A laboratory scale approach to wettability restoration in chalk core samples

Wettability in chalk has been studied comprehensively to understand fluid flow mechanisms impacting coreflooding experiments. Wettability becomes paramount in understanding the parameters influencing chalk-fluid interactions. The main objective of this work is to evaluate as to which degree the wettability in chalk core samples can be controlled in the laboratory. Kansas chalk samples saturated with brine (1.1 M/64284 ppm NaCl) and an oil mixture (60% - 40% by volume of Heidrun oil and heptane) were aged at a constant temperature of 90oC with aging time as the laboratory control variable. A multimodal method incorporating contact angle measurements, wettability index via USBM test, and SEM-MLA analysis was applied in evaluating wettability. A systematic approach was applied with the three different methods to quantify the degree of uncertainty linked to a) wettability estimation and b) the aging procedure to control wettability alteration of Kansas chalk. With a comprehensive suite of samples, we were successfully able to alter the wettability of chalk cores

Evaluation of silicate and polymer systems for disproportionate permeability reduction in oil reservoirs

Master's thesis in Petroleum engineeringThe main objective of this work is to screen and evaluate various commercially existing polymers and silicate systems mixed with crosslinkers and/or activators for their gel-forming capabilities for the water management purposes in high water cut producing wells in the matured fields. A thorough evaluation has been done for these chemicals to evaluate their behaviour before, during and after gelation. The properties measured and monitored include gelant system's viscosity and pH, gelation time and kinetics of the gelation process, gel stability, gel strength from Maximum Compressional Pressure (MCP) tests, gel shrinkage and post-gelation time behaviour. Traditional tube testing, also known as bottle testing, was done for the different polymer systems mixed with various crosslinkers wherein the mixtures were prepared and kept in the oven at temperatures of 40°C, 60°C and 80°C. Associative polymers were found to be very effective in forming gels with zirconium (III) crosslinker at high temperatures. For the rheology measurements, dynamic oscillatory tests were performed for the different silicate systems mixed with activators to determine the onset of gelation (sol-gel transition point or gel point) and the viscosity increase as a function of time at different temperatures. Gel point plays an important role in the designing of successful water-shutoff treatments since it is needed to determine the time required for the injected gelant system to gel so that the time gap is sufficient for the successful placement of the prepared system. The effects of the different factors, such as silicate and activator concentrations, temperature, the concentration of divalent ions (Ca2+) etc., are investigated. The sodium silicate system was found to gel faster at lower temperatures compared to the potassium silicate system while at high temperatures the potassium silicate system gels faster than the sodium silicate system. Therefore, an appropriate silicate system can be chosen for conformance-improvement treatment depending on the important parameters like gelation time required, time required to inject and place the gelant system at the designated areas, available activator systems, depth of the reservoir, reservoir temperatures and maximum injection rates that can be achieved without damaging the reservoir among other factors. In addition to bulk measurements and dynamic oscillatory tests, one core flood experiment was performed with associative polymer on the water-wet Berea sandstone core to investigate the effect of Disproportionate Permeability Reduction (DPR). The Berea core has shown a significant drop in the effective permeability to water and potential DPR effects after polymer injection

Impact of Wettability on Rock Mechanics and Oil Recovery: A Comparative Study on Different Outcrop Chalks

Chalk reservoirs are highly fractured and are known for their remarkable storage capacity as a reservoir rock for the petroleum industry. Chalk is a sedimentary carbonate rock primarily made up of calcium carbonate (calcite, CaCO3) and is a very important reservoir rock in the Norwegian and Danish Continental Shelfs. Water flooding has been used as a secondary production method in chalk reservoirs as it provides pressure maintenance to the reservoir and is a proven improved oil recovery (IOR) method to produce more oil from the production facilities. Ekofisk field in the Norwegian Continental Shelf is a successful example of production by water flooding method, where seawater is used as the injection fluid. The initial estimated oil recovery was 18% as mentioned in the initial development plan of the field and today’s estimates lie well above 50%. However, seawater has also shown to enhance reservoir compaction due to water weakening of the chalk formation. It can, for example, lead to buckling and loss of well pipes, arching of overburden rocks leading to stress redistributions, and the porosity/permeability decline of the producible formation, all physical effects that alter the ultimate recovery and recovery rates of oil-bearing chalk reservoirs. The detection of subsidence of the Ekofisk field in the Norwegian North Sea around 35 years ago has been linked to the compaction of chalk formations due to porosity reduction associated with field production. It attracted the attention of oil and gas researchers across the globe and since that time, considerable research has been carried out concerning chalk behavior, especially on how the pore fluid composition alters the mechanical properties of chalk. Research on chalk, so far, has primarily been carried out on water-wet systems. The studies have shown that when reactive brines are injected through chalk at elevated temperatures, chemical reactions occur between the rock and the injected brine, which affects chalk mechanical stability. It has been found that the divalent ions, such as magnesium (Mg2+), calcium (Ca2+) and sulfate (SO42-) play an important role in defining chalk mechanics. Mg2+ ions in the injected brines lead to dissolution of calcite, which in turn leads to precipitation of new mineral phases such as magnesite, huntite, talc, anhydrite etc. Both Mg2+ and SO42- ions also adsorb on the chalk surface leading to a reduction in the strength of the rock. [...

