Introduction to unconventional resource potential in the newly emerging, Lower Smackover (Brown Dense) Formation, northern Louisiana, USA: its geological characteristics and exploration potential

摘要

Geological characteristics and shale-gas exploration potential have been intensely evaluated, using newly collected core (137 m long) and a full suite of wireline logs from the Lower Smackover Formation (Brown Dense), northern Louisiana. The study results have revealed that the Brown Dense comprises three progradational parasequence sets, each set of which contains 15-25, small-scale parasequences that are expressed as highly serrated-log motif. Individual parasequences reflect distinctive lithologic variations of basal, laminated mudstones (offshore transitional deposit) and upper, ooid-peloid packstones (high-energy shallow marine deposit). The mudstones are mainly composed of calcite, quartz, dolomite and pyrite with moderate amounts of diagenetic clays, whereas in the pack-stones the predominant calcite content is readily apparent with small amounts of other minerals. Matrix pore types comprise dominant interparticle and intraparticle pores in the mudstones, but mainly interparticle pores in the packstones. The pyrite occurrence is proportionally related to the organic-matter content that shows high-low amount couplets within parasequence-scale, lithologic variations. Porosity and permeability show a positive correlation with effective porosity ranging from 1 to 6% and permeability varying from less than 0.1 mu d to larger than 1mD. As compared with stratigraphic packages, three types of the porosity and permeability trend can be recognized, including positive, negative and random relationships. These features are likely influenced by the degree of pressure solution (i.e., stylolites). Rock-Eval/TOC analysis has shown that organic matter consists mainly of type-II oil-prone kerogen with TOC ranging from 0.55 wt% to 1.73 wt%. The transformation ratio of organic matter is estimated up to 80% that is broadly equivalent to the earliest gas window, supported also by T-max values, showing late oil to wet-gas windows. Mechanical rock properties measured from static and dynamic methods have confirmed that rock brittleness of the cored well is considered to be good to excellent. In this study and unpublished proprietary data, we have found that mineral framework and organic-matter layering play an important role in controlling mechanical properties. The study results have tentatively concluded that the newly emerging Brown Dense shale has a high exploration potential, if completion and development strategies will become optimized.