Drill Cuttings Re-Injection:An Eco-FriendlyOffshore Waste Disposal Technique

摘要

Subsurface re-injection of cuttings has received industryinterest in cutting waste, improving safety and cost reduction. This method can significantly reduce the hazard and costassociated with delivery of waste from offshore to an onshoredisposal site. Proper job planning requires data on surfacegeology, formation description and log analysis for deciding asuitable injection zone, rate of injection and fluid rheology. Three main types of drilling muds namely Water Based Muds(WBM), Oil Based Muds (OBM)and Synthetic Oil Based Muds(SOBM)are employed for onshore /offshore drilling toovercome the down-hole problems associated with varyinggeological setting and tectonics of the region. Offshore drilling produces pollutants in the form ofdrilling muds, cuttings, etc. Water-based muds are not only lessharmful to environment and cheaper compared to oil-based(OBM)and synthetic-based muds, but also help in providingbetter conditions for formation evaluation. Though strictenvironmental legislation around the world is limiting thedisposal options of OBM, still it has its own advantages indeeper well sections having high temperature and pressure regime and directional drilling. In the case of using oil based orsynthetic based muds, various options for disposal or treatmentof these drilling fluids and cuttings are:Separate the oil fromthe cuttings by solvent extraction? Thermally destruct the oil in the cuttings byincinerating? Collect the cuttings and move them to an approveddisposal site onshore? Re-inject the cuttings into underground formationsOut of various options for disposal or treatment of drillingfluids and cuttings, reinjection of drill cuttings into suitablestratigraphic horizons, is the most favored and eco-friendlyprocedure for OBM disposal. This method has already been inpractice in some of the offshore wells in India. With the adventof increasing exploration in both shallow and deep water, thescope of using OBM for hole stability in high temperature andpressure regimes will increase. Hence cuttings re-injection isexpected to have wider applications.