Quantifying the links between geochemical and geophysical properties of organic-rich carbonate mudrocks

Source rocks possess complex heterogeneous matrices with soft organic matter, consisting mainly of kerogen, interspersed within a stiff inorganic mineral framework that varies in composition. There is not a clear understanding nor adequate knowledge of how geochemical properties influence the rock physics, especially when predicting a seismic response. While many attempts have been made to use seismic to empirically quantify these properties for the purpose of exploration, those attempts have often failed due to the complexity of the elastic properties of kerogen and the laminated geometry of the rock. This is due primarily to uncertainty over how these properties change with maturity as a result of burial and subsequent uplift. Therefore, knowledge of (1) the elastic properties of kerogen, (2) the amount and geometric distribution of organic matter within the rock matrix, and (3) the impact of kerogen maturity on its elastic properties is needed to predict a seismic response. An elastic property modeling method has been developed to address this challenge based on the integration of high-resolution microscopy, geochemical analysis, and velocity measurements. Using this approach, endmembers are obtained that allow for building rock-physics models that can predict elastic uncertainty from mineral heterogeneity and estimate the elastic properties of organic matter. Digital images, geochemical data, and velocity measurements coupled with maturity modeling suggest that bulk and shear softening of kerogen can help distinguish between maturity-induced seismic responses.

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Computing elastic properties of organic-rich source rocks using digital images

The Leading Edge ◽

10.1190/tle40090662.1 ◽

2021 ◽

Vol 40 (9) ◽

pp. 662-666

Author(s):

Mita Sengupta ◽

Shannon L. Eichmann

Keyword(s):

Organic Matter ◽

Elastic Properties ◽

Focused Ion Beam ◽

Ion Beam ◽

Rock Physics ◽

Flow Property ◽

Source Rocks ◽

Digital Rock ◽

Rock Structure ◽

Imaging Resolution

Digital rocks are 3D image-based representations of pore-scale geometries that reside in virtual laboratories. High-resolution 3D images that capture microstructural details of the real rock are used to build a digital rock. The digital rock, which is a data-driven model, is used to simulate physical processes such as fluid flow, heat flow, electricity, and elastic deformation through basic laws of physics and numerical simulations. Unconventional reservoirs are chemically heterogeneous where the rock matrix is composed of inorganic minerals, and hydrocarbons are held in the pores of thermally matured organic matter, all of which vary spatially at the nanoscale. This nanoscale heterogeneity poses challenges in measuring the petrophysical properties of source rocks and interpreting the data with reference to the changing rock structure. Focused ion beam scanning electron microscopy is a powerful 3D imaging technique used to study source rock structure where significant micro- and nanoscale heterogeneity exists. Compared to conventional rocks, the imaging resolution required to image source rocks is much higher due to the nanoscale pores, while the field of view becomes smaller. Moreover, pore connectivity and resulting permeability are extremely low, making flow property computations much more challenging than in conventional rocks. Elastic properties of source rocks are significantly more anisotropic than those of conventional reservoirs. However, one advantage of unconventional rocks is that the soft organic matter can be captured at the same imaging resolution as the stiff inorganic matrix, making digital elasticity computations feasible. Physical measurement of kerogen elastic properties is difficult because of the tiny sample size. Digital rock physics provides a unique and powerful tool in the elastic characterization of kerogen.

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Rock-physics modeling for the elastic properties of organic shale at different maturity stages

Geophysics ◽

10.1190/geo2015-0713.1 ◽

2016 ◽

Vol 81 (5) ◽

pp. D527-D541 ◽

Cited By ~ 43

Author(s):

Luanxiao Zhao ◽

Xuan Qin ◽

De-Hua Han ◽

Jianhua Geng ◽

Zhifang Yang ◽

...

Keyword(s):

