Due to significant variations of the subsurface geology from the surface to the top of reservoir and requirement of different
fluid characteristics for drilling various hole there is a need to use various mud systems. These may include a simple spud
mud for surface hole section, an inhibitive drilling fluid for reactive shale section, a salt water-based mud for salt diapirs
and salt formations, and a highly lubricating mud for deviated hole sections with high dogleg severity.To optimize each of
these separate and distinct scenarios, there is a need to change the mud system while drilling to overcome the technical
challenges associated with these formations and wellbore profiles. The change over from one mud system to another is
typically done between casing points while constructing the well to overcome specific drilling challenges associated with
next whole section.There is significant time and effort required to clean the mud circulation system adequately before a mud
change over in order to avoid any contamination of the new mud system.This is especially true when displacing a waterbased mud by an oil-based mud or an oil-based mud by a water-based mud.If this is not done properly, contamination of
the new mud by the old mud could be a source of major problems due to partial or complete loss of functional ability of
the new mud system.
An adaptable drilling mud system that can easily be transformed from a spud mud system to an inhibitive, or a high lubricating
or a salt water mud can provide the industry a versatile fluid system with multiple hole section applications.This removes
much of the NPT associated with mud changeover, reduces the mud cost as compared to mixing a totally new mud system
and eliminates concerns regarding mud contamination as well as any disposal or recycling cost for the replaced system.
This paper describes a volcanic ash-based drilling mud that can be used as a spud mud to drill the surface hole, can easily
be converted to an inhibitive mud system to drill reactive shale sections of a borehole, a salt water-based mud to drill the
salt sections and also a high lubricating water-based drilling mud to reduce torque and drag problems in deviated and
horizontal boreholes. The flexible and easily convertible nature of the base volcanic ash-based drilling mud has potential to
reduce total drilling cost significantly as it eliminates a significant portion of non-productive drilling time associated with
mud changeover, cleaning of mud circulation system, new mud preparation, incorporation of new mud in the circulation
system and displacement of the old mud from the borehole by the new mud, etc.
Comparative Analysis of the Effect of Barite and Hematite on the Rheology of Water-Based Drilling Mud