Abstract
Unexpected waterflooding during production after fracturing can be a critical problem for newly completed wells. There are cases that reservoir evaluation has been properly done and water bearing zones identified, and the wells show high water cut after the completion. Typically near wellbore channeling or unwanted fracture height growth can cause such problem and a joint effort between cementing and fracturing may be a solution to reduce such risk to minimum.
Field-X is located in Jugger basin in western china. One of the major target oil zones is identified which is close to a water bearing formation in this field. There is evidence showing historically cementing bond was impaired because of the contamination from the formation water, which diverted the fracturing fluid from the perforated zones to the incompetent cement channels in the annulus. The result was a fracture geometry that deviated significantly from the design and waterflooding occurred when the water zone was connected.
A special cement slurry was formulated as a main solution to solve this problem. The cement's set-mechanical properties were tailored according to the pressure and temperature dynamics by a stress analysis simulator to ensure entire zonal isolation during the fracturing execution, and the slurry's waterproofing property was evaluated and verified in the laboratory by a series of special designed test procedures. Meanwhile, fracture design is completed with the consideration of height control, as lowered viscosity fluid and moderate pumping rate was employed for the completion.
The joint effort from cementing and fracturing design achieved positive results. Fifteen exploration wells from field-X has been successfully cemented with excellent bonding, and post fracturing treatment showed minimum water cut during flow back and production tests comparing to offset wells. The synergy between cementing and fracturing design proves its value for field-X as an effective measure to identify potential risks and provide solutions to similar scenarios, and it is believed to be valuable for hydrocarbon development in other complex areas.