Elastic Properties ◽

Rock Physics ◽

Source Rocks ◽

Modeling Framework ◽

Maturity Stages ◽

Rock Physics Modeling ◽

Physics Modeling ◽

Elastic Responses ◽

The Impact ◽

Organic Shale

Modeling the elastic properties of organic shale has been of long-standing interest for source rocks and unconventional reservoir characterization. Organic shales exhibit significant variabilities in rock texture and reservoir properties at different maturity stages, subsequently affecting their elastic responses. We have developed a new rock-physics modeling scheme honoring the maturity levels (immature, mature, and overmature), which are constrained by the evolution of the physical properties of organic shale upon kerogen maturation. In particular, at different maturity stages, the manners in which the compliant organic materials interact with the inorganic mineral matrix are characterized by different effective medium theories. On the basis of the developed rock-physics templates, organic shales have different elastic behaviors at different maturity stages. Ignoring the impact of kerogen maturation is insufficient to adequately characterize the elasticity of the whole organic shale system. Modeling results suggest that the elastic responses of organic shale are sensitive to two dominant factors — organic matter content and mineralogical composition. The elastic anisotropy characteristics are not only affected by the kerogen content and clay alignment but also depend on the morphology of kerogen distribution. Our results compare satisfactorily with data from ultrasonic velocity and log measurements, confirming validity and applicability of our modeling framework.

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ROCK PHYSICS TEMPLATE TO ESTIMATE THE EFFECTS OF TOTAL ORGANIC CARBON (TOC) AND MINERALOGY ON THE SEISMIC ELASTIC PROPERTIES OF IMMATURE SHALE RESERVOIR

Scientific Contributions Oil and Gas ◽

10.29017/scog.42.2.374 ◽

2019 ◽

Vol 42 (2) ◽

pp. 43-49

Author(s):

Harnanti Y Hutami ◽

Tiara Larasati Priniarti ◽

Ign Sonny Winardhi ◽

Handoyo .

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Total Organic Carbon ◽

Elastic Properties ◽

Rock Physics ◽

P Wave ◽

General Distribution ◽

Effective Elastic Properties ◽

Shale Reservoirs ◽

The Impact

The low porosity and permeability shale are nowadays known as self-resourcing reservoirs. In the unique organic shales, TOC has a signifi cant contribution to the elastic properties of rocks. TOC behaves like porosity to a density log and effects in decreasing density. To reduce the uncertainty due to TOC and mineral variability effect, a quantitative interpretation of shale reservoirs should be done properly to obtain the best image of shale systems. In this study, we built rock-physics templates (RPT) to esti mate seismic response by defi ning the relationship between total organic carbon (TOC) and effective elastic properties of shale reservoirs of a data set from South Sumatera Basin, Indonesia. RPT is carried out by incorporating the amount of organic matter into shale pore space as a solid-fi lling inclusion. Moreover, shale porosity is assumed to be fully water-saturated determined by the in-situ conditions. We have estimated the general distribution of pore geometry by investigating aspect ratio from the dataset. A solid background of shale from several different minerals is estimated by using effective medium theory. Properties of porous rocks for solid pore infi ll are estimated from a generalization of Brown-Korringa Equation. Effective elastic properties of bulk rock frame fi lled with a fl uid are obtained from Gassmann equations. Results show that increasing the TOC volumes generally reduces both P-wave and S-wave velocities, acoustic impedance, and density. On the contrary, the vp/vs ratio increased as the impact of immature organic matter which will be more affecting shale rigidity than its compressibility.

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Paleoenvironment of the Lower–Middle Cambrian Evaporite Series in the Tarim Basin and Its Impact on the Organic Matter Enrichment of Shallow Water Source Rocks

Minerals ◽

10.3390/min11070659 ◽

2021 ◽

Vol 11 (7) ◽

pp. 659

Author(s):

Mingyang Wei ◽

Zhidong Bao ◽

Axel Munnecke ◽

Wei Liu ◽

G. William M. Harrison ◽

...

Keyword(s):

Organic Matter ◽

Shallow Water ◽

Tarim Basin ◽

Water Environment ◽

Water Source ◽

Major Elements ◽

Source Rocks ◽

Middle Cambrian ◽

Sedimentary Environments ◽

The Impact

Just as in deep-water sedimentary environments, productive source rocks can be developed in an evaporitic platform, where claystones are interbedded with evaporites and carbonates. However, the impact of the paleoenvironment on the organic matter enrichment of shallow water source rocks in an evaporite series has not been well explored. In this study, two wells in the central uplift of the Tarim Basin were systematically sampled and analyzed for a basic geochemical study, including major elements, trace elements, and total organic carbon (TOC), to understand the relationship between TOC and the paleoenvironmental parameters, such as paleosalinity, redox, paleoclimate, paleo-seawater depth, and paleoproductivity. The results show that the Lower–Middle Cambrian mainly developed in a fluctuating salinity, weak anoxic to anoxic, continuous dry and hot, and proper shallow water environment. The interfingering section of evaporites, carbonates, and claystones of the Awatag Fm. have higher paleoproductivity and higher enrichment of organic matter. Paleosalinity, redox, paleoclimate, paleo-seawater depth, and paleoproductivity jointly control the organic matter enrichment of shallow water source rocks in the evaporite series. The degree of enrichment of organic matter in shallow water source rocks first increases and then decreases with the increase in paleosalinity. All the samples with high content of organic matter come from the shallower environment of the Awatag Fm.

