SPE Members
Abstract
A laboratory study was conducted to substantiate the exceptional hole-cleaning performance of "rheology engineered", biopolymer-based mud systems used in Prudhoe Bay, Alaska, horizontal wells. The study focused on the impact of very-low-shear-rate viscosity and evaluated the combined effects of rheology, flow rate, velocity profile, eccentricity, pipe rotation, and inclination on hole-cleaning efficiency.
The study confirmed that the rheological "fingerprints" of the biopolymer fluids provide optimum hole-cleaning and suspension. These benefits were attributed to the time-independent, yield-pseudoplastic behavior not obtainable with traditional viscosifiers. Engineering of the specially formulated biopolymer fluids represents a clear departure from conventional methods and field rheological concepts.
Rheological properties of the drill-in fluids were simulated by solutions of clarified xanthan gum. The biopolymer fluids consistently out performed pseudoplastic, hydroxyethyl cellulose fluids tested for comparison. Hole-cleaning studies were run on two flow loops; measurements were taken on several types of rheometers to characterize the fluids. Videotape recordings documented the interaction and interdependence among the hole-cleaning parameters and allowed measurement of velocity profiles in tubes and annuli.
Introduction
Specially designed, biopolymer-based drill-in fluids play a key role in the success of Prudhoe Bay, Alaska, horizontal wells. Oil-based muds formulated with Arctic diesel were used in the early stages of the development program. However, safety, health, and environmental issues clearly were of concern. Furthermore, poor hole cleaning, difficulty running liners to bottom, high costs, and production facility complications were associated with use of the oil-based muds.
Prudhoe Bay biopolymer fluids provide the proper balance among performance, cost, and environmental factors. In addition to being non-damaging and inhibitive, they exhibit optimal cuttings transport, suspension, and hydraulic characteristics. Their hole-cleaning capabilities and unique rheological properties are the focus of this paper.
The biopolymer fluids are "rheology engineered" mud systems.
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