Injection of seawater and mixtures with produced water into North Sea chalk formation: Impact of fluid–rock interactions on wettability and scale formation

Seawater has been injected into high temperature and natural fractured North Sea chalk reservoirs to improve oil recovery with great success. Previous studies have shown that seawater will improve the water wetness and cause enhanced compaction of the matrix. The composition of the produced water will be quite similar to initial formation water at the start of the water injection. The formation water contains various amounts of divalent cations like Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺. Later on, the composition will change due to the interaction between seawater and the chalk formation and some mixing with formation water. The fluid–rock interaction will involve dissolution of CaCO₃, substitution of Ca²⁺ by Mg²⁺ at the chalk surface, precipitation of CaSO₄, SrSO₄ and BaSO₄ depending on the reservoir temperature. Because of environmental reasons, it is desirable to re-inject produced water together with seawater. In the forthcoming research, we will study experimentally the effect of this re-injection on oil recovery and chalk compaction by using mixtures of produced water and seawater as injection fluid. Based on model studies using the OLI software package, the compatibility of mixtures of produced water and seawater has been studied at different temperatures by looking at the precipitation of CaSO₄, SrSO₄ and BaSO₄. Also the impact of changes in the concentrations of Ca²⁺ and Mg²⁺ due to surface substitution is modelled. The results are discussed in terms of possible scale formation in the producer and injector. In addition, actual chemical equilibrium reactions in the chalk matrix are discussed in relation to variation in temperature during continuous injection of seawater. Special focus is made on wettability modification, irreversible thermodynamics, and impact on the mechanical strength of the chalk matrix.     

Comparative aging and life histories in mammals

A comparative assessment of aging and longevity in mammals has four uses in aging research. These are: (1) hypothesis formulation and evaluation, (2) investigating the generality of putative aging mechanisms, (3) isolating key physiological factors influencing aging rate, and (4) allowing the most appropriate choice of animal models for particular research questions. The first use requires detailed information on a wide variety of species, and I will examine general patterns of aging in a sample of over 600 species of mammals. The second use requires the selection of several models as distantly related to one another as feasible. The third use is best served by evaluating species or populations as closely related to one another as possible, assuming that they differ substantially in aging rate. The fourth use requires a logic of animal model selection, as well detailed information about a wide range of species. Specific examples of each use will be given.     

The Health Maintenance Organization: II. Implications for psychotherapy.

Suggests that in an effort to make psychotherapeutic practice compatible with the benefit structure of the health maintenance organization (HMO), clinicians have modified various therapeutic practices, including goal setting, crisis management, the nature of the therapist–patient relationship, the timing and frequency of sessions, continuity and comprehensiveness of treatment, medical and nonmedical collaboration, the integration of pharmacology and psychotherapy, and termination. As a result, an "HMO" therapeutic orientation is emerging. A prototype of HMO therapy that combines features of the primary care model and the biodevelopmental model is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Health Maintenance Organization: I. Historical perspective and current status.

Discusses the history of health maintenance organizations and presents a modal program with special focus on the management of psychotherapy and psychopharmacology. The clinical demands of managed group practice are compared with fee-for-service care. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mental health care benefits and perceptions of health insurance agents.

Many professionals play a role in evaluating and defining health service coverage in the current marketplace. It is useful to professional psychologists to understand how their perceptions of the current coverage of mental health services are similar to or different from those of other professionals. The authors examined the views of health insurance agents. Both psychologists and insurance agents agreed that, mental health benefits were adequate to effectively treat mild mental health problems, coverage was inadequate to treat major mental illness. Psychologists and insurance agents differed in their perceptions of whether patients and therapists used benefits unnecessarily. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New wettability test for chalk based on chromatographic separation of SCN and SO4

Wettability, water-wetness or oil-wetness, is usually defined in terms of the method used to determine the wetting state of a porous medium. In the Amott test, which is most frequently used for porous media, the wetting indices of water and oil are determined by the extent of spontaneous imbibition of water and oil from the state of the corresponding residual fluid saturations of the core. Thus, the Amott fluid wetting index reflects the potential capillary energy associated with the spontaneous imbibition process, which results in a very insensitive way to detect wetting alterations close to neutral conditions. Unfortunately, the natural wetting state of many carbonate reservoirs is close to neutral conditions or preferential oil-wet. In this paper, the wetting state of porous chalk is characterized by the fraction of surface area covered by one of the two fluids, i.e. water or oil. As the new wettability test is based on the chromatographic separation of two water-soluble components, i.e. a tracer, SCN⁻, and a potential determining ion towards chalk, SO₄²⁻, the fraction of the surface area covered by water was decided to represent the new wetting index. Using a chalk core at residual oil saturation, the area between the effluent curves for SCN⁻ and SO₄²⁻ is proportional to the area contacted by water during the flooding process. The ratio between this area and the corresponding area obtained from a completely water-wet core will give a water index between 0 and 1, representing completely oil-wet and completely water-wet conditions, respectively. The method is excellent to be used close to neutral condition, which will give a wetting index of 0.5. Experimental results are presented for two different chalks at different wetting conditions. Furthermore, the change in the Zeta-potential of the chalk surface over the dispersion zone of SO₄²⁻ is visualised by a gradient in the Ca²⁺ concentration in the same region.     

