Hydrocarbon indication in Rio Bonito Formation sandstone:Implication for CO_(2)storage in São Paulo,Brazil

São Paulo State has witnessed CO_(2)storage-based investigations considering the availability of suitable geologic structures and proximity to primary CO_(2)source sinks related to bioenergy and carbon capture and storage(BECCS)activities.The current study presents the hydrocarbon viability evaluations and CO_(2)storage prospects,focusing on the sandstone units of the Rio Bonito Formation.The objective is to apply petrophysical evaluations with geochemical inputs in predicting future hydrocarbon(gas)production to boost CO_(2)storage within the study location.The study used data from eleven wells with associated wireline logs(gamma ray,resistivity,density,neutron,and sonic)to predict potential hydrocarbon accumulation and fluid mobility in the investigated area.Rock samples(shale and carbonate)obtained from depths>200 m within the study location have shown bitumen presence.Organic geochemistry data of the Rio Bonito Formation shale beds suggest they are potential hydrocarbon source rocks and could have contributed to the gas accumulations within the sandstone units.Some drilled well data,e.g.,CB-1-SP and TI-1-SP,show hydrocarbon(gas)presence based on the typical resistivity and the combined neutron-density responses at depths up to 3400 m,indicating the possibility of other hydrocarbon members apart from the heavy oil(bitumen)observed from the near-surface rocks samples.From the three-dimensional(3-D)model,the free fluid indicator(FFI)is more significant towards the southwest and southeast of the area with deeper depths of occurrence,indicating portions with reasonable hydrocarbon recovery rates and good prospects for CO_(2)injection,circulation and permanent storage.However,future studies based on contemporary datasets are required to establish the hydrocarbon viability further,foster gas production events,and enhance CO_(2)storage possibilities within the region.

Differential interformational velocity analysis as an effective direct hydrocarbon indicator under velocity reversal conditions,an example from the anomalously high temperature and over-pressured DF1-1 Gas Field in the Yinggehai Basin,South China Sea

In the DF1-1 Gas Field in the Yinggehai Basin, South China Sea, the velocity-depth plot and velocity spectra show significant variations from a linear trend, exhibiting a distinct reversal phenomenon. Velocity parameters derived from velocity spectral analysis of the seismic data and sonic logs indicate that the interval velocity reverses below 2,100 m (2.2 s two-way time (TWT)) in the DF1-1 Gas Field. Some direct hydrocarbon indicators (DHIs) models developed for the shallow strata cannot be simply applied to the moderately to deeply buried strata for direct exploration target recognition because the velocity reversal has caused the middle-deep gas reservoirs to exhibit a moderate or weak seismic amplitude. The hydrocarbon indicator method of “Differential Interformational Velocity Analysis (DIVA)” with the aid of other hydrocarbon indicating techniques was employed to effectively identify DHIs in the middle-deep strata under velocity inversion. The result has shown that the DIVA technique can be effectively used as a DHI in both the shallow and the middle-deep strata in the study area with the shallow strata characterized by Type I DIVA anomaly and the middle-deep strata characterized by the Type II DIVA anomaly.