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PETROLEUM POTENTIAL OF THE NEOPROTEROZOIC WESTERN OFFICER BASIN, WESTERN AUSTRALIA, BASED ON A SOURCE ROCK MODEL FROM EMPRESS-IA

The APPEA Journal ◽

10.1071/aj98018 ◽

1999 ◽

Vol 39 (1) ◽

pp. 322 ◽

Cited By ~ 2

Author(s):

G.M. Carlsen ◽

S.N. Apak ◽

K.A.R. Ghori K. Grey ◽

M.K. Stevens

Keyword(s):

Organic Matter ◽

Western Australia ◽

Depositional Environments ◽

Source Rocks ◽

Petroleum Potential ◽

Organic Facies ◽

Organic Growth ◽

Rock Model ◽

Depositional Controls ◽

The Impact

The sedimentology, palaeontology and geochemistry of Neoproterozoic, organic-rich, clastic and related carbonate deposits in Western Australia provide new insights into the first-order depositional controls on hydrocarbon source rocks in the Neoproterozoic. Organic facies are correlated with depositional facies, revealing the impact of organic productivity and transport of organic rich sediments on the accumulation of organic matter in different depositional environments. Sedimentation is largely limited to ramp, platform, shoal, lagoon and sabkha environments.Growth of benthic organisms in the photic zone was the primary process controlling the production of organic matter in the ramp-shoreline system of the Kanpa Formation. Storms and floods were the primary mechanism for moving organic rich sediments into dysoxic and anoxic depositional environments. Variations in organic facies are indicated by: 1) changes in the palynomorph assemblages, particularly the increase in acritarchs within shallow-water ramp facies and cyanobacterial filaments in quiet-water sediments; 2) organic-rich laminae, containing abundant cyanobacterial filaments and mat material; and 3) the oxidation state of preserved organic remains.Periods of high organic growth rates or periods of mass mortality may have led to the development of an anoxic zone at the water-sediment interface. In the shoal and lagoonal settings, higher rates of clastic sediment dilution combined with oxygenated conditions resulted in lower TOC and hydrogen depleted organic facies.Condensed sections overlying stromatolitic dolomites represent the most effective organic facies of all of the potential source laminae sampled in Empress–IA. Most of the Officer Basin succession is currently within the oil-generating window and hydrocarbon shows encourage further exploration.

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Geochemistry and depositional history of the Union Springs Member, Marcellus Formation in central Pennsylvania

Interpretation ◽

10.1190/int-2014-0228.1 ◽

2015 ◽

Vol 3 (3) ◽

pp. SV17-SV33 ◽

Cited By ~ 4

Author(s):

Anna K. Wendt ◽

Mike A. Arthur ◽

Rudy Slingerland ◽

Daniel Kohl ◽

Reed Bracht ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Water Column ◽

Appalachian Basin ◽

Depositional Environments ◽

Source Rocks ◽

Geochemical Data ◽

Inorganic Elements ◽

Central Pennsylvania ◽

Marcellus Formation

Debate continues over paleoenvironmental conditions that prevail during deposition of organic-carbon (C)-rich marine source rocks in foreland basins and epicontinental seas. The focus of disagreement centers largely on paleowater depth and the prevalence of anoxia/euxinia. The issues of paleodepth and water column conditions are important for prediction of lateral variations in source quality within a basin because the viability of a hydrocarbon play depends on a thorough understanding of the distribution of source rock quality and depositional environments. We used inorganic geochemical data from the Middle Devonian Marcellus Shale in the Appalachian Basin to illustrate interpretive strategies that provided constraints on conditions during deposition. Source evaluation typically relies on the analysis and interpretation of organic geochemical indicators, potentially also providing evidence of the degree of thermal maturity and conditions of the preservation of the organic matter. The Marcellus Formation is thermally mature, making the evaluation of the organic-carbon fraction for geologic interpretation inadequate. Because most labile organic matter has largely been destroyed in the Marcellus Formation, analysis of inorganic elements may be used as an alternative interpretative technique. Several inorganic elements have been correlated to varying depositional settings, allowing for their use as proxies for understanding the paleodepositional environments of formations. A high-resolution geochemical data set has been constructed for the Union Springs Member along a transect of cores from proximal to distal in the Appalachian Basin in central Pennsylvania using major, minor, and trace elemental data. Our results suggested that during deposition, the sediment-water interface, and a portion of the water column, was anoxic to euxinic. As deposition continued, euxinia was periodically interrupted by dysoxia and even oxic conditions, and a greater influx of clastic material occurred. Such variations were likely related to fluctuations in water depth and progradation of deltaic complexes from the eastern margin of the Appalachian Basin.

