Xinwei Liao

The Research of Gas Flooding of Horizontal Well with SRV in Tight Oil Reservoir

The characteristics of tight oil reservoir are low porosity and ultra-low permeability, thus stimulated reservoir volume (SRV) should be conducted whether applying the mode of vertical wells or horizontal wells production. Tight oil reservoir is mostly developed by natural depletion or water flooding recently, but the problems are existed, including low recovery factor with natural depletion and the difficulty of water injection. To further improve the development effect of tight oil reservoir, CO2 flooding is proposed. Based on changing tight oil reservoir in Ordos Basin, an oil sample of typical block is selected. The PVT experiments are conducted. The compositional numerical model of five-spot pattern is established with a horizontal well in the middle and 4 vertical wells on the edge. Based on the model, several CO2 flooding scenarios of horizontal well with different completion measures are studied. Furthermore, parameters such as the formation pressure, production rate, shut-in gas-oil ratio and total gas injection volume are optimized. The results of this study show that the recovery factor of horizontal well with SRV is higher than those of horizontal well and conventional fractured horizontal well. The study gives new ideas of CO2 flooding with volume fractured horizontal well for the Ordos Basin tight oil reservoir. It can be helpful for rapid and effective development of tight oil reservoirs in Ordos Basin.

Improving water-alternating-CO 2 flooding of heterogeneous, low permeability oil reservoirs using ensemble optimisation algorithm

Injecting CO2 into reservoir has been proven to be not only a feasible method for improving ultimate oil recovery, but also reducing CO2 emissions and greenhouse effects. In this paper, the advantages of optimisation algorithm and numerical simulation are combined to establish mathematics model of production optimisation of water-alternate-gas (WAG) flooding. Augmented Lagrange function (ALF) and logarithm transformation (LT) are applied to convert constrained problems into unconstrained ones. The ensemble optimisation algorithm (EOA) is used to solve the latter. Then, the optimisation technology of reservoir production is formed. The optimisation technology is applied in a low permeability oil reservoir to test its feasibility of improving oil production. The results indicate that the CO2 swept efficiency, miscible region and recovery, can be effectively improved by the optimisation technology which increases the economic benefit of the reservoir.

Numerical Analyses of the Effect of the Impurity in the Gas on the Solubility Trapping in the CO 2 Sequestration

The CO2 dissolved in the aquifer will increase the density of brine, which can result in the instability of the gravity and prompt the onset of the viscous finger. The viscous finger will lead to the convective mix, accelerating the process of CO2 solution in the brine. However, the gas stream in the CO2 storage usually contains the impurities such as N2, O2, and SO2, which can change the density difference in the process of solution, and affect the solubility trapping in the CO2 sequestration. In this paper, a numerical simulation method was used to study the effect of different impurities on the solubility trapping in the process of CO2 storage. Firstly, based on the PR-HV model, this paper calculated the solubility of CO2, N2, O2, and SO2 with different temperature and salinity and analysed the variation of the solubility. Then a multi-component numerical simulation model based on a certain aquifer layer was established to compare the CO2 dissolution rate and the onset time of the instability and analyze the influence of impurities in the CO2 stream on the solubility trapping. Finally, this paper clarified the impact on the CO2 storage and suggested that the concentration of the impurities should be controlled in a rational range for the perspective of the economy and efficiency. The results show that the solubility of CO2 is higher than N2 and O2 in the saline water, and close to that of SO2. We applied the solubility data to the numerical simulation. The results of the numerical simulation shows that with the increase of the concentration of N2 or O2, CO2 dissolution rate has a decrease, and the onset time of the instability has an increase. It meas the longer time CO2 plume keeping in the state of good flowing capability and low density. The onset of viscous finger will be postponed, leading to a negative influence on the solubility trapping and the risk of the CO2 leak through fractures and faults. On the contrary, SO2 can shorten the onset time of the instability, which accelerates the viscous finger and prompts the solubility trapping. A further conclusion is that the effect of SO2 on the viscous fingering is more significantly than N2 and O2. This paper deepens the understanding about the effect of the impure CO2 on the solubility trapping, and clarifies the effect of different impurities.

Technical feasibility and application effect of coupled CO2 sequestration and EOR in tight sandstone oil reservoir

This paper focused on the technical researches on CO2 sequestration and enhancing oil recovery by CO2 flooding. Experiments and numerical reservoir simulation were conducted to study the technical feasibility and application effect of implementing CO2 sequestration and EOR in tight sandstone oil reservoirs. Small maximum pore throat radius, inefficient mercury withdrawal and large residual volume in pore together implied that the bad connectivity among pores would result in high percolating resistance in reservoir. Several conclusions were obtained at last - the physical properties of the oil are favourable for conducting CO2 sequestration and EOR; miscible flooding performs better than immiscible flooding; CO2 sequestration and EOR are easier to be implemented in the reservoirs with preferable homogeneity. A technology combining WAG with profile modification was adopted to maximise the ability of CO2 injection and oil-producing for single well so that the benefit of CO2 sequestration and EOR can be improved more efficiently.

Determination of Dynamic Deliverability Equation for Fractured Horizontal Well in Tight Gas Reservoir

The deliverability equation of gas well is important for productivity evaluation and performance forecasting. For fractured horizontal well in stress-sensitive tight gas reservoir, due to the pressure-dependencies of gas properties, reservoir/fracture permeability and high-velocity non-Darcy flow, the deliverability equation would not be constant but is also dynamic. Traditionally, the relationship between reservoir/fracture permeability is commonly be obtained by laboratory experiments, which is expensive and time-cost. Besides, the predecessor’s studies which neglect the pressure-dependence of high velocity non-Darcy flow would also lead inaccuracy. Therefore, this paper presented a new method to quantify pressure-dependence of reservoir/fracture permeability as well as obtain dynamic deliverability equation for multi-fractured horizontal well in tight gas reservoir considering non-constant non-Darcy flow. This method is validated by an actual well in Sulige tight gas field in Ordos Basin, China. The result shows that this method is accurate and can contribute to the effective development of stress-sensitive tight gas reservoir