Reservoir Description Of The Subsurface Eagle Ford Formation, Maverick Basin Area, South Texas, USA
- Brian Driskill (Shell Exploration & Production) | Nathan Suurmeyer (Shell Exploration and Production Co) | Sarah Rilling-Hall (Shell Exploration and Production Co) | Andrew M. Govert (Shell Exploration and Production Co) | Amy Garbowicz (Shell Exploration and Production Co)
- Document ID
- Society of Petroleum Engineers
- SPE Europec/EAGE Annual Conference, 4-7 June, Copenhagen, Denmark
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.6.1 Open hole/cased hole log analysis, 5.8.2 Shale Gas, 5.1.3 Sedimentology, 1.12.2 Logging While Drilling, 1.6 Drilling Operations, 5.4.2 Gas Injection Methods, 1.6.9 Coring, Fishing, 5.1 Reservoir Characterisation, 4.1.2 Separation and Treating, 4.3.4 Scale, 5.1.1 Exploration, Development, Structural Geology, 5.5.2 Core Analysis, 6.5.4 Naturally Occurring Radioactive Materials, 2.2.2 Perforating, 4.1.5 Processing Equipment, 5.2.1 Phase Behavior and PVT Measurements, 2.4.3 Sand/Solids Control, 1.2.3 Rock properties, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc)
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The Cretaceous Eagle Ford Formation (EF) is a marl deposited during a highstand on a broad shelf along the paleo-Texas coast. In south Texas, the EF is thickest in the Maverick Basin, which is a small sag related to crustal thinning. Extensive datasets were collected to use in subsurface studies that support exploration and development activities, including core, cuttings, chemostratigraphy, biostratigraphy, and well logs. Computed X-ray tomography (CT) scans, thin sections, scanning electron microscopy (SEM) images, focused ion beam-SEM (FIB-SEM) volumes, and X-ray diffraction/X-ray fluorescence (XRD/XRF) tables were acquired from whole core and cuttings. The goal of the integrated study was to understand EF depositional processes and rock textures, and to create a predictive model for reservoir properties.
The regional EF study began with a correlation of 400+ wireline logs. The correlation involved a stratigraphic framework that was initially based on log character, and was then refined with ash correlations, biostratigraphy data, and chemostratigraphy data. Textural information seen in core, core CT scans, and the SEM/FIB-SEM work was compared to the framework. The data gave insights into patterns of fluctuating oxygen and energy levels in the EF, which were then included into an idealized depositional model.
The datasets show regional patterns of composite cycles in which properties such as TOC, porosity, carbonate content, and rock texture are predictable. SEM/FIB-SEM images show that pores in the EF are mainly intergranular or within organic matter (OM), and that the structure of OM pores is related to maturity level. Reservoir properties can be predicted along the EF trend using the SF. Cycles of the EF with good reservoir properties can be mapped with respect to hydrocarbon fluid zones to yield risk maps.
Combining biostratigraphical, sedimentological, chemical, and physical properties is the key to understanding depositional cycles and cycle architecture. Geographic and stratigraphic sweet spots for well productivity can then be predicted by understanding how and where different parts of a cycle are stacked. As each unconventional play is unique, what works for reservoir characterization and risk mapping in one play is not necessarily applicable to another. However, developing an understanding of the interaction of the main reservoir properties should lead to less uncertainty, particularly in areas of the play with few existing wells.
In the past seven years shale plays have shifted from almost a novelty to being one of the most important hydrocarbon resources in North America (Boughal, 2008; Stevens and Kuuskraa, 2009; Toon, 2011). Shale reservoirs, originally considered a source for gas, also produce liquids in some segments. The exploration of the Barnett, Haynesville, Bakken, Marcellus, Montney, and Eagle Ford has forced industry to acknowledge that shales are multifaceted and complex systems, such that a cookie-cutter approach to exploitation may not be successful (Mazerov, 2009). An early realization was that each play is unique and has its own characteristics that impact completion practices and production behavior. Movement of shale plays to the forefront of exploration has accelerated shale research and spotlighted the shortcomings of long-held models for their deposition. Recently published research suggests that shales are commonly subject to previously unsuspected depositional processes. For instance, flume work has provided convincing evidence that traction may be an important depositional mode and that suspension settling is not required for depositing very fine-grained sediments (Schieber et al., 2007, 2010; Schieber and Southard, 2009; Schieber and Zalmai, 2009; Schieber, 2011). Additionally, it is now apparent that shale source/reservoir systems typically vary laterally at km-scale, but vertically at cm-scale (Bohacs and Lazar, 2010; Minisini et al., 2011).
|File Size||14 MB||Number of Pages||23|