In unconventional reservoirs, forecasts of estimated ultimate recovery rely heavily on rock characterization (reservoir quality and completion quality) and information such as data from surface fluid samples and short-term production data. Less attention is paid to field-wide reservoir fluid typing and characterizing the distribution of fluid properties. However, today's higher oil prices in the US market provide the industry with a strong incentive for determining fluid composition in tight oil plays. Fluid composition plays an important role in the early business decision of accruing, holding, or releasing the acreage and in prioritizing resources for best developing the acreage. Downhole fluid sampling in ultra-low permeability formations, however, can be challenging.
Advanced mud fluid logging facilitates the direct acquisition of information on formation fluids in a continuous manner. This technique can be used to characterize the light hydrocarbon gases C1-C5; the results can be correlated with PVT data and fluid ratios can be inferred. Further, application of this method should, theoretically, enable quantitative analysis of hydrocarbon fluids before a well is completed. Advanced mud fluid logging enables reservoir fluid typing across the lateral by monitoring the changes in fluid composition.
Case studies from the Eagle Ford shale are used to demonstrate how mud fluid logging data from laterals can predict variability in the fluid compositions for a given area, in the context of production expectations. This study also provides suggestions for pressure management to delay the negative impacts of multiphase flow and upfront indication for artificial lift selection to optimize production performance. The ultimate goal of this study is to improve production expectation accuracy in tight liquid-rich plays. Understanding heterogeneity (in shale reservoirs) that impacts production should include analysis of reservoir fluid typing in the given area along with reservoir characterization.
In the last decade, unconventional reservoirs have been extensively exploited in the continental US. With the exception of the Bakken shale, the targeted plays have been primarily gas-rich. However in the last few years, the focus has shifted to liquid-rich plays or liquid-rich parts of plays. The understanding of reservoir fluid distribution in liquid-rich play is important for development planning and artificial lift selection.