Albert Permanyer

Facies-Related Diagenesis and Multiphase Siderite Cementation and Dissolution in the Reservoir Sandstones of the Khatatba Formation, Egypt's Western Desert

In the fluvio-deltaic, quartz-arenitic sandstones of the Jurassic Khatatba Formation in the Salam field (Egypt9s Western Desert), diagenesis and sedimentary facies control reservoir quality. Fluvial channel sandstones have the highest porosities (10-15%) and permeabilities (100-600 md), in part because of siderite cementation, which (1) inhibited compaction and quartz cement and (2) was later dissolved, creating intergranular secondary porosity (1/4 of total porosity). Fluvial crevasse-splay and marine sandstones have the lowest reservoir quality because of an abundance of depositional kaolin matrix and pervasive, shallow-burial Fe-dolomite cement, respectively. Siderite precipitation was multiphase and separated by distinct dissolution events. The earliest siderite precipitated near surface, within suboxic tropical coastal swamps containing predominantly meteoric waters. Some influence of marine waters is indicated by local enrichments in Mg and Ca. The next major siderite generation shows a trend to decreasing Mn and Ca contents, and is of shallow-burial origin. The last major siderite phase is Mg rich and interpreted as deeper-burial in origin. Some dissolution occurred during shallow burial related to climatically controlled meteoric water fluxing under unconformities. The most important dissolution, however, occurred during deep burial, resulting in (1) a major corrosion surface predating the last Mg-rich zone, (2) selective dissolution of some earlier zones, and (3) secondary porosity. This burial dissolution is interpreted to have been caused by cooling of compactional waters expelled from the basin along major faults. Other diagenetic phases observed include early-diagenetic pyrite, kaolin, quartz, bitumen, and late-diagenetic barite and illite. Kaolinite precipitated at shallow depths ( 130°C) during and/or after rapid Late Cretaceous burial. Quartz developed in two phases, separated by oil migration. This paper illustrates that, in fluvio-deltaic quartz arenites deposited under the influence of humid tropical climate, reservoir quality can be largely controlled by the contrasting pathways of carbonate diagenesis followed by the different sedimentary facies. This paper also documents a case in which siderite dissolution generated significant secondary porosity in reservoir sandstones, and where both siderite cementation and dissolution took place in multiple phases during different diagenetic stages, including early, shallow-burial, and deep-burial diagenesis. The present study also shows that, in multiphase siderite cements, the earlier growth zones can be selectively dissolved and replaced by later siderite zones (i.e., recrystallized) during burial diagenesis. These findings contrast with the general thought that siderite cements are not susceptible to generation of significant secondary porosity by dissolution and that earlier-formed siderites are essentially stable during diagenesis.

FTIR and SUVF spectroscopy applied to reservoir compartmentalization: a comparative study with gas chromatography fingerprints results

Abstract The purpose of this study was to evaluate reservoir continuities and geochemical evolution of oils from individual reservoirs by using gas chromatography (GC) fingerprints method and to compare the results with those obtained from Fourier transform infra red (FTIR) and synchronous ultra violet fluorescence (SUVF) spectroscopy techniques. Six crude oils which belong to different levels of exploitation were selected from Alam El Bueib (AEB) oil field (Western Desert, Egypt). The samples studied belong to three different reservoir units in different wells. The results show that the all-independent techniques provide results in good agreement and that the oils characteristics and their evolution in the reservoir can be described similarly by fingerprints GC, FTIR and SUVF spectroscopy. The FTIR and SUVF spectroscopy techniques therefore constitute a rapid and non-expensive alternative for reservoir organic geochemistry studies.

Assessing petroleum oils biodegradation by chemometric analysis of spectroscopic data.

This study was conducted to classify petroleum oils in terms of their biodegradation stage by using spectroscopic analysis associated to chemometric treatments. Principal Component Analysis (PCA) has been applied on infrared and UV fluorescence spectra of Brazilian and Pyrenean oils. For Brazil samples, the method allowed to distinguish the biodegraded oils from the non-affected ones. Pyrenean sampling including oils at different levels of biodegradation has been chosen to follow their alteration rate. PCA loadings have shown spectral regions which have differentiated oils after biodegradation whereas Simple-to-use Interactive Self-Modelling Mixture Analysis (SIMPLISMA) has permitted to obtain a repartition in terms of components families (saturated, aromatic and polar ones) characterizing chemical composition of oils at different biodegradation degrees. Results are in good agreement with conclusions of usual hydrocarbon biomarker analysis.

Prediction of Source Rock Origin by Chemometric Analysis of Fourier Transform Infrared—Attenuated Total Reflectance Spectra of Oil Petroleum: Evaluation of Aliphatic and Aromatic Fractions by Self-Modeling Mixture Analysis

This study describes a new methodology for the interpretation of Fourier transform infrared (FT-IR) attenuated total reflectance (ATR) spectra of Algerian, Brazilian, and Venezuelan crude oils. It is based on a comparative study between a chemometric treatment and the classical one, which refers to indices calculation. In fact, the combined use of FT-IR indices and principal component analysis (PCA) has led to the classification of the studied samples in terms of geographic distribution. Quantitative analysis has been successfully realized by the supervised method partial least squares (PLS), which has permitted the prediction of the locations of oils. We have also applied another mathematical processing method, simple-to-use interactive self-modeling mixture analysis (SIMPLISMA), to evaluate the aromatic and aliphatic composition of the oils by extracting pure spectra representative of the different fractions.