An Integrated Seismic Reservoir Characterization Workflow for Sweet Spot Identification in Unconventional Resource Plays in Triassic Yanchang Formation, Erdos Basin, China

Abstract

A huge volume of organic-rich shale is developed in the deep or semi-deep lacustrine depositions in Triassic Yanchang Formation, Ordos Basin. Recent horizontal drilling and hydraulic fracturing shows high hydrocarbon (shale gas) production potential in the shale formation. However, previous reservoir characterization efforts are mainly focused on the use of well logs and cores. Although the results are very informative, strong heterogeneity of lacustrine shale could lead to substantial uncertainty in interwell volumes. Consequently, this work presents an integrated seismic reservoir characterization workflow based on full-azimuth, high-density 3D seismic data to demarcate the most prolific reservoir volumes for further productive infill wells. The workflow begins with prestack simultaneous inversion for elastic properties, followed by a petrophysical evaluation to determine a spatial distribution of shale gas reservoir quality (RQ). The analysis shows that the inverted acoustic impedance is a good indicator of total organic content (TOC) richness and porosity, where low impedance corresponds to high TOC and high porosity, relating to favorable reservoir. In addition, the well completion quality (CQ) is evaluated through prestack azimuthal inversion for descriptions of natural fractures and geomechanical modeling to investigate shale fracability. The results obtained demonstrate moderate minimum horizontal stress and high brittleness in the targeted shale formation with high possibility to form complex hydraulic fractures. The RQ and CQ are finally combined together by way of weighted average for sweet spot identification with high evaluation values representing high hydrocarbon production capacity volumes. The integrated shale reservoir characterization value is corroborated with the available wells drilled within the survey area and further helps to determine optimal well locations and to locate hydraulic fracture treatments. And the proposed characterization methodology can be a good reference for other lacustrine shale plays.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016