Logging to an individual log file for each individual thread

I think I have worked out the issue. The steps follow:

• Create an an individual ILoggerRepository object (loggerRepository in this example) on each thread.
• Set the ThreadContexts property for the log file name.
• Use the XmlConfiguratior to configure the repository.
• Use the LogManager to Get the named logger (in the XML configuration file) using the named LoggerRepository for that thread.

In return I get a new configured logger pointing to the respective file for that thread.

The XML configuration is the same as it was originally and shown here for completeness:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>    
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
  </configSections>
  <log4net>
    <logger name="ProductionLogger">
      <appender-ref ref="XmlAppender"/>      
      <level value="ALL"/>
    </logger>
    <appender name="XmlAppender" type="log4net.Appender.FileAppender">
      <file type="log4net.Util.PatternString" value="D:\Temp\Logs\%property{LogName}.log" />
      <immediateFlush value="true"/>
      <appendToFile value="true" />
      <layout type="log4net.Layout.SimpleLayout" />
    </appender>
  </log4net>
</configuration>

The code to create the loggers is below. Each time this code is run it is run in its own thread.

ILoggerRepository loggerRepository = LogManager.CreateRepository(logFileName + "Repository");
ThreadContext.Properties["LogName"] = logFileName;
log4net.Config.XmlConfigurator.Configure(loggerRepository);
ILog logger = LogManager.GetLogger(logFileName + "Repository", "ProductionLogger");

This seems to work with no issues so far. I will be moving forward with this solution for the moment but I will update this post if I find out anything else.

Adam's answer has worked pretty well for me, but there is one this I would like to add. If there is a possibility of your logFileName being reused in your application, you will need to check to make sure the repository does not already exist.

string repoName = String.Format("{0}Repository", logFileName);

// Check for existing repository
ILoggerRepository[] allRepos = LogManager.GetAllRepositories();
ILoggerRepository repo = allRepos.Where(x => x.Name == repoName).FirstOrDefault();

// If repository does not exist, create one, set the logfile name, and configure it
if (repo == null)
{
    repo = LogManager.CreateRepository(repoName);
    ThreadContext.Properties[KEY_LOG_FILE] = logFileName;
    log4net.Config.XmlConfigurator.Configure(repo);
}

// Set logger
ILog logger = LogManager.GetLogger(repoName, logName);