Combined Remote Perconditioning and Postconditioning Failed to Attenuate Infarct Size and Contractile Dysfunction in a Rat Model of Coronary Artery Occlusion

Objective: Although preconditioning remains one of the most powerful maneuvers to reduce myocardial infarct size, it is not feasible in the clinical setting to pretreat patients prior to acute myocardial infarction (MI). The purpose of this study was to investigate the effect of more clinically relevant therapies of remote perconditioning, postconditioning, and the combined effect of remote perconditioning and postconditioning on myocardial infarct size in an anesthetized rat model. Methods: Anesthetized rats were subjected to 45 minutes of proximal left coronary artery occlusion followed by 2 hours of reperfusion. Remote perconditioning was performed 5 minutes after left coronary occlusion with 4 cycles of 5 minutes of occlusion and reperfusion of both the femoral arteries. Postconditioning was applied immediately prior to 2 hours of full reperfusion with 6 cycles of 10 seconds occlusion–reperfusion of the coronary artery. The combined effect was produced by preceding the postconditioning regimen with remote perconditioning, after 5 minutes of left coronary occlusion. Results: Remote perconditioning and postconditioning alone failed to reduce infarct size expressed as percentage of the risk zone (42.2% ± 3.9% and 45.0% ± 4.3%). The combination of remote perconditioning and postconditioning also failed to reduce infarct size (45.3% ± 4.1%) as compared to the untreated ischemia–reperfusion group (48.7% ± 3.4%). Hemodynamics including left ventricular end-systole and end-diastolic pressures, +dP/dt, −dP/dt, and heart rate did not show any improvement in the conditioning groups. Conclusion: This study shows that remote perconditioning and postconditioning alone or combined neither improve hemodynamics nor reduce infarct size in the rat model of MI. </jats:sec

Formulation of ayurvedic medicines and extracts of medicinal plants as an alternative therapeutic treatment option for nephrolithiasis

The incidence of nephrolithiasis, commonly known as kidney stone, is increasing worldwide with significant health and economic burden. Approximately 2 million people every year in India are affected by kidney stones. It affects all ages, genders, and races, but between the ages of 20 and 49 years, it affects most frequently in men than women. Different types of stones include calcium stones, cysteine stones, struvite or magnesium ammonium phosphate stones, uric acid stones, and drug-induced stones. This review article provides information about general pathophysiology, epidemiology, clinical presentation, and pharmacological treatment, which includes ayurvedic and herbal medicines for nephrolithiasis. Further understanding of the pathophysiological link between nephrolithiasis and systemic disorders is necessary for the development of new therapeutic options

Effect of Initial Wettability on Rock Mechanics and Oil Recovery: Comparative Study on Outcrop Chalks

Brines containing surface-active divalent ions such as Ca2+, Mg2+ and SO42− impact the stiffness, strength and time-dependent deformation of water wet Mons outcrop chalk. This study documents how stiffness and strength of wettability-altered oil and water-saturated (mixed wet) Mons chalk compare to water-saturated and water wet samples during hydrostatic loading and creep. During hydrostatic creep, the strain rate response to magnesium chloride (MgCl2) brine injection is compared for water wet and mixed wet samples. For the mixed wet samples, the oil production was estimated during compaction and non-equilibrium MgCl2 flow. The results presented here were then compared to a similar test series on Kansas outcrop chalk. The differences were interpreted in terms of difference in physical parameters such as porosity and pore size. Two Mons samples were wettability-altered and tested in parallel to two completely water wet samples from the same chalk block at hydrostatic conditions and 130 °C. It was found that beyond the experimental uncertainty, the stiffness and yield strength measurements showed insignificant differences for water wet and mixed wet Mons samples. This is contrary to Kansas chalk where mixed wet samples were systematically stronger and stiffer than water wet samples. In the following creep phase, both water wet and wettability-altered Mons chalk samples gave trends comparable to each other during a stagnant phase and a following MgCl2 injection phase at varying flow rates. Similar observations were reported for water wet and wettability-altered Kansas chalks as well. Further, the same chemical reactions were observed for Kansas and Mons chalks and were found to be insensitive to the initial wettability and oil/water saturations. The oil production observations from Mons chalk showed that 43% of the total oil was recovered during early-stage compaction with no flow, whereas Kansas chalk did not produce any oil at no-flow conditions. After the oil recovery from the first 2–3 pore volumes of brine flow, no further oil production was observed due to compaction or non-equilibrium brine flow in any of the two chalk types.publishedVersio

Sequential acid-autoclave and microwave-alkali pretreatment of rice straw for bioethanol production

Two-step acid-autoclave and microwave-alkali pre-treatment process of rice straw have been carried out for bioethanol production. The reaction conditions of both the steps are optimized using Response Surface Methodology. The studies reveal that the optimum conditions for acid-autoclave pretreatment are found to be 1.90 per cent acid concentration, 51.85 min time and 1:17.51 solid:liquid ratio with maximum release of reducing sugars (16.94 g per 100 g) and minimum release of furfurals (0.93 g per 100 g). For second step pretreatment i.e. microwave-alkali, optimized conditions are observed to be 3.75 percent alkali concentration, 9.16 min time and 475W microwave power with minimum lignin content of 2.96 percent in pre-treated straw. Scanning electron micrographs reveal extensive damage of silicified waxy surface and disruption of the cell wall structure of straw after two step pre-treatment process. It has been concluded that sequential pre-treatment of rice straw using acid-autoclave and microwave-alkali process efficiently remove hemicellulose and lignin from straw, thereby increasing accessibility of cellulose to enzymatic hydrolysis for enhanced production of fermentable sugars and bioethanol