Category: Technical Papers

09 Nov 2012

Affordable Permanent 3D VSP for Onshore and Offshore Applications

Summary
Down-hole seismic monitoring in the form of time-lapse 3D VSP has emerged as a technically viable alternative in areas where reservoir monitoring via conventional 4D seismic recorded on surface is not expected to be technically successful due to low SNR or insufficient repeatability. But even after the technical case is proven for time-lapse 3D VSP – often a major and protracted task – a larger hurdle remains to make the technique affordable on a field-wide scale. We discuss how the emerging technology of Distributed Acoustic Sensing (DAS) may be used to clear this hurdle both onshore and offshore.

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13 Mar 2012

First Downhole Application of DAS for Hydraulic Fracturing Monitoring

Summary

The first exploration-and-production downhole field trial of distributed acoustic sensing (DAS) fiber-optic technology was conducted during the completion of a tight gas well in February 2009.

DAS is a novel technology that allows the detection, discrimination, and location of acoustic events on a standard telecom single-mode fiber several kilometers long. Using a combination of the measurement of backscattered light and advanced signal processing, the DAS interrogator system segregates the fiber into an array of individual microphones. To date, the technology has been applied mainly in the defense and security industries. One of the most exciting applications for downhole application of DAS is in the area of hydraulic fracturing of tight-sand and shale-gas reservoirs. Balancing the cost of hydraulic-fracture stimulation with the production benefit is crucial in tight-sand and shale-gas developments because, after drilling costs, the completion is the largest single cost component of the well.

Recordings can be made while tools are run in hole, bridge plugs are set and perforations are shot and during the fracture-stimulation treatment. The technology is sufficiently reliable and sensitive to detect and monitor these in-well activities. The fidelity of the recordings made during hydraulic-fracturing and flowback operations provides a step-change improvement in the ability to perform real-time and post-job diagnostics and analyses of the stimulation.

The different case studies presented in this paper will illustrate how, even in its earliest form, DAS has the potential to enhance the capability of monitoring and understanding in-wellbore activities. The technology enables the optimization of hydraulic-fracturing design and execution, which can drive down completion costs and lead to increased well productivity and ultimate recovery.

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13 Mar 2012

Real-Time Downhole Monitoring of Hydraulic Fracturing Treatments Using Fiber Optic DTS and DAS

Abstract
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.

Introduction
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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23 Sep 2011

Field Trials of DAS For Geophysical Monitoring

Summary

Distributed Acoustic Sensing (DAS), a rapidly evolving fiber-optic based technology for permanent in-well and geophysical monitoring, was used to record VSP data in two field trials in Shell assets onshore Canada and USA. Useful in-well velocity data were gathered from the entire length of the well from wellhead to TD (up to 4 km), which compared well with geophone recording and sonic log data. Walk-away VSP data yield images that are nearly equivalent to images from conventional borehole geophones in terms of signal to noise ratio and resolution. Permanently installed fiber-optic infrastructure will enable low-cost non-intrusive geophysical monitoring.

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