Deep Gas Accumulation Research Articles

Geochemistry and origin of the Bozhong 19-6 condensates: Implications for deep gas accumulation in the Bohai Bay Basin

Geochemistry and origin of the Bozhong 19-6 condensates: Implications for deep gas accumulation in the Bohai Bay Basin

Analysis of deep gas accumulation conditions of the Upper Paleozoic in the southern Huanghua Depression

Influenced by sedimentary and tectonic factors, the accumulation conditions and models of Permian reservoirs in southern Huanghua Depression are unclear. Based on geochemical data of source rocks and petrophysical property data of reservoirs, by means of seismic interpretation, geochemical testing and profile analysis of typical reservoirs, the accumulation conditions are clarified, and the accumulation model is put forward. The study show that the intensity of secondary hydrocanbon generation is a favorable condition for the formation of gas field. The thrust structural traps in Huanghua Depression were mainly formed in the Indosinian, and anticline traps were mainly developed in the Yanshanian and Himalayan. Several source-reservoir-cap assemblages were developed inside the buried hill. Strong tectonic activity created good migration paths for natural gas, and the matching of trap formation, tectonic activity and hydrocarbon expulsion is the key factor of the accumulation of gas. On this basis, the typical gas accumulation pattern is established.

Fault Systems and their Control of Deep Gas Accumulations in Xujiaweizi Area

Abstract:A study of faults and their control of deep gas accumulations has been made on the basis of dividing fault systems in the Xujiaweizi area. The study indicates two sets of fault systems are developed vertically in the Xujiaweizi area, including a lower fault system and an upper fault system. Formed in the period of the Huoshiling Formation to Yingcheng Formation, the lower fault system consists of five fault systems including Xuxi strike‐slip extensional fault system, NE‐trending extensional fault system, near‐EW‐trending regulating fault system, Xuzhong strike‐slip fault system and Xudong strike‐slip fault system. Formed in the period of Qingshankou Formation to Yaojia Formation, the upper fault system was affected mainly by the boundary conditions of the lower fault system, and thus plenty of multi‐directionally distributed dense fault zones were formed in the T2 reflection horizon. The Xuxi fault controlled the formation and distribution of Shahezi coal‐measure source rocks, and Xuzhong and Xudong faults controlled the formation and distribution of volcanic reservoirs of Y1 Member and Y3 Member, respectively. In the forming period of the upper fault system, the Xuzhong fault was of successive strong activities and directly connected gas source rock reservoirs and volcanic reservoirs, so it is a strongly‐charged direct gas source fault. The volcanic reservoir development zones of good physical properties that may be found near the Xuzhong fault are the favorable target zones for the next exploration of deep gas accumulations in Xujiaweizi area.

Unraveling the complexity of deep gas accumulations with three-dimensional multimodal CARS microscopy

