This paper analyses the reasons that lead to channeling of the oil and water wells in the Daqing Oilfield. Considering the developed layers' adjustments in the future, a new kind of chemical plugging technique is introduced to shut off the channels without abandoned adjacent layers. To realize the aim of both protecting the adjacent layers and plugging channels, the following steps are usually adopted. First, the channeling intervals should be perforated by a special perforating gun. Second, circulating the channels by a high velocity flush to make sure the agent can be squeezed into it easily. Finally, run the plugging string that carries the agent to the desired depth, increase the pressure to squeeze the agent into the channel, and then waiting for the solidification. Up to now, 12 wells have been treated by this technique. The channeling intervals' thickness is between 1.97 and 38.7 feet. The plugged channels can resist 2175.5psi pressure and the treatments' success ratio was 100%. Applications and excellent results proved that the technique can mitigate contradictions between different layers in the water-flood and polymer-flood area, and it can realize the goal of separate zone injection or separate zone oil production in the Daqing Oilfield.
Introduction
Channeling of injected water or polymer in oil/water wells is a constant and urgent problem in the late stage of high water cut period in the Daqing Oilfield, which directly leads to casing damage, unreasonable water injection and polymer injection. With long-term water flooding development and the application of fracturing, acidizing and even polymer flooding, the interlayer pressure diffenence becomes higher, and the cement job quality of the newly drilled wells becomes poor under this pressure, and the interbeds of old wells---wells in the basic well pattern, infilled well pattern for the first time or for the second time---can not withstand liquid flushing under the high pressure, and thereby, channeling happens without exception. For example, according to the statistics of the west block in North-2 area of Daqing Oilfield, channeling happened when some polymer solution in the polymer flooding layer enters into the water flooding layer, and oil carried with polymer solution was produced from 31 oil wells in the water flooding area, and channeling occured in 2 water injection wells, which made the effect of polymer flooding poor.
In order to meet the demands of each production factory in the Daqing Oilfield, solve the problem of interlayer channeling without abandoning any oil layer and polluting adjacent oil layers, new requirements are put forward for the current chemical plugging technique, because plugging channels in water injection wells and polymer injection wells can radically solve a series of issues caused by channeling and has better effect than plugging channels in oil wells. Therefore, a special chemical plugging technique without abandoned layers was researched to realize separate zone water injection and polymer injection, and after applications, it can mitigate casing damnage, be beneficial to adjusting injection layers and production layers and will play a significant role in improving development effect of Daqing oilfield.
Analysis of Current Chemical Plugging Techniques
At present, the chemical plugging techniques that are widely applied in the Daqing oilfield are categorized into three major types.
The first technique is plugging channeling intervals by a high strength and short thickening time plugging agent (such as Qingning, Epoxy Resin). Its advantages are short thickening time, high strength, withstanding high pressure difference, long period of validity, small plugging radius and easy plugging removal. And its disadvantages are that high load is needed to trip out strings and the strings are often stuck.
The second technique is plugging channeling intervals by a gel-plugging agent with lower strength and longer thickening time (such as high polymer, polyacrylamide). Its advantages are that tube strings would not be stuck, large amounts of the agent can be squeezed into formations, and the period of validity is long. Its disadvantages are high cost, long distance to immerge into formations, and difficult plugging removal.