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Diagenetic Trends of Synthetic Reservoir Sandstone Properties Assessed by Digital Rock Physics

Minerals ◽

10.3390/min11020151 ◽

2021 ◽

Vol 11 (2) ◽

pp. 151

Author(s):

Maria Wetzel ◽

Thomas Kempka ◽

Michael Kühn

Keyword(s):

Elastic Properties ◽

Pore Space ◽

Rock Physics ◽

Mineral Dissolution ◽

Ct Scans ◽

Micro Ct ◽

Digital Rock Physics ◽

Gravity Driven ◽

Stress Dependent ◽

The Impact

Quantifying interactions and dependencies among geometric, hydraulic and mechanical properties of reservoir sandstones is of particular importance for the exploration and utilisation of the geological subsurface and can be assessed by synthetic sandstones comprising the microstructural complexity of natural rocks. In the present study, three highly resolved samples of the Fontainebleau, Berea and Bentheim sandstones are generated by means of a process-based approach, which combines the gravity-driven deposition of irregularly shaped grains and their diagenetic cementation by three different schemes. The resulting evolution in porosity, permeability and rock stiffness is examined and compared to the respective micro-computer tomographic (micro-CT) scans. The grain contact-preferential scheme implies a progressive clogging of small throats and consequently produces considerably less connected and stiffer samples than the two other schemes. By contrast, uniform quartz overgrowth continuously alters the pore space and leads to the lowest elastic properties. The proposed stress-dependent cementation scheme combines both approaches of contact-cement and quartz overgrowth, resulting in granulometric, hydraulic and elastic properties equivalent to those of the respective micro-CT scans, where bulk moduli slightly deviate by 0.8%, 4.9% and 2.5% for the Fontainebleau, Berea and Bentheim sandstone, respectively. The synthetic samples can be further altered to examine the impact of mineral dissolution or precipitation as well as fracturing on various petrophysical correlations, which is of particular relevance for numerous aspects of a sustainable subsurface utilisation.

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Seismic petrophysics workflow applied to Delaware Basin

Interpretation ◽

10.1190/int-2019-0157.1 ◽

2020 ◽

Vol 8 (2) ◽

pp. T349-T363

Author(s):

Yoryenys Del Moro ◽

Venkatesh Anantharamu ◽

Lev Vernik ◽

Alfonso Quaglia ◽

Eduardo Carrillo

Keyword(s):

Elastic Properties ◽

Reservoir Characterization ◽

Weighted Average ◽

Rock Physics ◽

Seismic Inversion ◽

Source Rocks ◽

Amplitude Variation With Offset ◽

Geomechanical Properties ◽

Delaware Basin ◽

Seismic Amplitudes

Petrophysical analysis of unconventional plays that are comprised of organic mudrock needs detailed data QC and preparation to optimize the results of quantitative interpretation. This includes accurate computation of mineral volumes, total organic carbon (TOC), porosity, and saturations. We used TOC estimation to aid the process of determining the best pay zones for development of such reservoirs. TOC was calculated as a weighted average of Passey’s (empirical) and the bulk density-based (theoretical) methods. In organic mudrock reservoirs, the computed TOC log was used as an input to compute porosity and calibrate rock-physics models (RPMs), which are needed for understanding the potential of source rocks or finding sweet spots and their contribution to the amplitude variation with offset (AVO) changes in the seismic data. Using calibrated RPM templates, we found that TOC is driving the elastic property variations in the Avalon Formation. We determined the layering and rock fabric anisotropy using empirical relationships or modeled in the rock property characterization process because reflectivity effects are often seen in the observed seismic used for well tie and wavelet estimation. A Class IV AVO response was seen at the top of the Avalon Formation, which is typical of an unconventional reservoir. We then performed solid organic matter (TOC) substitution to account for variability of elastic properties and their contrasts as expressed in seismic amplitudes. To complete the characterization of the intervals of interest, we used conventional seismic petrophysical methods in the workflow and found that the main driver modifying the elastic properties for the Avalon shales was TOC; this conclusion serves as a foundation in integrated seismic inversion that may target lithofacies, TOC, and geomechanical properties. Seismic reservoir characterization results are critical in constraining landing zones and trajectories of the horizontal wells. The final interpretation may be used to rank targets, optimize drilling campaigns, and ultimately improve production.

