Abstract

The injection of a gas phase through a water saturated porous medium can reduce the water saturation not only by displacement mechanisms but also by evaporation mechanisms. In the presence of brine, this process can induce salt crystallization and precipitation within the porous medium with a risk of permeability alteration. In the field of gas production and storage, the occurrence of such a phenomenon can have detrimental consequence on the well productivity or injectivity. In this work, we investigated experimentally and numerically the effect of dry gas injection on salt precipitation and permeability impairment. State of the art equipment designed for high throughput coreflood experimentation was used to capture the dynamic of salt migration using X-Ray radiography. A set of experiments have been conducted on a sample of Bentheimer sandstone (10mm in diameter and 20 mm in length) as well as a two layers composite sample with a significant permeability contrast. Experiments were conducted using Nitrogen and KBr brine with different boundary conditions (i.e. with and without capillary contact). Results showed that salt precipitation results from the interplay of different parameters, namely pressure gradient, brine salinity, capillary forces and vapor partial pressure. Experimental observations indicate that in the case of dry gas injection, salt systematically precipitates but permeability alteration is observed only if a capillary contact is maintained with the brine. We built a 2D flow model integrating two-phase Darcy flow, capillary forces, salt effect on vapor partial pressure, dissolved salt transport, as well as the different PVT equilibria needed to describe properly the systems. Once calibrated, the model showed good predictability of lab scale experiment and thus can be used for parametrical study and upscaled to the well bore scale.

Highlights

  • In the field of natural gas production as well as gas storage in aquifer, salt deposition is considered as a potential risk for gas wells

  • The origin of the drying is that the water mole fraction in the gas phase at equilibrium depends on pressure

  • We present a comprehensive experimental investigation of the effect of gas flow in a sandstone sample initially saturated with water or brine

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Summary

Introduction

In the field of natural gas production as well as gas storage in aquifer, salt deposition is considered as a potential risk for gas wells. In the context of gas storage in aquifer, experiments have been conducted by [5,6] where dry gas was injected in brine saturated sandstone samples with different salt concentrations in the brine. They showed that the drying rate is proportional to the gas velocity and that any dissolved salt in the water can be transported by capillary flows induced by drying and can even accumulate near the injection surface. We present a comprehensive experimental investigation of the effect of gas flow in a sandstone sample initially saturated with water or brine. Experiments were simulated using an in-house advanced compositional model (CooresFlow)

Experimental set-up
1: Core 2: Top inlet 3: Top outlet 4: Bottom inlet 5: Bottom outlet 6
Experimental procedure
Sample properties and fluids
Effect of salt
Experimental observations
Lateral capillary contact effect
Numerical interpretation
Physical and numerical model
Salt precipitation modelling
Capillary contact modelling
Findings
CONCLUSIONS
Full Text
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