A study of capillary pressure and capillary continuity in fractured rocks

The production of oil is challenging in fractured reservoirs due to the large transmissibility contrast between matrix and fracture, and primary recovery is often low. The recovery efficiency depends on the relationship between the fracture and matrix permeabilities, and is strongly dependent on the wettability of the matrix, which reflects the imbibition potential of the reservoir. High demands and rising oil prices has increased focus on improved oil recovery from large, low recovery oil fields. Some of the world’s largest remaining oil reserves are found in oil‐wet, fractured, carbonate reservoirs. The understanding of multiphase fluid flow in oilwet fractured reservoirs has been studied in this thesis, especially the influence of capillary pressure. The presence of capillary pressure is important in recovery mechanisms like spontaneous imbibition, waterflooding and gravity drainage. The centrifuge method is a frequently used method to measure capillary pressure, and relies on establishing a stable saturation for each rotational speed. There exists no global, absolute requirement for equilibrium, and this size is often based on experience, and is strongly dependent on the sensitivity of the measuring apparatus. The benefits of using an automated, high resolution camera in volume measurements have been demonstrated, and the impact of accuracy on the time to reach equilibrium saturation at a given rotational speed is illustrated. Another difficulty when generating the capillary pressure curve using a centrifuge is the large uncertainty related to solving the integral problem associated with the calculation of the capillary pressure curve from production data. Methodologies for direct measurement of saturation to avoid this uncertainty have been proposed, eliminating the need for mathematical approximate solutions to obtain the local capillary pressure curve. The Nuclear Tracer Imaging Centrifuge (NTIC) method has the capability to measure the local water saturation during centrifugation, thus limiting the redistribution of fluids and the need to solidify phases, drawbacks associated with other methods for direct measurement of capillary pressure. Improved capillary pressure curves are presented, and the reliability and reproducibility in the NTIC capillary pressure curves have been demonstrated. The curves generally coincided with results from other existing centrifuge methods. The correct measurement of saturation as a function of capillary pressure will increase the confidence in simulations where the input multiphase controls the flow patterns and the recovery. The impact of wettability on capillary continuity in fractured rocks has been studied extensively, but is still not fully understood. Two visualization methods, to measure the in situ fluid saturation development in fractured rocks, are reviewed and illustrate the benefits of applying complimentary imaging to study the impact of fractures and wettability on multiphase flow in fractured reservoirs. Separately, each technique provided useful insights to local phenomena, but collectively, when combining the resolutions and observations made, a better explanation of observed phenomena could be obtained. The concept of wetting phase bridges observed during waterfloods in stacked waterwet homogenous chalk plugs has been extended to a heterogeneous limestone rock type with an oil‐wet wetting preference. The study shows how droplets of oil forming on the fracture surface contribute to the fluid transfer between two separated matrix blocks across an open fracture. The presence of droplets, evolving into bridges across the fracture, may be important for gravity drainage, reducing the capillary retained oil in each isolated matrix block. Droplets growth is impacted by the wettability of the interface between fracture and matrix and flow rates. Spontaneous transport of oil, i.e. transport without associated pressure increase, across the fracture was observed when there was an affinity between mobile fluid and the wettability of the fracture surface. Injection rates and pressure across the fracture controlled droplet growth and the potential for the droplets to bridge the fracture to form a continuum in the capillary pressure curve. The importance of fracture capillary pressure in waterfloods of fractured limestone rocks was demonstrated in a numerical reproduction of experimental results. The results showed not only that there was a dependency of the presence of capillary pressure in the fracture, but also there was a strong dependency of the distribution of the capillary pressure inside the fracture network on the development of waterfronts during water injection

New Insight from Visualization of Mobility Control for Enhanced Oil Recovery Using Polymer Gels and Foams

Several enhanced oil recovery (EOR) methods have been designed and developed in the past decades to maintain economic production from mature reservoirs with declining production rates. This chapter discuss mitigation of poor sweep efficiency in layered or naturally fractured reservoirs. EOR methods designed for such reservoirs all aim to reduce flow through highly conductive pathways and delay early breakthrough in production wells. Two approaches within this EOR class, injection of foam and polymer, specifically aim to improve the mobility ratio between the injected EOR fluid and the reservoir crude oil. Reduction in fracture conductivity may be achieved by adding a crosslinking agent to a polymer solution to create polymer gel. This may also be combined with water or chemical chasefloods (e.g. foam) for integrated enhanced oil recovery (iEOR). Polymer gel and foam mobility control for use in fractured reservoirs are discussed in this chapter, and new knowledge from experimental work is presented. The experiments emphasized visualization and in situ imaging techniques: CT, MRI and PET. New insight to dynamic behaviour and local variations in fluid saturations during injections was achieved through the use of complementary visualization techniques

Melanin-Concentrating Hormone acts through hypothalamic kappa opioid system and p70S6K to stimulate acute food intake.

