Multimodal Carbonates: Distribution of Oil Saturation in the Microporous Rock Regions

Improved oil recovery from tight carbonate formations may provide the world with a major source of lower-rate power over several decades. Here we provide an overview of the Arab D formation in the largest oil field on earth, the Ghawar. We investigate the occurrence of microporosity of different origins and sizes using scanning electron microscopy (SEM) and pore casting techniques. Then, we present a robust calculation of the probability of invasion and oil saturation distribution in the nested micropores using mercury injection capillary pressure data available in the literature. We show that large portions of the micropores in Arab D formation would have been bypassed during primary drainage unless the invading crude oil ganglia were sufficiently long. Considering the asphaltenic nature of oil in the Ghawar, we expect the invaded portions of the pores to turn mixed-wet, thus becoming inaccessible to waterflooding until further measures are taken to modify the system’s chemistry.

Development of HFU-based permeability prediction models using core data for characterisation of a heterogeneous Oligocene sand in the Nam Con Son basin

Core data by both routine and special core analysis are required to understand and predict reservoir petrophysical characteristics. In this research, a total number of 50 core plugs taken from an Oligocene sand (T30) in the Nam Con Son basin, offshore southern Vietnam, were tested in the core laboratory of the Vietnam Petroleum Institute (VPI). The results of routine core analysis (RCA) including porosity and permeability measurements were employed to divide the study reservoir into hydraulic flow units (HFUs) using the global hydraulic elements (GHEs) approach. Based on five classified HFUs, 16 samples were selected for special core analysis, i.e., mercury injection capillary pressure (MICP) and grain size analyses for establishing non-linear porosity-permeability model of each HFU based on Kozeny-Carman equation, which provides an improved prediction of permeability (R2 = 0.846) comparing to that by the empirical poro-perm relationship (R2 = 0.633). In addition, another permeability model, namely the Winland R35 method, was applied and gave very satisfactory results (R2 = 0.919). Finally, by integrating the results from MICP and grain size analyses, a good trendline of pore size distribution index (λ) and grain sorting was successfully obtained to help characterise the study reservoir. High λ came with poor sorting, and vice versa, the low λ corresponded to good sorting of grain size.

Ocena parametrów przestrzeni porowej łupków menilitowych z odsłonięcia w Birczy

Celem pracy było scharakteryzowanie przestrzeni porowej łupków menilitowych występujących w odsłonięciach powierzchniowych z rejonu Birczy w jednostce skolskiej. Wszystkie próbki zostały pobrane z całego profilu stratygraficznego w jednym odsłonięciu w Birczy o długości 1 m. Struktura porowa próbek łupków wygrzanych w 105°C była mierzona metodą porozymetrii rtęciowej (ang. mercury injection capillary pressure, MICP) w temperaturze otoczenia oraz metodą adsorpcji azotu w temperaturze wrzenia ciekłego azotu. Ze względu na deformację przestrzeni porowej pod wpływem wysokich ciśnień roboczych rtęci, z krokami ciśnienia od 0 do 4136,84 bara, mikropory i mezopory można błędnie interpretować. Jako metodę uzupełniającą zastosowano więc pomiar adsorpcji azotu w celu prawidłowego obliczenia całkowitej połączonej objętości porowej. Na wykresach dV/dD (pochodnych objętości względem średnicy) połączono wyniki z obu technik pomiarowych, uzyskując pełniejszy obraz rozkładu objętości porów. W pracy przedstawiono możliwość dokładniejszego obliczenia objętości porów na podstawie nowego podejścia do analizy wykresów pochodnych. Obie metody zapewniają również kompleksową ocenę parametrów struktury porów, w tym powierzchni właściwej (ang. specific surface area, SSA), objętości mikro- i mezoporów oraz rozszerzonego zakresu rozkładu wielkości porów (ang. pore size distribution, PSD). Porównując wyniki metody adsorpcyjnej z użyciem azotu z wynikami porozymetrii rtęciowej, należy pamiętać o różnicach w zakresach obu technik badawczych oraz o tym, że azot i rtęć rejestrują struktury porowe w znacząco odmienny sposób. Zatłaczanie rtęci do struktury porowej jest regulowane przez przewężenia porów, podczas gdy zjawisko adsorpcji jest kontrolowane przez powierzchnię porów. Zastosowanie porozymetrii rtęciowej i adsorpcji azotu do łupków menilitowych pokazuje, jak użycie tych dwóch metod może wpłynąć na uzyskanie wzajemnie uzupełniających się informacji, które weryfikują obliczenia objętości porowej głównej skały macierzystej dla karpackich rop naftowych.

