Abstract
The rocks of interest in the present study (mudstones) show inherently a heterogeneous pore-size distribution in the matrix. They can present organic and inorganic pores and the transport mechanism through pores is different, and, therefore, it is necessary to describe their organic and inorganic porosity. This work uses different microscopy techniques to characterize mudstones from the Galembo Member of the Cretaceous La Luna Formation, Middle Magdalena Valley Basin, Colombia. These rocks present several pore types, including interparticle pores due to flocculation of clay minerals, organoporosity due to burial and thermal maturity, intraparticle pores from organisms, intraparticle pores within mineral grains, and microchannels and microfractures. The existence of interconnected pores in such complex fracture-pore system provides effective pathways for primary gas migration and it also provides a storage space for the residual hydrocarbon in mudstones, which is important for the primary migration and storage in gas reservoir rocks. The pore connectivity is high and increases towards the top of the sedimentary sequence.
Highlights
It is well known that worldwide conventional oil and gas supply is declining around the world while costs are going up
We report the occurrence of organoporosity in nonlaminated to slightly laminated foraminifera wackestones in two ways: (1) organic matter with a pendular morphology filling pore spaces between calcite crystals, with pores showing an elongated and angular shape, some of them interconnected; (2) laminar solid organic matter with low content of interconnected microporous space, with isolated pores, which according to Loucks et al [37] can be associated to immature organic matter
We illustrate several examples of a variety of pore types that are present in the Galembo Member of the La Luna Formation, using the classification proposed by Slatt & O’Brien [29]
Summary
It is well known that worldwide conventional oil and gas supply is declining around the world while costs are going up. The energy industry is focusing on the unconventional resources (tight gas sands, coal-bed methane, heavy oil and gas shales), with hydrocarbons in rocks of nano-meter scale porosity and low permeability, evaluating their potential in many sedimentary basins. The conventional techniques are not applicable to unconventional reservoirs due to the complex properties of gas shales, and, while their characterization is very important for production planning, these low permeability rocks are very challenging to characterize due to their complex nano-meter scale pores and mineral structure. According to reports from the National Hydrocarbon Agency ing.cienc., vol 16, no. 31, pp. 169-205, enero-junio. 2020
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