Hi, Wendy -
If you filed Probate Papers or Affidiavits of Heirship on your Grandmother in the counties where the properties are located, then eventually one of the oil companies will come looking for you.
If you did not, you may want to consider doing so. All you need is a Certified Copy of her Probate Matters or an Affidavit listing the present day heirs of your Grandmother. File it or them in the County Clerk's Records where the properties are located and the oil and gas companies can find you.
Landmen will research the records and when they find where you own interests they will contact you. When they do, you can request copies of their titie notes or Title Run Sheets on the properties for your files.
That's a whole lot of work for free.