Reef Reservoirs Research Articles

Assessment of options for the development of a stacked storage complex in the Northern Michigan Basin, USA

The Northern Michigan Basin (NMB) Carbon Storage Assurance Facility Enterprise (CarbonSAFE) Integrated Pre-Feasibility Project is part of the U.S. Department of Energy’s (DOE) CarbonSAFE initiative. The objective of the NMB CarbonSAFE pre-feasibility project was to assess the feasibility of an integrated, commercial-scale carbon dioxide (CO2) storage complex in the NMB, which includes one or more deep saline geologic formations with sufficient capacity to permanently store at least 50 million metric tons of CO2 over a 20- to 30-year period. Subsurface injection of CO2 into depleted oil reservoirs for enhanced oil recovery (EOR) was also evaluated in the pre-feasibility study as an additional geologic storage mechanism because there are hundreds of depleted pinnacle reef reservoirs in the NMB, along with an established CO2-EOR operation, a feature that distinguishes this area from most other locations in the United States. Additionally, these reefs are co-located with the most favorable saline formations in the basin – the St. Peter sandstone and the Bass Islands dolomite – making stacked storage a real possibility. The study demonstrates that there are multiple locations in the northern Michigan study area that could support a commercial-scale storage complex with either saline storage or associated storage via CO2-EOR in the depleted pinnacle reefs alone (i.e., each storage mechanism has sufficient capacity alone) or via a combination of the two storage mechanisms. The term stacked storage refers to the concept of using both mechanisms together, in the same area, to achieve the required storage capacity. Key sites were identified in the northern part of the southern Michigan Peninsula that had sufficient geologic storage, nearby CO2 sources, a favorable social and economic setting, and a strong developed team.

Characteristics and Mechanism of Upper Permian Reef Reservoirs in the Eastern Longgang Area, Northeastern Sichuan Basin, China

Abstract As a typical kind of lithologic reservoirs, reef reservoirs are generally featured by their large single-well reservoir thickness, good reservoir physical properties, and high gas well productivity. The Upper Permian Changxing Formation is an important natural gas exploration target in the Sichuan Basin, which hosts a large reef gas reservoir and is mainly distributed along the Kaijiang-Liangping Trough. Comprehensive analyses are implemented to investigate reservoir characteristics and identify controlling factors of reef reservoirs in Changxing Formation in the Eastern Longgang Area, Northeastern Sichuan Basin, including core, logging, and seismic data analyses. Changxing Formation reservoirs in the study area mainly occur in the reef-shoal complex, which are featured by wide distribution, large thickness and generally good physical properties. Reservoir rocks are dominantly composed of bioclastic dolomite and silty-fine dolomite (with grain phantom structure), while the main reservoir space consists of residual intergranular pores, intergranular dissolution pores, and karst vugs. In the seismic profiles, typical mound-shaped chaotic reflections can be clearly seen. It is suggested by the main reservoir development controlling factor analysis that the distributions of reef reservoirs are typically controlled by sedimentary facies belts, while the scale of the reef-shoal complex is determined by the pene-sedimentary micro-paleo-geomorphology. Dolomitization can not only significantly preserve the primary pores but also enhance the permeability of rocks. Moreover, karstification is the key to high-quality reef-shoal reservoirs.

Significant advancement in geological theories and new discoveries of natural gas in China since the 11th Five-Year Plan

