As operators shift from appraisal to full-scale field development of their core assets in unconventional plays, they are increasingly confronting challenges surrounding the placement of wells—spacing between wells, vertical position in the reservoir, lengths and orientation of the laterals—parameters that are critical to maximizing field economics.
Modeling the subsurface and simulation of production results based on different field development scenarios is a common method used to optimize recovery; however, variability in well performance leaves remaining uncertainties and requires that both the reservoir and the completion be addressed thoroughly and properly in the production simulation. Reservoir quality can be addressed with log measurements taken along the lateral, which provides a good understanding of where the wellbore is located in the reservoir, as well as with seismic surveys, which measure deeper formation characteristics using active sources.
A more comprehensive way of assessing completion quality and the effectiveness of hydraulic fracture stimulation is with microseismic measurements, a passive methodology that uses sound to detect the energy created by rock as it cracks and assess the hydraulic fracture geometry as the wells are stimulated with fracturing techniques.
Microseismic measurements are currently the best way operators can understand the geometry that is being created during the hydraulic fracturing process—where and in which direction the complex hydraulic fracture network is going, the length of the fracture network into the reservoir, and whether it is growing up or down into unwanted intervals. The information can be used to create a feedback loop, enabling operators to improve fracturing techniques based on what they have learned.
As field development progresses there is a growing number of infield wells drilled adjacent to and hence potentially interfering with existing producers. The capabilities of microseismic analysis are being expanded with new techniques in data acquisition and processing.
The oil and gas industry has long known that the seismic energy produced from hydraulic fracturing contains information about the geomechanical deformation that occurs during stimulation. Moment tensor inversion (MTI) is a seismic data-processing technique that extracts that information from microseismic measurements and uses it in the modeling and simulation of the complex hydraulic fracture network that is created. Advances in signal processing, presentation and interpretation of MTI data now make it possible to calibrate the fracture design model and reduce uncertainty in the simulation.
Understanding the fracturing process
The technique analyzes the radiation pattern of the seismic amplitudes at different locations to determine the fracture plane and slip and define the mode of fracturing as shear or tensile opening. MTI data also enhance microseismic interpretation of fracture geometry by including the additional source parameters for each microseismic event.
By processing microseismic data with more detail and certainty, the advanced MTI processing service can be used to model discrete fracture networks, validate stimulation design and analysis, and evaluate multiple production scenarios, resulting in better decision-making in the field. Schlumberger has developed a comprehensive workflow in an exploration and production platform that now incorporates MTI results in designing hydraulic fracturing to enhance understanding of the reservoir.
Introduced in 2013, the Schlumberger MTI analysis has been deployed in several oil and gas shale well projects throughout North America. Recent projects in Canada and in the U.S. have illustrated that MTI data can help reduce uncertainty when assessing the completion quality and forecasting production results. The applications for this approach are numerous but also include the important questions operators face when deciding on well spacing patterns in unconventionals.
Advances in microseismic technology mark a breakthrough in enabling operators to obtain precise, actionable information about the hydraulic fracture geometries as wells are stimulated and use that information to improve decision-making going forward.
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