Some blocks of Tahe Oilfield are typical heavy oil reservoirs, which have the characteristics of high density, high viscosity and poor fluidity. According to statistics, the viscosity of ground crude oil is as high as 18×104 mPa·s ( 60 °C ). The key to heavy oil recovery is to reduce the viscosity of crude oil and improve the fluidity of crude oil. Most of the Tahe work area adopts the mining method of mixing and reducing viscosity.
    Plata condensed light into the production tubing in the well completion string and the tubing string with a packer combination. Because there is no packer in the light pipe column, the doping operation can be directly carried out at the bell mouth; for the packer column, the packer separates the ring space up and down. In order to meet the requirements of the thinning production, it needs to be sealed. The upper part of the spacer is designed with a thin sliding sleeve to ensure the smooth passage of the diluted passage. The conventional sliding sleeve is mainly composed of an outer cylinder, a mandrel (including a seal), a ball seat (including a reduced diameter mechanism), and two flow passages ( A channel and B channel). Among them, the A channel is a valve hole that connects the oil pipe and the annulus; the B channel is the inner channel of the sliding sleeve, as shown in Fig. 1 .
Figure 1 blended sliding sleeve structure
    When entering the well, the A flow path is blocked by the sealing mechanism on the mandrel, and the B flow path is unblocked, and the well washing and the slurry can be performed. When the product is to be tested for production, it is necessary to pitch the ball to open the A- flow channel, and put the ball of the corresponding size from the oil pipe to pressurize the oil pipe, push the mandrel down, expose the A channel, and connect the oil pipe to the annulus to perform the thinning operation. After that, the oil pipe is pressed until the ball seat is knocked off, so that the B flow path is re-opened, and the heavy oil flows into the A flow path to mix with the thin oil to achieve the purpose of reducing the viscosity of the crude oil.
    For heavy oil wells with relatively serious losses, considering the safety of well control, it is usually stopped to directly test and seek production. On the one hand, the test string needs to meet the requirements of the dilution; on the other hand, if the test effect is not good, the acid pressure transformation is also required, and the test string also needs to meet the acid pressure requirement. The conventional sliding sleeve has a diameter reducing mechanism, which has a certain influence on the transformation effect. In order to overcome this deficiency and meet the requirements of the rarex production and the possible acid pressure construction in the later stage, the annulus pressure control valve has been developed and achieved good results. Apply the effect.
1 annulus pressure control valve
1.1 Structural design
    The structure of the annulus pressure control valve is shown in Figure 2. It consists of an upper joint, an O -ring, a valve hole, a shear pin, an outer sleeve, a self-locking mechanism, a movable valve body and a lower joint.
1— upper joint; 2—O -shaped seal ring; 3— valve hole; 4— shear pin;
5— movable valve body; 6— outer sleeve; 7— self-locking mechanism; 8— lower joint
Figure 2 annular pressure control valve structure
1.2 Working principle
    When the annulus pressure control valve enters the well, the valve hole is closed, and the oil pipe and the annulus are not connected at this time. When the lost well needs to be used for the slurry or the acid pressure well needs to be diluted, the valve hole of the control valve needs to be opened, and the pressure is applied from the annulus. The pressure acts on the bearing end face of the movable valve body, and the pressure end face The pressure can be transmitted to the shear pin. When the pressure received by the pressure receiving end exceeds the shearing force of the shear pin, the shear pin breaks off, the annular pressure pushes the movable valve body downward, and the valve hole gradually emerges. . The outer surface of the movable valve body and the inner surface of the self-locking mechanism have ratchet teeth. When the movable valve body moves downward to the surface ratchet and the ratchet teeth of the self-locking mechanism engage with each other, the valve hole is completely opened; The function of the lock structure keeps the movable valve body fixed, and the oil pipe and the annular flow passage are formed.
1.3 technical characteristics
1 ) The ratchet bite firmly
    The outer surface of the movable valve body is inclined upward, and the inner surface of the self-locking structure is inclined downward, and the two are closely engaged, and the movable valve body can be effectively fixed.
2 ) Flexible design of cutting pin
    Specifically, according to the lower depth of the annulus pressure control valve, the density of the killing mud and the setting requirements of the packer, a suitable number of pins can be selected to meet the construction requirements.
1.4 main technical parameters
    The common annulus pressure control valve commonly used in Tahe Oilfield has a large outer diameter of Φ127mm , a small inner diameter of zui is Φ61mm , a total length of 0.78m , a working temperature of 150 °C , and an inner diameter of the casing is Φ152 to Φ168mm .
1.5 Scope of application
    The annulus pressure control valve has the characteristics of annulus pressure control and large internal diameter. Combined with the actual working conditions of Tahe Oilfield, it can be used in the following operations:
1 ) Killing operation
    Similar to the common killing slip sleeve, firstly, when the well string is inserted into the well and the well repair operation is carried out later, if the wellbore is blocked and the circulation cannot be established, the annular hole can be opened to open the valve hole and establish the killing circulation passage.
