William DV | The Ohio State University (original) (raw)

Papers by William DV

The role of the residual bitumen in the shale gas storage capacity is investigated for potential ... more The role of the residual bitumen in the shale gas storage capacity is investigated for potential terrestrial shale gas reservoirs in the Yanchang area, southern Ordos Basin, China. The Upper Triassic organic-rich Yanchang shales comprise of thermally mature Chang 7 Shale (average TOC 5.12 wt.%, Type IeII 1 kerogen, T max 443e458 C, Ro 0.83%e1.02%) and relatively mature Chang 9 Shale (average TOC 4.40 wt.%, Type I eII 1 kerogen, T max 443e476 C, Ro 0.88%e1.10%). The mineralogy of Yanchang shales is dominated by clay minerals (average 48.85%) and quarts (average 31.7%). A series of low pressure nitrogen adsorption/ desorption and high pressure methane sorption experiments were conducted on pretreated fresh drilling cores (including three groups of core samples: one original group, one group extracted by dichloro-methane and the other group extracted by trichloromethane) selected from Yanchang shales to demonstrate the role of the residual bitumen in the shale gas potential. Low pressure nitrogen sorption method was used to elucidate the effect of the residual bitumen on the pore structure of Yanchang Shales. The results show that the specific surface area and pore volume and pore surface area of shale samples after the extraction greatly increase and their growth was closely related with pores of >30 nm and <10 nm respectively. A negative correlation between the surface area and TOC was observed widespread in Yanchang shales, indicating that the residual bitumen that blocks the pores and pore-throats dramatically influences the methane sorption capacity in the mature shales. Based on nitrogen adsorption/desorption isotherms, ink-bottle-shaped micropores and mesopores likely acting as narrow necks of those pores well developed and were most likely influenced by the residual bitumen, which is favorable for adsorption accumulation but disadvantageous for the seepage of shale gas. The methane sorption isotherms measured on moisture-equilibrated shale samples suggest that the dissolution in the residual bitumen could be an important gas storage mechanism in Yanchang low mature lacustrine shales.

Based on a detailed description and analysis of outcrops and drilling cores, onsite gas desorptio... more Based on a detailed description and analysis of outcrops and drilling cores, onsite gas desorption, and laboratory testing data, shale lithofacies characteristics and its effect on gas storage of the Silurian Longmaxi Formation marine shale in the southeast Sichuan Basin have been studied. Twelve types of shale lithofacies are classified based on the organic matter content and mineral composition, of which 9 types were identified in the study area based on their dramatically differences in color, grain size, lamination, organic matter content, mineralogy, density, and other physical properties. The bottom of the Longmaxi shale Formation is primarily organic-rich siliceous shale with stable distribution of thickness and good continuity. The upper section has characteristics of rapid vertical and lateral change in lithofacies, exhibiting a strong spatial heterogeneity. Organic-rich siliceous shale in the lower section, showing the highest content of gas desorption in situ, has a high content of organic matter, a high brittleness index and good permeability, which is conducive to shale gas storage, hydraulic fracturing, and exploitation. Organic-rich argillaceous shale was also observed to have the highest methane adsorption capacity. The interval with lithofacies association of organic-rich siliceous shale with organicrich argillaceous shale interlayer is the pay zone for shale gas generation and accumulation.

