Initial Brine Saturation Research Articles

Permeability change induced by dissociation of gas hydrate in sediments with different particle size distribution and initial brine saturation

Permeability is critical to understand gas production behavior from hydrate reservoirs. The effects of particle size distribution and initial brine saturation on effective permeability of hydrate-bearing sediment during hydrate dissociation are poorly understood. In this study, X-ray CT imaging and Lattice Boltzmann simulations are combined to obtain a better understanding of sediment permeability changes during hydrate dissociation and the effects of particle size distribution and initial brine saturation. The results reveal that the dissociation of hydrate induced by depressurization starts from the part in contact with gas, causing a gradual increase in sediment effective permeability with decreasing hydrate saturation. When a critical hydrate saturation below 0.1 is reached, a sharper increase in permeability is found in sediments initially saturated with 50% brine than with 100% brine. To investigate the underlying relationship between hydrate morphology and sediment permeability, two topological parameters of an isolated hydrate cluster, equalivalent diameter and shape factor, are introduced. Phase topology analysis of hydrate clusters confirms that the partial water saturation method causes a more heterogeneous spatial distribution of hydrate at pore-scale. It also suggests that sediment with a narrower particle size distribution shows a faster increase in permeability and a more uniform hydrate morphology evolution with dissociation, no matter whether it is initially 50% or 100% brine saturated. A slower effective permeability increase and hydrate morphology evolution are achieved in initially 100% brine-saturated sediments, implying a more uniform dissociation of hydrate in pore space.

A Mechanistic Pore-Scale Analysis of the Low-Salinity Effect in Heterogeneously Wetted Porous Media

Low-salinity (LS) waterflooding has been a topic of substantial recent interest in the petroleum industry. Studies have shown that LS brine injection can increase oil production relative to high-salinity (HS) brine injection, but contradictory results have also been reported and a mechanistic explanation of these findings remains elusive. We have recently developed a pore-scale model of LS brine injection in uniformly wetted networks (Watson et al. in Transp Porous Med 118:201–223, 2017), and we extend this approach here to investigate the low-salinity effect (LSE) in heterogeneously wetted media. We couple a steady-state fluid displacement model to an innovative tracer algorithm and track the evolving salinity front as oil and HS brine are displaced from the network. The wettability of the pore structure is locally modified where water salinity falls below a critical threshold, and simulations show that this can have significant consequences for oil recovery. Our results demonstrate that, for heterogeneously wetted networks, the oil-wet (OW) pores are the only viable source of incremental oil by LS brine injection. Moreover, we show that a LS-induced increase in the displaced OW pore fraction is a necessary, but not sufficient, condition to guarantee additional oil production. Simulations further suggest that the initial OW pore fraction, the average network connectivity and the initial HS brine saturation are factors that can determine the extent of incremental oil recovery following LS brine injection. This study clearly highlights that the mechanisms of the LSE can be markedly different in uniformly wetted and in non-uniformly wetted porous media.

Development of a Microfluidic Method to Study Enhanced Oil Recovery by Low Salinity Water Flooding.

Microfluidics is an appealing method to study processes at rock pore scale such as oil recovery because of the similar size range. It also offers several advantages over the conventional core flooding methodology, for example, easy cleaning and reuse of the same porous network chips or the option to visually track the process. In this study, the effects of injection rate, flood volume, micromodel structure, initial brine saturation, aging, oil type, brine concentration, and composition are systematically investigated. The recovery process is evaluated based on a series of images taken during the experiment. The remaining crude oil saturation reaches a steady state after injection of a few pore volumes of the brine flood. The higher the injection rate, the higher the emulsification and agitation, leading to unstable displacement. Low salinity brine recovered more oil than the high salinity brine. Aging, initial brine saturation, and the presence of divalent ions in the flood led to a decrease in the oil recovery. Most of the tests in this study showed viscous fingering. The analysis of the experimental parameters allowed to develop a reliable and repeatable procedure for microfluidic water flooding. With the method in place, the enhanced oil recovery test developed based on different variables showed an increase of up to 2% of the original oil in place at the tertiary stage.

The impact of asphaltene deposition on fluid flow in sandstone

Asphaltene deposition in oil reservoirs is a contentious issue affecting both well and reservoir productivity. Though the phenomenon has been previously studied in several laboratory experiments, the uniformity aspects of the asphaltene deposit are usually overlooked. We have previously developed an experimental workflow to create a uniform deposit of asphaltene inside the core sample. In this study, the impact of this uniform deposit on fluid flow is quantified through imbibition, corefloods and relative permeability experiments. In addition, the lab results are used in a field scale simulation to investigate the impact of deposition on field performance. The results exhibit a shift in the wettability state where a reduction in both water imbibition rate and capacity are observed after deposition. Besides, up to 25% reduction in absolute permeability is detected. Results of pressure drop experiments across the core conducted on the exposed rocks indicate a change in the wetting characteristics, with the exposed rocks becoming more mixed/intermediate wet and varying with the change in the initial brine saturation in the rock. Subsequently, the relative permeability set is affected where a shift in the oil residual saturation, a downgrade in the oil curve and an upgrade in the water curve are observed. Upscaling this new data to field scale indicated a loss of more than half of the well productivity and an earlier breakthrough if waterflooding is implemented.