2 ) Heavy oil blending
    At present, Tahe Oilfield has applied it to the dilute operation. After the valve opening of the control valve is opened, the mixing of heavy oil and thin oil can be realized, thereby achieving the purpose of viscosity reduction.
2 field application
TH245CH Tahe oilfield well is a heavy body region sidetrack wells, using four open well structure. In order to achieve the purpose of avoiding water, the sidetracking point is raised, the three-in-one expansion pipe is used for cementing and completion, and the four- hole Φ120.65mm drill bit is used for open- hole completion. The well needs to be evaluated by stratification, and the test needs to be diluted. In order to meet the needs of both acid pressure and doping, the packer and the annulus pressure control valve are lowered into the column.
2.1 column structure
    The well acid pressure completion string combination is: oil pipe + annulus pressure control valve + casing packer + oil pipe + hydraulic anchor + naked eye packer + ball seat + screen tube + round head blind block shoes, including Both the tube packer and the open-hole packer are hydraulic packers that require a ball; a pressurized set. As shown in Figure 3 .
Figure 3 TH245CH well structure
    The open-hole packer is used to seal the upper open-eye section, so that the fracturing fluid only acts on the lower reservoir section; the hydraulic anchor mainly plays the role of anchoring, protecting the open-hole packer and the oil pipe during acid pressure construction; Used in conjunction with the round head blind block shoes to catch the lost ball seat and avoid falling objects; the function of the casing packer is to protect the lower expansion pipe when the annular space is pressurized to open the annulus pressure control valve. .
2.2 Construction steps
1 ) In order to smoothly enter the completion string, the wellbore treatment such as scraping, through-pass and simulated well is carried out.
2 ) Dismantle the well, enter the acid pressure completion string, and install the oil tree.
3 ) Replacing the slurry, washing the well, setting the packer, and sealing the seal: after connecting the pressurized pipeline, the column is positively pressurized, and the pressure is gradually increased by 5.0 , 8.0 , 11.0 , 14.0 , 17.0 , 20.0 MPa , each after 3min relief regulator to 0, step by step is repeated again once the positive pressure, the relief remains after stabilizing for 3min to 0, openhole packer and packer sleeve completely packer; annulus pressure after 15.0 MPa , no pressure drop for 15min , the seal is qualified, the pressure is reduced to 5.0MPa ; then the positive pressure is reduced from 0 to 22.0MPa to 19MPa , indicating that the seat is being shot down. At this time, the annular pressure control valve is still at Disabled.
4 ) Acid pressure construction: pump pressure 17.4 ~ 93.1MPa , sleeve pressure 4.7 ~ 19.2MPa , displacement 0.5 ~ 5.9m3 / min ; total injection liquid 655m3 , squeezed into the formation total liquid volume 625m3 ; stop pump 20min pressure drop, The pump pressure was reduced from 17.4MPa to 17.0MPa . During the acid pressure construction, the packer was well sealed and effectively protected the annulus.
5) Test, seeking yield: Ground testing process performed after heavy See, first n-doped squeeze a light oil volume into the well tubing, the formation of heavy squeeze back, after opening the control valve annulus pressure: sequentially adding the annulus Pressure 3.8 , 32.0 , 18.0 , 3.8MPa , the pressure drop shows that the control valve is open, and then the dilution production can be carried out.
2.3 Working condition analysis
1 ) The inner diameter of the annular pressure control valve is 61mm , which is almost the same as the inner diameter of the Φ73.0mm (inch) tubing ( 62mm ), which realizes the large diameter of the column; the high displacement of Zui and the large displacement of Zui are 93.1MPa and 5.9m3 respectively. /min is conducive to acid pressure construction.
2 ) After the packer is set, the annular pressure is 15MPa , and the valve opening pressure of the annular pressure control valve is 32MPa . The pressure difference is large, which is beneficial to the field operation, packer and control valve. The pressure settings do not interfere with each other and can work normally.
3 conclusions
1 ) There is a significant diameter reduction mechanism inside the conventional sliding sleeve, which imposes certain restrictions on the pump pressure and displacement of the acid pressure construction, which affects the effect of reservoir transformation.
2 ) The annulus pressure control valve adopts the method of annular pressure to save the time of pitching, waiting for the ball, etc., avoiding the problem that the sealing is not strict due to the midway opening caused by the misplacement of the steel ball or the multiple presses of the ball seat. It can replace the killing well or the mixing slip sleeve for the killing of the Tahe oilfield or the thick oil mixing operation.
3 ) The successful application of the annulus pressure control valve in the TH245CH well indicates that the control valve has reliable performance and can meet the requirements of acid pressure and dilute operation of the Tahe heavy oil well.
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