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2018 AAPG International Conference and Exhibition

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Importance of Natural Fracture Prediction for Successful Hydraulic Fracturing

Abstract

Hydraulic fracturing is the main stimulating technique designed to enhance recovery of tight gas, shale gas, and other unconventional resources. Following main factors can affect the result of hydraulic fracturing: thickness and lithology of reservoir rocks, permeability, density, skin factor, presence of impermeable rocks over and below the reservoir, reservoir pressure, amount of hydrocarbons in place and significant natural fractures. In contrast to the great commercial success of hydraulic fracturing in tight reservoirs the results of fracturing are proven difficult and frequently unsuccessful in many naturally fractured reservoirs. Zone with enhanced fracture network generally coincides with zones of intensive or total circulation loss during drilling, naturally fractured reservoirs have low oil rates and high water cut rate. Thus, knowledge of the location and extend of the natural fractured zones is crucial for the planning and executing successful fracking operations. Among several methods currently used to identify the location and extend of natural fracturing before drilling, Duplex Wave Migration technique (DWM) is the most reliable and only direct method to identify location and extent of natural and induced fracturing. Duplex wave is a result of two reflections: the first reflection is at sub-horizontal boundary, and the second is at sub-vertical boundary (or vice versa). In comparison with conventional 3D anisotropic pre-stack depth migration (PSDM), the Duplex Wave Migration allows forming images of sub-vertical boundaries (from 60 to 90 degrees). DWM allows to obtain from land seismic data the information on strike, direction and acoustic properties of sub-vertical boundaries. The method was tested in different parts of the world and its advantages are described in many papers. In these papers and case studies, DWM fracture prediction method was compared with reflection amplitude, reflection curvature and its derivatives, coherency cube, spectral decomposition, and tracking technology, azimuthal anisotropy of P- wave velocity, amplitude cube. Based on these comparisons, the Duplex Wave Migration method was the only method that would consistently and accurately image vertical fracturing in both shale and carbonate reservoirs. The reliability of method has been consistently proven by more than 50 horizontal and vertical wells. Duplex Wave Migration (along with conventional seismic imaging methods) can add significant value and reduce risks for fracking operations.