Field Service is probably the closest fit.  Worksheet Templates are worth exploring as a way of recording the details of work done, and you can invoice based on timesheets booked against the Field Service tasks.

Field Service is effectively an extension of the Projects app, so you don't really have to choose between them.

Hello Steve,

What Odoo version and host do you use? I just checked the related modules and i will try to answer your question with some workflow possibilities :

"For my small oilfield business we go to numerous wellsite in a day and we record information about the wellsite's"
> I think you can use projects app just like what you thought it would be. you can define a project and it's name, and in those project you will defining many tasks for your personnels. here you can later write the information about the wellsite's inside the description tab, along tracking how much time estimated for your personnel to check on each task using with timesheet app (if needed). 

"At the end of the day I need to send a report to the customers with this information.  Once the reports are completed I need to create a field ticket showing all of the locations we visited with the cost of the  the services performed for approval."
> you can input each task and its cost into a sales module. but it seems like from the odoo side there are no fastest way to input each task into a single sales order (or quotation). you can develop a custom module to work on that functionality so each task can be included into a one sales order. Along with this custom module, you can create a location information from the task so when the task is "ported" into sales order, it will also have the location information as well.

"Once all the field tickets have been approved I need to create an invoice for each ticket."
> you can easily create invoice from the sales module once the sales status has become "Sales Order" (or you can call it, "approved by customer")

"For the wellsite records created I would not to be able to retrieve those historical records if we visit those same wellsite in the future.  Then we would duplicate that record to reduce the amount of redundant inputting for data that does not change."
> i think there would be no additional action needed for this. if you need to create record, you can do so. if you need old record to be duplicated, then go ahead. unless if you wish to "lock" it so everyone cannot change it, then its possible by developing a module for locking each task.

I think that's the possible flow to make your business operation works with odoo. 

I Hope this helpful, best regards,

Altela (altelasoftware.com)