Second EAGE Workshop on Geochemistry in Petroleum Operations and Production

It is becoming more and more important to identify isolated aquifers. Here we show that the combination of chlorine and bromine isotopes have the potential to identify them. In an isolated and immobile aquifer, the main transport processes that can be expected are diffusion and gravitational settling. Both processes are expected to produce non-detectable changes in anion concentration while producing significant isotope variations. We then show that these patterns are indeed found in a case study of a presumably relatively well isolated aquifer .

Formation water from the Al Wajh Formation (Oligocene-Lower Miocene) and Adaffa Formation (Upper Cretaceous) was geochemically fingerprinted to constrain fluid migration pathways from surface infiltration toward the present position of the groundwater regime from the deep sedimentary column in the Northern Red Sea Basin. Multi-isotopic analyses on inorganic fluids were performed to assess potential flow pathways for the analogue migration of organic phases. Depleted strontium isotopic ratios (87Sr/86Sr = 0.707307 - 0.708012) of formation brines from the sedimentary sequence suggest the occurrence of hydrothermal interaction with the underlying igneous basement (87Sr/86Sr = 0.70292-0.70316), likely to be triggered by temperature-triggered hydrothermal reactions. Fluid migration must be structurally-controlled or by depositional hiatus of salt layers, as halite dissolution from the seal cap of Miocene evaporites (Mansiya Formation) has not been evidenced. Boron (11B) and iodine (129I/127I) isotopic fingerprints indicate: a) the contact of formation water to a clay-rich, organic-rich rock type, likely to be of Late Eocene and Late Cretaceous age; b) the potential release of adsorbed boron from clay minerals and biophyllic iodine from organic matter; and c) the subsequent migration of iodine-enriched formation water (from the organic source) to the present groundwater horizon at Al Wajh Formation.

We present Heat Flow combined with biomarker analysis aim to get source rock maturity map from Kais Formation carbonate microfacies, which is known as a productive reservoir. Part of Kais Formation which is consist of carbonate rock, rarely considered as an internal source rock. The microfacies of Kais Formation has controlled the maturity of source rock. The study area is located at Salawati Basin, Indonesia. Multi cluster analysis, carbonate micro facies typing, facies seismic characterization, are conducted to obtain facies classification and environmental deposition. Biomarker evaluation and frametogram m/z focused on Klamono Block. showed biodegradation phase and origins of the hydrocarbon. We conducted 1D burial history analysis to obtain basin evolution and 3D burial history for modeling source rock maturation. History of submergence on the onshore area (Kawista-1) indicates that the maturity of Kais Formation (figure 1) as a source rock begins in Early Miocene and reaches 0.9 % Ro at the bottom. Kais formation achieves ideal maturity in the area of the research block, maturity ranges from 0.55 to 1.3% Ro in the north, and maturity rises towards the northwest.

A reservoir geochemical study in the Gullfaks field and its surroundings fields was performed to detect compositional differences in petroleum, from different reservoirs and sectors, which may be related to its complex filling history. The molecular composition of hetero- and polycyclic aromatic hydrocarbons, C7 hydrocarbons together with δ13C data indicate that oils from the Gullfaks South field derived mainly from more terrestrially-dominated source facies, whereas oils from the Gullfaks and Gullfaks West fields sourced mainly from marine algal material. Although, the oil sample from the Gullfaks West field has the lightest δ13C values of n-alkanes and isoprenoids, petroleum from the Brent Group and the Cook Fm. reservoirs in the Gullfaks field were not distinguished isotopically in spite of having been filled from different source basins. In contrast, hetero- and polycyclic aromatic hydrocarbons as well as light hydrocarbons allowed discriminating oil populations into the Gullfaks field, which were not differentiated using biomarkers and δ13C data. Here, the δ13C values of Pr and Ph coupled with molecular data of heterocyclic aromatic hydrocarbons and light hydrocarbons were very useful to discriminate oils from the Gullfaks area, whose compositions are more associated with source facies and depositional environment variations into Upper Jurassic source rocks.

Petroleum biodegradation causes systematic variation in oil molecular composition. Most biodegradation in the reservoir takes place in a basal degradation zone, near the OWC or in transition zones where free water is available for the transport of nutrients. The reservoir temperature history and oil mixing are the primary controls on oil biodegradation. The shape of the molecular composition gradients and final oil quality are controlled by the relationship between biodegradation rate, fresh oil charge rate, diffusion of oil components towards the biodegradation zone, and mixing of fresh and degraded oil. In this work, we review the systematic variations in molecular composition resulting from in-reservoir oil biodegradation and its main controls. We also present some case histories to demonstrate how these processes impact compositional and fluid property gradients (API gravity and viscosity) in heavy and extra-heavy oil accumulations.

Our goal in this paper is to provide new experimental evidences for the dependence of the streaming potential coupling coefficient of carbonate rocks with the saturation, comparing our data with the predictive model developed by Revil et al. (2007), including the Corey or the van Genuchten exponent, often used to describe multi-phase flow in the vadose zone. We show that the relative permeability, the relative streaming potential coupling coefficient and the capillary pressure could be described in a consistent way for carbonates using the van Genuchten approach. We measured the streaming potential coupling coefficient of natural saturated and unsaturated carbonate rocks. Saturation was achieved with NaCl brines with salinities ranging from 2×10-3 Mol L-1 to 2.0 Mol L-1. The magnitude of the coupling coefficient increases with decreasing salinity similarly to the trend observed for sandstones. The permeability has a low impact on the values of the streaming potential coupling coefficient at high and low salinity. The zeta potential has been calculated at full saturation using a modified version of the Helmholtz-Smoluchowski equation that accounts for surface electrical conductivity.

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Polymer flooding is a mature Enhanced Oil Recovery (EOR) topic that has been studied and successfully applied in a number of hydrocarbon reservoirs. Barium Sulphate (BaSO4) is a serious scale risk that has been encountered in various oil fields. The study illustrates the BaSO4 scale behavior in the polymer flooding process. The behavior of brines mixing and the formation of BaSO4 is different in the polymer flooding compared to the normal water flooding in terms of the timing and amount of scale. This difference depends on the system properties such as polymer viscosity, adsorption and injection brine salinity. Sulphate scale deposition presents a risk in the near wellbore region of production wells that cannot be controlled by continual injection, so a batch treatment called a scale squeeze is required to be applied to the near wellbore region. Different EOR methods impact the scale risk and so have the potential to impact squeeze treatment frequency, chemical cost and differed oil associated with such treatments. The use of low salinity, low sulphate brine combined with polymer not only improves oil recovery, but it also reduces the scale risk in the reservoir and the wellbore.

Our team elaborated a family of smart tracers that bypass the lack of conventional methods of characterization hence ensuring the reliability of oil/water estimation by providing useful information gathered directly into the targeting zone. We preferred to replace the use of (i) chemical (isotopic or ionic composition footprints) and (ii) radioactive tagging elements by fluorescent tracers. The disadvantages of the use of radioactive elements is due to restricting regulation limits in their implementation on field in some areas. As well, chemical tracers such as fluorobenzoic acids (FBAs) - routinely used for field tracer campaigns because of their low quantification limit - require fine analyses which cannot be performed on-line or in standard labs. Moreover, with years of use, their background is becoming ever more present.

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