An Abu Dhabi operator faced a drilling challenge in the Bu-Hasa field. It wanted to
drill trouble-free through the difficult Simsima formation, which primarily consists of badly fractured and vuggy limestones. Previous drilling attempts suffered from excessive
mud losses, even with aerated mud systems.

The operator was concerned with drilling performance when attempting to penetrate severe loss zones due to the impact on wellbore integrity. It needed a special drilling fluid that could produce optimum hydraulics on the bit and help prevent mud losses, and would result in a well bore they could case and cement without problems. The operator invited Halliburton’s Baroid Fluid Services to engineer a fluid solution designed to meet these challenges in order to maximize its wellbore value.

Non-damaging fluid
Baroid’s MAXDRIL-N fluid is a non-damaging drilling fluid designed to provide low plastic viscocity and a high yield point with a low funnel viscosity. These properties and its high

Solutions tackle specific situations

Each well presents the operator with a special set of downhole conditions even when the operator is drilling wells in a thoroughly tested and analyzed mature field.
Deeper holes, directional or horizontal wells and multiple laterals may require different drilling fluid designs, even in a consolidated formation.
In most wells — after the initial planning — drilling fluid represents the first opportunity for mediation or enhancement of the well bore, since it makes first contact with subsurface zones.
In a horizontal well offshore Qatar, an operator chose the MAXDRIL-N mixed metal system for a 5,770-ft (1,760-m) horizontal leg. The fluid contributed to excellent overall drilling performance and hole stabilization. It showed good cuttings transport and left a slick hole with minimal fill on connections.
In addition, the drilling fluid allowed a high penetration rate of more than 500 ft/hr (152 m/hr) in the Nahr Umr sand. The mixed-metal system exceeded performance expectations and offered the right solution for long horizontal sections in this area.
The company, working with a Norwegian operator, used the milling system to drill a record-breaking 1,703 ft (519 m) of 13 1/8-in. hole in an offshore well. The fluid was shear thinning and offered a flat rheological profile with a high solids-carrying capacity at low shear rates. It offered the operator improved lifting capacity in the annulus.
This family of mixed-metal silicate fluids with sized calcium carbonate offers a better replacement for mixed-metal hydroxide fluids. It specializes in maintaining borehole integrity with better hole cleaning for casing milling and highly deviated or horizontal drilling situations. It also gets a high recommendation for these operations in unconsolidated, unstable, stressed or faulted formations, and it forms a low-permeability filter cake that blocks passage of solids and fluids into formations.
low-end yield point generate hole cleaning efficiency at a low flow rate, resulting in a reduction of equivalent circulating density. It quickly gels up as fluid is lost to a fractured, vugular formation, which can reduce or halt fluid losses as fluid velocity declines and viscous drag increases. In addition, increased effective viscosity and decreased shear rate adjacent to the wellbore help reduce seepage losses. And, with its suspension characteristics and thixotropic properties, it requires low pressure to break the gel. Its laminar flow, flatter velocity profile generates telescopic layers with high velocity at the central layers and reduces to zero toward the borehole, resulting in decreased friction-pressure losses.

The fluid mixed metal silicate system drilling fluid was tested in the Bu-Hasa field by drilling a 121¼4-in. hole through the Simsima formation to the Shalaif formation. The results of the first hole drilled were more than satisfactory. The hole was drilled with an average rate of penetration of 113 ft/hour (34 m/hour), and the 95¼8-in. casing was run and cemented to the surface without incident. Subsequently two additional wells were drilled with the same fluid with similar results.

The operator estimates cost savings on each well averaged US $65,000 from a combination of lower fluid losses and faster drilling. In addition, there are lower health, safety and environmental risks compared with using an air drilling package.

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