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With traditional sandstone oil reservoirs coming to the end of their useful lives, there is interest in extracting oil and gas from shale and carbonate rocks. Recovered samples often contain hydrocarbon material, sometimes in a fairly mobile form, sometimes in a tarry form. There is also an interest in studying forms of porous carbon, such as biochar, both for their soil-remedial properties, and for carbon sequestration. Biochars, depending on heat-treatment temperature and duration, also frequently contain resid- trains to quantify the measurements. This study also applies NMR cryoporometry, to measure structure: pore-size distribution and pore volumes of the rock, and of the stable carbon skeleton. It has the significant advantage of being usable even when there are liquids and volatile components already in the pores. In porous rocks, combining mobility and structural information will provide a measure of the difficulty of removing the tar/oil from the rock.In biochar, combining the mobility of the labile components with the structural information for the stable biochar skeleton will inform calculations of lifetime of the labile components within the biochar. The NMRC data will also inform estimates of the lifetime of the biochar carbon skeleton.

Lacustrine carbonate rocks form important hydrocarbon accumulations along the Brazilian continental margin, some of which are contained in oil fields in which coquinas are one of the main reservoirs (viz. Campos Basin). The complexity and heterogeneity of these deposits make them a challenge in terms of reservoir description. For the necessary classification and paleoenvironmental interpretation of the coquinas, it is essential to evaluate many aspects including biological (such as carbonate productivity), sedimentological (energy regime in the depositional environment, transport of bioclasts, terrigenous supply), taphonomic (fragmentation of shells, abrasion) and diagenetic processes. The facies analysis applied in this study is considered a more appropriate classification approach to understand these coquinas, since it is more flexible and comprehensive than the existing classifications for carbonate rocks. The material investigated here consists of rock samples of the coquinas from the Atol Quarry of the Morro do Chaves Formation (Barremian/Aptian), Sergipe-Alagoas Basin. These rocks that crop out in the Atol quarry complex can be considered as a case study for similar coquinas reservoirs found in the Brazilian continental margin basins. Six sedimentary facies were described, using the main taphonomic (fragmentation of shells) and compositional (presence of micrite and siliciclastic matrix) features as a diagnostic criteria. Two carbonate facies, two mixed carbonate-siliciclastic facies and two siliciclastic facies (mudstones) were identified. From the facies succession, combined with a review of the literature on the subject, the following depositional paleoenvironments were defined: high-energy lake platform, lacustrine delta in a high-energy lake platform and lake-centre. In this paper, a new facies model for the studied coquinas succession is proposed.

Abstract:Modern scanning electron microscopes often include software that allows for the possibility of obtaining large format high-resolution image montages over areas of several square centimeters. Such montages are typically automatically acquired and stitched, comprising many thousand individual tiled images. Images, collected over a regular grid pattern, are a rich source of information on factors such as variability in porosity and distribution of mineral phases, but can be hard to visually interpret. Additional quantitative data can be accessed through the application of image analysis. We use backscattered electron (BSE) images, collected from polished thin sections of two limestone samples from the Cretaceous of Brazil, a Carboniferous limestone from Scotland, and a carbonate cemented sandstone from Northern Ireland, with up to 25,000 tiles per image, collecting numerical quantitative data on the distribution of porosity. Images were automatically collected using the FEI software Maps, batch processed by image analysis (through ImageJ), with results plotted on 2D contour plots with MATLAB. These plots numerically and visually clearly express the collected porosity data in an easily accessible form, and have application for the display of other data such as pore size, shape, grain size/shape, orientation and mineral distribution, as well as being of relevance to sandstone, mudrock and other porous media.

Many scales of heterogeneity are present in elastic reservoirs. Important heterogeneities occur at the small scale as a result of episodic or periodic fluctuations in the depositional process. These fluctuations are manifested as quasi-periodic grain size variations at scales of 10–3 to 1 metre. In the hierarchical description of sediments (the basis of sequence stratigraphy), these periodic stratal elements are known as laminae or beds. The fluctuating grain size elements result in well determined variations in pore and pore-throat size distributions. The effects of pore throat distributions on two-phase flow are reflected in capillary pressure curves, which may differ strongly as a function of absolute permeability (especially for permeabilities less than 1 Darcy). When stratal elements of contrasting grain size, sorting and permeability occur in close proximity, significant differences in local capillary pressures may occur over short distances. In common flow situations, these capillary pressure gradients can be comparable to or greater than pressure gradients induced by either viscous or gravitational effects. Such conditions occur when (a) permeability varies over very short distances (e.g., centimetres for the lamina scale), (b) flow rates are low (i.e., frontal advance rates are less than 1 metre/day), and (c) permeability contrasts are significant (i.e., of one order of magnitude or greater). These conditions occur in many laminated clastic reservoirs. This paper shows how a knowledge of sedimentary architecture (stratal elements) can be exploited to scale-up these capillary effects. A multiphase flow upscaling methodology based firmly on the length scales represented within the hierarchy of stratal elements is presented. We refer to our approach as the geopseudo approach since it incorporates the flow/structure interactions at the lamina, bed and formation scales (i.e., it includes the geology in an appropriate manner). The Rannoch Formation of the Brent Group (North Sea) provides an interesting practical example where large scale production performance is seen to be affected by the interaction of capillary forces with small-scale structure. Introduction The hierarchy of stratal elements in sedimentary rocks is well understood by stratigraphers. The smaller scale elements (laminae and beds) are commonplace in many elastic (sandstone) reservoirs. These elements are described by periodic variations in grain size and these give rise to very repetitive fabrics within reservoir units. In many reservoir models this repetitive aspect of sediment heterogeneity is not acknowledged. In these models, reservoir parameters are normally assigned from measurements on small-scale core-plug samples. These are not necessarily representative of the grid blocks used in large scale simulations, because each grid block contains many stratal elements. P. 365^