The development of geologic theories and exploration findings of natural gas in China supplement each other. Since the 11th Five-Year Plan in 2006–2010, geologic theories of natural gas in China has achieved notable advancement in many aspects, of which, are mainly reflected in the following seven aspects. Among them, there are two research progresses in the basic geological theory enumerated as follows. (1) The formation mechanisms of three types of natural gas that have been studied broadly including highly evolved coal-based source rocks, crude oil pyrolysis gas, and biogas. The cracked gas mode of coal-based source rocks, whole process hydrocarbon-generating mode of humus-type organic matter, and continuous biogas generation mode have been thoroughly advanced. (2) The theory of genetic identification between crude oil pyrolysis gas and kerogen pyrolysis gas, aggregated crude oil pyrolysis gas and dispersed crude oil pyrolysis gas, organic and inorganic gases, coal-type gas and oil origin gas, has been enriched extensively. There are five theoretical advances in the field of hydrocarbon accumulation in large gas fields: (1) the theory of hydrocarbon accumulation in ancient carbonate rock, “five paleo-structures control accumulation”, has been proposed innovatively; (2) the accumulation theory of tight sandstone gas in craton basins, foreland basins, and rift basins have been well-established; (3) the accumulation mode of “three-micro conveying, near-source enrichment, and sustained preservation” for ultra-deep and weak deformation zones has been established; (4) the accumulation theory of volcanic gas reserves in rift basins with basic elements of hydrocarbon generation troughs has been established and improved; (5) lastly, the accumulation theory of offshore high-temperature, overpressure, and deepwater gas were methodically deepened. The development of geologic theories of natural gas has promoted many new exploration discoveries. The accumulation theory in ancient carbonate reservoirs paved the way for the exploration of Anyue gas field in the Sichuan Basin, the largest single reserve in China. The new understanding of tight sandstone gas accumulation in the foreland thrust belt helped the first gas field discovery in the size 1 × 1012 m3 in an ultra-deep layer in the Kuqa Depression. The accumulation theory of ultra-deep reef reservoirs has guided the exploration of Yuanba gas field, the deepest-buried reef gas field in China. The theory of offshore hydrocarbon accumulation has led to remarkable discoveries in the South China Sea. Some of the said discoveries are the Dongfang 13-2 gas field, the largest gas field in China located in self-supported areas, and the Lingshui 17-2 gas field, which is a hundred billion cubic meters in size and is located in the deepwater exploration field.

The tectonic evolution of the eastern Mediterranean basin and its control on hydrocarbon distribution

Recent discoveries of giant, deep-water gas fields in the Eastern Mediterranean Basin (EMB) have revealed abundant hydrocarbon resources and significant exploration potential in turbidite and reef reservoirs (e.g., in the Tamar and Levantine fields, and the Zohr and Calypso fields, respectively). However, further exploration is currently constrained by the lack of detailed knowledge on the development of the basin. This paper presents a systematic model of the tectonic evolution of the EMB based on an analysis of new 2D seismic data and relevant published literature, assesses the main petroleum systems operating in the basin, and identifies prospective zones for future exploration. The modeling of a sequence of 12 prototype basins, restored from the seismic data, enable the tectonic evolution of the EMB to be divided into three stages: a rift stage, a ‘drift’ stage (including post-rift thermal subsidence), and a ‘convergence and transformation’ stage. This latest stage can be divided into four chronologically and geographically distinct sub-stages.The structural and stratigraphic architecture of the EMB, and hence the hydrocarbon distribution in the basin, evolved during the rifting of continental fragments from Gondwana (e.g., the Tauride–Anatolian plate, and the Kyrenia, Troodos, and Eratosthenes micro-plates), followed by their northward drift and collision with Eurasia. Six hydrocarbon plays are identified in this paper, two of which are previously unrecognized: the Mesozoic intra-platform reef play in the Eratosthenes Seamount, and the Mesozoic and Miocene ‘double-stacked’ platform-margin reef play in the ‘high–low structure belt’ south of the Eratosthenes Seamount. These two high-quality reef plays, together with stratigraphic and fault-block traps in the northern Levant Basin, are identified as the most prospective hydrocarbon exploration targets in the EMB.

Geochemical characteristics of natural gases from different petroleum systems in the Longgang gas field, Sichuan Basin, China

Located in the Sichuan Basin, China, the Longgang gas field consists of three vertically developed petroleum systems with the Triassic Leikoupo Formation as a dividing interface. There is one marine petroleum system below the interface and one continental petroleum system above it. The marine petroleum system is composed of coal measures, the main source rock in the Longtan Formation, and marine reef reservoirs in the Changxing and Feixianguan formations. The continental petroleum system can also be subdivided into two sets. One is the Xujiahe petroleum system sourced from the Xujiahe coal measures in the Upper Triassic formation. The other is a Jurassic petroleum system that is sourced from Jurassic lacustrine black shales. The gas pools in the marine system contain H2S gas. The gases are very dry and the δ13C1 and δ13C2 values display less negative values with an average of −29.2 and −25.0‰, respectively. The gases are humic origin generated at highly to over mature stages from coal measures of the Longtan Formation. The natural gas in the continental petroleum system does not contain H2S. The natural gases from the Xujiahe petroleum system are mainly wet gases with a few dry gases, and belong to typical humic type sourced from coal measures of the Xujiahe Formation. All the gases from this Jurassic petroleum system are wet gases and the alkane gases show more negative carbon isotopic values typical of sapropels. These are derived from the lower Jurassic lacustrine black mudstone. The three sets of petroleum systems in the Longgang gas field are vertically well separated. Each system has its own source rock, and there are no gases from other sources despite multiple tectonic events in the past. The reservoirs had been in a relatively stable tectonic condition with excellent seals by cap rocks during the gas accumulation period.

