Characterizing carbonate reservoir fracturing from borehole data – A case study of the Viséan in northern Belgium

Abstract

Fractured carbonate rocks are widely used as hydrocarbon or geothermal reservoirs.To provide a better understanding of the distribution and characteristics of such fractures, a general workflow will be presented for the characterization of fracturing from borehole data, by exploration and statistical analyses of integrated datasets. In a case study of Viséan limestones in a Belgian borehole, both cores and geophysical well logs were used to investigate which factors control the characteristics of partially open veins, which contribute to permeability. Relationships between multiple variables were tested statistically. Lithology, geochemistry and geophysical well log values were taken into account, as well as quantified veins, vugs and stylolites from cores. Although natural joint frequencies appeared hard to quantify from the available data, partially open vein characteristics could be well quantified. The results show that differential compaction controlled the development of fractures. Fracturing occurred preferentially in massive reefal buildup boundstones in contrast to layered wacke-to grainstones. Layer-parallel slip along bedding surfaces could also have reduced fracture development in the latter limestones. Frequencies of cemented veins and partially open veins are positively correlated, which suggests that the partially open veins result from either re-opening by dissolution, or (re-)opening due to a later fracturation phase. In summary, this multi-source study provides a workflow for fracture characterization from boreholes, as well as insights into the factors controlling the distribution and characteristics of partially open veins, which enhance reservoir permeability.

Relationship between stylolite morphology and the sealing potential of stylolite-bearing carbonate cap rocks

“…Some partially open veins with remaining porosity are connected with microfractures, which contribute to enhance permeability. This result is also in agreement with the conclusion of van der Voet et al (2020).…”

“…The driving force for compaction can either be either the overburden load or tectonic stresses. The two can be distinguished by the orientation of stylolites: parallel the bedding or in any other orientation, respectively (e.g., Park and Schot, 1968;Laronne Ben-Itzhak et al, 2012;Rustichelli et al, 2015;Paganoni et al, 2016;Koehn et al, 2016;Beigi et al, 2017;Rashid et al, 2017;van der Voet et al, 2020). As an ubiquitous diagenetic product, bedding-parallel stylolites in carbonate successions are of importance for hydrocarbon seepage due to their possible influence on local and regional fluid flow in the subsurface (Bruna et al, 2013;Rustichelli et al, 2015;Gomez-Rivas et al, 2022).…”

Controls of dolomitization and bed thickness on fracture networks in Lower Carboniferous carbonates in southern Belgium

“…Fracture characteristics of these carbonates were studied based on borehole cores (Van der Voet et al, 2020c) as well as from image logs ( Van der Voet et al, 2020b).…”

Tectonic Fracture Formation and Distribution in Ultradeep Marine Carbonate Gas Reservoirs: A Case Study of the Maokou Formation in the Jiulongshan Gas Field, Sichuan Basin, Southwest China

“…Tectonic fractures are important reservoir spaces and seepage channels. − In reservoirs with tectonic fractures, reservoir permeability can often increase by 1–3 orders of magnitude. Therefore, tectonic fractures correspond to more favorable petrophysical properties of carbonate reservoirs and a higher oil and gas production capacity and have great practical significance for oil and gas field exploration and development. , …”

“…Therefore, tectonic fractures correspond to more favorable petrophysical properties of carbonate reservoirs and a higher oil and gas production capacity and have great practical significance for oil and gas field exploration and development. 8,9 Tectonic stress is the cause of the formation of tectonic fractures in carbonate reservoirs, which controls the interaction, extension direction, geometry, and mechanical properties of the fractures. For areas that have experienced strong tectonic stress, tectonic fractures are widely distributed with strong regularity.…”