Huiqing Liu

Experiments on water flooding in fractured-vuggy cells in fractured-vuggy reservoirs

Abstract Based on the theory of scaling criteria, a physical experimental model of fractured-vuggy cell which meets the geometric similarity, kinematic similarity, dynamic similarity and characteristic parameters similarity was designed. The factors affecting fluid flow and water flooding characteristics, and the EOR features of different displacing modes were studied by experiments. The experimental results show that: Oil and water displacement effect caused by the density difference between oil and water is the main mechanism of water flooding; Injection rate has no effect on the remaining oil and water-cut; Fracture-vuggy connection is the dominant factor controlling water-free recovery, ultimate limit of remaining oil and water-cut variation in the fractured-vuggy cell; Oil-water viscosity ratio has an important effect on oil production rate, oil replacement ratio and economic limit remaining oil; When the filling degree is low, it has no effect on remaining oil, but when the filling degree is high, the remaining oil contains both “attic oil” and the oil existing in porous media; Foam flooding after water flooding enhances oil recovery by starting the attic oil at the top of vugs, and the remaining oil is in the center of the vugs after foam flooding; Polymer flooding after water flooding enhances the economic limit recovery by increasing the oil production rate and oil draining ratio, but it has no effect on the limit remaining oil of water flooding.

The Synthesis and Characterization of Methacrylic Acid Ester-maleic Anhydride Copolymer as a Lube Oil Pour Point Depressant

Abstract The authors synthesized methacrylic acid ester (AE) monomers by direct esterification of methacrylic acid and fatty alcohols using paratoluenesulfonic acid as catalyst, hydroquinone as polymerization inhibitor, and toluene as solvent. Then, methacrylic acid ester-maleic anhydride (AM) copolymers were prepared by solution free radical copolymerization with benzoyl peroxide as initiator. The structures of the monomer and copolymer were confirmed by IR. Differential scanning calorimetry (DSC) was selected as the research method to investigate the wax formation process in the lube oils without and with adding AM. The results show that it possess the best solidification point depression (ΔSP) when the molar ratio of the reaction materials is 3:1 and the polydispersity is 1.81. It can execute a maximum depression of solidification point (SP) of the tested lube oils by 29, 21, and 20°C, respectively. The AM additive has little effect on the total amount of wax, but just shift the precipitation toward lower temperature.

Mechanistic Simulation Studies on Viscous-Elastic Polymer Flooding in Petroleum Reservoirs

Based on the theory and application developments of polymer flooding on enhancing oil recovery, an improved mathematical model has been developed to simulate the mechanism of viscous-elastic polymer flooding. IMPES method has been presented to solve the polymer flooding model considering the viscosifying effect of elasticity, the effect of decreasing residual oil and the degradation of polymer molecules. The validation of the model is approved by an experiment. A simulation example was carried out using the developed numerical simulator. The enhanced oil recovery mechanism was discussed for viscous-elastic polymer flooding, and corresponding influencing factors were also studied.

The Distribution of Ni and V in Resin and Asphaltene Subfractions and Its Variation During Thermal Processes

Ni and V deactivate catalysts and promote coking during heavy oil upgrading. Distribution of metals and metalloporphyrins, and its variation in thermal process, would benefit the more efficient upgrading. Majority of metals concentrate in resins and asphaltenes. To thoroughly study the metals distribution in these fractions, both were subdivided. It is indicated that the interactions between metalloporphyrins and asphaltenes play a significant role in metals distribution. Variation of metals distribution showed that the trend metals concentrated into heavier subfractions and was enhanced by thermal treatment and inhibited by hydrogen sources. Synergism was observed between hydrogen and hydrogen donor for the inhibition.

Study on Commercial Pour Point Depressants Lowering Cold Filter Plugging Point for Daqing Diesel Fuels

Ethylene-vinyl acetate copolymer is widely used as commercial pour point depressants (PPDs) all over the world. The authors describe four commercial PPDs for evaluating the sensitivity of Daqing diesel fuels. The content and carbon number distribution of n-alkanes in the Daqing diesel fuels were analyzed by high-temperature gas-phase chromatography. The structures of the commercial PPDs were confirmed by IR spectra. The results indicate that the n-alkanes carbon distributions display an obvious normal distribution in the Daqing diesel fuels. Commercial PPDs can maximumly depress cold filter plugging point of the tested diesel samples by 7°C, 3°C, 5°C, and 0°C, respectively. The distributions of high carbon n-alkanes are all narrow so that wax crystals precipitate more easily at low temperatures, and as a result, the interaction between PPD molecules and wax crystal molecules is not good.

Flow Characteristics of Heavy Oil through Porous Media

Abstract Performance of flowing through a capillary and porous media for different kinds of heavy oil at different temperatures have been studied by experiments in this article. It shows that the heavy oil containing asphaltene-colloids displays yield-stress rheology (Bingham fluids). The displacing pressure difference increases linearly with the increase of the flow rate. However, the start flowing pressure is different for different heavy oil samples at different temperatures. The higher the temperature is, the lower pressure the heavy oil needs to flow; and when the temperature is high enough, the start flowing pressure equals zero. The minimum temperature at which the start flowing pressure equals zero is called converting temperature. Also, the more viscous the heavy oil is, the higher the converting temperature will be. An exponential relationship of yield stress and temperatures has been obtained for different kinds of heavy oils by the experiments of heavy oil flowing through a capillary. A logarithmic relationship of converting temperatures and the dead oil mobility at 50°C has been obtained for heavy oil through different porous media. When a temperature is lower than the converting temperature, the start flowing pressure gradient decreases as a log tendency with the increase of temperature when different heavy oils are flowing through different porous media. For the existence of the start flowing pressure gradient, the heavy oil production rate is different from that for the Newton fluid and it is adverse to the development of heavy oil reservoirs. The test results are favorable to choose the reasonable temperature for heavy oil transportation running in a pipe or well bore and also determine the temperature limitation for different production rates for a specific well sample. It is also important for improving the development effect efficiently.

