The Development and Application of Cement Sheath Squeezing and Acid Washing String

In the process of cementing in screen pipe during or after well completion, cement slurry may leak into the screen pipe section and cause damage to the formation due to packer failure or wellbore enlargement at the packer setting position. In order to reopen the oil zone and rebuild access for oil and gas production, the cement sheath squeezing with an acid washing string were developed on the basis of the independently-developed cement sheath squeezing device. The packer assembly at both ends of the cement sheath squeezing device can seal the annulus between the extrusion device and the screen pipe. Then, the cement sheath outside the screen pipe is crushed due to high pressure from throttling and pressure-transmitting assembly. The seal tube at the bottom of the string can open the washing valve at the bottom of the artificial hole and thus build a back-cycling well washing access. In this way, the crushed cement sheath can be backwashed out to the ground and formation permeability near the wellbore can be recovered. The cement sheath squeezing and acid washing string have been tested in five wells in the Shengli Oilfield, with 100% success. After the execution of squeezing, the communication between the plugged screen pipe section and the formation was regained. The successful development of the string provided a new method to solve the problem of cement leaking into the formation in the screen pipe section after well completion of cementing at the top of the screen pipe.