Formation Damage or Limited Perforating Penetration? Test-Well Shooting May Give a Clue
Authors: Weeks S.G. 
Published: December 2007

This is not another attempt to reinvent the wheel, but an example of combining established engineering methods, limited production performance data, and simulated perforating tests to help solve a practical problem. By obtaining a better picture of existing perforations, wellbore conditions can be appraised better, and a more effective stimulation program can be designed.

Introduction

Clear and effective communication between the wellbore and the reservoir is a minimum requirement for any successful completion. When objective intervals that are indicated to be productive by open-hole logs, flow tests, or core data fail to yield expected production rates, it is suspected that either the perforations are inadequate or the formation is damaged, or both. Test-well shooting under simulated well conditions can give a clue to the effectiveness of perforating techniques and can also help in planning nonroutine completions.

This kind of testing indicated the nature of perforations made during initial completions of 20,000-ft objectives in the Mississippi Salt Basin. As a result of the tests additional perforating charges were developed and completion and stimulation were planned that effected production from wells that initially were nonproductive.

The deeper Jurassic Age gas tests in the Mississippi Salt Basin (see Fig. 1) have been notorious for restricted flow performance. For example, in the southeastern part of the Basin, Well A, a Norphlet sandstone test below 18,000 ft, was perforated with 2-in. No-Plug jets with oil-base mud in the wellbore. After the mud was removed, the well tested less than 3.5 MMcf/D of gas, or about one-fourth the flow rate after subsequent stimulation. Well B, a Smackover limestone test at an offset location, failed to yield any flow after being perforated with 1 9/16-in. Hyper jets. This objective interval was perforated under what would be considered favorable conditions for a gas completion.1 Before perforating, the mud in the wellbore had been displaced with nitrogen and the well was shot with a pressure differential into the wellbore. After the well failed to flow, a 1.2-psi/ft fluid gradient was necessary to effect breakdown. After stimulation, the well had a stabilized flow rate of 11.2 MMcf/D of gas with 4,500 psi flowing tubing pressure. In the northwestern part of the Basin, Well C, a Smackover sandstone discovery at about 20,000 ft, flowed approximately 10 MMcf/D of gas, with 9,500 psi flowing tubing pressure during sustained open-hole testing. Later, during cased-hole completion operations, which included perforating with 2-in. No-Plug jets with inverted oil-base mud in the hole, less than half this rate of flow was established. Reperforating with more than 700 No-Plug jets (1 5/16 in.), with inhibited oil in the hole, resulted in only nominal improvement. There was no flow from Well D, an offet confirmation test, after perforating with 2-in. No-Plug jets or reperforating with 1 9/16-in. Hyper jets. Neither was flow established from Well E, at a nearby location, after perforating with 2-in. No-Plug jets and displacing the invert oil-base mud in the wellbore with nitrogen. This was especially startling, since 2 years earlier the offset location achieved considerable notoriety as a result of a blowout during drilling operations.