Unable to remove user from SharePoint Group using PowerShell

Question

I am trying to remove a user from a SharePoint Group using PowerShell.
I can see the user in the Site Collection as part of the SharePoint Group, however, when I attempt to run the script, I get an error message stating "Can not find the user with ID: 10"
Below is the PowerShell script that I am using:
$url = "https://sharepointdev.spfarm.spcorp.com/sites/desitecoll"
$userName = "spfarm\sp2013_svc"
#$userName = "spfarm\spprofileimport";
$site = New-Object Microsoft.SharePoint.SPSite($url)
$web = $site.OpenWeb()
$siteGroups = $web.SiteGroups;
Clear-Host
$mySiteGroups = @();
foreach($group in $siteGroups)
Write-Host $group
$mySiteGroups += $group;
}#foreach
$members = $web.SiteGroups[$mySiteGroups[0]];
$owners = $web.SiteGroups[$mySiteGroups[1]];
$visitors = $web.SiteGroups[$mySiteGroups[2]];
#Remove the user from the specified SharePoint Group
$spUser = Get-SPUser -Identity $userName -Web $url
Write-Host $spUser.ID
Remove-SPUser -Identity $spUser -Web $url -Group $owners
$web.Update();
$web.Dispose();
Write-Host "User " $userName "removed from " $owners
Please advise.

Answer 1

I had to update the code to the following because Get-SPUser was not working properly:
$url = "https://sharepointdev.spfarm.spcorp.com/sites/desitecoll"
$userName = "spfarm\spprofileimport";
$site = New-Object Microsoft.SharePoint.SPSite($url)
$web = $site.OpenWeb()
$siteGroups = $web.Groups;
Clear-Host
$mySiteGroups = @();
foreach($group in $siteGroups)
Write-Host $group
$mySiteGroups += $group;
}#foreach
$members = $web.Groups[$mySiteGroups[0]];
$owners = $web.Groups[$mySiteGroups[1]];
$visitors = $web.Groups[$mySiteGroups[2]];
#Convert the user name to an SPUser account
$spUser = $web.Site.RootWeb.EnsureUser($userName);
Write-Host $spUser.ID
Remove-SPUser -Identity $spUser -Web $url -Group $owners
$web.Update();
$web.Dispose();
Write-Host "User " $userName "removed from " $owners
Was I not using Get-SPUser correctly?