Influences of adsorption/desorption of shale gas on the apparent properties of matrix pores

Abstract The adsorption/desorption effects impact the petro-physical properties of matrix pores during gas depressurizing production, such as effective pore radius, effective porosity, apparent permeability, which will further impact the gas flow regime. In this paper, the dynamic models of effective pore radius and apparent permeability under the action of gas adsorption/desorption are derived. The mathematical model of shale gas flow is established considering the effects of adsorbed gas on apparent properties and gas flow regime. After that, the model is solved and validated using a finite volume method and experimental and field data. Finally, the variations of apparent parameters of matrix pores and gas flow regimes during gas production, and the influences of adsorption on gas production are demonstrated. The results show that the effective pore radius, porosity and apparent permeability increase during gas production; the gas flow regime in stimulated reservoir volume (SRV) changes from slip flow to transition flow; if the impacts of adsorbed gas on gas production is overlooked, both original gas in place (OGIP) and gas production will be significantly overestimated. The cumulative gas production changes slightly as the adsorption layer thickness increases, but the gas recovery factor decreases.

Three-dimensional physical modeling of waterflooding in metamorphic fractured reservoirs

Abstract To understand water-oil displacement characteristics and the mechanism of improving waterflood efficiency in metamorphic fractured reservoirs, taking JZ251S oil field as an example, a large-scale physical simulating model which meets the geometric similarity, kinematic similarity, dynamic similarity and dual media characteristic parameters similarity based on the theory of scaling criteria was designed to simulate the development of the reservoir by horizontal wells. The mechanism of water displacing oil in dual media reservoirs, the factors affecting fluid flow and waterflood characteristics, and the enhanced oil recovery (EOR) features of different water injection patterns were studied by experiments. The results show that: (1) Capillary imbibition is the main mechanism of enhancing matrix oil recovery in a dual media reservoir which is controlled by waterflooding; (2) whether or not there is crude oil draining from matrix, the water cut trend after water breakthrough can be divided into two stages, the first stage is quick rise stage of water cut in early water breakthrough period and the second stage is slow rise stage of water cut in mid-high water cut period; (3) displacement rate is the main factor controlling water-free production period, water cut trend and ultimate recovery; (4) compared with continuous injection, intermittent injection can give full play to the function of oil-water gravity segregation, reducing the water cut and improving the production rate of initial stages greatly.

Mechanism simulation of oil displacement by imbibition in fractured reservoirs

Abstract The mechanism model of both static and dynamic imbibition considering capillary pressure and gravity was presented based on the imbibition mechanisms and seepage theory. The validation of the model was performed using published experiment data. Then, this model was employed to study the impacts of oil viscosity, matrix permeability, core size, interface tension, and displacement rate on imbibitions. The results show that, the recovery decreases as oil viscosity increases, and the initial imbibition rate is much faster for lower viscosity oil. Imbibitions recovery is positively related to matrix permeability, the differences of oil recovery for low-permeability to tight oil reservoirs are obvious. Imbibitions effect is negatively related to core size. If the interface tension is low, imbibitions cannot occur without consideration of gravity. But it can occur even in very low interface tension scenario with consideration of gravity. On the whole, the recovery first increases and then decreases as the interface tension decreases. The gravity and capillary play different roles at different ranges of interface tension. There exists an optimal value range of displacement rate in fractured reservoir, which should be optimized with a sufficient oil production rate to achieve higher recovery.

The Adaptability Research of Steam Flooding Assisted by Nitrogen Foam in Henan Oilfield

With the further study on foaming agent performance, steam flooding assisted by nitrogen foam has been applied more widely. But the flexibility of this technology in heterogeneous shallow layer heavy oil reservoir has not been fully researched. Through introducing a new dimensionless parameter — foam comprehensive evaluation index (FCEI), we use physical simulation to evaluate foaming agents. Then we make five sand filling tubes modeling permeability contrast in the light of Henan heterogeneous shallow layer heavy oil reservoir. Based on two kinds of foam-injected methods (steam following or not) impact analyses, the applicability of foam to multi-permeability contrast is further discussed. Furthermore, we use numerical simulation to optimize parameters including foam slug size, nitrogen steam ratio, foam injection interval and productioninjection ratio, which applied to this type of reservoir.nThe obtained results show that through foaming coefficient and decay coefficient, FCEI can unify the criteria of foam screening by taking foam volume and half-life into consideration. On even ground, compared with cold foam flooding, the oil production of unit foaming agent of hot foam flooding stays 1.24 % higher. There exists none negative correlation between foam’s contributions to each layer’s flooding efficiency and permeability. Two methods both indicate that the middle permeability layer, of which the producing degree is similar with lower ones, has great exploitation potential. When injected with cold foam, the start-up pressure of heterogeneous formations increases linearly along with the increase of permeability grade, but for hot foam, this value increases in function of power. And to higher permeability contrast layers, hot foam is better. Finally, under hot foam slug injection condition, the optimum foam slug size is 0.02PV, the optimum nitrogen steam ratio is 20:1, the optimum foam injection interval is 90 days and the best production injection ratio is 1.32:1. Based on the study, this technology has been applied for selected field sites in 2011, and preliminary results have been achieved. The results demonstrate that this research can play an important guiding role in applying steam flooding assisted by nitrogen foam to heterogeneous shallow layer heavy oil reservoir.