Conceptualizing a dual porosity occurrence in sandstones by utilizing various laboratory methods

Dual porosity in sandstones is considered as a key parameter that controls hydrocarbon production. Understanding of distribution of secondary pores, might give some insights about the heterogeneity of the reservoir for a particular area and as a result can help to produce more oil applying more efficient well-planning and design techniques. The studied oilfield is located about 40 km offshore Brunei Darussalam. In order to find out mechanisms that could lead to the development of secondary pores number of studies was conducted including helium porosity measurements, Mercury Injection Capillary Pressure, Micro-CT images (µ-CT images), X-Ray Diffraction, Petrography analysis, Scanning Electron Microscopy with Energy Dispersive Spectroscopy and Focus Ion Beam Scanning Electron Microscopes. The results showed that effective porosity that was formed by secondary pores was caused by the erosion, fracturing, and dissolution of sedimentary grains, authigenic minerals that are a part of pore-filling cement, and authigenic replacive minerals.

QEMSCAN-Assisted Interpretation of Imbibition Capillary Pressure for Multiporosity Carbonate Rocks

Summary In this paper, we present an experimental study that explores the potential links between the imbibition capillary pressure Pci and the pore systems and/or mineralogy for carbonate reservoirs undergoing waterflood. A systematic workflow has been formulated to ensure the data quality ofPci, minimize uncertainty in derivingPci from centrifuge tests, and analyze the data considering the pore-size distribution from mercury injection capillary pressure (MICP) and mineralogy from Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN). The workflow starts with assessing the centrifuge production data for gravity-capillary equilibrium at each speed. Then, the quality-checked data are used to generate six differentPci curves using analytical and numerical models. The resulting curves provide a measure of the variability in solutions for various rock types and assist in the selection of the most-representativePci curve. Finally, the representative Pci curves of all rock samples are analyzed together with the MICP and QEMSCAN data to examine the change in Pci curves as a result of changes in the number and character of rock types, pore systems, dominant pore-throat radii, and mineralogy. Findings from this study shed light on the impact of mineralogy and pore systems on Pci. From the mineralogy perspective, the presence of dolomite, microporous calcite, or rutile and anatase (TiO2) within the rock composition is found to affect the Pci of the carbonate samples used in this study. The rock samples with these minerals should be separated from other bimodal samples before attempting to obtain a correlation between Pci and pore systems. The data analysis further reveals that some bimodal samples of medium permeability yield a better waterflood imbibition efficiency than those of the high-permeability samples. This observation is attributed to a better communication between the micropore and macropore systems, and a closer proximity of the peak radii of the micro- and macropore systems of the medium-permeability samples.

A New Method for Predicting the Permeability of Sandstone in Deep Reservoirs

Capillary pressure curve data measured through the mercury injection method can accurately reflect the pore throat characteristics of reservoir rock; in this study, a new methodology is proposed to solve the aforementioned problem by virtue of the support vector regression tool and two improved models according to Swanson and capillary parachor parameters. Based on previous research data on the mercury injection capillary pressure (MICP) for two groups of core plugs excised, several permeability prediction models, including Swanson, improved Swanson, capillary parachor, improved capillary parachor, and support vector regression (SVR) models, are established to estimate the permeability. The results show that the SVR models are applicable in both high and relatively low porosity-permeability sandstone reservoirs; it can provide a higher degree of precision, and it is recognized as a helpful tool aimed at estimating the permeability in sandstone formations, particularly in situations where it is crucial to obtain a precise estimation value.