Influence of abnormal water injection well on qualified rate and treatment countermeasures

: More heterogeneous oil reservoir in the process of waterflooding oil field, reasonable water injection is to improve the recovery efficiency, an important means to slow down the natural decline, strengthen the daily management of injection Wells, according to the influencing factors of injection Wells anomalies corresponding measures, improve the water time, improve the qualified rate of water injection, truly underground "good enough water and injection water" goal, It is the most economical and effective way to improve oil recovery.


Question raising
At present, the test data of stratified injection well are in accordance with the data admission standards, and the normal service period is four months.In the four months, due to the complexity of underground geological conditions, the influence of the interlayer contradiction is very big, each section of the water quantity is very uneven, to make each interval water quantity can't meet the requirements of injection allocation, allocate water mouth or big, last time or congestion, or big or small, cannot under the existing injection pump pressure, injection oil pressure meet the requirements of injection allocation.The irrationality of underground water injection directly affects the development effect of oil well.

Analysis of abnormal cause of stratified injection well
Abnormal zonal water injection well refers to the zonal water injection well whose injection pressure or injection water volume changes suddenly under the condition of constant system pressure.The main causes of abnormal Wells are as follows.

The dynamic change of stratum results in abnormal water injection
According to the development of oil layer in reasonable injection interval and low layer of injection allocation, the time of leveling and underlining, historical water absorption and the change of surrounding oil Wells, the leveling and underlining can be divided into two categories: gradually worsening injection volume and suddenly decreasing injection volume.The abnormal causes of 9 test Wells were analyzed, and the abnormal changes of injection water after test were caused by the variation of formation water absorption in 4 Wells, which accounted for 44.4% of the total abnormal Wells.For example, after the test on February 27, 2013, the oil pressure and water injection volume of North 2-3-125 were 13.9mpa and 80m3.Since April 14, 2013, the water injection volume of this well has gradually decreased.After the test on April 24, 2013, the oil pressure and water injection volume were 13.9mpa and 48m3.On April 25, 2013, two pressure gauges were used to verify the injection pressure in the field.The pressure of the two pressure gauges was basically consistent with that of the original well.In addition, after testing, no spout spout was found to be large, and it was preliminarily determined that the reason for water volume rise was caused by the variation of water absorption in the formation.reasons affecting the qualified rate of water injection are as follows: First, the efficiency of stratified testing and deployment is low.The average time of single well testing and deployment is 4.5 days due to the need for repeated quantitative testing, surface replay, and dropping and fishing nozzle.Second, because the interlayer interference has a great influence on the decline method test, the pass rate of test data is low, and the pass rate of reinspection is about 80%.Third, due to the small segment of some subdivided Wells, the flow rate of the fluid changes when it passes through the upper and lower tools, and the test instrument is difficult to locate in the stable flow rate section, resulting in the deviation of the test flow.In the testing process, restricted by factors such as the accuracy of the depth counter of the drawworks, the shrinkage degree of the steel wire and the wear of the centralizer of the flowmeter, the measured water volume deviation is large, which affects the allocation accuracy and shortens its stability period.After analyzing the abnormal causes of 9 test Wells, it was found that 1 well had abnormal injection water due to the large spout.For example, after the test of Well North 2-351-21 on May 16, 2013, the oil pressure was 14.1mpa and the water injection volume was 70m3.On August 25, the water injection volume reached 102m3 when the water injection pressure was 14.1mpa.The injection pressure is controlled at 12.5mpa and the injection volume is 73m3 due to the overflow scheme.On August 25, two pressure gauges were used to verify the injection pressure in the field.The pressure of the two pressure gauges was basically consistent with that of the original well gauge.It is preliminarily determined that the reason for the water increase is abnormal change of injection pressure caused by downhole pipe string or oil layer.On August 26, the water measured by the instrument under the test shift was basically consistent with the on-site water injection volume, indicating that the pressure was equal to the on-site pressure gauge.The test found that the partial II water injection volume exceeded the allocated water injection volume by a lot.After pulling out the water nozzle of this layer, it was found that the water nozzle was broken, and the water nozzle was restored to normal after replacement.

