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.

Heat-Resistant Hydrogel for Temporary Plugging in High-Temperature and High-Pressure Fractured Reservoirs

“…The network structure of organic hydrogels is formed by covalent bonds, , and the most frequently employed cross-linkers are phenol-formaldehyde systems and polyethyleneimine. − The rigid network structure endows polymer hydrogels with exceptional plugging ability and gel strength for lost circulation control. Gamage et al prepared a robust hydrogel consisting of a synthesized polymer and cross-linker, which exhibited the ability to temporarily plug fractures and was easily removed by additives. Bai et al developed a heat-resistant hydrogel with exceptional gel strength, viscoelasticity, and salt resistance.…”

Evaluation of High-Temperature Recrosslinkable Preformed Particle Gel for Fluid Loss Control during Drilling

“…The gelation time at high-temperature reservoirs is one of the challenges. Gamage et al [11] investigated an LCM pill that consists of a water-soluble polymer and a metal-based crosslinker for high-temperature applications up to 176°C. The minimum gelling time ranged from one to 5 hr, depending on the temperature.…”

Application of flexible colloid-fiber compound plugging technology in oil and gas wells with large differential pressure in the East China Sea

“…With the exploration of oil and gas field, large differential pressure reservoirs are becoming more common. The solid-free temporary plugging kill fluid is generally used to balance HTHP formation pressure [1][2]. It can be divided into foam type, viscous type and water absorption resin type.…”