Action in the geographically widespread Devonian-age Marcellus shale natural gas play in the northeastern United States – despite challenges ranging from financial to technological concerns – continues at an intense pace.
More than 130 rigs are actively drilling there, according to Ron Harris, senior geophysical adviser at Anadarko Petroleum Corporation. The majority of these wells are horizontal with lateral legs ranging between one and two kilometers.
Stimulation via hydraulic fracturing is de rigueur to enable the dense shale to give up gas in commercial amounts.
Like any play – shales in particular – the Marcellus harbors its share of challenges to keep the geoscientists and operators hard at work far beyond the so-called “bankers’ hours.”
Harris summarized a few of these challenges:
♦ Identifying shale “sweet spots,” which represent areas of higher productivity that are driven by several petrophysical properties such as porosity, permeability, brittleness and total organic content.
♦ Optimizing well designs and geosteering through detailed, seismically derived structure maps that identify subsurface features like fold axis, faulting and collapse associated with salt dissolution.
♦ Optimizing the stimulation program by understanding the variances in rock properties within the shale zone and the areal distribution of Young’s Modulus, Poisson’s Ratio and local stress regimes.
To do so, the company invested about $3.5 million to fund a proprietary 67 square-kilometer, wide-azimuth, multi-component 3-D seismic survey. The survey was recorded on the company’s Sproul State Forest property in central Pennsylvania to determine the effectiveness of modern 3-D/3C seismic data in extracting certain rock properties from the Marcellus shale.
The shale within the study area is about 60 meters thick and occurs at a depth of 2.6 kilometers.
Getting a Good Handle
The seismic survey was recorded and processed by CGG Veritas and processed once again by ION’s GX Technology group, which performed data integration as well.
The month-long survey occurred in 2009, when Anadarko already had one vertical well drilled on this property and was busy implementing frack jobs on two laterals.
“These were the first wells we drilled and completed in the Marcellus, which has more structural complexity than most shales in the United States,” Harris said.
“The geologist doing the steering must be highly proactive to keep the bit in zone while geosteering,” he continued, “as there’s so much structural deformation and folding due to the considerable orogenic activity that has occurred in this part of North America.
“By acquiring this (seismic) information early on, we could determine how we place our laterals as well as the length we want to drill them,” he said.
“We’ve now drilled a third lateral, and it’s the best so far,” he continued. “It agrees with some of the predictive rock properties from the seismic data, such as properties that show an increase in the total organic content, the presence of a larger number of fractures and better brittleness.
“What’s unique about this project, which recorded both P waves and shear waves, is we’ve been able to get a better handle on things like Poisson’s Ratio – the measure of how this rock is going to deform in one axis relative to another – and Young’s Modulus, which is a measure of the rock’s elasticity,” Harris noted.
“It’s been a good project for us at the beginning of our program,” he added, “so we can see what kind of challenges we would have, both structurally and from rock physics.”
Harris noted that the company might drill perhaps five to 10 additional wells to test the predictions made off of the survey.