Melanin-Concentrating Hormone (MCH) is one of the most relevant orexigenic factors specifically located in the lateral hypothalamic area (LHA), with its physiological relevance demonstrated in studies using several genetically manipulated mice models. However, the central mechanisms controlling MCH-induced hyperphagia remain largely uncharacterized. Here, we show that central injection of MCH in mice deficient for kappa opoid receptor (k-OR) failed to stimulate feeding. To determine the hypothalamic area responsible for this MCH/k-OR interaction, we performed virogenetic studies and found that downregulation of k-OR by adeno-associated viruses (shOprk1-AAV) in LHA, but not in other hypothalamic nuclei, was sufficient to block MCH-induced food intake. Next, we sought to investigate the molecular signaling pathway within the LHA that mediates acute central MCH stimulation of food intake. We found that MCH activates k-OR and that increased levels of phosphorylated extracellular signal regulated kinase (ERK) are associated with downregulation of phospho-S6 Ribosomal Protein. This effect was prevented when a pharmacological inhibitor of k-OR was co-administered with MCH. Finally, the specific activation of the direct upstream regulator of S6 (p70S6K) in the LHA attenuated MCH-stimulated food consumption. Our results reveal that lateral hypothalamic k-OR system modulates the orexigenic action of MCH via the p70S6K/S6 pathway

Drug-induced activation of SREBP-controlled lipogenic gene expression in CNS-related cell lines: Marked differences between various antipsychotic drugs

BACKGROUND: The etiology of schizophrenia is unknown, but neurodevelopmental disturbances, myelin- and oligodendrocyte abnormalities and synaptic dysfunction have been suggested as pathophysiological factors in this severe psychiatric disorder. Cholesterol is an essential component of myelin and has proved important for synapse formation. Recently, we demonstrated that the antipsychotic drugs clozapine and haloperidol stimulate lipogenic gene expression in cultured glioma cells through activation of the sterol regulatory element-binding protein (SREBP) transcription factors. We here compare the action of chlorpromazine, haloperidol, clozapine, olanzapine, risperidone and ziprasidone on SREBP activation and SREBP-controlled gene expression (ACAT2, HMGCR, HMGCS1, FDPS, SC5DL, DHCR7, LDLR, FASN and SCD1) in four CNS-relevant human cell lines. RESULTS: There were marked differences in the ability of the antipsychotic drugs to activate the expression of SREBP target genes, with clozapine and chlorpromazine as the most potent stimulators in a context of therapeutically relevant concentrations. Glial-like cells (GaMg glioma and CCF-STTG1 astrocytoma cell lines) displayed more pronounced drug-induced SREBP activation compared to the response in HCN2 human cortical neurons and SH-SY5Y neuroblastoma cells, indicating that antipsychotic-induced activation of lipogenesis is most prominent in glial cells. CONCLUSION: Our present data show a marked variation in the ability of different antipsychotics to induce SREBP-controlled transcriptional activation of lipogenesis in cultured human CNS-relevant cells. We propose that this effect could be relevant for the therapeutic efficacy of some antipsychotic drugs

Acute effects of orexigenic antipsychotic drugs on lipid and carbohydrate metabolism in rat

This study aims to investigate whether orexigenic antipsychotic drugs may induce dyslipidemia and glucose disturbances in female rats through direct perturbation of metabolically active peripheral tissues, independent of prior weight gain. Methods In the current study, we examined whether a single intraperitoneal injection of clozapine or olanzapine induced metabolic disturbances in adult female outbred Sprague–Dawley rats. Serum glucose and lipid parameters were measured during time-course experiments up to 48 h. Real-time quantitative PCR was used to measure specific transcriptional alterations in lipid and carbohydrate metabolism in adipose tissue depots or in the liver. Results Our results demonstrated that acute administration of clozapine or olanzapine induced a rapid, robust elevation of free fatty acids and glucose in serum, followed by hepatic accumulation of lipids evident after 12–24 h. These metabolic disturbances were associated with biphasic patterns of gluconeogenic and lipid-related gene expression in the liver and in white adipose tissue depots. Conclusion Our results support that clozapine and olanzapine are associated with primary effects on carbohydrate and lipid metabolism associated with transcriptional changes in metabolically active peripheral tissues prior to the development of drug-induced weight gain