Research Article| December 01, 2012 Unraveling the complexity of deep gas accumulations with three-dimensional multimodal CARS microscopy Robert C. Burruss; Robert C. Burruss * 1U.S. Geological Survey, Reston, Virginia 20192, USA *E-mails: burruss@usgs.gov; Albert.Stolow@nrc-cnrc.ca. Search for other works by this author on: GSW Google Scholar Aaron D. Slepkov; Aaron D. Slepkov 4Department of Physics and Astronomy, Trent University, Peterborough, Ontario K9J 7B8, Canada Search for other works by this author on: GSW Google Scholar Adrian F. Pegoraro; Adrian F. Pegoraro 2Emerging Technologies Division, National Research Council, Ottawa, Ontario K1A 0R6, Canada3Department of Physics, Queen’s University, Kingston, Ontario K7L 3N6, Canada Search for other works by this author on: GSW Google Scholar Albert Stolow Albert Stolow * 2Emerging Technologies Division, National Research Council, Ottawa, Ontario K1A 0R6, Canada3Department of Physics, Queen’s University, Kingston, Ontario K7L 3N6, Canada *E-mails: burruss@usgs.gov; Albert.Stolow@nrc-cnrc.ca. Search for other works by this author on: GSW Google Scholar Geology (2012) 40 (12): 1063–1066. https://doi.org/10.1130/G33321.1 Article history received: 16 Feb 2012 rev-recd: 30 Apr 2012 accepted: 27 May 2012 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Robert C. Burruss, Aaron D. Slepkov, Adrian F. Pegoraro, Albert Stolow; Unraveling the complexity of deep gas accumulations with three-dimensional multimodal CARS microscopy. Geology 2012;; 40 (12): 1063–1066. doi: https://doi.org/10.1130/G33321.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The origin of natural gas accumulations in thermally mature basins is poorly understood. Unraveling complex contributions from hydrocarbon cracking, mixing, redox alteration, and deeper sources requires analysis of gases trapped during specific periods of basin history. Fluid inclusions can provide such samples, but their unambiguous characterization is challenging. Here we show that three-dimensional (3-D) multimodal nonlinear optical microscopy of geologic materials allows mapping and molecular identification of trapped methane and water using coherent anti-Stokes Raman scattering, imaging of crystallographic features using second harmonic generation, and identification of higher hydrocarbons using two-photon excited fluorescence. Spatially resolved, molecule-specific characterization of fluid inclusions will improve models of natural gas generation, migration, and accumulation. We believe that these broadly applicable methods will potentially transform the characterization of geological materials. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Soil gas composition above gas deposits and perspective structures of the Carpathian Foredeep, SE Poland

Abstract In 2001 a surface geochemical survey was carried out in the Carpathian Foredeep, in the area between Jaroslaw and Radymno (SE Poland) where multihorizon gas deposits were discovered. These deposits accumulate microbial CH 4 with small amounts of N 2 and higher molecular weight gaseous hydrocarbons. Soil–gas composition in the hydrocarbon fields in the study area is relatively different from the original composition of natural gas occurring in the subsurface reservoir. In 449 analyzed soil gas samples collected from 1.2 m depth relatively low concentrations were found for CH 4 (median value 2.2 ppm) and its homologues (median value of total alkanes C 2 –C 4 – 0.02 ppm). Alkenes were encountered in 36.3% of the analyzed samples (mean value of total alkenes C 2 –C 4 – 0.015 ppm) together with distinctly higher concentrations of H 2 (maximum value – 544 ppm, mean value – 42 ppm) and CO 2 (maximum value – 10.26 vol.%, mean value – 2.27 vol.%). Individual, very high concentrations of CH 4 (up to about 35 vol.%) resulted from sub-surface biochemical reactions whereas higher alkanes detected in soil gases (up to about 68 ppm) originated from deep gas accumulations. Both the H 2 and alkenes may be indirect indicators of deep hydrocarbon accumulations. Carbon dioxide may also be useful for hydrocarbon exploration, revealing increased concentrations in those sampling sites where CH 4 concentrations are strongly depleted, presumably due to bacterial oxidation. These relationships are valid only for the study area and should not be extended as an universal principle. The interpreted zones of cumulative anomalies of CH 4 , higher molecular weight gaseous hydrocarbons, H 2 and CO 2 related to the results of geological and geophysical studies directly or indirectly point to the presence of undiscovered, deep gas accumulations and suggest larger sizes for known deposits. The character of the anomalies along with the relationships between the components of soil gases support the opinion that gas accumulations occur at various depths. Moreover, the results indicate that the surface geochemical pattern is significantly influenced by tectonic discontinuities.

Seismic precursors of a basaltic paroxysmal explosion track deep gas accumulation and slug upraise

[1] Basaltic volcanoes, though fed with low-viscosity magma, occasionally produce sudden paroxysmal explosions that are unforecasted and whose triggering mechanism remains poorly elucidated. Here we report on the first detection of seismic signals precursory to such an explosion on 5 April 2003, at Stromboli volcano (Italy). This strongest event in the past 73 years was preceded by ∼25 h of seismic tremor variation, broadly coincident with strong geochemical anomalies in crater plume emissions, followed by ∼15 h of tilt-related long-period inflation pulses of increasing amplitude. These precursory signals are best explained by accelerating growth and leakage of a bubble melt “foam” layer formed at ∼10 km depth, whose collapse triggered the fast ascent of CO2-rich gas slugs and then the explosion. Our results open new perspectives for the forecasting of such paroxysmal explosions and associated hazards.

