GUMBO & REACTIVE SHALE
Water-based drilling fluids often outperform non-aqueous drilling fluids in terms of ECD management; reservoir analysis; environment, health and safety protection; and penetration rates. However, without proper shale inhibition, the water phase of drilling fluids will hydrate clay, gumbo and reactive shales causing swelling, wellbore instability, high torque and drag, and stuck pipe. Shale inhibition is affected by differential pressure, chemical osmosis (water activity), diffusion osmosis (ion exchange) and the establishment of a fluid/shale membrane. Drilling fluids inhibit shale hydration through these five mechanisms:
- Polyol Chemistry, which reduces water activity and enables membrane development.
- Emulsified Phase, which improves the membrane and coats formation surfaces with non-aqueous film.
- Supplemental salinity, which lowers the water activity.
- Silicates, which precipitate into pore spaces and onto the surfaces of shales and cuttings.
- Amine, which actively bonds to exchange sites in clays.
Regardless of the base-fluid, the drilling fluid / shale membrane is the key to success in properly inhibiting highly reactive shales. The emulsified phase of non-aqueous drilling fluids (oil, mineral or synthetic-based) provides an ideal semi-permeable membrane, while supplemental salinity provided by calcium chloride controls the water activity of the emulsified phase. In water-based drilling fluids, the membrane must be built through the use of polyol chemistry. Shales with minimal and less reactive clays, such as targets to many onshore unconventional plays, can often be inhibited without the full establishment of a membrane. The scientists at the Newpark Technology Center’s laboratory can analyze shale samples, determining the quantities and types of clays present in the shales. Based on decades of shale inhibition expertise, the scientists can then formulate an appropriate inhibition package for that shale.
HPWBM Inhibits Shale, Offshore Mediterranean Sea: While drilling directionally through a highly reactive shale with a conventional KCl-Polymer drilling fluid, an operator encountered hole stability issues, including sloughing shale, stuck pipe, lost bottom hole assemblies and difficulty running casing. Newpark proposed the DeepDrill high-performance water-based system because of its proven history of inhibiting and protecting even the most reactive shales.
Water-based Drilling Fluid Solution for a Challenging Deepwater Gulf of Mexico Field: The development of a deepwater field in the Gulf of Mexico presented several challenges for one operator, including complex hole geometries, stacked formations, salt structures, highly-reactive shale, depleted zones and the threat of gas hydrate formation.
Novel Invert Emulsion System Using a Polyglycerol Internal Phase: The drilling performance of non-aqueous fluids is improved by using a polyglycerol as the emulsified phase in place of the calcium chloride brine, establishing the shale/fluid membrane and controlling water activity.
Application of High Performance Water-Based Mud in Woodbine Horizontal Wells: In the design of a high-performance water-based drilling fluid solution for Woodbine sandstone laterals, the Newpark laboratory used x-ray diffraction and x-ray fluorescence analysis of cuttings from a nearby offset well to determine that the sandstone contained interstitial shales with illite and mixed layer clays. Inhibitor advice was relayed to the technical team, who formulated and implemented an Evolution system for that play.
DeepDrill System Eliminates Losses, Improves Logging in Deepwater 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.