Down-Hole Raman Reservoir Spectrometer (DRRS): A Novel New Raman Spectroscopy Logging Technology for the Rapid Appraisal of Shale Gas Resource Potential
The DRRS is a wireline conveyed chemical sensing logging instrument used to evaluate the resource potential of hydrocarbons in unconventional reservoirs. It is able to detect and quantify low ppm concentrations of methane and other light hydrocarbons in wellbore fluids as well as discriminate in real time between the presence of such gases in the free and solubilized states. We present the results of two successful DRRS field trials that have been conducted in evaluation of the Marcellus shale formation in the Appalachian basin, PA. We also describe a methodology for quantitatively estimating an upper limit on dissolved higher HCs during DRRS logging. The technical objective of the field trials was to identify and quantify HC composition and resource density as well as the most favorable location(s) for the placement of a lateral. Field trial-1 was conducted in an uncased well in central northern PA, where the Marcellus was only ~3 m thick. The results of several logging runs established the clear presence of methane entering the well bore to a vertical resolution of better than ~20 cm. No hydrocarbons >C2 were detected in the resultant plume. Field trial-2 was conducted in a cased well in Potter County, PA, where the Marcellus shale was almost 30 m thick. Based on Spectral Gamma Ray logging, the Marcellus in this part of PA is composed of three distinct lithofacies (Basal, Middle and Upper zones), easily recognized by their petrophysical rock properties (TOC, Sg and porosity). We present a novel test methodology that was developed to evaluate resource potential in cased hole wells that avoids surfacing of hydrocarbons and associated complexities. The acquired DRRS data provides, in real time, an estimate of the composition and relative richness of all three zones within the Marcellus shale. The results of Field trial-2 showed that the most productive interval was the Upper zone, producing gas to the well bore at a considerably faster rate than the Basal zone. These results challenge an established paradigm of unconventional resource evaluation which is focused mostly on high Uranium and TOC intervals for placement of laterals. Based on measured plume concentrations in the two field trials, the estimated resource density (i.e., the mass of methane per volume of rock) is far greater in the Upper zone relative to the Basal Marcellus. Based on our DRRS results, we would preferentially target the lateral to optimize production from the Upper zone.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017