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title: How Calcite Dissolution and Veins Reveal Fluid Flow
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A look into new studies on carbonate reservoirs, as well as a recently proposed automated screening for AVA analysis. ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­    ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­  

| View in browser Tuesday, 3 November 2026 I have been reading an interesting book by Jean-Baptiste Fressoz called More and More and More: An All-Consuming History of Energy, published in 2024. The book challenges the long-held popular (mis)conception that the history of energy is characterized by coal replacing wood, oil and gas replacing coal, and therefore, that petroleum is going to be replaced by nuclear or renewables.   The true history shows that the emergence of each energy technology is a new layer added to the previous energy resources. I do not want to ruin the whole story, so I recommend reading the book for yourself!   Now, let’s dive into this week’s research stories.   Rasoul Sorkhabi   Editor, Core Elements How Calcite Dissolution and Veins Reveal Fluid Flow Thin-section photograph of a carbonate reservoir in Victory field, Kansa. Blue epoxy shows porosity. (source: Kansas Geological Survey) Limestones are “messy” reservoir rocks because calcite can easily be dissolved, flow, and reprecipitate. Thus, depending on how many times these processes happen, they can alter the reservoirs’ fabric.   Nevertheless, a large number of oil and gas reservoirs are carbonate, and two recent studies in AAPG Bulletin offer some interesting insights to help us better understand these reservoirs. Let’s review.   #1. Solubility of Calcite in Petroleum Basins Stephen Ehrenberg and Per Aagaard, who have long studied carbonates, have published a new paper in the a recent issue of AAPG Bulletin.   Porosity types: Reservoir rock porosity may be primary (depositional) or secondary (post-depositional). Secondary porosity is created through fracturing or dissolution. Dissolution is particularly important in carbonates. Secondary pores are generated in three stages: Eogenetic (early burial), Mesogenetic (deep burial) Telogenetic (long burial associated with unconformities) New study: The researchers calculated calcite solubility as a function of reservoir temperatures from 50 to 200 degrees Celsius for a given salinity (NaCl) and partial pressure of carbon dioxide (pCO2). Calcite dissolves by interacting with carbon dioxide and water to form calcium and bicarbonate ions. There is a positive correlation between calcite solubility and increasing temperature (depth). Nevertheless, calcite may also show retrograde solubility if water moves through fractures upward to lower temperature levels. #2. Calcite Veins as a Marker of Fluid Flow In a recent issue of AAPG Bulletin, Chinese scientists used calcite veins to document fluid flow generations in a carbonate reservoir.   Basin and reservoir: The study focused on the Triassic-age Qinglong Formation in the Hongqiao area of the Suebi Basin in eastern China.   What they did: The research included petrography, fluid-inclusion analysis, stable carbon, oxygen, and strontium isotope analysis of host rock and calcite veins, laser-ablation spot U-Pb dating of calcite veins, and basin modeling. The core samples came from three wells in the basin. What they found: The researchers found six phases of calcite veins: C1 dated 142 Ma and originated from hydrocarbon fluids mixed with formation water C2 (115 Ma) formed from deep hydrothermal fluids related to Tanlu fault zone activity C3 (97 Ma) and C4 (85 Ma) were derived from formation water mixed with meteoric water C4 dated 85 Ma and formed from intraformational water mixed with deep-seated strata water C5 (60 Ma) formed from intraformational water mixed with deep-seated strata water C6 (42-38 Ma) sourced from deep-seated, strontium-rich crustal fluids Additionally: Primary oil inclusions are present in C1, C2, and C5 veins. During C1, C2, and C5 events, oil of various thermal maturity migrated into the reservoir rock. During C3 and C4 events, the uplift of the reservoir led to oil leakage. Go deeper: To learn more about carbonate porosity and research in that area, read these older Bulletin articles:   Ehrenberg and colleagues: January 2006 Ehrenberg and colleagues: February 2012 Mazzullo and Harris: May 1992   I was also reminded of my own research on calcite vein analysis in Wyoming reservoir rocks, published in AAPG Memoir 85. Sponsored AAPG to Speak at Reuters Events: Energy LIVE 2026   Energy LIVE returns to Houston, December 8-9, convening 1,000+ energy leaders to explore capital, innovation & the future of American energy. Register & save 15% with AAPG’s code ‘LIVEPartner15’. LEARN MORE Seismic Screening Amplitude Variation with Angle (AVA) Method AVA screening (Interpretation, August 2026) In a recent issue of Interpretation, Ramses Meza proposed an automated screening for AVA analysis.   Seismic amplitude analysis: Geophysicists often use seismic attributes such as amplitude anomalies to highlight prospect candidates before drilling. Two related amplitude anomalies include amplitude variation with offset (AVO) and amplitude variation with angle (AVA). Angle and offset are linked through the geometry of seismic data. Amplitude of a seismic reflector is modeled from two attributes: Intercept (amplitude at zero offset) and gradient (rate of amplitude change with offset, which means slope with squared sine of incident angle). Intercept and gradient are controlled by changes in P-wave velocity, rock density, and Poisson’s ratio across a seismic reflector. AVA and AVO are derived from a semiquantitative analysis of near- and far-angle stacked seismic volumes. AVO/AVA classes: Class 1: High impedance reservoirs with “dim” seismic spots. Strong positive intercept and negative gradient. Class 2: Near-zero impedance contrast reservoirs. Very difficult to interpret unless there is a clear amplitude increase with offset. Weak positive intercept and negative gradient. Class 3: Low-impedance reservoirs often with “bright spot” anomalies. Amplitude increases with offset. Strong negative intercept and negative gradient. Class 4: Low-impedance reservoirs with decreasing amplitude. Strong negative intercept and positive gradient. The new study: Meza discusses an automated screening method that decomposes the input near- and far-angle data into independent seismic volumes, each corresponding to an identified AVA class. This analytical method applies conditions to the selected complex seismic trace attributes to capture diagnostic features of each AVA class. The method was demonstrated on seismic data from an offshore field in Western Australia. Want to help AAPG grow? Consider supporting AAPG's free resources, like this one, by donating today. AAPG thanks our advertisers for their support. Sponsorship has no influence on editorial content. If you're interested in supporting AAPG digital products, reach out to Cait Williams.   You received this email because you signed up for newsletters from AAPG. To stop receiving this newsletter, unsubscribe or manage your email preferences.   AAPG  1444 S. Boulder Ave., Tulsa, Oklahoma 74119, USA (918) 584-2555 \| 1 (800) 364-2274 (US and Canada) www.aapg.org |
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