Formation Diagenesis Research Articles

A New Quantitative Approach for Element-Mineral Determination Based on “EDS (Energy Dispersive Spectroscopy) Method”

With the continuous development of hydrocarbon exploration, how to efficiently, economically, accurately, and comprehensively obtain mineral species, composition, and structure and diagenesis information has become one of the hot topics in both the academia and industry. By scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), a new method of qualitative mineral identification and quantitative measurement is established. Typical tight sandstone reservoir rock samples in the Ordos Basin are selected; through the element surface scanning image of “mineral element composition” and “pixel element combination”, mineral types are distinguished, and mineral parameters such as types, characteristics, and content are rapidly and accurately determined. Meanwhile, such results achieved via the new method are compared with conventional XRD and TIMA methods. The results show that the new method exhibits several advantages: cost advantages compared to XRD experiment analysis technology and TIMA system and ability to analyze low content minerals which XRD techniques are hard to identify; it allows quantitative characterization on the phenomenon of mineral miscibility, which is of great significance to explore the mineral diagenetic evolution.

Volcanic Rock Diagenesis and Characteristics Analysis of Yingcheng Formation in Yaoyingtai Area

Research on volcanic rock diagenesis have important reference value in volcanic rock secondary pore formation, evolution and reservoir prediction. Using the core data, flakes, imaging logging, geochemicals analysis and lithologies-lithofacies characteristics of Yaoyingtai area in Yingcheng Formation, Changling fault depression, we research on the volcanic rock diagenesis, reservoir space types, characteristics and relationships. The results are shown that: The research area mainly develop volcanic rock mantle thermal liquid alkali metasomatism and other 11 diagenesis types, and base on diagenesis formation mechanism and the effects of the reservoir spaces, which is divided constructive and destructive.

Impact of injected CO2 on reservoir mine ralogy during CO2 -EOR

An investigation of the impact of injected CO2 on reservoir mineralogy was completed as part of the geochemical monitoring and modelling of the Pembina Cardium CO2 Monitoring Project southwest of Drayton Valley, Alberta, Canada. Oil production at the pilot is primarily from the upper two of three stacked sandstone units of the Cardium Formation in the Pembina field. Core analyzed included samples from each of the three sandstone units, and encompassed three distinct time periods: pre-water flood (1955), pre- CO2 flood (2005), and post- CO2 flood (2007). The results of whole rock analysis (XRF, ICP, and XRD), and microscopy (polarizing and electron microprobe) suggest the three separate sandstone units are both texturally and compositionally similar regardless of when the core was recovered. Framework grains are predominately sub-angular to sub-rounded quartz/chert (up to 90.0 wt%), and include smaller amounts of lithic fragments (shale), feldspar (k-feldspar, and albite), mica (muscovite and chlorite), and fluor-apatite. Authigenic pyrite is found as finely disseminated rhombs throughout the formation. Clay minerals present are predominantly kaolinite and illite. Kaolinite appears as fine discrete pore filling books, and is considered to be authigenic. Illite occurs as a major constituent of shale fragments, as well as fine pore bridging strands. The sandstone’s irregular pores are cemented to varying degrees by silica and/or carbonate minerals (calcite and siderite). Dissolution features associated with formation diagenesis, including the degradation of detrital grains (quartz and feldspar), the partial and/or complete removal of carbonate cements, and the presence of residual clays, are found in core from each of the three time periods. Attributing dissolution features in post- CO2 flood core to the interaction of minerals and carbonic acid is difficult due to the geologic history of the formation.

Seismic Expressions of Monterey Formation Diagenesis: Examples from Offshore California: ABSTRACT

Diagenesis of the diatomaceous rocks in the Monterey Formation in California coastal and offshore basins involves changes from amorphous biogenic silica to a stable crystalline quartz facies. In the intermediate stage, the transformation undergoes passage from the Opal-A to the Opal-CT phase. Associated with this diagenetic process is a marked increase in bulk densities between the different silica phases, owing to loss of porosity from compaction and solution recrystallization caused by increase in burial load and other physical factors. The sharp density contrast between the silica phases is manifested by an acoustic impedance boundary that may be expressed on seismic records. This seismic event can be distinct and independent of structural configuration, and in many places cuts through stratigraphic boundaries. Several examples of seismic records from offshore California demonstrate the diagenetically caused reflection cutting through Monterey and post-Monterey formations. Current and future exploration efforts in offshore California will continue to center on the widespread Monterey Formation. In addition to being the main source rock, the Monterey is also the reservoir rock. Recent discoveries indicate that oil production is mainly from the highly permeable, fractured, silica-rich sections. It is therefore important to recognize the diagenetic boundaries on seismic records and tomore » delineate the more brittle quartz-rich facies where the reservoir quality is expected to be better than the intermediate Opal-A or Opal-CT facies. Furthermore, these boundaries could also provide good diagenetic traps off the flanks of structures where updip unaltered impermeable rocks hinder fluid migration.« less

Role of Diagenesis in Formation of Stratigraphic Traps in Aux Vases of Illinois Basin: ABSTRACT

The Aux Vases Sandstone, a prime exploration target in the Illinois basin, is a prolific but enigmatic reservoir that has produced nearly a billion bbl of oil. Detailed outcrop and subsurface study shows that much of this production is from diagenetically influenced stratigraphic traps in a complex tidal-sandbar system. The complexity of this system makes identification End_Page 526------------------------------ of traps difficult. The sandbars are composed of fine to medium-grained, cross-bedded, clean, well-sorted quartz arenites. The Aux Vases typically possesses preserved, primary, interparticle porosities of 15-25%, and permeabilities of 40-250 md. Reduction of porosity and permeability in the tidal bars is caused by quartz overgrowths, pressure solution at quartz grain contacts, and authigenic chlorite cement. The sandbars grade laterally and vertically into interbar and tidal flat sediments composed of fine-grained, bioturbated or ripple-bedded quartz wackes and arenites that typically have 15-20% porosity but are impermeable. The clay matrix of the interbar wacke sediments causes a reduction in permeability, as does the authigenic chlorite and illite cement in the fine-grained arenites associated with the wackes. Exploration has been hampered because (1) bars of reservoir quality are not easily distinguished from interbar sediments on electric logs; (2) resistivity logs usually show excessively high water saturation; and (3) sandbar trends are difficult to predict. Study of electric logs has shown that a spontaneous potential (SP) of 75 mV or greater is a good indicator of relatively clean, well-sorted, sandbar sediments. An SP less than 75 is an indication of interbar sediments. SEM and x-ray analyses suggest that water adsorbed on mixed layer clays is interpreted on electric logs as free water, accounting for the high water saturation readings. Prediction of sandbar trends is difficult because there are two trend directions: the dominant trend is northwest-southeast, parallel to the shorelin ; however, many bars trend east-west, or roughly normal to shoreline. The two trend directions are commonly juxtaposed, thereby adding to the complexity. End_of_Article - Last_Page 527------------