Impact of Water-Based Drilling-In Fluids on Solids Invasion and Damage Characteristics

Abstract

Drilling the U-formation (shale and sandstone) in Saudi Arabia requires high drilling fluid density (±95 lbm/ft 3 ) to mechanically stabilize the shale and balance the reservoir pressure. Two fluids have been used to drill this formation: KCl/BaSO 4 /CaCO 3 and potassium formate/CaCO 3 drilling fluids. Barite is added in the first fluid with CaCO 3 to reduce the amount of solids needed to formulate the drillin fluid. However, BaSO 4 is insoluble in acids and requires chelating agents (DTPA) to remove it from the formation. Formate drill-in fluids with low solids content can be used, but they are expensive and corrosive at pH values less than 7-8. A third drilling fluid was developed recently by Al-Yami et al. (2007) to overcome some of the problems associated with these two systems.The objectives of this study are to determine solids invasion and damage characteristics for the three fluids. Coreflood tests were conducted using reservoir cores at bottomhole conditions. The cores were then examined by environmental-scanning-electronmicroscope (ESEM) analysis to investigate solids invasion, solids type, and location of damage.The three drilling fluids examined did damage the core plugs either through external filter cake, internal filter cake, or both. The ESEM images showed that the least damage occurred when Mn 3 O 4 water-based drill-in fluid was used. The highest damage was observed when barite/CaCO 3 mud was examined. This was followed by the potassium formate drill-in fluids. Kaolinite booklets were not attacked by the filtrate of the three drill-in fluids examined. The damage that was noted with potassium formate mud resulted from incompatibility of mud filtrate with the formation brine where potassium chloride crystals were noted in the cores.

Minimizing Formation Damage in Drilling Operations: A Critical Point for Optimizing Productivity in Sandstone Reservoirs Intercalated with Clay

“…Al-Yami et al [63]. They observed that the filtrate from KCOOH RDF did not cause migration of kaolinite with booklet-form physiochemical characteristics, and the environmental scanning electron microscopy (ESEM) and energy-dispersive spectroscopy indicated precipitation of potassium chloride within the pore structures of the reservoir (Figure 8).…”

“…They observed that the filtrate from KCOOH RDF did not cause migration of kaolinite with booklet-form physiochemical characteristics, and the environmental scanning electron microscopy (ESEM) and energy-dispersive spectroscopy indicated precipitation of potassium chloride within the pore structures of the reservoir (Figure 8). Al-Yami et al [63] only considered one individual species-namely, booklet kaolinite-and did not consider other individual species of clay minerals of varying physicochemical characteristics, such as platy kaolinite, vermicular kaolinite, or blocky kaolinite. It is most often the case for kaolinite to become detached from grain walls and then migrate and flocculate or deflocculate after interaction, before being eroded by drilling fluids.…”

Drilling Fluids

“…There are six scenarios in which drilling fluids can cause a damage of the formation [213]: 1. fluid-to-fluid incompatibilities, e.g., emulsions generated between invading OBM filtrate and formation water; 2. rock-to-fluid incompatibilities, e.g., contact of potentially swelling smectite clay or deflocculatable kaolinite clay by nonequilibrium aqueous fluids, such as fresh water, that have the potential to reduce near-wellbore permeability severely; 3. solids invasion, e.g., the invasion of weighting agents or drilling cuttings into the formation; 4. phase trapping/blocking, e.g., the invasion and entrapment of waterbased fluids in the near-wellbore region of gas wells; 5. chemical adsorption/wettability alteration, e.g., changes in the wettability and fluid flow characteristics in the critical near-wellbore area because of emulsifier adsorption; 6. biological activity, e.g., the introduction of bacteria into the formation during drilling and the subsequent generation of slimes, which reduce the permeability. Moreover, in over-balanced drilling, solids invade the formation [214]. These invading particles, which are suspended in the drilling fluid, tend to plug the pore throats and cause a formation damage.…”

Prevention of Barite Sag in Water-Based Drilling Fluids by A Urea-Based Additive for Drilling Deep Formations

“…Barite (BaSO 4 ) is a common weighting material used to attain the desired density of drilling and completion fluids [2,11] because barite has a high density, low production cost, and less environmental impact [12,13]. However, the invasion of solid particles causes formation damage and reduces the permeability near the wellbore [14,15]. Another issue encountered with barite-weighted fluids is solids sag or barite sag.…”