Exploring a carbonate reef reservoir – nuclear magnetic resonance and computed microtomography confronted with narrow channel and fracture porosity

The complexity of hydrocarbon reservoirs, comprising numerous moulds, vugs, fractures and channel porosity, requires a specific set of methods to be used in order to obtain plausible petrophysical information. Both computed microtomography (μCT) and nuclear magnetic resonance (NMR) are nowadays commonly utilized in pore space investigation. The principal aim of this paper is to propose an alternative, quick and easily executable approach, enabling a thorough understanding of the complicated interiors of the carbonate hydrocarbon reservoir rocks. Highly porous and fractured Zechstein bioclastic packstones from the Brońsko Reef, located in West Poland were studied. Having examined 20 thin sections coming from two different well bores, 10 corresponding core samples were subjected to both μCT and NMR experiments. After a preliminary μCT-based image analysis, 9.4 [T] high-field zero echo time (ZTE) imaging, using a very short repetition time (RT) of 2 [μs] was conducted. Taking into consideration the risk of internal gradients' generation, the reliability of ZTE was verified by 0.6 [T] Single Point Imaging (SPI), during which such a phenomenon is much less probable. Both narrow channels and fractures of different apertures appeared to be common within the studied rocks. Their detailed description was therefore undertaken based on an additional tool – the spatially-resolved 0.05 [T] T2 profiling. According to the obtained results, ZTE seems to be especially suitable for studying porous and fractured carbonate rocks, as little disturbance to the signal appears. This can be confirmed by the SPI, indicating the negligible impact of the internal gradients on the registered ZTE images. Both NMR imaging and μCT allowed for locating the most porous intervals including well-developed mouldic porosity, as well as the contrasting impermeable structures, such as the stylolites and anhydrite veins. The 3D low-field profiling, in turn, showed the fracture aperture variations and contributed to the recognition of pore geometry. Analogously, the authors believe that such a spatially-resolved profiling could also be successfully implemented to study unconventional reservoirs. Finally, it has been concluded that although it is possible to investigate the connectivity of a given pore space solely using μCT, a detailed labeling process might turn out to be too time consuming and require a sound experience in that field. Therefore it is proposed to follow a preliminary μCT modeling by the direct and non-invasive set of NMR experiments.

Discovery and theoretical and technical innovations of Yuanba gas field in Sichuan Basin, SW China

Abstract To solve the difficulties in exploration and development in Yuanba ultra-deep gas field in Sichuan Basin, SW China, the article studies the mechanism of quality reef reservoirs development and gas accumulation and innovates techniques in ultra-deep seismic exploration, drilling, completion and testing. Through the reconstruction of dynamic depositional evolution process and regional depositional framework of homoclinal ramp-rimmed platform in Upper Permian, three theories are put forward: first, “early beach-late reef, multiple stacking, arrangement in rows and belts” is the sedimentary mode for the reservoirs in the Changxing Formation of Yuanba area; second, “dissolution in early exposure stage and dolomitization during shallow burial giving rise to the pores in matrix, overpressure caused by cracking of liquid hydrocarbon during deep burial inducing fractures” is the reservoirs development mechanisms; third, “coupling of pores and fractures” controls the development of high quality reservoirs in deep formations. From correlation of oil and source rock, it is concluded that the Wujiaping Formation and Dalong Formation of deep-water continental shelf are the major source rocks in the Permian of northern Sichuan Basin. The hydrocarbon accumulation mode in ultra-deep formations of low-deformation zones is characterized by “three-micro (micro-fault, micro-fracture interbed crack) migration, near-source enrichment, and persistent preservation”. Through seismic inversion using the pore structure parameters of pore-fracture diadactic structure model, the high production gas enrichment area in Yuanba gas field is 98.5 km2. Moreover, special well structure and unconventional well structure were used to deal with multiple pressure systems and sealing of complex formations. A kind of integral, high pressure resistant FF-level gas wellhead and ground safety linkage device was developed to accomplish safe and environmentally friendly gas production.

