Solids-Free Fluid-Loss Pill for High-Temperature Reservoirs

Abstract

Summary The leakage of reservoir fluids into a wellbore during perforation, workover, or other completion operations is a substantial concern, especially in high-temperature wells where existing fluids used to mitigate reservoir-fluid influx offer poor performance. To maintain the hydrostatic integrity of the wellbore during these operations, a thermally stable, solids-free fluid-loss pill has been developed. The pill is composed of synthetic polymers and crosslinkers in monovalent high-density brine. Under ambient-pressure and -temperature conditions, the pill flows as a viscous liquid and remains fluid for more than 6 months. Upon exposure to elevated temperatures (200 to 375°F), the pill crosslinks to form a robust gel that can act as an appropriately weighted, low-fluid-loss pill. This pill can temporarily seal the reservoir, enabling well control during completion operations. Gelled samples of the fluid-loss pill have maintained integrity for up to 3 weeks under high-pressure/high-temperature (HP/HT) conditions in laboratory testing, with minimal signs of collapse. The gel can be readily destroyed with an oxidative breaker providing a substantial reduction in viscosity. At the end of the completion process, the timing of gel removal is completely controlled by the timing of the breaker addition. In addition to gel-stability tests, formation damage caused by the gel and the fluid loss of the pill were assessed by coreflooding experiments by use of Berea core plugs. Average fluid loss over 3 days at 320°F was approximately 50 cm3. Restoration of the Berea core permeability after the treatment exceeded 85% of the initial permeability, with low lift-off pressures observed. This paper presents full laboratory data on the development of the thermally stable, solids-free fluid-loss pill, including gel-stability, fluid-loss, and breaker testing.