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Rock types and hydrocarbons distribution in an unconventional oil and gas field: Montney Formation, Septimus field, northeast British Columbia, Canada
- Author / Creator
- Hernandez Medina, Stephany
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.
- Graduation date
- Fall 2021
- Type of Item
- Master of Science
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.