fax 01-972-952-9435. AbstractSince the recent trend of oil price opened new vistas in IOR/EOR scenario, the laboratory study looked at different new type of super (S) and viscoelastic (S v ) surfactants that provide both IFT lowering and mobility control. The paper is basically focusing on evaluation of viscoelastic surfactants as mobility controlling agents used as pre-flush, co-surfactant and post-buffer media. The experimental work is extended to their effects on bulk phase and interfacial rheological properties, surface and interfacial tension, phase behavior, wettability, flow properties in porous media and displacement efficiency using various injection protocol. Beside determination of mobility, mobility ratio, normal and differential displacement curves, the solution structure was analyzed by transmission and backscattering photon correlation spectroscopy.Measurements and core studies confirmed that the viscoelastic surfactants might be used to replace traditional mobility controlling agents (polymers) over a wide temperature and pressure range. Their sensitivity to shear rate and other degrading effects is much less than found for high molecular weight synthetic and biopolymers. Thus, the viscoelastic surfactants may offer an excellent opportunity for mobility control in various enhanced oil recovery techniques independent of injection protocol. Their positive influence on recovery efficiently can be explained by mobility control, front stabilization (buffering) and profile correction. The viscoelastic surfactants may also improve the "microscopic displacement efficiency", which is not widely recognized as a significant part of the displacement mechanism, and hence the recovery efficiency. General conclusion of the laboratory studies is that viscoelastic surfactants may open new vistas in chemical flooding.
Direct interpretation methods for determination of the relative permeability data by linear, non-steady-state, two-phase fluid displacements conducted via constant rate and constant pressure laboratory core tests, are presented. The equations necessary for processing of the displacement test data obtained after the breakthrough of the displacing fluid phase are derived by neglecting the capillary end-effects at sufficiently high flow rates and verified by various experimental data. The total mobility and the mobility ratio of the immiscible fluids are related to the characteristic parameters of the displacement process and the cumulative injected fluid pore volume. The general correlation functions of the characteristic parameters of the immiscible displacement process in porous media are facilitated to conveniently describe the relative permeability functions. These functions allow for accurate determination of the characteristic parameters of immiscible displacement by least-squares linear regression of experimental data. Therefore, the present analytic method determines the relative permeability functions uniquely, rapidly, and more accurately than the previous direct interpretation methods, auxiliary functions, and graphical and analytical methods, and offers a possibility of determining the relative permeability functions from constant pressure and constant rate displacements data. Introduction Relative permeability is an essential petrophysical data required for characterization of multiphase flow in petroleum reservoirs. Frequently, the relative permeability data of the two-phase flow in porous media is determined by interpreting the data of the laboratory displacement tests carried out with cylindrical core plugs extracted from petroleum reservoirs. The Darcy law and the material balance equations, with appropriate initial and boundary conditions, are applied to describe the flow of the various fluid phases in porous media. This theoretical description of flow is used to infer for the relative permeability data by processing of the experimental data using a suitable method. This is an inverse problem and development of better methods for its solution has occupied many researchers. Especially, the achievement of the uniqueness in the calculated relative permeability data is of a great concern. In this respect, direct interpretation methods are favored over the indirect regression or matching methods. Honarpour et al.1 give a comprehensive review of the experimental methods for determination of the values of relative permeability. In general, two basic laboratory methods have been facilitated by the petroleum industry:the steady-state method, where both fluids, usually considered incompressible, are injected simultaneously into the core, andthe non-steady-state method, where only one fluid is injected into the core to displace another fluid present in a core plug. The processing of the steady-state test data is relatively simple, but the experiments are tedious, because attaining a steady average saturation value over the core length after each saturation alteration requires a long time, typically several hours. On the other hand, the laboratory tests of the non-steady-state displacements at different flow conditions can be performed within a relatively short time, but the evaluation of the data is a complex task. In both methods of measurements, the unfavorable capillary end-effects, appearing at the inlet and outlet faces of the core plug, further complicate the processing of the experimental data, unless the displacement can be carried out at a sufficiently high rate to minimize the end-effects. However, a rapid flow is usually difficult to accomplish in core plugs and does not represent the actual flow conditions in typical reservoir displacements. Nevertheless, the end-effects are often neglected for development of simplified interpretation methods.
The primary aim of the research project was to develop such chemical systems, which triggered by mixing with water will form the blocking phase. As a novelty, water sensitive homogeneous solutions and water external microemulsions were developed, which are stable until they are diluted with water forming thus stable macroemulsions. Transformation of different metastable systems to stable ones in reservoir space having high water saturation may radically restrict the water flow through their high viscosity and entrapment of the dispersed particles by the pores. As dispersed phases organic silicon compounds, tensides and natural crude oil fractions were tested. The transformation and structure of phases and size of particles were analyzed by photon correlation spectrometry, rheometry, while the flow properties were studied in natural sandstone systems. The core studies confirmed that all metastable systems reduce the flow of water by 80–90% in water-saturated sandstone. Using chemical-free postflush the flow resistance remains substantial against water in case of silicones; meanwhile the permeability deterioration against oil or gas is negligible. The metastable systems are effective and single step disproportional permeability modifying fluids. The metastable systems may offer an excellent opportunity for water shutoff in matured oil and gas fields and gas storage facilities. The unique properties of the techniques are that flow resistance may occur only in water saturated reservoir space and in case of technical failure; the flow barrier can be eliminated by oil and gas injection. Introductions The idea of water shut-off treatments has arisen already in 1922 when injection of silicate solutions into oil producing wells with the aim at in-situ gelation to form a blocking phase was patented. However, as far as the hydrocarbon industry is concerned, a real necessity to control flow profile around wells became known only in the middle of the sixties. Since that time a great variety of polymer methods using polymer solutions, rigid and weak gels as diverting/blocking agents and disproportional permeability modifiers have been developed. The most frequently reported methods form three main groups: injection of polymer solution, in-situ cross-linking of chain like polymers and in-situ polymerization of monomers. Their general feature is that they are based on application of macromolecular materials. Such a common denominator cannot be found as far the blocking mechanism is concerned. Since the philosophy of profile correction methods is that deliberate formation damage or a drastic mobility reducing effect must be developed in a right reservoir space and in a proper stage of production, the different known techniques, in a wider sense, can be classified as follows: Mobility control by modification of rheological propertiesInjection of polymer solutions;In-situ cross-linking of linear polymer;In-situ polymerization of monomers;Combined, multifunctional methods;Precipitation of gel-like inorganic compounds;Precipitation of crystalline inorganic compounds.
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