Psychotherapy in a staff model health maintenance organization: Providing and assuring quality care in the future.

Discusses characteristics of effective health maintenance organization therapy. These characteristics include a problem-solving orientation, crisis intervention preparedness, clear definition of patient and therapist responsibilities, flexible and creative use of time, interdisciplinary cooperative treatments, use of multiple formats and modalities, a family practitioner model that allows for intermittent treatment throughout the life cycle, and quality assurance and utilization review procedures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adsorption IV. An evaluation of polyethylene glycol as a sacrificial adsorbate towards ethoxylated sulfonates in chemical flooding

The feasibility of using polyethylene oxide (PEG) as a sacrificial adsorbate in surfactant flooding applying ethoxylated sulfonates in mixture with some of the corresponding ethoxylated alcohol, has been tested in different ways. Static adsorption of the surfactants has been performed using both quartz and kaolinite as adsorbents. Equilibrium times of 24 h showed decreased adsorption of the surfactants for both of the adsorbents. The sacrificial effect of PEG was greater for quartz than for kaolinite. PEG with an average molecular weight of 4000 was found to be most favorable. pH changes between 3.5 and 7.6 have small effects on the sacrificial behavior of PEG towards both of the adsorbents.Long-term dynamic adsorption studies in Berea cores were conducted by circulating the flooding solution through the cores. The addition of 0.3 wt% PEG, after the adsorption equilibrium of the surfactants had established, resulted in a fast desorption of the surfactant, about 30%. The desorption was only temporary, and a slow readsorption of the surfactant to the initial level occurred. A pressure build-up was also registered. PEG added to the surfactant solution from the beginning showed a very slow surfactant adsorption. Also in this case a pressure build-up over the core was observed. For a oil-containing reservoir core the sacrificial effect of PEG was negligible.The concentration of each of the adsorbates, i.e., the ethoxylated sulfonate and the ethoxylated alcohol, and the PEG was quantified, and the adsorption behavior of each of them is discussed. All the adsorption experiments were conducted using synthetic seawater at 80°C.     

Adsorption VII. Dynamic adsorption of a dual surfactant system onto reservoir cores at seawater salinities

The adsorption of a dual surfactant system of the type nonylphenyl-6-ethoxy-sulfonate (6EOS) and dodecyl-benzene-sulfonate (DDBS) in the mole ratio of 1:1 has been studied by: (a) static adsorption onto kaolinite, (b) nonequilibrium long-term dynamic adsorption on a reservoir core, and (c) dynamic slug injection in a Berea core. The studies were conducted at 70 °C using artificial seawater. The corefloods were performed at residual oil saturation. The static adsorption of the mixture showed that DDBS adsorbed more strongly than 6EOS at surfactant concentration below the CMC. The plateau adsorption appeared to be quite similar, but significantly higher than for pure 6EOS. The long-term dynamic study was conducted by circulating the dual surfactant solution through the core for 16 weeks, and the slug injection was performed by injecting 0.5 PV of the surfactant mixture followed by a xanthan solution. In both cases it appeared to be a selective adsorption until the surfactant mixture, forming the most stable micelles, was obtained. Further adsorption at surfactant concentration above the CMC seems to be governed by a linear relationship between the two surfactants. Possible impacts on surfactant flooding, using dual surfactant mixtures of this type, are discussed.     

The effects of temperature on the water weakening of chalk by seawater

Seawater is injected into the high temperature North Sea chalk reservoirs to improve oil recovery with great success. Increased compaction of the rock, which also is a significant contribution to the oil displacement, is observed in the water-flooded area. Very recent laboratory studies at high temperature documented that enhanced compaction took place when chalk cores were flooded by seawater under stress. The special composition of seawater, regarding reactive ions towards the chalk surface, appeared to be the reason. In this paper, two different water-weakening mechanisms are discussed: (1) Substitution of Ca²⁺ at the inter-granular contacts by Mg²⁺ and (2) Chemical dissolution. The effect of temperature is opposite for the two mechanisms. The impact of temperature on chalk compaction is studied both in a static (cores aged in water) and dynamic (cores flooded with water) way by performing hydrostatic tests by use of standard triaxial cells. Distilled water was used as a reference fluid in the static tests at 80–130 °C. The mechanical strength of chalk containing seawater was opposite to chalk containing distilled water. With seawater, the chalk became weaker as the temperature increased, while using distilled water, the chalk became stronger as the temperature increased. In the dynamic creep tests, at 50–130 °C, the cores flooded with seawater were significantly weaker than cores flooded with seawater without sulfate, but the difference in mechanical strength decreased as the temperature decreased. The mechanism for enhanced chemical induced weakening of chalk by seawater is discussed.