Experimental investigation of CO2 huff and puff in a matrix-fracture system

Abstract The purpose of this experimental study is to evaluate the efficiency and performance of cyclic CO 2 injection on recovery of heavy oil from a matrix-fracture system and to study the feasibility of carbon storage in a fractured medium. In this study; different laboratory experiments on one of the Iranian heavy oil and brine reservoir samples were performed. The Minimum Miscibility Pressure (MMP) between the oil sample and carbon dioxide at reservoir temperature (80 °C) was estimated using Vanishing Interfacial Tension (VIT) technique (2424 Psi). In order to perform the cyclic CO 2 injection tests; two sets of six 8.6 cm diameter and 15 cm long tight carbonate core samples have been prepared and saturated with reservoir oil at initial brine saturation conditions. The saturated cores were placed in a long vertical sleeveless core holder, which has been specially designed to simulate fluid flow in a matrix-fracture system. The total number of two CO 2 huff and puff tests, 4 cycles each, with 24 and 48 h soaking periods were performed on the system at reservoir temperature conditions. The results of experiments confirmed the effectiveness of this method for stimulating heavy oil saturated matrix-fracture system; furthermore it is concluded that longer soaking period will result in the higher oil recovery. This difference is pronounced at early cycles. The results also indicated that additional 24 h soaking period will result in approximately 10% increase in oil recovery.

Wettability Effects on Capillary Pressure, Relative Permeability, and Irredcucible Saturation Using Porous Plate

An understanding of the mechanisms by which oil is displaced from porous media requires the knowledge of the role of wettability and capillary forces in the displacement process. The determination of representative capillary pressure (Pc) data and wettability index of a reservoir rock is needed for the prediction of the fluids distribution in the reservoir: the initial water saturation and the volume of reserves. This study shows how wettability alteration of an initially water-wet reservoir rock to oil-wet affects the properties that govern multiphase flow in porous media, that is, capillary pressure, relative permeability, and irreducible saturation. Initial water-wet reservoir core samples with porosities ranging from 23 to 33%, absolute air permeability of 50 to 233 md, and initial brine saturation of 63 to 87% were first tested as water-wet samples under air-brine system. This yielded irreducible wetting phase saturation of 19 to 21%. The samples were later tested after modifying their wettability to oil-wet using a surfactant obtained from glycerophtalic paint; and the results yielded irreducible wetting phase saturation of 25 to 34%. From the results of these experiments, changing the wettability of the samples to oil-wet improved the recovery of the wetting phase.

Compressional wave velocity measurements through sandy sediments containing methane hydrate

An experimental apparatus was built to measure P-wave velocity (vP) of sandy sediment during hydrate formation from brine and free methane gas. The influences of hydrate saturation, initial brine saturation, conversion ratio of water to hydrate, and grain size of sand upon vP were investigated. The experimental results demonstrate that vP strongly depends on both hydrate saturation and initial brine saturation, whereas the influence of the grain size of sand is unremarkable. During the formation of hydrate for different experimental runs at identical initial brine saturation, vP increases with the increase of hydrate saturation; while it decreases dramatically with the increase of initial brine saturation for a given hydrate saturation. The correlation between vP and conversion ratio of water into hydrate was studied, and it was found that the relation between vP and the conversion ratio of water to hydrate is approximately the same for different experimental runs, regardless of how big the differences in initial saturation of brine and the size of sand grain are. vP was calculated for four different hydrate distribution models. The results suggest that low conversion ratio of water to hydrate, hydrate mainly acts as a load component of a dry frame matrix, whereas at higher conversion ratio of water to hydrate it partly acts as a cement that coats grains at grain contacts, and thereby leads to a dramatic increase in vP. Compared with the hydrate saturation, the conversion ratio of water to hydrate has a large role in distributing hydrate in the pores of sediments.

