Deep water Drilling –Borehole Stability

•The geology of deepwater drilling is different from that on land and in shallow water.
–The formations, for example, are relatively young and very reactive.
–The clays and silts have not been altered by extreme heat or pressure and are not significantly dewatered.
•Sands are often unconsolidated and have not been compacted.
•Shallow clay formations, referred to as gumbo, are very soft and sticky.
•Cuttings from these formations can cause hole packoff, plugged flow lines, balling of bit and bottom-hole assembly, and reduced Rate of Penetrations (ROPs).
•Young clays contain high volumes of water and can be extremely sticky and problematic regardless of the degree of inhibition.
•Swelling and dispersion of the reactive shale must be addressed when drilling in deep water.
–Synthetic, diesel, mineral, PHPA, enhanced chloride and lignosulfonatesystems all have been used in deepwater applications.
–Synthetic and oil-base muds provide excellent inhibition, virtually eliminate problems with gumbo
•Water-base systems will require additives to increase performance and to minimize trouble with soft, sticky gumbo and for hydrate inhibition.
–Amines
–Glycols
–PHPA
–Silicate
–KCL