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Source Rock Evaluation and Hydrocarbon Generation Model of a Permian Alkaline Lakes—A Case Study of the Fengcheng Formation in the Mahu Sag, Junggar Basin

Minerals ◽

10.3390/min11060644 ◽

2021 ◽

Vol 11 (6) ◽

pp. 644

Author(s):

Yong Tang ◽

Wenjun He ◽

Yubin Bai ◽

Xiang Zhang ◽

Jingzhou Zhao ◽

...

Keyword(s):

Organic Matter ◽

Evaluation Criteria ◽

Junggar Basin ◽

Source Rocks ◽

Geochemical Data ◽

Generation Model ◽

Hydrocarbon Generation ◽

High Hydrocarbon ◽

Hydrocarbon Generation Potential ◽

Alkaline Lake

The alkaline lake source rocks of the Fengcheng Formation are developed in the Mahu Sag of the Junggar Basin. Different from traditional continental fresh water and saltwater lake source rocks, alkaline lake source rocks lack targeted evaluation criteria, and it is unknown whether their hydrocarbon generation models are consistent with traditional models. Therefore, in the present study, evaluation standards and hydrocarbon generation models of alkaline lake source rocks are discussed based on geological and organic geochemical data and a systematic summary of the geochemical characteristics of the Fengcheng Formation source rocks. The Fengcheng Formation source rocks are mainly diamictite with mixed argillaceous rock and dolomite; most total organic carbon (TOC) values range from 0.2–1.4%; and the kerogen is primarily oil-prone type II, reaching low- to high-maturity stages. Based on the types of organic matter in source rocks and the relationships between organic matter abundance parameters, the evaluation standard of alkaline lake source rocks is proposed. The Fengcheng Formation is mainly composed of good to excellent source rocks (55.5%) with high hydrocarbon generation potential. The single-peak hydrocarbon generation model of the Fengcheng Formation is similar to that of traditional freshwater or saltwater lakes, with a high hydrocarbon generation rate, two to five times that of the traditional model; its main particularity is in the formation of naphthenic crude oil from the kerogen of bacteria and algae. A new understanding of the hydrocarbon generation potential and model of alkaline lake source rocks in the Fengcheng Formation can provide support for tight oil and shale oil exploration in the Mahu Sag.

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Petrophysics and rock physics modeling of diagenetically altered sandstone

Interpretation ◽

10.1190/int-2014-0048.1 ◽

2015 ◽

Vol 3 (1) ◽

pp. SA107-SA120 ◽

Cited By ~ 3

Author(s):

Zakir Hossain ◽

Yijie Zhou

Keyword(s):

Electrical Properties ◽

Elastic Properties ◽

Rock Physics ◽

Theoretical Models ◽

Elastic Wave Velocity ◽

Secondary Effects ◽

Velocity Measurements ◽

Rock Physics Modeling ◽

Physics Modeling ◽

Mathematical Relationships

We worked to establish relationships among porosity, permeability, resistivity, and elastic wave velocity of diagenetically altered sandstone. Many such relationships are documented in the literature; however, they do not consider diagenetic effects. Combining theoretical models with laboratory measured data, we derived mathematical relationships for porosity permeability, porosity velocity, porosity resistivity, permeability velocity, velocity resistivity, and resistivity permeability in diagenetically altered sandstone. The effects of clay and cementation were evaluated using introduced coefficients in these relationships. We found that clean sandstone could be modeled with Kozeny’s relation; however, this relationship broke down for clay-bearing and diagenetically altered sandstone. Porosity is the first-order parameter that affects permeability, electrical, and elastic properties; clay and cement cause secondary effects on these properties. Rock physics modeling results revealed that cementation had a greater effect on elastic properties than electrical properties and clay had a larger effect on electrical properties than elastic properties. The relationships we provided can greatly help to determine permeability, resistivity, and velocity from porosity and to estimate permeability from resistivity and velocity as well as to determine resistivity from velocity measurements.

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