Influence of soil moisture on the results of surface geochemical survey applied to petroleum exploration

The quality of results obtained from surface geochemical exploration depends not only on the character of deep petroleum accumulations but also on the influence of many sub-surface factors. One of important factors is the presence of soil moisture in the sampling interval. This research presents the influence of soil moisture on concentrations of gaseous hydrocarbons in sampled soil gases. The comparative analysis was made on for two populations of gaseous hydrocarbon (methane, ethane, propane, i-butane, n-butane, propylene, 1-butene) concentrations measured in soil gas samples collected from the water-saturated (“wet” sampling interval) and water-free (“dry” sampling interval) environments. The comparison was based upon chromatographic analyses of 2974 samples of soil gas, in which 684 samples originated from “wet” sampling intervals and 2290 samples were taken from “dry” interval. Samples were collected in the areas of known gas deposits located in the Fore-sudetic Monocline (SW Poland). Samples collected from the “wet” intervals reveal higher concentrations of almost all analyzed hydrocarbons in comparison with samples from “dry” intervals. Highest differences were observed for methane concentrations and lowest — for total alkanes C 2–C 4. The increase of concentrations in “wet” sampling intervals can be explained by sub-surface accumulation of hydrocarbons caused by decreasing permeability of water-saturated soils, by the different solubilities of alkanes and alkenes in water as well as by recent generation of methane and alkenes. Considering the results obtained from the area of the Tarchaly gas deposit, it was found that surface pattern of methane anomalies does not reflect the presence of deep gas accumulations, as well as the total alkanes C 2–C 4 distribution. Hence, the procedure was proposed of elimination of soil moisture influence on the pattern of surface methane anomalies. The procedure includes normalization of measured methane concentrations to the reference levels of geochemical background, which characterize “wet” and “dry” sampling intervals. As a result, the distribution of anomalous methane concentrations was obtained, which, along with the distribution of total alkanes C 2–C 4, confirms the presence of assessed accumulation of gaseous hydrocarbons. Therefore, the proposed method is correct and supports the application of methane indicator as a petroleum exploration tool.

DEEP BASIN GAS: A NEW EXPLORATION PARADIGM IN THE NAPPAMERRI TROUGH, COOPER BASIN, SOUTH AUSTRALIA

Deep basin hydrocarbon accumulations have been widely recognised in North America and include the giant fields of Elmworth and Hoadley in the Western Canadian Basin. Deep basin accumulations are unconventional, being located downdip of water-saturated rocks, with no obvious impermeable barrier separating them. Gas accumulations in the Nappamerri Trough, Cooper Basin, exhibit several characteristics consistent with North American deep basin accumulations. Log evaluation suggests thick gas columns and tests have recovered only gas and no water. The resistivity of the entire rock section exceeds 20 Ωm over large intervals, and, as in known deep basin accumulations, the entire rock section may contain gas. Gas in the Nappamerri Trough is located within overpressured compartments which witness the hydraulic isolation necessary for gas saturation outside conventional closure. Furthermore, the Nappamerri Trough, like known deep basin accumulations, has extensive, coal-rich source rocks capable of generating enormous hydrocarbon volumes. The above evidence for a deep basin-type gas accumulation in the Nappamerri Trough is necessarily circumstantial, and the existence of a deep gas accumulation can only be proven unequivocally by drilling wells outside conventional closure.Exploration for deep basin-type accumulations should focus on depositional-structural-diagenetic sweet spots (DSDS), irrespective of conventional closure. This is of particular significance for a potential Nappamerri Trough deep basin accumulation because depositional models suggest that the best net/gross may be in structural lows, inherited from syndepositional lows, that host stacked channel sands within channel belt systems. Limiting exploration to conventionally-trapped gas may preclude intersection with such sweet spots.

