Estimating Density, Formation Volume Factor, Compressibility, Methane Solubility, and Viscosity for Oilfield Brines at Temperatures From 0 to 275 ° C, Pressures to 200 MPa, and Salinities to 5.7 mole/kg

Abstract

New correlations for density of methane-free sodium chloride brine and solubility of methane in sodium chloride brines, valid over wide ranges of pressure, temperature, and salinity, are presented. Both correlations agree with the best available measurements within experimental error over most of the range of validity. These new correlations are combined with published correlations for methane partial molar volume to provide accurate and internally consistent estimates of brine density, specific volume, formation volume factor, and coefficient of isothermal compressibility at pressures above or below the bubble point pressure.

The brine density correlation is valid for temperatures from 0 to 275 ° C (32 to 527 ° F), pressures from 0.1 to 200 MPa (14.5 to 29,000 psi), and sodium chloride content from 0 to 6 moles/kg H ₂O (0 to 26% by weight). The methane solubility correlation is valid for temperatures from 20 to 360 ° C (68 to 680 ° F), pressures from 0.9 to 200 MPa (130 to 29,000 psi), and sodium chloride content from 0 to 6 moles/kg H ₂O (0 to 26% by weight).

A modification of an existing correlation for brine viscosity is also presented, extending its range of applicability to temperatures between 20 and 300 ° C (68 to 572 ° F), pressures between 0.1 and 200 MPa, and salinity between 0 and 5.4 moles NaCl/kg H ₂O (0 to 25% NaCl by weight).

Introduction

Oil companies today produce in excess of 33 million cubic metres of water per day (210 MMbbl/day). The associated cost of handling this water production is estimated to exceed $40 billion per year ⁽¹⁾. Understanding and dealing with these costs requires accurate knowledge of the water properties. Properties such as density, viscosity, and solubility affect the volume and movement of water through the reservoir, in the well bore, and at the surface facilities. As water production continues to increase, so does the importance of our understanding of the properties of the produced water.

Many experimental studies of the behaviour of systems comprising water, sodium chloride, and methane have been reported in the physical chemistry literature during the last 25 years. By and large, the results of these studies have not been widely disseminated within the petroleum engineering community. In this paper, we present new correlations based on the published data for estimating those properties of primary interest to the petroleum engineer, namely the density, specific volume, methane solubility, formation volume factor, coefficient of isothermal compressibility, and viscosity.

The next two sections of the paper discuss the development of the new brine density and methane solubility correlations. The third section shows how the brine density and methane solubility correlations may be combined with previous work to calculate internally consistent values for reservoir brine density, specific volume, coefficient of isothermal compressibility, and solution gas-water ratio at pressures above or below the bubble point pressure. The final section presents a modification of a published brine viscosity correlation, extending its range of applicability to temperatures of 300 ° C (572 ° F) and pressures of 200 MPa (29,000 psi).