The increasing enthusiasm for continental shale gas exploration in China has made the Shahezi sha... more The increasing enthusiasm for continental shale gas exploration in China has made the Shahezi shale in the Changling Fault Depression an important research target due to its impressive demonstrated gas capacity. In this work, geochemical and petrologic analyses, field emission-scanning electron microscopy (FE-SEM) observation, low-pressure adsorption isotherms and mercury intrusion porosimetry (MIP) were conducted on 19 core samples to comprehensively analyze the reservoir characteristics of different lithofacies. The results show that the Shahezi shale has the characteristics of low content of organic matter (OM), high R o , high content of clay minerals and small fractions of calcite. The kerogen is type III, dominated by vitrinite and inertinite. Clay minerals are dominated by the mixed illite-smectite, followed by illite and a small amount of chlorite. The Shahezi shale develops three kind of stratification structures according to the thickness of laminae: laminated structures, bedded structures, and massive structures. On the basis of TOC, mineral composition and petrologic texture, eight types of lithofacies were recognized. The organic pores show strong heterogeneity and are poorly developed, while clay-related pores are ubiquitous. The Shahezi shale has a high pore volume (PV) (0.005-0.031 ml/g, averaging 0.0173 ml/g) and specific surface area (SSA) (2.57-27.48 m 2 /g, averaging 16.61 m 2 /g), indicating an excellent storage capacity. Low-pressure CO 2 and N 2 isotherms and MIP were utilized to construct the whole-range pore size distribution (PSD). Based on the whole-range PSDs, mesopores were observed to contribute most to the PV, followed by macropores. Micropores and mesopores account for more than 99% of SSA. The reservoir capacity of different lithofacies is following the order in terms of PV and SSA, from high to low: organic-medium massive mixed shale (OMMMS), organic-medium massive argillaceous shale (OMMAS), organic-rich laminated argillaceous shale (ORLAS), organic-medium laminated argillaceous shale (OMLAS), organic-rich bedded mixed shale (ORBMS), organic-rich bedded siliceous shale (ORBSS), organicmedium bedded argillaceous shale (OMBAS), organic-poor shale (OPS). The main controlling factors of pore structure for the Shahezi shale are clay minerals rather than OM, which is similar to the continental Chang 7th shale but contrary to the Longmaxi shale. However, the Shahezi shale is mainly of low TOC and strong heterogeneity pores development result from OM macerals, while the Chang 7th shale is mainly of low maturity. R o play an important role in promoting pore development. Only high content of calcite can greatly improve the pore space due to its solubility. This work contributes to the theory of continental shales and how to identify continental high-quality shale reservoirs.

Pore connectivity is one of the most important characteristics of shale reservoirs because it sig... more Pore connectivity is one of the most important characteristics of shale reservoirs because it significantly impacts the effective pore space, the fluid migration, and the gas production. In this work, pore connectivity and its primary controlling factors were investigated using a combination of field emission-scanning electron microscopy (FE-SEM), focused ion beam-scanning electron microscopy (FIB-SEM), mercury intrusion porosimetry (MIP), and nuclear magnetic resonance (NMR). The results show that using the difference between NMR and MIP is a reliable method to characterize pore connectivity. NMR pore size distribution (PSD) curves converted from T 2 spectra, and MIP PSD curves were observed to have consistent shapes. The amplitude of NMR PSD curves is higher than that of MIP PSD curves for S-group pores (< 200 nm), while the relationship is opposite for L-group pores (200 nm-10 μm), which may be due to the permeability of shale. A low permeability allows a smaller amount of mercury to intrude into the small pores. Based on experimental results, the pores of 8-20 nm make a contribution of 5%-11% to pore connectivity, whereas the pores of 200-700 nm are mainly interparticle pores and microfissures, contributing from 38% to 72% of pore connectivity. Stratification and pore morphology in the Lower Cambrian Wangyinpu and Guanyintang shales in the Xiuwu Basin are the two critical influencing factors of pore connectivity. The pore connectivity of well-laminated shale is higher than that of less-laminated shale. The laminated structures are usually composed of argillaceous and siliceous lamina, which tend to give rise to fissures during hydrocarbon generation or under confining stress. As a result, the pores around the microfissures are more likely to be communicating. Shales with the structure of uniformly distributed organic and inorganic minerals have the best pore connectivity. Both the interparticle pores and microfissures between organic matter and inorganic minerals or between inorganic minerals can effectively connect organic pore networks and greatly improve the pore connectivity.

In order to better understand the impact of fractal features of pore-throat structures on effecti... more In order to better understand the impact of fractal features of pore-throat structures on effective physical properties of tight gas sandstones, this paper carried out constant-rate mercury ‡ ‡ Corresponding authors. This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited.

Shale gas storage is a dominant factor to economically evaluate the shale play. A series of Lower... more Shale gas storage is a dominant factor to economically evaluate the shale play. A series of Lower Silurian Longmaxi marine shale samples in southeast Chongqing, China, were collected to investigate the reservoir characteristics, and a suit of methane adsorption isotherms were fitted using a supercritical Ono−Kondo model to better understand the adsorption capacity of Longmaxi shale. The saturated adsorption of a monolayer presents a greatly positive relationship with the total organic carbon (TOC) content. A negative relationship with clay was observed due to the predominant influence of organic matter on the methane adsorption. Methane adsorption also increases with increasing pressure and decreases with increasing temperature. On the basis of the relationships, one new estimation algorithm related to TOC content, pressure, and temperature was established to calculate the methane adsorption capacity on the basis of the Ono−Kondo model. Furthermore, with higher TOC content, the adsorption capacity of shales correspondingly increases and the maximum of the adsorption capacity tends to a deeper depth. Considering geological characteristics of Longmaxi shale, one new gas-in-place (GIP) model was proposed to apply, considering the controlling factors, TOC, porosity, gas saturation, pressure, and temperature. The relationships of GIP, adsorbed gas, and free gas with increasing depth shows that (1) free gas increases rapidly and equally; (2) adsorbed gas initially increases rapidly at less than 1000 m, and then decreases with depth increases; and (3) GIP rapidly increases at shallow depths, and then gently increases more than 1000 m.