GASFIELDS, NW GERMAN BASIN: SECONDARY GAS MIGRATION AS A MAJOR GEOLOGIC PARAMETER

The observable concentration of the major deep gas accumulation areas in the NW German Basin is the result of focused secondary migration. Gas generated in several effective depocenters (regional structural lows) from Late Carboniferous source beds migrated into adjacent regional structural highs. The preferred migration paths are qualitatively predictable on the basis of present basin geometry. Optimal conditions for gas accumulations exist where the presently trapping regional highs have also been sites of favorable reservoir development. On‐going and future deep‐gas exploration efforts in the basin can be regarded as quite hopeful.

Preservation of Porosity in the Deep Woodbine/Tuscaloosa Trend, Louisiana

Summary Cores of the Woodbine/Tuscaloosa formation from False River field, Pointe Coupee Parish, LA. contain sandstones from 20,000 ft (6562 m) with anomalously high porosities and permeabilities. Porosities greater than 25% and permeabilities of hundreds of millidarcies are common. Scanning electron microscopy (SEM) shows that individual grains of these olive-green semifriable sandstones are coated with chlorite. The chlorite occurs as 7 to 10 micron- (µm-) wide hexagonal plates that arrange themselves edgewise one crystal thick on grain surfaces. Sandstones with continuous chlorite coatings around quartz grains display little framework compaction and minor development of secondary quartz overgrowths; however, interbedded sandstones with little or no chlorite often are cemented completely by secondary quartz. Intermediate between these extremes are sandstones with incomplete or poorly developed chlorite coatings; these display outgrowths of secondary quartz rather than overgrowths of an envelope nature. Petrographic and SEM data indicate an early diagenetic origin for the chlorite, which apparently ceased to form once detrital grains were coated with a single layer of crystals. This layer was sufficient to mask nucleation sites for silica overgrowths, and in addition may have prevented compaction by pressure solution, thereby allowing the sandstones to be buried to great depths without appreciably reducing porosity. A late dissolution event resulted in the formation of some secondary porosity, but the bulk of the observed porosity is relict primary in origin, formed in the manner previously described. Reservoir engineers and petrophysicists might ask themselves what effects the micropore system produced by the chlorite coatings will have on irreducible and critical water saturations as well as porosity logs. Introduction In mid-1965, Chevron Oil Co. discovered a deep gas accumulation in Pointe Coupee Parish, LA, in what is now called False River field. The field is 12 miles (20.81 km) downdip of the Lower Cretaceous Edwards shelf margin (Fig. 1) and production is from Woodbine/Tuscaloosa sandstones at about 20,000 ft (6462 m). A core of a water-bearing sandstone was taken from below 21,000 ft (6890 m) in the discovery well, Alma Plantation Well 1, with reported measured porosity values up to 26% (unstressed) and permeability values as much as 200 md. With this well the deep Woodbine/Tuscaloosa play was born. That these porosity values are anomalously high is illustrated in Fig. 2, which plots porosity vs. depth for an average reservoir sandstone. The high porosity values for the Alma Plantation Well 1 depart markedly from the normal trend. This observation prompted our study. Chlorite in a Deeply-Buried Sandstone Petrography Selected portions of the deep sandstone core in the Alma Plantation Well 1 are shown in Fig. 3, along with petrophysical data. Intervals with high porosity were recovered as crumbly fragments and are semifriable. The sandstones are fine grained and well sorted. The only important internal sedimentary structure is a faint graded bedding. A few marine shells are present, but adjacent shales are barren of fossils. Core samples from the nearby Crochet Well 1 also were examined. These samples ranged from crumbly and semi friable to hard and almost quartaitic. Core analyses of selected intervals from the two wells are shown in Tables 1 and 2. Petrography Selected portions of the deep sandstone core in the Alma Plantation Well 1 are shown in Fig. 3, along with petrophysical data. Intervals with high porosity were recovered as crumbly fragments and are semifriable. The sandstones are fine grained and well sorted. The only important internal sedimentary structure is a faint graded bedding. A few marine shells are present, but adjacent shales are barren of fossils. Core samples from the nearby Crochet Well 1 also were examined. These samples ranged from crumbly and semi friable to hard and almost quartaitic. Core analyses of selected intervals from the two wells are shown in Tables 1 and 2.