Increase Reservoir Contact in Shales

Date: 10/29/2009

In shale reservoirs, success depends on maximizing the amount of reservoir rock in contact with the well. Towards that end, operators rely heavily on horizontal wells and hydraulic fracturing. And while recent advances in these technologies have been key to the economic viability of these developments, said Doug Pferdehirt, Schlumberger reservoir production group president, there is considerable room for improvement.

"The challenge now is to continue to make step changes in our ability to contact larger volumes of the reservoir, to further increase reservoir contact in the most cost effective, efficient, and environmentally responsible manner possible," Pferdehirt told attendees at a recent Discovering Unconventional Gas conference.

The need to continually hone the industry's ability to exploit shales is driven by the fact that each shale reservoir is unique, with its own set of challenges. That means moving operations from one shale reservoir to another by simply repeating what worked in the past is not an option.

In the Marcellus shale, for example, clay content variability poses a challenge to establishing and retaining conductivity and has been related to changes in local stresses. The Marcellus also exhibits variability in natural fractures, faulting, reservoir pressures, and rock properties. All these uncertainties, as well as special water management issues, demand drilling, well location, and fracturing operations are specific to the Marcellus shale.

The answer to this shale complexity and heterogeneity is better reservoir characterization and operating efficiency. Towards that end, the industry has done much to improve its understanding of natural fractures from core analysis and image logs, and distributed stresses from sonic logs. It has also gained greater understanding of the growth and structure of hydraulic fractures in shales using microseismic monitoring. Rotary steerable systems and multistage completion hardware have added significant efficiencies to drilling and fracturing.

The real step change in increasing reservoir contact with the well will come, Pferdehirt said, through the integration of these and other key technologies and processes.

"This integration could include sonic data, rock properties, and reservoir pressure to determine geomechanically how to place the well for improved drilling efficiency and well stability," he said. "Or it could be the evaluation of fracture growth and complexity through the integration of microseismic data with image logs, sonic data, and seismic attributes like curvature and the natural fracture network."

The quest to optimize the volume of reservoir rock in contact with each well, Pferdehirt concluded, benefits greatly from optimized well and fracture placement that require real-time measurement and real-time control. However, he added, there is no "one size fits all" solution to developing shale gas reservoirs because there are significant differences between basins and a high degree of variability within each reservoir.

"For tomorrow, therefore, I am convinced that many opportunities exist for additional step changes in the efficiency and economics of shale developments," he said. "As we continue to understand the complexity and heterogeneity of the shales more deeply, we see the need for increasing focus on characterization and optimization. What has primarily been a cost-driven exercise is now becoming much more technology-intensive. The next step will be increasingly higher degrees of technology and process integration that will lead to robust, results-driven industrialization."

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