The Lower Silurian Longmaxi marine shale from the productive shale gas block of southeastern Chon... more The Lower Silurian Longmaxi marine shale from the productive shale gas block of southeastern Chongqing, Southern China, is one of the most important marine shale gas exploration formations in southern China; geologists have recently made significant shale gas discoveries there. However, the marine shale in southern China is noticeably heterogeneous, leading to difficulties in predicting potential productive zones in the shale formation. To better determine the "sweet spots" in the black shale formation, we carefully examined the heterogeneity of the Lower Silurian Longmaxi marine shale, which is controlled by sedimentary setting, and analyzed the macro-and micro-heterogeneity based on detailed core descriptions, optical microscopy, field emission scanning electron microscopy (FE-SEM), geostatistical analysis of well logging data, geochemical testing data and reservoir property testing data. According to our research, four sedimentary subfacies were recognized and have distinct heterogeneity features within and among them in terms of thickness, mineral composition, organic matter content, pore type and pore structure. The deep water shelf subfacies (DWS) of black carbonaceous and siliceous shale that was formed in anoxic, still water has a stable sedimentary thickness and mineral composition with an total organic carbon (TOC) content generally greater than 2 wt.%; furthermore, the DWS subfacies mainly has organic and intragranular pores, showing the least heterogeneity due to the highest pore throat homogeneity coefficient. The shallow water shelf subfacies (SWS) of gray-black siliceous and argillaceous shale was deposited in shallow water with relatively intense hydrodynamics and has a relatively stable sedimentary thickness and the lowest pore structure coefficient; however, it also comprises various shales and organic matter contents and mainly has intergranular pores showing a moderate heterogeneity that is relatively greater than the DWS subfacies heterogeneity. The tidal flat subfacies (TF) comprises gray calcareous shale with argillaceous siltstone that was greatly influenced by terrigenous sediment input. This facies mostly has a noticeably variable sedimentary thickness and mineral composition with a TOC that is generally less than 1 wt.% and well-developed microfractures, indicating high heterogeneity caused by a low homogeneity coefficient and a poor sorting coefficient of the pore throats. The lagoon subfacies (L) consists of black carbonaceous and siliceous shale formed in anoxic water between the sea and the land and has a relatively stable shale thickness and mineral composition but poor lateral and pore throat connectivity. This subfacies mainly has microfractures and intergranular pores, indicating extremely high heterogeneity. The paleotomography differences in the sedimentary environment determine the sedimentary thickness of the shale, the mineral composition, the organic matter content and other factors; these factors contribute to the macroscopic heterogeneity. Diagenesis controls the pore structure and pore type by compaction, cementation, and dissolution, combined with the generation of hydrocarbons and other phenomena. This process determines the microscopic heterogeneity.

To directly measure the gas content in the Benxi and Shanxi subformations of the Ordos Basin in N... more To directly measure the gas content in the Benxi and Shanxi subformations of the Ordos Basin in NW China, a series of canister desorption tests were carried out on 33 over-mature Lower Permian to Upper Carboniferous fresh shale cores (>3000 m) at both the reservoir temperature (75−80°C) and an elevated temperature of 95°C. Organic chemistry and X-ray diffraction analyses of 33 replicate samples were used to establish relationships between the gas content and rock composition. Geochemical measurements show that the total organic carbon (TOC) contents range from 0.49 to 13.7 wt %. The organic matter is mainly type III arising from lagoon and delta depositional settings. The dominant minerals are clay (25−97 wt %, average 59 wt %) and quartz (1−62 wt %, average 33 wt %). A new ternary diagram is proposed based on the origin and brittleness of the minerals. Multiple linear regressions of emitted gas volumes with respect to the full mineralogy and TOC show a strong positive correlation with TOC and a weak one with clay composition. This is consistent with independent highpressure methane adsorption experiments in the literature. Elevating the temperature resulted in an incremental gas production of 12% for the Lower Permian Shanxi facies versus 62% from the Upper Carboniferous Benxi shale (with a weighted average of 43%). This may be indicative of more significant gas adsorption (related to the pore size distribution and specific surface areas) in the Benxi lagoon environment, which has more functional components (TOC and clay) and micropore volume than the Shanxi delta deposits, which are more quartz-rich.