GULF OF MEXICO
An operator planned to drill a well in Green Canyon 82. On previous wells in that block, the operator experienced significant losses of synthetic-based fluid in the intermediate section. The current well plan included an extensive formation evaluation program at total depth, which would necessitate leaving the wellbore exposed for several days while logging and coring. Conditioning trips would only be made if hole conditions deteriorated. Synthetic-based fluids were eliminated from consideration for the intermediate section, based on the expected cost of losses. A water-based solution was preferred for the production section in order to maximize the clarity of the formation evaluation. However, for a fluid to be considered, it had to be able to stabilize the formation throughout the extensive logging run and normal drilling operations.
Newpark recommended the DeepDrill® high-performance water-based system as an environmentally responsible and economical alternative to synthetic fluid. Through the use of multiple shale inhibition mechanisms including polyol chemistry, salinity, and silicates, the DeepDrill system creates of a semi-permeable membrane over the formation, controls water activity and firms up cuttings, thereby providing the necessary shale hydration inhibition to allow wellbore stability in a water-based solution, even through extensive periods without circulation.
As a water-based solution, the DeepDrill system decreases the risk of lost circulation by decreasing equivalent circulating density (ECD) compared to synthetic-based fluid. With its low compressibility factor, a water-based system’s mud weight is constant under varying pressures. Non-aqueous fluids compress causing an increase in density with increased hydrostatic pressure. Aqueous fluids do not. Therefore, increases in pressure losses due to circulation are added to a mud weight very similar to that measured at the surface, minimizing ECD.
The DeepDrill system provided satisfied performance criteria defined by the operator by providing adequate wellbore stability while avoiding massive mud losses experienced on prior wells employing synthetic-based systems. The most significant losses were observed when running casing and cementing the intermediate section. However, these losses were offset with volume gain from dilution. Dilution was the most effective method of controlling solids as the solids control equipment was less than adequate.
A DeepDrill Inhibitor (DDI) concentration of 20% was maintained in the system for membrane development. Drilling performance was aided by good drilling practices including regularly-scheduled short trips and sweep regimens. FlexFirm silicate provided inhibition for cuttings, aiding solids control by preserving cuttings integrity in the annulus. This helped shakers to remove cuttings efficiently. FlexFirm also improved wellbore stability while drilling and during the extensive formation evaluation program at total depth.
|Interval (MD)||Hole Size||Liner (MD)||Mud Density
|Drilling Days||Logging / Coring / CSG
|6,644’ – 9,510’||12 1/4" X 14 3/4"||11 7/8” @ 9,510’||12.3 – 12.8||6||No Logging|
|9,510'-12,883'||10 5/8" X 12 1/4"||9 7/8" @ 12,825'||13.3-13.6||9||6|
|12,883'-14,435'||8 1/2"||7" @ 13,969'||13.7-15.35||5||8|