Characterizing and producing from reservoirs in landslides: challenges and opportunities

Abstract

AbstractLandslides can consist of rotational slips, translational glide blocks, topples, talus slopes, debris flows, mudslides and compressional toes which can combine in different proportions to form complex landslides. The mass movement can be subaerial or submarine, occur over wide ranges of scale and can vary in rate from creep to catastrophic failure. Complexity of the landslide reflects the controlling factors including the strength of the deforming material and triggering mechanisms such as earthquakes, imposed load, increasing topographic relief and removal of toe material.Processes of landslide deformation include slip on discrete surfaces, distributed shear within the landslide, vertical thinning and lateral spreading through shear, fluidization, porosity collapse and loss of material from the top or toe of the complex. These processes control the quality of the resultant reservoirs. This leads to a greater range of reservoir types than conventional faulted reservoirs, with a proportionate upside and downside potential and difficulty in quantifying uncertainty.This paper uses examples from the literature, outcrops and subsurface datasets (including the Statfjord Field and the Halten Terrace in Norway) to outline the complexity of reservoirs in landslides and the challenges and opportunities in finding and producing them. We present workflows for seismic and subseismic characterization for exploration and reservoir scale based on geomorphological principles. Seismic mapping is achieved by classifying the form of the reflectors (both slip surfaces and the bounding envelope of the landslide) from an atlas of geometric and structural styles and is applied to both the Halten Terrace example and the Statfjord Field. We present a new workflow for reservoir characterization in which integration of structural, biostratigraphic, sedimentological and dynamic data gives key information on process, timing and heterogeneity of the reservoir. For the Statfjord field, important maps of the landslide block stratigraphy derived from a subcrop map and communication maps based on a c. 130 well dataset can be correlated to outcrop analogues and used to develop a predictive tool for landslide reservoir extent and quality, both in this field and others.