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Microbial communities are highly complex systems, yet are assembled from basic building blocks of some of the simplest organisms on Earth. We currently have ample information on many individual microbial taxa, but we lack fundamental understanding of how complexity emerges as microbial communities are assembled. As microorganisms almost always exist in complex communities, a series of experiments were implemented in order to study the factors involved in community assembly. Here, focus was placed on investigating two assembly processes described by the metacommunity concept: neutral assembly, dominated by stochastic processes, and species sorting, where the environment selects for the emerging complex community. The process of assembling a complex microbial community on different rock substrates was studied in a series of interlinked experiments. In an experiment examining colonisation of two end-member igneous rock types over the course of 1.5 years, it was hypothesised that neutral processes would dominate at the outset, with environmental selection and thus species sorting becoming more important with time. The results indicate that the opposite is true: the communities are selected for at the outset and converge through neutral processes to a more complex community as the environments become more similar over time. Other experiments were set up in order to probe different factors controlling the assembly of complex microbial communities. Microbial environmental engineering was studied by investigating microbially-mediated rock weathering and its effect on the emerging community. The role of priority effects in building a complex community from simple building blocks was investigated using strains isolated from the colonisation experiment, by mixing together single isolates with some time lag into a co-culture. Lastly, the impact of environmental perturbation on viability of communities at different stages in the assembly process was studied using stresses such as freeze-thaw and desiccation. Together, these experiments have given greater insight into the various factors that influence the assembly of a complex microbial community.

Abstract: The identification and characterization of flow units is as significant in unconventional reservoirs as it is in conventional reservoirs. In both reservoir types, this designation guides production designs by identifying high and low flow reservoir intervals. But in unconventional reservoirs – unlike conventional reservoirs – flow units may also predict the distribution of fluid type, related to the size and connectivity of the pore structures pores. In unconventional reservoirs, an improved understanding of how the pore system is affected by the depositional rock fabric or by diagenetic processes could lead to the comprehension of how these factors may have controlled the distribution of hydrocarbons. This study focuses on the Montney play at and surrounding Septimus Field, in South Peace region, an example of a tight-oil/gas reservoir where hydrocarbon columns lack an obvious top seal and less dense fluids underlie more dense fluids. It applies a well-based data set, including wells with log suites and three wells with long cores, in investigate the roles of rock composition and fabric, mineralogy, diagenetic events, and petrophysical properties to develop. sedimentological and diagenetic models that aid our understanding of fluid distributions. The dataset used in this study is a southwest-northeast transect of thirteen wells that penetrate the Montney Formation in the Septimus area. Our analysis applies a probabilistic cluster model (GAMLS) to well logs (gamma-ray, neutron porosity, and density) to identify and define rock types in the Montney Formation. Four endmember-rock types (RT) were identified, and each rock type was initially defined by a unique log signature. Comparison to mineralogical, geochemical, and petrophysical (porosity-permeability relationship, pore throat and pore size) data developed from core samples indicates that each rock type is also characterized by unique rock properties. Mineralogical analysis showed that rock types main mineralogical difference was in the proportion of (%) K-feldspar + plagioclase, quartz and clays. Furthermore, this compositional differences were reflected in the fabric, mineral assemblage, and diagenetic events for each of the four rock types. Petrophysical analysis reflect that these compositional differences also had an impact on the porosity-permeability relationship, additionally to the presence of the bitumen saturation observed occluding the different pore types present for each rock type. We then further calculate capillary entry pressures under reservoir conditions and under different fluid properties to identify differences in the capillary entry pressure for the four rock types. Capillary entry pressures reflected the impact the bitumen saturation coating the pore throat radii of the rock types and in turn in the capillary entry pressures. From our analysis we were able to confirm that rock types under the influence of a medium to light oil are expected to have lower capillary entry pressures in comparison to same rock types under the influence of a gas fluid composition. In addition, this analysis confirms that oil with a lower surface tension penetrated more easily the pore throats of these rock types, occluding the remanent pore space and leading to gas, with a higher surface tension accumulate under oil (a denser fluid), leading to these unconventional fluid distributions at Septimus field. In conclusion, we have demonstrated an effective workflow to define and map flow units in the Montney Formation. Our analysis shows that the Montney reservoir in Septimus field can be effectively classified from well logs as a combination of four rock types. We have also demonstrated that these rock types distinctly differ in their mineralogical composition, organic carbon content, rock fabric and, in turn, their petrophysical properties, furthermore, we have demonstrated that rock types can be used to map petrophysical properties and compared to fluid distribution at a field scale.