The influence of the years of plugging nozzle and injection well string due to poor water quality results in abnormal testing
In recent years, the water quality of the outlet of the water injection station has been greatly improved, but the water injection quality is still poor due to the secondary pollution of oil layer caused by pipeline and pipe string corrosion.It has been shown that the worse the injection water quality is, the lower the qualified rate of injection water is.Injection water quality is poor, easy to cause the blockage of the plug.The whole well shows that the water injection pressure increases, the water injection volume decreases, and the water absorption of individual sections decreases or does not absorb water.Such abnormal water injection Wells are easy to be found and can be tested and verified in time.For abnormal Wells that cannot be found in time, individual intervals of injection Wells are blocked, but the amount of water injected into other intervals with strong water absorption capacity is increased, and the data application range of the whole well is not exceeded.Such abnormal water injection Wells can only be found in the normal test cycle, and the abnormal water injection takes a long time, causing great harm.In the process of water injection well, the water nozzle will be blocked due to poor water quality, so that the pressure of the well will rise and the water volume will drop.Although the proportion of Wells with poor water quality is not very large, it does affect the qualified rate of water injection, especially at the end of the water injection area.For example, in the test of Well North 2-361-23 on March 2, 2013, the partial v original water absorption was 15 m3.On April 22, 2013, the on-site water injection was abnormal.When tested on May 12, 2013, the water absorption of this section was only 5 m 3 .
Tab. 3 The effect of faucet plugging on water absorption In some Wells, due to the long interval between operations, the pipe string is severely scaled and corroded underground, resulting in obstruction and blockage of the test instrument.Currently, the string is replaced only when the operation is required.In my opinion, a specific number of years should be specified for the string of water injection well.After a certain number of years, it is necessary to run the string again, so as to ensure the testing work.If you wait until the operation is blocked or stuck, it will affect the normal test and the qualified rate of water injection.

The poor quality of the well washout caused the abnormal test
The quality of well washing directly affects the qualified rate of water injection.In the field management process, there are many reasons affecting the well washing quality.First, the current well washing mode is that the mine geological team organizes and arranges vehicles for well washing, and the oil production team supervises, and one tank car does not continuously wash well, so the tank car is used for well washing, and the well washing capacity is limited.Second, in the process of well washing, there is often a stop in the middle of the process, waiting for tank car sewage, which can not ensure the continuity of well washing, and the stolen goods in the well can not be cleaned.This is because the flushing fluid must be continuously circulated in order to carry the loot from the bottom hole and the string.As can be seen from the table below, well north 2-351-31 was washed twice by tank truck on March 24, 2013, but no effect was found after washing.

Low precision of pressure taking equipment and instrument in water injection well results in abnormal testing
The measurement deviation of the pressure gauge used in the field before and after checking is also the cause of the change of injection volume.There is a big gap between the accuracy of the pressure gauge and the on-site management requirements of the injection well.For example, the pressure gauge in the well group of North 2-351-19 was 12.9mpa during the test on January 23, 2013.After the test, the pressure gauge used in the well was checked, and the pressure value was 13.1mpa under the same injection volume.A total of four gauges were changed for verification.Under the same injection volume, only one of them showed injection pressure of 12.9mpa, while the other three gauges had the highest pressure of 13.2mpa and the lowest pressure of 12.8mpa, with the upper and lower error of 0.4mpa.But these tables are all in the prescribed range, a qualified table.At present, daily water injection volume comparison under the same pressure is required for on-site inspection of water injection well, but the existing pressure extraction equipment is difficult to meet the requirements.Abnormal Wells caused by unknown abnormal reasons account for 2.22% of the total number of abnormal Wells.Most of these Wells are Wells with reduced water absorption, and the accuracy of pressure taking equipment and pressure gauge has a great impact.What is discussed above is that under the condition of constant system pressure, but in actual injection well management, we often encounter the pump pressure fluctuation has a certain influence (not all) on the injection water quantity, thus affecting the qualified rate of water injection.There are many production teams at the end of such well water injection network, about 7 Wells.

Conclusion
In the process of managing abnormal water injection well and improving the qualified rate of water injection, we have realized: 4.1 Reporting and tracking analysis of abnormal testing Wells will help solve and cure abnormal water injection Wells in the future.

4.2
The main means to ensure the days of water separation in stratified injection Wells and improve the qualified rate of stratified injection is to do a good job in the equipment management of water injection well data admission.4.3 Pay attention to injection water quality and well washing quality, reduce the number of abnormal injection Wells, can effectively improve the qualified rate of stratified injection water.

Abnormal water injection due to test impact
The fourth is to implement the complete and accurate collation of on-site data.Check all on-site data of water injection Wells every month, do not estimate interest rate for inconsistent or false data, and strictly deal with them.Do a good job in testing and tracking, contact with the test team to jointly analyze the abnormal Wells and some key Wells, and deal with them in time, increase the number of days for water separation, and improve the qualified rate of layered water injection.The qualified rate of water injection was improved by taking comprehensive measures and strengthening the management of abnormal water injection Wells under the condition of increasing the number of stratified Wells and stratified Wells.