In the shale plays, the traditional technique was characterized as ‘pump and pray.’ This meant that operators often made their best picks for likely perforating targets based on less than scientific methods—to put it politely.

The reasoning was logical. Shale formations often lack character, and logs run in them frequently exhibit straight lines. So picking the best spot to initiate a frac treatment was anybody’s guess. Nevertheless, operators and service companies struggled valiantly to pick perforation zones based on where they hoped the best spots would be, with very little scientific justification.

Today, Schlumberger proposed an innovative three-step technique designed to place and orient frac perforations in the best position every time. Key to this claim was the development of the in-situ stress testing tool, which is an innovative reverse-application of one of the company’s most reliable and profitable services, the Modular Formation Dynamics Tester (MDT)*. Details can be found in SPE 124147.

At the core of the technique is the MDT tool’s Pump-Out Module. Traditionally, this device has been used during formation testing to pump contaminated formation fluid back into the mud column until an uncontaminated sample could be acquired. The new technique reverses the process and uses the pump-out module as a ‘pump-in module’ to initiate a mini-frac while acquiring vital pressure measurements and transmitting them to surface in real-time. Here’s how it works.

The pump-out module is installed between two inflatable packer modules creating in essence a very accurate mini-frac tool. The 4-ft long packers straddle a 3-ft gap. The tool is positioned opposite a likely zone, packers are inflated and a mini-frac is attempted. With just a few tests, the best zones for fracing can be identified.

You may be asking, “Wait a minute, how are these so-called ‘likely zones’ identified?”
It’s a three step process. The first step involves logging the entire section using the Platform Express* (or similar) logging suite including the ECS* Elemental Capture Spectroscopy tool, and FMI* Fullbore Formation MicroImager device, along with a 3-D Sonic tool and sidewall coring tool. This constitutes the first step and the subsequent analysis helps select perforating targets and determine their optimum orientation .

The second step is to test the selected zones as earlier described. The final step is to run a post-mini-frac FMI tool and 3-D sonic log to image the minifracs and as a determination of stress anisotropy.

The application of the three-step process takes the guesswork out of picking perforation zones for multistage frac jobs. In several tests, the system has provided conclusive results that indicate that it’s better to shoot in silicaceous zones and to orient perforations in the direction of minimum horizontal stress.

To prove the point, two wells were treated using identical pumping techniques. In one, all zones were perforated in the shale; in the other all were shot in the silicaceous zones—even though they were thin and widely spaced. Production results confirmed that it’s better to shoot in even marginally sandy areas that to shoot the pure shales if you hope to get a good quality fracture network.

Skeptics will be thinking, “Wow, all those logs must be expensive.”

The response is, “Not half as expensive as fracing in the wrong place.” In the comparison test mentioned earlier the difference in production performance was almost a factor of three. At that rate, the logs will be paid for in a short time.

*Mark of Schlumberger