Method for determining the time of plugging removal in the near wellbore zone of a polymer injection well

Abstract

The application discloses a method for determining the deblocking time of the near-well zone of a polymer injection well. The method comprises the following steps: S1, injecting a polymer solution into the polymer injection well; S2, measuring the injection pressure, and obtaining a relationship curve between the injection amount and the injection pressure according to the injection amount and the injection pressure of the polymer solution; and S3, determining the deblocking time according to the relationship curve: when the injection pressure is stable and then obviously decreases without a relieving trend, the deblocking time of the polymer injection well is determined. Based on the research on the solution percolation of a polymer flooding system in the near-well zone, the dynamic adsorption law of the polymer on the surface of rock minerals is determined, the dynamic adsorption has a process from quantity change to quality change, and the inflection point of the quality change is related to the formation of the near-well zone blockage, so the discrimination of the inflection point constitutes the selection of the deblocking measure time, and the application is formed.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of determination method of polymer injection well near wellbore zone unblocking opportunity, belong to oilfield development stimulation injection technology field. BACKGROUND

[0002] Polymer flooding enhanced oil recovery technology is one of the important technologies of oilfield production and stable oil control water, and has obtained huge technical and economic benefits for oilfield development.In the implementation process of polymer flooding technology, with the extension of injection time, the continuous increase of polymer injection amount, the polymer is dissolved degree and adheres or adsorbs on the wellbore wall and the surface of formation rock, thereby forming a blockage in the wellbore and near wellbore zone flow channel, and then leading to the rapid increase of injection pressure (this process is similar to the process of thrombosis in patients with high blood pressure), even part of the injection polymer well bottom hole pressure approaches the formation fracture pressure, and cannot meet the injection requirement, which affects the normal production of oilfield, and therefore there are many methods of simulating polymer plugging near wellbore zone and unblocking method, and all these methods are based on the understanding of near wellbore zone percolation process.Although there are many unblocking techniques and methods for injection polymer well, there is no relevant report on when to unblock the injection polymer well.Therefore, it is necessary to provide a determination method of unblocking opportunity. SUMMARY

[0003] The purpose of the present application is to provide a determination method of polymer injection well near wellbore zone unblocking opportunity, and timely unblock the injection polymer well.

[0004] The determination method of polymer injection well near wellbore zone unblocking opportunity provided by the present application comprises the following steps:

[0005] S1, injecting polymer solution into the injection polymer well;

[0006] S2, measuring the injection pressure, and obtaining the relationship curve between the injection amount and the injection pressure according to the injection amount of the polymer solution and the injection pressure;

[0007] S3, determining the unblocking opportunity according to the relationship curve: when the injection pressure is stable and then significantly decreases without relief trend, it is the unblocking opportunity of the injection polymer well.

[0008] In the above determination method, the concentration of the polymer solution is 500-5000 mg / L;

[0009] The polymer used is acrylamide polymer.

[0010] In the above determination method, the injection amount of the polymer solution is more than 1000 PV.

[0011] In the above determination method, the injection rate is 0.3-100 ml / min.

[0012] In the above determination method, "significant decrease" refers to a decrease of more than 10%.

[0013] This invention is based on the study of polymer-based oil displacement systems in near-wellbore solution flow, which determined the dynamic adsorption law of polymers on rock and mineral surfaces. This adsorption dynamic involves a process of quantitative change leading to qualitative change, and the inflection point of qualitative change is precisely related to the formation of near-wellbore blockage. Therefore, the determination of this inflection point also constitutes the selection of the timing of unblocking measures, thus forming this invention. Attached Figure Description

[0014] Figure 1 This is the data curve of the indoor acrylamide polymer injection experiment in Example 1 of the present invention.

[0015] Figure 2 This is the actual production data curve of an oilfield during the injection of acrylamide polymer in Example 2 of the present invention. Detailed Implementation

[0016] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0017] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0018] Example 1

[0019] A conventional chemical flooding physical simulation displacement device was used, employing a core sample with a diameter of 2.5 cm, a length of 10 cm, a gas permeability of 1500 mD, a water permeability of 500 mD, and a porosity of 29%. The polymer used was SNF3640 at a concentration of 1500 mg / L, and the water used to prepare the polymer had a salinity of 2000 mg / L, including Ca... 2+ Ions 13 mg / L, Mg 2+ Ions 8 mg / L, ISCO pump, displacement rate 10 ml / min. Specific steps are as follows:

[0020] 1. Prepare 5000 mL of a polymer solution with a concentration of 1500 mg / L;

[0021] 2. Test the pore volume (PV) of the core sample;

[0022] 3. Incorporate core samples and polymer solutions into the displacement device process;

[0023] 4. Adjust the Isco pump flow rate to 10 ml / min and begin injecting the prepared polymer solution into the core.

[0024] 5. Record the volume and viscosity of the polymer solution flowing from the tail end of the core sample, as well as the injection pressure at the inlet. The results are as follows: Figure 1 As shown.

[0025] Depend on Figure 1 It can be seen that when the outflowing PV volume is 600, the injection pressure of the polymer solution decreases by more than 10% and continues to decrease, because the normal fluctuation of the indoor injection pressure is generally less than 5%.

[0026] Therefore, when PV volume = 600, it is the opportune time to unblock the near-wellbore area of ​​the polymer injection well after blockage.

[0027] Example 2

[0028] Injection volume and injection pressure curves of a well in a Bohai oilfield are shown below. Figure 2 As shown, after a period of polymer injection, the injection pressure begins to decrease at the position indicated by the arrow, which is the opportune time to unblock the polymer injection well.

[0029] Both the indoor experimental data and the field production data in Examples 1 and 2 show a phenomenon of decreasing injection pressure followed by an increase in injection pressure. Furthermore, the production data includes multiple time periods where the injection pressure decreases and then increases again.

[0030] However, the first pressure drop interval is the undisturbed phase (as indicated by the arrow), and is the most representative. Data from different injection wells in many field studies show commonalities, with little difference in timeframe, all ranging from 6 to 8 months. Normal pressure fluctuations in injection wells generally do not exceed 0.2 MPa. However, during this field implementation, the pressure drop exceeded 1 MPa, with a fluctuation range of nearly 20%, indicating an anomaly. This anomaly precisely validates the ideas presented in the indoor experimental research.

Claims

1. A method for determining the timing of unclogging the near-wellbore zone of a polymer injection well, comprising the following steps: S1. Inject polymer solution into the polymer injection well; S2. Measure the injection pressure, and obtain the relationship curve between the injection volume and the injection pressure based on the injection volume of the polymer solution and the injection pressure; S3. Determine the timing for unblocking based on the relationship curve: When the injection pressure stabilizes and then drops significantly again without any relief, this is the timing for unblocking the polymer injection well.

2. The determination method according to claim 1, characterized in that: The concentration of the polymer solution is 500–5000 mg / L; The polymer used is an acrylamide-based polymer.

3. The determining method according to claim 1 or 2, characterized in that: The injection volume of the polymer solution is above 1000 PV.

4. The determination method according to any one of claims 1-3, characterized in that: The injection rate is 0.3–100 ml / min.

5. The determination method according to any one of claims 1-4, characterized in that: A significant decrease refers to a decrease of more than 10%.

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