Where do the fracs go?


The quest for the most efficient field frac network

As unconventional resources development has evolved, it is clear that the key to maximum reservoir drainage is a systematic drilling pattern and an efficient field frac network that achieves maximum connectivity to the formation. This requires as many wells as possible on a given acreage, and as many stages per well as possible, without communication between stages and between wells. To achieve this, frac spacing must be exact and frac dimensions must be uniform.

Unfortunately, it is impossible to achieve either consistent frac spacing or uniform frac volume using plug-and-perforate, currently the most popular method, or with open-hole packers and ball-drop sleeves.

Drawbacks of plug-and-perforate

plugandperfThe limitations of plug-and-perf are well known and documented. This technique attempts to stimulate multiple perforation clusters simultaneously, with no control over which clusters actually fracture and how big each fracture is. Variable frac gradients along the lateral ensure that all fracs are not equal. Studies using radioactive tracers have revealed that many clusters are not stimulated at all, while others receive varying amounts of treatment (see SPE 144326). A study of production logs (SPE 144326) confirms that finding, concluding that a about a third of all perforation clusters do not contribute to production. Furthermore, the uneven stimulation indicates uncontrolled frac dimensions.

When multiple parallel wellbores are completed using plug-and-perf, the effect of the variable, frac pattern is multiplied, with gaping areas of the formation unreached by the stimulation.

Drawbacks of open-hole packers with ball-drop sleeves

openHoleWith ball-drop sleeves and open-hole packers, frac ports are precisely located, but fracs are not. With an uncemented annulus, the frac or fracs can initiate anywhere between packers, or even at a packer, where the formation is already stressed.

Another identified shortcoming of open-hole packers is inter-stage communication, leading to even more uncertainty about frac placement and frac volume. In one field, pressure measurements during completion of 13 wells confirmed communication around packers in 80 of 185 stages (43%).

Multistage Unlimited cemented casing sleeves

ncssleevesrealworldWith Multistage Unlimited technology, you know where the fracs initiate and you know exactly how much proppant is in each frac. With cement sealing the annulus, fracs initiate only at the sleeve ports, exactly maintaining the designed stage spacing.

Multistage Unlimited technology also helps control frac growth. For each stage, actual frac-zone pressure can be monitored in real time via the coiled tubing string (deadleg) while the frac is pumped down the coiled tubing/casing annulus. By observing the formation’s pressure response, pump rate and sand loading can be adjusted on the fly.

The bottom line

Multistage Unlimited technology delivers the most efficient frac network for maximum reservoir drainage.

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