The effect of clays, salinity and saturation on the high-frequency electrical properties of shaly sandstones

The effects of frequency, clay content, clay type, ionic concentration and saturation on the complex impedance of various shaly sandstone rocks have been investigated in a detailed and systematic manner. Synthetic samples have been used, so as to allow full control over clay content, clay type and clay distribution, hi addition, selected outcrop and reservoir samples with varying concentrations of clay were also used. Experimental measurements of complex impedance were made as a function of applied stress and saturation, for samples having differing amounts of clay, over a frequency range from 10 Hz to 2 MHz. In addition, the influence of ionic concentration (salinity) was also investigated. The modulus of impedance for the bulk sample response for fully saturated samples was frequency independent in the frequency range from approximately 10 kHz to 600 kHz. A strong linear correlation between the average complex impedance values and clay content was observed, with clay type influencing the magnitude of impedance. However, the reactance and dielectric constant were strongly frequency dependent. They both exhibited a power law dependency with frequency for the montmorillonite and illite synthetic shaly samples. It was possible to deduce correlations between the exponents from the reactance with clay content, and to a lesser extent clay type. The illite shaly samples usually showed the highest dielectric constant values, with the lowest belonging to the kaolinite samples. All samples showed strong relationships with salinity as the concentration was varied from 60,000 ppm to 15,000 ppm, with the modulus of impedance increasing as salinity decreased. The bulk sample response was frequency independent over all salinity concentrations. The dielectric constant showed increasing values as the salinity decreased, with a power law relationship best fitting the data. As the samples were desaturated, a frequency dependency developed for the modulus of impedance as a ftinction of saturation. As the samples were de-saturated the dielectric values decreased in magnitude. The concept of double layer thickness, and the variation in the cationic exchange capacity (CEC) with brine salinity and clay type, were used to explain the responses observed. Using this concept, the data was modelled using equivalent RC circuit models, and an impedance network model. It was found possible to model the data using combinations of capacitors and resistors.EThOS - Electronic Theses Online ServicePetroleum Development Oman (PDO)GBUnited Kingdo

Unusual Magneto-Structural Features of the Halo-Substituted Materials [Fe-III(5-X-salMeen)(2)]Y: a Cooperative [HS-HS]<->[HS-LS] Spin Transition

X-ray structures of the halo-substituted complexes [Fe-III(5-X-salMeen)(2)]ClO4 (X=F, Cl, Br, I) [salMeen=N-methyl-N-(2-aminoethyl)salicylaldiminate]at RT have revealed the presence of two discrete HS complex cations in the crystallographic asymmetric unit with two perchlorate counter ions linking them by N-H-amine...O-perchlorate interactions. At 90 K, the two complex cations are distinctly HS and LS, a rare crystallographic observation of this coexistence in the Fe-III-salRen (R=alkyl) spin-crossover (SCO) system. At both temperatures, crystal packing shows dimerization through C-H-imine...O-phenolate interactions, a key feature for SCO cooperativity. Moreover, there are noncovalent contacts between the complex cations through type-II halogen-halogen bonds, which are novel in this system. The magnetic profiles and Mossbauer spectra concur with the structural analyses and reveal 50 % SCO of the type [HS-HS][HS-LS] with a broad plateau. In contrast, [Fe-III(5-Cl-salMeen)(2)]BPh4.2MeOH is LS and exhibits a temperature-dependent crystallographic phase transition, exemplifying the influence of lattice solvents and counter ions on SCO

Insights into oil recovery mechanism by Nothing-Alternating-Polymer (NAP) concept

This paper introduces new oil recovery mechanisms for oil recovery by polymer injection in heavy oil reservoirs with strong bottom aquifers. Due to unfavorable mobility ratio between aquifer water and oil and the development of the sharp cones significant amount of oil remains unswept. To overcome these issues, for the case demonstrated in this paper, a polymer injection pilot was executed with three horizontal injectors, located a few meters above the oil/water contact. The injectivity issues resulted in frequent shutdowns of the injectors. Interestingly, the water cut reversal and oil gain continued during the shut-in periods. This observation has led to the development of a new cyclic polymer injection strategy, in which the injection of polymer is alternated with intentional well shut-ins. The strategy is referred to as Nothing-Alternating-Polymer (NAP). It was found that during polymer injection, the oil is recovered by conventional mobility and sweep enhancement mechanisms ahead of the polymer front. Additionally, during this stage the injected polymer squeezes the existing cones and creates a barrier between the aquifer and the oil column, suppressing the aquifer flux and hence the negative effect of the cones or water channels (blanketing mechanism). Moreover, injection of polymer pushes the oil to the depleted water cones, which is then produced by the water coming from the aquifer during shut-in period (recharge mechanism). During the shut-in or NAP period, the aquifer water also pushes the existing polymer bank and hence leads to extra oil production. The resistance caused by polymer adsorption reduces the extent of fingering of water into polymer bank. The NAP strategy reduces polymer loss into aquifer and improves the polymer utilization factor expressed in kg-polymer/bbl of oil, resulting in a favorable economic outcome.Petroleum Engineerin