Strata Cementing

the process of reinforcing loose, weakly cemented rock in the face zone of oil, gas, or water strata to prevent the washing of large amounts of sand into a borehole.

Strata cementing consists in the injection of liquid binders into the face zone which, when hardened, reinforce the rock and increase its resistance to erosion. The permeability of the strata to a liquid or gas remains largely unchanged. Among the materials used for strata cementing are cement mortar, cement and sand mortar, and resin-forming chemical substances. Solutions of the reinforcing substances are injected into the strata by pump units through a tubing column lowered into the borehole down to the exploited stratum. After injection into the strata, the hardening time for cement mortar or cement and sand mortar is about 48 hours. Phenol alcohols (primary condensation products of phenol and formaldehyde) are used as resin-forming chemical substances for strata cementing. Hardening of the phenol alcohols (resins) occurs when they are heated or are in the presence of acids. There are two basic techniques for strata cementing with resins: for boreholes with a face temperature of up to 60°C, hydrochloric acid solutions are used, and for boreholes with a face temperature of 60°C and higher, no acidic solutions are used.