Abstract
The authors analyse the process of water re-injection in the hydrocarbon reservoirs/fields in the Upper Miocene sandstone reservoirs, located in the western part of the Sava Depression (Croatia). Namely, this is the “A” field with “L” reservoir that currently produces hydrocarbons using a secondary recovery method, i.e., water injection (in fact, re-injection of the field waters). Three regional reservoir variables were analysed: Porosity, permeability and injected water volumes. The quantity of data was small for porosity reservoir “L” and included 25 points; for permeability and injected volumes of water, 10 points each were measured. This study defined selection of mapping algorithms among methods designed for small datasets (fewer than 20 points). Namely, those are inverse distance weighting and nearest and natural neighbourhood. Results were tested using cross-validation and isoline shape recognition, and the inverse distance weighting method is described as the most appropriate approach for mapping permeability and injected volumes in reservoir “L”. Obtained maps made possible the application of the modified geological probability calculation as a tool for prediction of success for future injection (with probability of 0.56). Consequently, it was possible to plan future injection more efficiently, with smaller injected volumes and higher hydrocarbon recovery. Prevention of useless injection, decreasing number of injection wells, saving energy and funds invested in such processes lead to lower environmental impact during the hydrocarbon production.
Highlights
Numerous geological variables are analysed numerically and spatially
This study analysed injected water volumes into the Neogene hydrocarbon reservoir located in the Sava Depression (Northern Croatia) as primary and accompanied porosities and permeability as secondary variables
All selected statistical interpolation methods were from the primary group of methods created for the small datasets, namely inverse distance weighting, nearest neighbourhood and natural neighbourhood
Summary
Numerous geological variables are analysed numerically and spatially. The results are applied for creation of different geological models with different scales. The selected field and reservoir are named as “field A/reservoir L” in the Lower Pontian sandstones of the Kloštar Ivanic Formation. In both reservoirs a currently active water-flooding regime for increasing recovery and period of production is present. All used datasets were small, i.e., contained fewer than 20 measured points projected at the reservoir 2D section This was a challenging task, depending on: (a) distribution of injection and measurement wells, (b) number of fault zones, (c) number of wells with production and log data. The results should show how to map the injected water volumes in similar reservoirs and geological provinces, which is one of the often skipped tasks in observation of production history. In future, some heavy oil reservoirs (like the abandoned Križ Oilfield) could be considered as a target for application of microbial enhanced oil recovery (MEOR), as was shown as a successful pilot project on low-temperature heavy oil reservoirs in Russia [4]
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