A study and application of high-resolution methods for reef reservoir identification

Reefs represent a special type of carbonate trap that plays a key role in the migration, accumulation, and formation of a reservoir. They have commonly been the targets of exploration and development. However, reefs have complex interior structures and easily grow as thin, interbedded geological frames with reef microfacies that include the cap, core, and base of the reef. Because of the inherent drawbacks of seismic signals, including their low frequencies and narrow bandwidths, it is difficult to accurately identify reef reservoirs. Fortunately, the seismic frequency, phase, energy, waveform and other dynamic and geometrical properties can be used to compensate for the energy, expand the frequency bandwidth, and decompose and reconstruct the wavelet to obtain high-resolution seismic data. These data can highlight certain seismic responses of reefs, including boundary reflections, dome-shaped reflections from the reef outline, strong reflections from the reef cap, reflections from the reef bottom, and onlap reflections from the reef flanks. Some impedance response regularities, such as the lower impedance of the reef cap relative to the reef core and biodetritus beach and the fluctuating impedance of the reef-flat complex, are observed by combining log data with geological and high-resolution seismic data for a reef reservoir inversion. These methods were applied to the Changxing Formation in the Yuanba Gas Field. Good prediction results were obtained with a high consistency between the log and seismic data in a comparative analysis with the original seismic data and well logs.

Analyzing the Performance of Closed Reservoirs Following CO2 Injection in CCUS Projects

This paper discusses the use of a 2-D numerical model representing a typical depleted pinnacle reef reservoir to generate synthetic data for multiple CO2 injection periods after a prolonged period of oil and gas production. The data are analyzed with conventional pressure-transient analysis and injectivity-index approaches from petroleum reservoir engineering practice.Pressure falloff data from multiple shut-in periods, with and without boundary effects, indicate that the system response is similar to that of a composite reservoir with different total mobility and total compressibility values in the inner (CO2-rich) and outer (CO2-free) regions. The total mobility of the inner zone can be approximated by the total mobility of the gas phase in the vicinity of the CO2-oil front, while the total mobility of the outer zone corresponds to the total mobility of the oil phase in the undisturbed region.The injectivity index, calculated as injection rate divided by the pressure buildup from reference conditions, yields a quasi-stable value during the transient period which can be correlated to the permeability-thickness product of the injection zone. During the boundary-dominated (pseudo-steady-state) period, a flowing material balance plot can be utilized to determine an apparent injectivity index, which is higher than the true injectivity index because of multi-phase skin effects.

Structure characteristics and major controlling factors of platform margin microbial reef reservoirs: A case study of Xiaoerbulak Formation, Lower Cambrian, Aksu area, Tarim Basin, NW China

Abstract The structure characteristics and major controlling factors of platform margin microbial reef reservoirs in the Lower Cambrian Xiaoerbulak Formation in the Aksu area, Tarim Basin were analyzed based on 5 outcrop sections, 162 thin sections, 12 SEM samples, 52 sets of porosity and permeability data. Macroscopically, small-scale microbial reefs form the platform margin. A single microbial reef has several microbial reef progradation complexes, including reef front, fore reef, reef crest, and back reef, but microscopically, they have different kinds of microstructures. The reservoir spaces in the reefs can be divided into microbial structure reservoir space, including fenestral, frame, moldic, and oversized dissolution pores, and non-microbial structure reservoir space, including microcracks and stylolites. The statistical results of porosity and permeability show that in the Yutixi Section, porosity and permeability of the microbial reef reservoirs are generally below 5% and 1.0×10 −3 μm 2 respectively, characteristics of extremely low porosity and permeability reservoirs; while the reef reservoirs in the Sugaitebulake Section have a wide porosity range between 3% and 10%, and permeability range between 0.1×10 −3 μm 2 and 50×10 −3 μm 2 and strong heterogeneity, are low-medium porosity, low-medium permeability reservoirs. This demonstrates different microbial reefs have big differences in physical properties, and even the reservoir in the same reef has obvious heterogeneity. Paleotopography controls the formation of microbial reefs and sedimentation controls the facies distribution and the primary porosity development. Dissolution, controlled by the two former factors, finally decides evolution of reservoir pores.

