospect
(1) By optimizing the supporting tools such as the cable-controlled intelligent water distributor and the over-cable packer, the connection process between the cable and the cable-controlled intelligent water distributor is optimized.The service life of the tool is increased from 600 days before optimization to 855 days, which improves the reliability of the cable-controlled intelligent injection process and provides a solution for solving such problems.
(2) The improvement of the reliability of wireline controlled intelligent injection separation technology will lay the foundation for the construction of the next 2000 well scale pilot area, help to tap the potential of remaining oil in the later stage of ultra-high water cut, guide block development, and improve the development effect and efficiency.
(3) In order to further improve the process reliability, it is recommended to carry out the analysis of the acid and alkali resistance of the steel body and internal sealing components of the cable-controlled intelligent water distributor, and develop the cable-controlled water distributor that can be applied within a certain pH value of 6~8 to improve the process adaptability.

Figure 1
Figure 1 Structure of flow control valve After optimization, the flow control valve has realized continuous adjustable nozzle opening equivalent of 0~Ø 14 mm, torque of 8 N • m, and leakage under 10 MPa pressure difference of less than 1 m ³ / D. The flow control valve can be opened and closed smoothly under the differential pressure.During the operation of the flow control valve, the operating current of the motor is always lower than the protection current (150 mA).The test data of flow control valve is shown inTable 1. Table1.Data of flow control valve test

Figure 3 .
Figure 3. Structure diagram of improved cable packer

Table 1 .
Table1.Data of flow control valve test