Lost circulation or total loss of drilling fluid or cement slurries in the cavernous formation, permeable zones and natural/induced fractured zones during the drilling and/or cementing operation can be an expensive and time-consuming problem. The consequences of lost circulation could be from the possibility of a blowout to the complete loss of well. Typical solutions for lost circulation has been a pill containing in-soluble materials like platelets, fibers or sized particulates. However, such in-soluble or non-removable materials can cause permanent damage to the producing zones by plugging pores due to in-soluble fines migrations. In some cases, plug dislodgment the can cause premature return of the lost-circulation itself.

This paper describes the results from our laboratory development of two different kind of acid soluble cement systems namely (a) traditional Portland cement based system with appropriate amount of CaCO3 and (b) Magnesium-Oxychloride-Cement (MOC). In both these systems, sized CaCO3 has been used to enhance the bridging effect at highly permeable formations. In addition, we have carried out extensive research to optimize the final set cement compressive strength by optimizing particle size distribution of CaCO3 In addition to bridging capabilities, these fluids can be foamed to enhance the capability of preventing severe lost circulations. Quick setting and 100% acid solubility properties of the MOC systems is the key for minimizing the damage of the producing zones from fines plugging and/or deeper invasion. Laboratory results such as thickening time, compressive strength, and rate of acid solubility will be discussed to compare these two systems in terms of their application pros and cons. In addition, other plausible applications for such acid soluble settable systems will be discussed for both oil and gas wells as a temporary plugging materials.

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