Coalbed methane producibility from the Mannville coals in Alberta, Canada: A comparison of two areas

International audienceThe Mannville coals in the Fenn area, Alberta Plains, have desorbed gas content averaging 8.57 cm3/g (275 scf/t), which is similar to the same coals in the Corbett Creek area, almost 400 km away. Vitrinite reflectance values are also similar, although the coals at Corbett Creek are situated about 300 m shallower, which points to a rank excursion from Hilt's burial law curves at Corbett Creek. Coals from both areas are within the “oil window”. The Medicine River Seam in the Fenn area has higher total inertinite content and greater proportions of inertodetrinite and detrovitrinite, suggesting that peat deposition occurred in swamps and marshes and were prone to periodic flooding. At Corbett Creek, the Mannville coal seams are characterized by greater concentrations of telo-inertinite, which contributes to coal meso-porosity and the potential for free gas storage in the open cell lumens, and to an increased gas flow along lithotype boundaries (horizontal permeability). Non-fluorescing vitrinite was present mostly in the upper Medicine River Seam, which was deposited in a regressive environment. The lower Medicine River Seam, which formed during a marine transgressive phase, contained greater amounts of fluorescing vitrinite. The Mannville coals in the Fenn area are moderately under-pressured in relation to those at Corbett Creek, which may have an impact on gas retention capacity. The difference in absolute coal permeability (1-3.5 mD at Fenn versus 3-4 mD at Corbett Creek), which is likely the result of higher in-situ stresses in the deeper Mannville coals at Fenn, has had an effect on both gas and water production rates from these coals. However, the largest impact on gas production volumes has been made by the application of horizontal drilling technology, initially at Fenn, and more recently by multiple horizontal wells drilled at Corbett Creek

Nanopore structures of isolated kerogen and bulk shale in Bakken Formation

Pores that exist within the organic matter can affect the total pore system of bulk shale samples and, as a result, need to be studied and analyzed carefully. In this study, samples from the Bakken Formation, in conjunction with the kerogen that was isolated from them, were studied and compared through a set of analytical techniques: X-ray diffraction (XRD), Rock-Eval pyrolysis, Fourier Transform infrared spectroscopy (FTIR), and gas adsorption (CO 2 and N 2 ). The results can be summarized as follows: 1) quartz and clays are two major minerals in the Bakken samples; 2) the samples have rich organic matter content with TOC greater than 10 wt%; 3) kerogen is marine type II; 4) gas adsorption showed that isolated kerogen compared to the bulk sample has larger micropore volume and surface area, meso- and macropore volume, and Brunauer–Emmett–Teller (BET) surface area; 5) deconvolution of pore size distribution (PSD) curves demonstrated that pores in the isolated kerogen could be separated into five distinct clusters, whereas bulk shale samples exhibited one additional pore cluster with an average pore size of 4 nm hosted in the minerals. The comparison of PSD curves obtained from isolated kerogen and bulk shale samples proved that most of the micropores in the shale are hosted within the organic matter while the mesopores with a size ranging between 2 and 10 nm are mainly hosted by minerals. The overall results demonstrated that organic matter-hosted pores make a significant contribution to the total porosity of the Bakken shale samples

Nanoscale pore structure characterization of the Bakken shale in the USA

Understanding the pore structures of unconventional reservoirs such as shale can assist in estimating their elastic transport and storage properties, thus enhancing the hydrocarbon recovery from such massive resources. Bakken Shale Formation is one of the largest shale oil reserves worldwide located in the Williston Basin, North America. In this paper, we collected a few samples from the Bakken and characterized their properties by using complementary methods including X-ray diffraction (XRD), N 2 and CO 2 adsorption, and Rock-Eval pyrolysis. The results showed that all range of pore sizes: micro ( < 2 nm), meso (2–50 nm) and macro-pores ( > 50 nm) exist in the Bakken shale samples. Meso-pores and macro-pores are the main contributors to the porosity for these samples. Compared with the Middle Bakken, samples from Upper and Lower Bakken own more micro pore volumes. Fractal dimension analysis was performed on the pore size distribution data, and the results indicated more complex po re structures for samples taken from the Upper and Lower Bakken shales than the Middle Bakken. Furthermore, the deconvolution of the pore distribution function from the combination of N 2 and CO 2 adsorption results proved that five typical pore size families exist in the Bakken shale samples: one micro-pore, one macro-pore and three meso-pore size families. The studies on the correlations between the compositions and the pore structures showed that mostly feldspar and pyrite affect the total pore volume of samples from Middle Bakken Formation whereas clay dominates the total pore volume of samples from Upper/Lower Bakken Formation. TOC and clay content are the major contributors to the micro-pore size family in the Upper/Lower Bakken. Also, it was observed that the increase of hard minerals could increase the percentage of macro-pore family in the Middle Bakken Formation