Determination of reasonable test time of periodic injection well in Punan Oilfield

: There were 232 stratified injection Wells in Bunan Oilfield in 2020, including 69 year-round injection Wells and 163 periodic injection Wells. There are many periodic injection Wells and the pressure recovery is slow after injection. After the test, the pressure fluctuates greatly, and the data cannot be reported outside in time, which affects the water distribution. In 2020, according to our actual statistics, the water injection pressure of 38 Wells had a difference of more than 2MPa from the qualified pressure point of the test data before the test of stratified injection well. The reason of pressure discrepancy is mainly related to periodic water injection. In view of this situation, we conducted an investigation on the cycle injection Wells of the whole mine in 2020. The pressure recovery curve was plotted according to the daily injection volume and the length of periodic injection stop time. At the same time, the method of determining the reasonable testing time of periodic injection well is put forward, which provides scientific basis for determining the testing time of periodic injection well.


Pressure recovery of periodic water injection well after water injection
There are three reasons for periodic water injection in punan oilfield.One is to take periodic water injection directly at the initial stage of transfer; Second, intermittent water injection can supplement energy in order to control the water cut rising rate of oil Wells.Third, because the water absorption can not pass the winter, the winter cycle stop injection.Therefore, we made statistics on the recovery of water injection pressure in 38 Wells after water injection was resumed (see Table 1).The time required for pressure to return to normal for different types of Wells was calculated based on different injection allocation and shutdown cycles (see Table 2).≤3 months 50 According to the data in the table, if the daily injection is less than 30m3 and the injection stop period is less than 3 months, the average days of single well pressure recovery is 24 days; if the injection stop period is 5 months, the average days of single well pressure recovery is 33 days.With daily injection of 30m3 to 60m3 and injection stop period <3 months, the average days of single well pressure recovery was 36 days, and the average days of single well pressure recovery was 45 days for Wells with injection stop period of 5 months.The daily injection allocation was greater than 60m3, the injection stop period was less than 3 months, and the average single well pressure recovered stable days was 50 days.The data in Table 2 can be used to make curves of the average pressure recovery days of Wells with different injection volumes and stoppage periods (see Figure 1).It can be seen that the longer the stoppage time, the longer the pressure recovery time.

Determination of reasonable test time of periodic injection well
2.1 Determine a reasonable test time on the pressure recovery curve According to the above investigation, we drew a single well pressure recovery curve for Wells with different daily injection volume and injection shutdown period, and determined a reasonable test time through the pressure recovery curve.For example, well 7P166-16, with daily injection of 35 m3, will be shut down in August and September 2020.In fact, the well was washed and transferred to injection on September 27.The initial injection pressure was 4.7mpa, and the pressure gradually recovered with the extension of injection time.The pressure recovered to 7.5MPa and stabilized on October 25.The pressure recovery time was 30 days.The stratification test was carried out on November 1st and finished on November 3rd.The qualified pressure point is 7.7mpa (see Figure 2).Water injection was basically stable under this pressure when tested in the first half of 2003.The injection was 35 m3 per day, the injection stop period was 2 months, and the pressure recovered and stabilized for 30 days.The injection was 50m3 per day, the injection stop period was 2 months, and the pressure recovered steadily for 35 days The injection was 40m3 per day, the injection was stopped for 3 months, and the pressure recovered steadily for 35 days  It can be seen from the table that compared with the curve method, the error of single well is within 5 days, which is basically consistent with the actual situation and can be used to guide production.

Figure 1 .
Figure 1.Curve of average well pressure recovery days with different daily injection rates and shut-down periods

Figure 4
Figure 4 7P143 Water injection pressure recovery

Table 1 .
Recovery statistics of periodic injection well pressure in Punan Oilfield

Table 2 .
Summary of pressure recovery of periodic injection Wells water injection

Table 3
Calculation method and curve method to determine the reasonable test time comparison table For the same well, the pressure recovery time is different at different time periods or with different injection amounts.It is not fixed, but dynamic and constantly changing.According to the pressure recovery time of periodic injection well after well opening, selecting appropriate test time is an effective way to reduce retesting Wells and ensure the normal water distribution of injection well.3.4Thepressure recovery law of under-injection Wells is inconsistent with the above formula.All the Wells involved in calculation can complete injection allocation, even if injection allocation is consistent with actual injection.