AAPG Annual Convention and Exhibition

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Acquiring and Accounting for Stress and Fractures in Shale Oil and Gas Wells


Achieving optimal exploitation of unconventional reservoirs requires a combination of accurate well placement, stress determination, and fracture mapping. Ultra low permeability formations found in shale oil and gas plays require hydraulic stimulation to build a conductive network of both hydraulically stimulated fractures and the naturally occurring formation fracture network. We combine acoustic measurements to estimate both isotropic and anisotropic elastic stress in transverse isotropic formations with basic imaging in both water and oil based mud systems. Using near wellbore stress and imaging to enhance reservoir modeling or simply normalize properties across each stage an optimized multi-stage stimulation program is proposed. By understanding stress and fracture variations across the production zone we can suggest stages and perforation positions that have similar properties and avoid stimulating high stress zones, zones with swelling clays that might accept proppant but close off after stimulation, and fracturing that if stimulated might communicate with undesirable zones. We will review and compare converted shear results from logging-while-drilling (LWD) unipole transmitters and receivers to other commonly utilized sonic tools. For fracture imaging we will examine the challenges associated with eccentering, mud weight, cuttings, and mud type. We will show test results as well as modeling and compare that to what we see in real world log examples. This paper suggests a low cost solution to normalize and increase the total number of contributing perforation clusters in horizontal, transverse isotropic environments found in shale oil and gas wells.