Determining Seal Effectiveness and Potential Buoyant Fluid Migration Pathways using Shallow High-resolution 3-D Seismic Imaging: Application for CO2 Storage Assessment on the Inner Texas Shelf

Meckel, Timothy; Bangs, Nathan; Trevino, Ramon

Typically seal prediction focuses on wireline log and petrophysical flow properties that can be measured on cored seal specimens (i.e. capillary fluid threshold entry pressure).The lateral continuity of seals is difficult to predict. One way to overcome the spatial limitation is to observe long-term fluid history behavior by investigating overburden. Such analysis relies on the premise that prior or current migration of buoyant fluids has ‘tested' a more extensive area of seal coverage and variability, including faults. Indications of shallow migration and/or re-accumulation are suggestive of poor seal quality, and such indications may be helpful in identifying likely migration pathways, further delineating the mechanism or process of seal failure. Such analyses have been used to predict seal risk for hydrocarbon prospects and seem appropriate for understanding seal risks for CO2 storage prospects. Typically the near-surface interval is poorly imaged in commercially available seismic data given acquisition and processing optimized for deeper reservoir systems. We present recently-collected shallow high-resolution 3-D seismic data and describe how they can be used to assess seal integrity and potential migration in inner Texas shelf, northern GOM offshore CO2 storage prospects. For this study ~1,100 line km of 3-D seismic data were collected using the "P-Cable" acquisition system (12 25-m long streamers with 12.5 m spacing) focused on upper 1 sec TWTT over a prospective storage area. The site is offshore southern Galveston Island, adjacent to the San Luis Pass salt dome, in Texas state waters. The region has both commercial gas accumulations and abundant dry holes. Criteria were developed for identifying potential natural (hydrocarbon) fluid migration systems over geologic time, with an emphasis on how that understanding can be used to demonstrate effective (or alternatively leaking) seals and for identifying the likely migration pathways that may limit or render unsuitable a specific storage target. Collecting such data prior to initiating a storage project may also serve as a baseline for future time-lapse (4-D) surveys to demonstrate containment or identify non-containment. Several lines were shot twice for evaluating repeatability; perspectives on this application will be provided.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013