Fluid/Pore-Mineral Transformations During Simulated Steam Injection: Implications For Reduced Permeability Damage
Authors: Hebner B.A. , Bird G.W. , Longstaffe F.J. 
Published: March 2010

A factorial design experiment was used to identify the hydrothermal reactions between the pore fluid, kaolinite, quartz and dolomite under conditions that simulate in-situ steam injection. One gram samples of kaolinite, quartz and dolomite mixed in the proportions 1:1:0.05 or 1:1:1 were reacted with 10 ml of solution at 250 °C and 300 °C for five and seven-day periods at neutral, intermediate and high pH. X-ray diffraction was used to identify the solids and inductively coupled argon plasma analysis was used to determine changes in the fluid composition.

These reconnaissance experiments showed that smectite is synthesized rapidly and is then transformed to analcime in sodic-rich alkaline solutions. Maintaining a high sodium concentration in solution and an alkaline pH appear to be the most important control in this process.

The rapid transformation of kaolinite and smectite into analcime could have a beneficial effect on permeability and recovery rates during thermal in-situ projects.

Introduction

This study was conducted to identify and examine the reactions between kaolinite, quartz and dolomite under conditions typical of in-situ steam injection. Temperatures are in the range of 200 °C to 300 °C and pressures can reach 13.8 MPa(1).

The hydrothermal reactions between kaolinite, quartz and dolomite at 25 °C to 300 °C have been discussed in several publications(2–5). These investigators have reported that clays of the smectite group are a common reaction product. Smectite is a swelling clay which can expand and/or disperse when contacted by low salinity water and contribute to formation damage via pore plugging. As little as two per cent smectite can cause a 50 fold reduction in permeability(5). The effects of smectite clays during conventional oil recovery operations have been discussed extensively in the technical literature and no attempt will be made to review them. The effects of smectite formation during thermal recovery operations are less well known although its growth has been recorded in post-steam cores(6). Young et al.(7) summarize the effects of clay formation damage in steam environment and discuss its control through clay stabilizing agents.

A factorial design was chosen for these experiments because it allows the evaluation of the combined effects of several variables in a single experiment(8,9). A maximum of four independent variables, temperature, pH, ionic composition of the pore fluid and time were in operation simultaneously during these experiments. Predicting the hydrothermal reactions in this multi-component system becomes more realistic when the interaction of several variables can be considered.

Experimental Procedures

Experimental Design

In these experiments, two of the variables were set at one of two levels: temperature 250 °C or 300 °C and duration, 5 or 7 Days. In addition, fluid composition was varied by using different quantities of NaCl, NaOH, Na2CO3, Na2B1O7, 10H2O and Na2HPO4 to adjust the salinity and pH of the starting solutions. NaOH was used to adjust the pH in most of the experiments which was set at one of three levels, neutral (pH 7), intermediate (pH 10) or high (pH 12) at room temperature, The pH at run temperature was not calculated but will be different from that at room temperature.