Shales make up over 75% of the drilled formations, and over 70% of the borehole problems are related to shale instability. The oil and gas industry still continues to fight borehole problems. The problems include hole collapse, tight hole, stuck pipe, poor hole cleaning, hole enlargement, plastic flow, fracturing, lost circulation, well control. Most of the drilling problems that drive up the drilling costs are related to wellbore stability.
These problems are mainly caused by the imbalance created between the rock stress and strength when a hole is drilled. The stress-strength imbalance comes about as rock is removed from the hole, replaced with drilling fluid, and the drilled formations are exposed to drilling fluids.1 While drilling, shale becomes unstable when the effective state of the stress near the drilled hole exceeds the strength of the hole. A complicating factor that distinguishes shale from other rocks is its sensitivity to certain drilling constituents, particularly water. Shale stability is affected by properties of both shale (e.g. mineralogy, porosity) and of the drilling fluid contacting it (e.g. wettability, density, salinity and ionic
Clay and shale react with the water phase of a drilling fluid to promote stickiness, increase swelling, and induce sloughing. Shale and clay stabilizers adhere to the borehole wall the surfaces of drill cuttings. This encapsulation can effectively seal their surfaces and inhibits their reaction with the fluid, minimizing sticking, swelling, and sloughing, and increasing borehole stability. Our portfolio of specially engineered additives is designed to inhibit reactive shales in water-base drilling systems and reservoir drill-in fluids. Our shale inhibitors are designed to enhance drillability while maintaining low toxicity for environmental acceptability.
Drilling practices and the physical & chemical properties of drilling fluids can either enhance or erode borehole stability. Our borehole stabilizers serve as “preventive medicines” that help operators avoid the difficult and expensive tasks associated with remediating an unstable formation.