Establishment of Cement Sheath Channeling Model and Experimental Study on the Laws of Channeling Sealing

Abstract

With the continuous development of oilfield, the number of channeling wells gradually increased due to the change of the reservoir physical properties and the measures for increasing production and injection. The development layers which are interrupted by the channeling causes serious interlayer interference. The key to achieving effective plugging is to analyze the sealing laws of chemical plugging agent in channeling. In this paper, a set of physical simulation equipment was innovatively developed to simulate the experimental process of cement sheath channeling sealing. The artificial cracks are used to simulate the cement sheath channeling, and the channeling structure is controlled by the number, length and width of crack. The sealing laws of cement sheath channeling are analyzed from channeling structure, injection cycle and injection rate which are based on the breakthrough pressure, microstructure of channeling model and plugging rate of core. The experimental results show that, the structure of the channeling model directly affects the sealing effect. The more complex the structure is, the lower the breakthrough pressure is and the more difficult to seal channeling. The plugging agent could not closely fit the wall of the crack or plugging agent breaks at the positions where the crack width and direction changed or the intersection of the crack. Most of the plugging agent flow through the crack and enter into the high-permeability layer, which makes the plugging rate greater than 93%. The microstructure of core section show that only a small amount of plugging agent is found in the front of low-permeability core, and the plugging rate is less than 6%. Injection cycle is also one of the important parameters that affect the sealing effect of channeling. For a relatively simple structure, high sealing strength can be achieved by one cycle of chemical sealing, while a complicated channeling require two or three cycle of sealing to ensure the effect. The change of injection rate has little effect on the breakthrough pressure of channeling model, but the lower injection rate can prolong the breakthrough time and enhance the flushing resistance of plugging agent in channeling model. The field test of channeling sealing has been carried out in Daqing Oilfield and the channeling has been effectively blocked. The average data of 8 wells show that the daily liquid production has decreased by 6 m³/d, the water cut has decreased by 7.1%, and the daily oil production has increased by 2.9t. The research on the sealing law of cement sheath channeling has important guiding significance for channeling.