Experimental Study of Wettability Alteration to Preferential Gas-Wetting in Porous Media and Its Effects

Summary In a recent theoretical study, Li and Firoozabadi [Li, K. and Firoozabadi, A.: "Phenomenological Modeling of Critical-Condensate Saturation and Relative Permeabilities in GasCondensate Systems," paper SPE 56014 available from SPE, Richardson, Texas (2000)] showed that if the wettability of porous media can be altered from preferential liquid-wetting to preferential gas-wetting, then gas-well deliverability in gas-condensate reservoirs can be increased. In this article, we present the results that the wettability of porous media may indeed be altered from preferential liquid-wetting to preferential gas-wetting. In the petroleum literature, it is often assumed that the contact angle through liquid-phase θ is equal to 0° for gas-liquid systems in rocks. As this work will show, while θ is always small, it may not always be zero. In laboratory experiments, we altered the wettability of porous media to preferential gas-wetting by using two chemicals, FC754 and FC722. Results show that in the glass capillary tube θ can be altered from about 50 to 90° and from 0 to 60° by FC754 for water-air and normal decane-air systems, respectively. While untreated Berea saturated with air has a 60% imbibition of water, its imbibition of water after chemical treatment is almost zero and its imbibition of normal decane is substantially reduced. FC722 has a more pronounced effect on the wettability alteration to preferential gas-wetting. In a glass capillary tube θ is altered from 50 to 120° and from 0 to 60° for water-air and normal decane-air systems, respectively. Similarly, because of wettability alteration with FC722, there is no imbibition of either oil or water in both Berea and chalk samples with or without initial brine saturation. Entry capillary pressure measurements in Berea and chalk give a clear demonstration that the wettability of porous media can be permanently altered to preferential gas-wetting.

Uncertainty and sensitivity analysis for gas and brine migration at the Waste Isolation Pilot Plant: permeable shaft without panel seals

Latin hypercube sampling, partial correlation analysis, stepwise regression analysis and examination of scatterplots are used in conjunction with the BRAGFLO model in an uncertainty and sensitivity analysis of gas and brine movement at the Waste Isolation Pilot Plant. Topics investigated include (1) gas production due to corrosion of steel and microbial degradation of cellulosics, (2) gas saturation and pressure in the repository, (3) gas movement in anhydrite marker beds, and (4) gas and brine movement through a short, low permeability shaft seal to the Culebra Dolomite. Important variables identified in the analysis include initial brine saturation of the waste, stoichiometric terms for corrosion of steel and microbial degradation of cellulosics, corrosion and microbial degradation rates, porosity of the Salado Formation, transition (disturbed) zone porosity, marker bed (anhydrite) permeability, and seal permeability. Published by Elsevier Science Limited.

Uncertainty and sensitivity analysis for gas and brine migration at the Waste Isolation Pilot Plant: Permeable shaft with panel seals

Uncertainty and sensitivity analysis techniques based on Latin hypercube sampling, partial correlation analysis, stepwise regression analysis and examination of scatter plots are used in conjunction with the BRAGFLO model to examine two-phase (i.e., gas and brine) flow at the Waste Isolation Pilot Plant (WIPP), which is being developed by the US Department of Energy as a disposal facility for transuranic waste. The following topics are investigated to develop insights on factors that are potentially important in establishing compliance with applicable regulations of the US Environmental Protection Agency (i.e., 40 CFR 191, Subpart B; 40 CFR 268): (1) gas production due to corrosion of steel; (2) gas production due to microbial degradation of cellulosics; and (3) gas migration through a sealed shaft to the Culebra Dolomite. Important variables identified in the analysis include initial brine saturation of the waste, stoichiometric terms for corrosion of steel and microbial degradation of cellulosics, and seal permeabilities.

Uncertainty and Sensitivity Analysis for Gas and Brine Migration at the Waste Isolation Pilot Plant: Fully Consolidated Shaft

Uncertainty and sensitivity analysis techniques based on Latin hypercube sampling, partial correlation analysis, stepwise regression analysis, and examination of scatterplots are used in conjunction with the BRAGFLO model to examine two-phase flow (i.e., gas and brine) at the Waste Isolation Pilot Plant, which is being developed by the US Department of Energy as a disposal facility for transuranic waste, to provide insights on factors that are potentially important in showing compliance with applicable regulations of the US Environmental Protection Agency. Specific regulations include Petitions to Allow Land Disposal of a Waste Prohibited Under Subpart C of Part 268 (40 CFR 268.6), which implements the Resource Conservation and Recovery Act and establishes maximum environmental concentrations for regulated chemicals such as volatile organic compounds (VOCs) and heavy metals, and Environmental Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes (40 CFR 191, Subpart B), which places a probabilistic limit on allowable radioactive releases from a disposal facility over a 10,000-yr time period. The primary topics investigated are (a) gas production due to corrosion of steel, (b) gas production due to microbial degradation of cellulosics, and (c) gas migration into anhydrite marker beds in the Salado Formation,more » which is the host unit into which the waste will be emplaced. Gas production and movement is of particular importance in establishing compliance with 40 CFR 268.6 because of its influence on the movement of VOCs. Important variables identified in the analysis include (a) initial brine saturation of the waste, (b) stoichiometric terms for corrosion of steel and microbial degradation of cellulosics, and (c) gas barrier pressure in the anhydrite marker beds.« less