Hydrocarbon fluid inclusions and source rock parameters: A comparison from two dry wells in the western offshore, India

Fluid inclusions represent the direct evidence of paleofluids and can provide valuable information on the evolution of sedimentary basins and oil-bearing strata. Hydrocarbon fluid inclusion(s) (HCFIs) are the vestiges of oil from the geological formations. The paper delineates the paleotemperature (T_h)/ oil window, the oil quality of HCFIs and Raman peaks corresponding to hydrocarbon species of HCFIs using fluid inclusion techniques, and source rock potential of hydrocarbon generation, thermal maturity, the quantity of organic matter, and the kerogen types obtained through Rock-Eval pyrolysis data from two dry wells RV-1 well of Mumbai offshore and KKD-1A well of Kerala-Konkan Basin. The present study compares the fluid inclusion parameters as well as the source rock geochemical characteristics of these two dry wells to address the scientific problem of the wells going dry. Further, evaluated whether the results agree with an earlier finding from a case study of two wells named KK4C-Al (Kerala-Konkan basin) and RV-1 well where only a few parameters such as temperature of homogenization (T_h) & API gravity were utilised, and the chances of getting oil in the nearby areas of these two wells were reported. In the present study, the fluid inclusion parameters such as the palaeotemperature (T_h), API Gravity and Raman spectra were obtained from micron sized fluid inclusions at different depths for a quick assessment of nature of oil inclusions within the two dry wells. Along with fluid inclusion parameters, different source rock parameters obtained from Rock-Eval Pyrolysis analysis (secondary data) such as S1, S2, S3, T_max, Hydrogen Index (HI), Oxygen Index (OI), Potential Yield (PY), Production Index (PI) and Total Organic Carbon Content (TOC) were also considered for a detailed source-rock evaluation of two wells (RV-1 and KKD-1A) and the results act as the supporting evidence to address the reason for the wells gone dry.
Temperature of homogenisation (T_h) of hydrocarbon Fluid Inclusion Assemblages (FIAs) from both the wells fall in the oil window (60–150 ℃) range indicating that there was a conducive thermal condition favourable for oil generation in these two basins. API gravity of oils in RV-1 well of Mumbai offshore (48–53) was lighter when compared to those in KKD-1A (18–22) of Kerala-Konkan basin. Raman spectra of HCFI samples could decipher important hydrocarbon species from RV-1 well samples. Raman spectra of KKD-1A well show less prominent peaks (broad) only. Pyrolysis data shows that Paleocene–Early Eocene source rocks of Panna formation of RV1 well are mature enough to generate hydrocarbons. On the other hand, Paleocene aged source rocks of Kasargod formation of KKD-1A well are immature. Source rock maturity therefore could be considered as crucial in hydrocarbon generation in these two wells even if oil-window was achieved. This study reports that, in RV-1 well, even though it is a dry well in a proven basin, the oil window, API gravity of oils and constituents from HCFIs of RV-1 well and the source-rock maturity opens up a demand for detailed exploration in nearby areas of RV-1 in the Mumbai offshore basin hopeful of finding a high-value prospect for oil, whereas the fluid inclusion studies in the HCFIs of KKD-1A well of Kerala-Konkan basin is showing only a minimal chance of oil generation that too of a heavy nature and the source rock immature characteristics suggesting only minimal generation of hydrocarbons. Due to the heaviness of the available oil in the KKD-1A well impedes migration. Our study suggests that there is no potential for finding oil in the nearby areas of KKD-1A well of Kerala-Konkan basin.