Real-Time Downhole Monitoring of Hydraulic Fracturing Treatments Using Fiber Optic DTS and DAS
In order to make commercial and development decisions effectively and more rapidly, new appraisal and testing technologies are needed to maximize early data collection and subsequent subsurface understanding as quickly as possible. For Unconventional Gas and Light Tight Oil (UGLTO) projects, some of this critical data can be derived from hydraulic fracture stimulation and inflow profiling activities.
For UGLTO projects, achieving an optimum hydraulic fracture stimulation is a continuous endeavor beginning as early as possible; and balancing the cost of completion vs. production performance is critical as the completion/stimulation is a large cost component of the well and heavily influences production rate/ultimate recovery. The fast paced development and introduction of new completion technologies requires diagnostic technology that can help us understand stimulation effectiveness, assess new completion technologies, and evaluate which zones are the most productive.
One emerging technology, fibre optic distributed sensing has the potential of providing key insights during both the hydraulic fracturing and initial flowback. The passive nature of fibre optic sensors allows intervention-free surveillance, which makes fibre-optic technology an effective platform for permanent sensing in producing wells. Until recently, the oil & gas industry fibre optic sensing technology has focused mainly on temperature (DTS) profiling along the wellbore. In 2009, it was first demonstrated how fibre optic distributed acoustic sensing (DAS) can also be used for downhole applications. Where hydraulic fracture diagnostics based on DTS alone in the past sometimes yielded ambiguous results, the combination of both acoustic and temperature sensing provides a step-change improvement in the ability to perform real-time and post-job diagnostics & analyses of the stimulation.
The different horizontal well case studies presented in this paper will illustrate how the combination of DTS and DAS has the potential to enhance the monitoring, assessment, and optimization of openhole and limited entry designed hydraulic fracture stimulation treatments.
Given the low productivity of Unconventional Gas and Light Tight Oil (UGLTO) reservoirs (microdarcy permeability), the key element of successful exploitation is the ability to optimally create multiple hydraulic fractures to ensure sustained and high production rates are delivered during the production phase. Because the completion of a well can be the largest single well cost component, balancing the expense of hydraulic fracture stimulation versus the production benefits is crucial for the economic development of these reservoirs.
Real-time fracture monitoring in recent years has become a critical diagnostic tool for understanding hydraulic fracture deployment success in wellbores, leading to improved delivery and placement of the stimulation treatments. The diagnostics used have been primarily focused on determining the stimulation character such as fracture geometry, proppant placement in the fracture and fracture conductivity (Barree et al., 2002).
To better understand the complexity created by hydraulic fracturing treatments, composite fibre optic cables can be installed in a well to monitor the temperature profile as well as the acoustic signal distribution during completion operations (Paul Huckabee, 2009).
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