Insight into Heterogeneous Calcite Cementation of Turbidite Channel-Fills from UAV Photogrammetry

Abstract

Diagenesis is a key controlling factor on sandstone porosity and permeability. Understanding type, paragenetic sequence and spatial patterns of cements is thus important for assessing sandstone hydrocarbon reservoir properties. In this study Unmanned Aerial Vehicle (UAV) photogrammetry is used to evaluate the shape and spatial distribution of calcite concretions developed within the sand-prone fill of a turbidite channel. The studied channel-fill is entrenched into hemipelagic marlstones and include a lower conglomeratic sandstone loaded with marlstone rip-ups and an upper fill featuring a range of turbidite bed types, which, up-section and off the channel axis, are progressively finer grained and less amalgamated. Concretion shape analysis highlighted a continuum of equant to oblate shapes with flat-lying major axes and a cumulative volume fraction of ca. 22%. Equant to sub-equant concretions are ubiquitous and occur at different heights within beds, often developing around marlstone rip-ups. Conversely, elongated concretions are either strata-bound concretions or completely cemented beds which become volumetrically dominant up section and off the channel axis. The interparticle pore-space of concretions represents on average ca. 22% and is tightly filled by poikilotopic and blocky calcite cement precipitated near to maximum burial depth, whereas host sandstones lack calcite cements and show smectite clay cement and an average preserved porosity of ca. 15%. The oxygen and carbon isotopes of calcite cements point to the marlstone as the main source of carbonate ions, suggesting concretions developed during burial by either diffusion from rip-ups and mud caps or recrystallization of, matrix micrite. Results suggest that the process by which the carbonate-rich component was eroded from the substrate and trapped within the channel-fill is a key control on spatial distribution of calcite concretions, likely to reflect on spatial variability of reservoir properties.

Reservoir Potential Assessment of the Tortonian–Calabrian Sediments from Offshore Makran (Southwest Pakistan) through a Multidisciplinary Approach

“…The presence of dolomite cement in sandstone reservoirs is further reported by various researchers (Taylor and Gawthorpe, 2003;Sliaupa et al, 2008;Zhang and Li, 2020) and is considered to reduce reservoir porosity (Zamanzadeh et al, 2011), indeed it is assumed to be the reason for low sandstone porosity in the studied reservoir strata. Additionally, calcite cement is also reported from sandstone bodies of shallow marine environments (Walderhaug and Bjørkum, 1998;Xiong et al, 2016) and turbidite channel-fills (Marini et al, 2019). However, this assumption needs further investigation using detailed petrographic and mineralogical studies for the sandstone reservoirs in Offshore Makran, subject to the availability of more new data.…”

Calcite‐cemented concretions in non‐marine sandstones: An integrated study of outcrop sedimentology, petrography and clumped isotopes

“…Sandstone texture (grain size and sorting) and architectural bounding surfaces in sediments operate to control calcite cementation through their influence on the spatial distribution of permeability (Mozley & Davis, 1996; Cavazza et al ., 2009; Arribas et al ., 2012; Marini et al ., 2019). The most important textural control on cementation observed in this study is that preferential cementation of concretions occurs at tops or bottoms of sand beds.…”

Basin topography and depositional styles controlled by collisional tectonics in the Alps-Apennines junction (Tertiary Piedmont Basin, NW Italy)

“…Carbonate content, along with the foraminiferal assemblage observable on this section, indicates that these mud clasts were eroded from the channel marly substrate. Calcite cement characteristics, grain to grain contacts and carbon and oxygen stable isotopes (Milliken et al, 1998;Marini et al, 2019) indicate that the concretions formed during burial diagenesis and that the marlstone surrounding CdV and forming the rip-ups in the sandstone represent the dominant source of carbonate ions for calcite precipitation. Recently, the spatial distribution of these concretions has been assessed with the aid of UAV photogrammetry, showing that highly elongated concretions up to several metres long are associated to fine grained tops and comparatively more abundant in channel margin locations and in the uppermost part of the channel-fill (Marini et al, 2019).…”