Reef Reservoir Identification by Wavelet Decomposition and Reconstruction: A Case Study from Yuanba Gas Field in China

The organic reef is a special type of carbonate reservoir which always dominates the spatial distribution, reserves and accumulations of natural gas. However, it is difficult to determine the organic reef’s internal structure and gas reservoirs due to numerous adverse factors such as the low resolution of seismic data, depth of burial, strong anisotropy, irregular spatial distribution and complex internal structure. A case study of wavelet decomposition and reconstruction technology applied to elucidate the features of organic reef reservoirs in the Changxing formation from Yuanba gas field shows that the seismic record reconstructed by high frequency signal can adequately describe the internal properties of organic reef reservoirs. Furthermore, the root mean square amplitude ratio of both low and high frequency data obtained from the reconstructed seismic data clearly show spatial distribution of gas and water in reef reservoirs.

Middle Miocene mound-shaped sediment packages on the slope of the Xisha carbonate platforms, South China Sea: Combined result of gravity flow and bottom current

Deep-water mound-shaped sediment packages on the northern slope of the Xisha carbonate platforms in the northern South China Sea were analyzed by integrating high-resolution multi-channel seismic and drilling data. The mounds are distributed in the Beijiao depression of the Qiongdongnan Basin within the T41–T40 seismic horizons, which correspond to the middle Miocene. Mound-shaped reflections were identified both in the NE–SW and NW–SE oriented seismic profiles. The mound shapes are most prominent in the center of the NW–SE oriented seismic profiles, and the undulating tops flatten out towards the NW and SE. Similar reflections are mostly asymmetric, with steeper eastern flanks in the NE–SW oriented seismic profiles, and they are mostly round in shape. The wave impedance from the inversion calculation is 6–8×106kg/(m2·s). It is much lower than that of the reef reservoir in the LH11-1 Reef Oilfield. Paleogeographic analysis shows that the Xisha uplift was dominated by tropical shallow carbonate platforms, while the Beijiao depression became a bathyal environment in the middle Miocene. Drilling data confirmed that the mound-shaped sediment packages are mainly composed of calcareous mudstone. Therefore, we infer that the mound-shaped sediment packages could be reef complexes or they were presumably built by combined gravity flow and bottom current.

Seismic Profile Characteristics of Reefs and Hydrocarbon Detection Technology in Northwest Palawan Basin

In the hanging wall of faults which controlled the Paleocene depression in the Northwest Palawan Basin in the South China Sea, a large number of ancient terrain height reefs and thick mudstones are well developed, forming important reservoir cap combination type in the study area. Through years of exploration and development, 27 reef oil and gas fields have been discovered. In this article, the Northwest Palawan basin evolution and reef formation in this basin have been discussed, and the seismic response characteristics of reef oil and gas reservoir discovered in this basin are summarized, which lay a solid foundation for valid identification of reef reservoirs. Meanwhile, the reef reservoirs after containing oil and gas are characterized by high impedance and lowfrequency. The sparse spike inversion method and filtering method by setting threshold value of seismic attribute have been used to detect hydrocarbon bearing conditions of reefs to improve the reef reservoir exploration success rate.

Porosity Inversion under the Sequence Stratigraphy Framework

Carbonate reef reservoir buried deeply, show great heterogeneity, Therefore, effective reservoir prediction is the key to the biohermal reservoir. In practical research, based on of the single well sequence stratigraphic framework, combined with these sequence stratigraphic framework and seismic section, found the reservoir development area in the longitudinal, which sq1-HST and sq3-HST is the main period of reservoir development, and then through the seismic Seismic multiple-attribute inversion, predicted porosity of system tracts of reservoir development in the sequence stratigraphic framework. Porosity inversion results shown, Changxing formation reservoir is mainly distributed in the central and north-central of Jiannan area.

An imaging case study of Ragay SC43, Philippines: From 2D to 3D PSDM Processing

SUMMARY Ragay SC43 Block is located off the southern tip of Bondoc Peninsula, between the Ragay Gulf and the Sibuyan Sea. Huge carbonate reef was developed and complex faulting system dominated in the shallow sediment in this area. This results in a very complex subsurface geology with strong lateral velocity contrast, which made high resolution PSDM processing essential for the successful structure imaging in this area. With dense model representation and optimized inversion regularization, a more detailed velocity model is derived by high resolution tomography update technology. High resolution velocity model is achieved in shallow sediments as well as between huge reef and surrounding sediments. Together with high fidelity controlled beam migration technology, the carbonate reef reservoir was much better imaged which gives valuable information for the future E&P activities in this area.

