High Resistivity Well Cement for Underground Wells Suitable for Sealing Monitoring Equipment

Abstract

This paper presents cement design and evaluations for application in underground wells with monitoring equipment. Cement was needed to secure the suite of instruments in the nearly horizontal monitoring holes and to seal them preventing the movement of fluids along the length of the wells. Design criteria included an electrically resistive cement, with the resistivity of no less than 1000 Ohm-m, and cement heat of hydration temperature not exceeding the temperatures allowed by the installed instruments and their cables insulation, set to be below 75oC. Additionally, cement was to have low rheological parameters to easily flow into tight spaces between the cables and the equipment (on the order of 5 mm) while still being stable and able to provide a tight seal against the cable insulation and a PVC pipe (no shrinkage). The paper discusses cement laboratory design and evaluations showing effect of various additives on cement resistivity, compressive strength, toughness, shear bond strength with Teflon coated wire. Electrical resistivity of above 2,000 Ohm-m was achieved. Optimization of the final field applicable formulations, following American Petroleum Institute (API) procedures showed that designs needed further modifications likely due to the significant variations in the performance of granulated blast furnace slag intended for the job execution and slag tested in the early laboratory tests.