A study of capillary pressure and capillary continuity in fractured rocks

The production of oil is challenging in fractured reservoirs due to the large transmissibility contrast between matrix and fracture, and primary recovery is often low. The recovery efficiency depends on the relationship between the fracture and matrix permeabilities, and is strongly dependent on the wettability of the matrix, which reflects the imbibition potential of the reservoir. High demands and rising oil prices has increased focus on improved oil recovery from large, low recovery oil fields. Some of the world’s largest remaining oil reserves are found in oil‐wet, fractured, carbonate reservoirs. The understanding of multiphase fluid flow in oilwet fractured reservoirs has been studied in this thesis, especially the influence of capillary pressure. The presence of capillary pressure is important in recovery mechanisms like spontaneous imbibition, waterflooding and gravity drainage. The centrifuge method is a frequently used method to measure capillary pressure, and relies on establishing a stable saturation for each rotational speed. There exists no global, absolute requirement for equilibrium, and this size is often based on experience, and is strongly dependent on the sensitivity of the measuring apparatus. The benefits of using an automated, high resolution camera in volume measurements have been demonstrated, and the impact of accuracy on the time to reach equilibrium saturation at a given rotational speed is illustrated. Another difficulty when generating the capillary pressure curve using a centrifuge is the large uncertainty related to solving the integral problem associated with the calculation of the capillary pressure curve from production data. Methodologies for direct measurement of saturation to avoid this uncertainty have been proposed, eliminating the need for mathematical approximate solutions to obtain the local capillary pressure curve. The Nuclear Tracer Imaging Centrifuge (NTIC) method has the capability to measure the local water saturation during centrifugation, thus limiting the redistribution of fluids and the need to solidify phases, drawbacks associated with other methods for direct measurement of capillary pressure. Improved capillary pressure curves are presented, and the reliability and reproducibility in the NTIC capillary pressure curves have been demonstrated. The curves generally coincided with results from other existing centrifuge methods. The correct measurement of saturation as a function of capillary pressure will increase the confidence in simulations where the input multiphase controls the flow patterns and the recovery. The impact of wettability on capillary continuity in fractured rocks has been studied extensively, but is still not fully understood. Two visualization methods, to measure the in situ fluid saturation development in fractured rocks, are reviewed and illustrate the benefits of applying complimentary imaging to study the impact of fractures and wettability on multiphase flow in fractured reservoirs. Separately, each technique provided useful insights to local phenomena, but collectively, when combining the resolutions and observations made, a better explanation of observed phenomena could be obtained. The concept of wetting phase bridges observed during waterfloods in stacked waterwet homogenous chalk plugs has been extended to a heterogeneous limestone rock type with an oil‐wet wetting preference. The study shows how droplets of oil forming on the fracture surface contribute to the fluid transfer between two separated matrix blocks across an open fracture. The presence of droplets, evolving into bridges across the fracture, may be important for gravity drainage, reducing the capillary retained oil in each isolated matrix block. Droplets growth is impacted by the wettability of the interface between fracture and matrix and flow rates. Spontaneous transport of oil, i.e. transport without associated pressure increase, across the fracture was observed when there was an affinity between mobile fluid and the wettability of the fracture surface. Injection rates and pressure across the fracture controlled droplet growth and the potential for the droplets to bridge the fracture to form a continuum in the capillary pressure curve. The importance of fracture capillary pressure in waterfloods of fractured limestone rocks was demonstrated in a numerical reproduction of experimental results. The results showed not only that there was a dependency of the presence of capillary pressure in the fracture, but also there was a strong dependency of the distribution of the capillary pressure inside the fracture network on the development of waterfronts during water injection

Pore-level foam generation and flow for mobility control in fractured systems

Pore-level foam generation, propagation, and sweep efficiency were visualized using silicon-wafer micromodels with an accurate representation of sandstone pore structure, grain shapes and sizes based on thin-section analysis. Foam generation by snap-off was observed both in the interior of the porous network (rectilinear snap-off) and at permeability discontinuities between fracture and porous matrix. Lamella creation by the two snap-off mechanisms identified here resulted in different foam textures. During foam injection for enhanced oil recovery, microvisual data revealed that the aqueous phase advanced as film flow along water-wet grains whereas discontinuous gas bubbles were located in the center of pores. Foam injection significantly enhanced sweep efficiency in fractured systems in terms of greater pore occupancy by gas and larger contact area with displaced fluid compared to continuous gas injection

Calcite-functionalized micromodels for pore-scale investigations of CO

Carbon capture and subsequent storage (CCS) is identified as a necessity to achieve climate commitments. Permanent storage of carbon dioxide (CO2) in subsurface saline aquifers or depleted oil and gas reservoirs is feasible, but large-scale implementation of such storage has so far been slow. Although sandstone formations are currently most viable for CO2 sequestration, carbonates play an important role in widespread implementation of CCS; both due to the world-wide abundancy of saline aquifers in carbonate formations, and as candidates for CO2-EOR with combined storage. Acidification of formation brine during CO2 injection cause carbonate dissolution and development of reactive flow patterns. Using calcite-functionalization of micromodels we experimentally investigate fundamental pore-scale reactive transport dynamics relevant for carbonate CO2 storage security. Calcite-functionalized, two-dimensional and siliconbased, pore scale micromodels were used. Calcite precipitation was microbially induced from the bacteria Sporosarcina pasteurii and calcite grains were formed in-situ. This paper details an improved procedure for achieving controlled calcite precipitation in the pore space and characterizes the precipitation/mineralization process. The experimental setup featured a temperature-controlled micromodel holder attached to an automatic scanning stage. A high-resolution microscope enabled full-model (22x27 mm) image capture at resolution of 1.1 µm/pixel within 82 seconds. An in-house developed image-analysis python script was used to quantify porosity alterations due to calcite precipitation. The calcite-functionalized micromodels were found to replicate natural carbonate pore geometry and chemistry, and thus may be used to quantify calcite dissolution and reactive flow at the pore-scale