大川中地区长兴组储层特征分析

针对大川中地区长兴组气藏勘探程度低、储层发育特征认识程度不高的问题，本文从长兴组地层发育的构造特征、地层展布特征、岩石学特征及测井响应特征等方面对长兴组储层特征进行了分析。认为研究区长兴组储层由于受2个台内高带和高带之间的凹地的影响，发育有泥–微晶灰岩、生物碎屑灰岩、砂屑灰岩以及生物礁灰岩等岩性。生屑灰岩、生物礁灰岩储层在研究区并不是广泛分布，而是呈点状的形式展布。储层总体上表现为低孔低渗储层，储集空间主要为孔型储层，局部发育裂缝–孔隙型储层。储层的测井响应较为明显，从孔隙度测井及电阻率测井上易于识别，表现为孔隙度曲线和电阻率曲线形状多呈“U”或“W”字型变化，很少呈现厚度小的尖刺状“V”字型特征。 In view of the questions in the mountain regions of Changxing group that gas reservoir exploration degree is low and that the development features of reservoir cognition degree are not high, from the Changxing formation and development of tectonic characteristics, characteristics of formation distribution, petrological characteristics and characteristics of logging response, this article analyzed the reservoir characteristics of Changxing group. Due to the two stages between highlands and the influence of the craters in highlands, mud-microcrystalline limestone, bioclastic limestone, calcarenite and biological reef limestone rocks are developed in the study area of Changxing group reservoir. Raw crumb limestone and biological limestone reef reservoir are not widely distributed in the study area, but in the form of dotted distribution. Reservoirs are generally characterized by low porosity and low permeability reservoir. The reservoir space is mainly for the groove reservoir, locally developed for the fracture-pore type reservoir. The logging response is more obvious, easily recognized from logging, and it shows that the curve shapes of the resistivity and porosity form a “U” or “W” type change, and rarely present thickness and small spikes of “V” characteristics.

Investigation of the Various Spectral Decomposition Methods to Detect and Explore Hidden Complex Reef Reservoir Structures and Their Hydrocarbon Potentials in Northwestern Part of the Persian Gulf

The Persian Gulf and its coastal areas are recognized as one of the biggest hydrocarbon basins in the world as world's largest petroleum reservoirs are located through its offshore and onshore oil and gas fields. Coastline countries of the Persian Gulf produce about 25% of the world's oil yearly and they have nearly two-thirds and one-third of the world's crude oil and natural gas reserves, respectively. In the Persian Gulf and south of Iran, Zagros orogeny process has a most important structural role as it causes many petroleum reservoirs into folds with northwest-southeast trends that are parallel with Zagros orogeny direction. However, there is good potential to explore new petroleum reservoirs in the Persian Gulf yet. One of these potential oilfields located northwestern of the Persian Gulf includes high petroleum potential, but with structural complexity and this investigation is focused to explore reservoir in its other horizons, specially Sarvak formation as the famous reservoir in the area. To achieve essential information from reservoir and locating it, we applied two useful seismic methods. Authors considered different advantages of the fast Fourier transform (FFT) and the continuous wavelet transform (CWT) as the most commonly applicable spectral analysis of seismic methods in an experimental investigation besides geological new findings. We found that the FFT can provide a good image from reservoir stratigraphic characteristics; it has specifically proven efficient even in carbonate reservoirs allowing individualization of geological bodies not easily defined in amplitude maps. Besides that, the CWT can provide an accurate and clear image from reservoir structural characteristics and low frequency shadows under petroleum reservoirs. We will prove our claims by using theoretical and experimental evidences. Objectives of this paper, beside geological evidences, are to show abilities of these two methods and to describes how, (1) the FFT method shows the distribution of the hidden reef boundaries and (2) the CWT shows the probable presence of hydrocarbons in purpose structure much better than the original seismic data and others methods.

Effects of Distinct Tectonic Evolutions on Hydrocarbon Accumulation in Northern and Southern Continental Marginal Basins of the South China Sea

AbstractThree distinct continental marginal basin types developed in the South China Sea, i.e. divergence, transform‐extensional and flexural‐extensional complex types, due to different boundary conditions. Differences of tectonic evolution in these basins resulted in great variations in sedimentary fill and associated hydrocarbon accumulating conditions. Source rocks of lacustrine and marine mudstones mainly developed in northern diverging continental marginal basins in the northern South China Sea. Although there developed good lacustrine sources, limited hydrocarbon accumulation occurred in the adjacent areas around these separated depressions with a relative small scope distribution. In the southern flexural‐extensional complex continental marginal basins of the South China Sea, the Zengmu basin underwent the peripheral foreland tectonic stage earlier than other basins such as the Liyue, Beikang and Nanweixi basins. An available hydrocarbon accumulating condition occurred in those basins, where there are not only large areas and thicknesses of depressions with the sources of coal‐bearing and marine mudstones, but also formation of a broad carbonate and reef reservoirs resulted from slow subsidence during the terminating period of the South China Sea spreading (about 15.5 Ma). The transform‐extensional basins in western continental margins of the South China Sea are characterized by natural gas accumulation due to very thick sediments and high heat flow values. Considering all kinds of geological conditions mentioned above, we suggest that the hydrocarbon‐bearing prospects in southern continental marginal basins are superior to the northern continental marginal basins.

Combined sustainable biomass feedstock combustion, CO2/EOR, and Saline Reservoir Geological Carbon Sequestration in Northern Lower Michigan, USA: Towards negative CO2 emissions

This paper presents the results of a combined biomass combustion and geological carbon sequestration feasibility study in Northern Lower Michigan, USA related to a proposed solid fuel-fired 600 MW electric power plant, the Wolverine Clean Energy Venture (WCEV), near Rogers City, MI, USA. The biomass feedstock resource assessment, focused on low intensity, high diversity forest and agriculture in the proposed plant bioshed (<120 Km), has the potential to provide sustainable, dry biomass fuel well in excess of the maximum annual co-firing potential of 20% and offset as much as 1 Tgy−1 of the estimated annual 5.1 Tgy−1 of CO2 emissions (using 100% western coal). CO2/EOR potential in the Northern Niagaran Pinnacle Reef Trend is substantial. To date, seven reef reservoirs have been converted to CO2/EOR floods and three of these fields are sufficiently mature to project recovery efficiency in excess of 40% of primary oil recovery. Using these observations and historic oil production data CO2/EOR potential, in a region adjacent to a proposed CO2 pipeline originating from the plant site, is estimated to be at least 7.2 Mm3 (45 MMB) of incremental oil. Analysis of produced fluids in the same region indicates 55 Mmt of geological carbon sequestration (GCS) potential in abandoned oil and gas fields. GCS capacity is estimated at 271 Mmt in two, Paleozoic, saline reservoir targets providing a combined GCS (with abandoned oil and gas field GCS) of 326 Mmt in the pipeline study area. Estimated, combined, GCS in the proposed pipeline fairway alone is in excess of CO2 emissions for a hypothetical 50 year design life of the WCEV project burning 100% coal of 255 Mmt. Realization of biomass co-firing potential at 20% would result in a 50 MMt offset of CO2 emissions during this 50 year period. Carbon capture and sequestration, including beneficial use in CO2/EOR, GCS in abandoned oil and gas fields, and saline reservoir GCS Sequestration at 90% of CO2 emissions from the proposed plant for a 50 year design life could result in the sequestration of 229.5 Mmt of CO2. These considerations support the potential for a net negative emissions profile of −24.5 Mmt for a hypothetical 50 year design life of the proposed WCEV project.

Depositional facies analysis and modeling of the Judy Creek reef complex of the Upper Devonian Swan Hills, Alberta, Canada: Discussion

2nd revised manuscript received February 17, 2010 Jack Wendte The article of Ma et al. (2009) in the September 2009 issue of the Bulletin fails to provide credible evidence or to cite references to support the stratigraphic framework and facies analysis on which their numerical modeling of the Judy Creek reef complex is based. Ma et al. (2009) subdivide the reef into a lower rimmed reef phase, consisting of the R1, R2, R3, and R4 cycles, and an upper ramp-bounded shoal complex, consisting of the R5A, R5B, and R5C cycles (p. 1238, 2d and 3d paragraphs). However, they do not present evidence or cite references to support these subdivisions. In the Wendte (1992) article, I subdivided the reef reservoir into two main phases of growth, an underlying rimmed-reef phase approximately 43 m (∼140 ft) thick and an overlying ramp-bounded shoal complex, up to 30 m (100 ft) thick, separated by a subaerial unconformity that I termed R4. The top of the ramp-bounded shoal complex …