Hongqing Song

A Study of Effective Deployment in Ultra-Low-Permeability Reservoirs With Non-Darcy Flow

Abstract Due to the existence of a threshold pressure gradient (TPG) in ultra-low-permeability reservoirs, the peripheral reserves of the wellbore are difficult to deploy effectively. The main problem is that it is hard to ensure that well pattern, well spacing, and drawdown pressure easily and accurately because of the existence of low-velocity non-Darcy flow in such reservoirs. Simple and accurate calculation methods of the problem are most popular with reservoir engineers, so effective deployment calculation methods of ultra-low-permeability reservoirs are presented in this article. They include control radius calculation, control distance calculation, control area calculation, and control coefficient calculation, which can be directly used in the evaluation of well pattern thickening of developed oilfields and reserves of undeveloped oilfields. Based on theory of fluid mechanics in porous medium considering TPG, the non-Darcy flow mathematic model was established to reveal the characteristics of pressure distribution of ultra-low-permeability reservoirs. According to the analytical solution of non-Darcy radial flow, the relationship between control radius for ultra-low-permeability medium and TPG under different drawdown pressures was established. A calculation method combined with ellipse flow theory for control coefficient is presented, which was used to characterize the producing degree of reserve in a rectangular pattern. The control radius and coefficient of ultra-low-permeability reservoirs can provide a theoretical foundation for reservoir evaluation and development design.

Analytical modeling of gas production rate in tight channel sand formation and optimization of artificial fracture

Permeability variation in tight channel sand formation makes an important role in gas production. Based on the features of channel sand formation, a mathematical model has been established considering anisotropy of permeability. The analytical solutions were derived for productivity of both vertical wells and vertically fractured wells. Simulation results show that, gas production rate of anisotropic channel sand formation is less than that of isotropic formation. For vertically fractured well, artificial fracture direction, drainage radius, permeability ratio and fracture half-length have considerable influence on production rate. The optimum fracture direction should be deviated less than π/8 from the maximum permeability direction (or the channel direction). In addition, the analytical model was verified by in situ measured data. The research provides theoretical basis for the development of tight channel sand gas reservoirs.

Study on distribution of reservoir endogenous microbe and oil displacement mechanism

In order to research oil displacement mechanism by indigenous microbial communities under reservoir conditions, indigenous microbial flooding experiments using the endogenous mixed bacterium from Shengli Oilfield were carried out. Through microscopic simulation visual model, observation and analysis of distribution and flow of the remaining oil in the process of water flooding and microbial oil displacement were conducted under high temperature and high pressure conditions. Research has shown that compared with atmospheric conditions, the growth of the microorganism metabolism and attenuation is slowly under high pressure conditions, and the existence of the porous medium for microbial provides good adhesion, also makes its growth cycle extension. The microbial activities can effectively launch all kinds of residual oil, and can together with metabolites, enter the blind holes off which water flooding, polymer flooding and gas flooding can’t sweep, then swap out remaining oil, increase liquidity of the crude oil and remarkably improve oil displacement effect.

Flow characteristics and a permeability model in nanoporous media with solid-liquid interfacial effects

AbstractMolecular dynamics simulations of water flow through nanotubes have demonstrated higher flow rates than the flow rates predicted using classical models and a significant change in flow patterns due to the thin film that forms on the solid wall of the tubes. We have developed a two-region analytical model that described the flow characteristics and permeability of fluid flow through nanoporous media and considered the solid-liquid interfacial effects. Our model considers the influence of various interfacial effects, including long-range van der Waals forces, double-layer repulsive forces, and short-range structure repulsive forces, and it establishes relationships between the permeability and the average pore diameter, porosity, surface diffusion, and contact angle by numerical calculations. Our results indicate that the permeability calculated using the present model (with interfacial effects) is more than 30 times the results that were calculated using the Kozeny-Carman equation (without interfac...

Rheological Modeling of Dispersion System of Nano/Microsized Polymer Particles Considering Swelling Behavior

Rheological behavior of dispersion system containing nano/microsized cross-linked polymer particle was studied considering particle hydration and swelling. Viscosity of the dispersion system depends on swelling kinetics of polymer particles. Under shear flow, dispersion of swollen polymer particles is shear thinning. According to experimental results, kinetics of particle swelling and hydration was described well by second-order kinetic equation. Relational expression between equilibrium particle size and influencing factors of swelling such as salt concentration and temperature was presented. Assume that swollen polymer particles are uniform and have a simple core-shell structure, interacting through a repulsive steric potential. The rheological modeling of such dispersion system at low shear rate was presented using the concept of effective volume fraction, which depends on swelling kinetics and interparticle potential. Cross model was introduced to describe shear-thinning behavior. The viscosity equation allows correlation of experimental data of relative viscosity versus shear rate or hydration time; accounting for effect of temperature and salt concentration on viscosity. Predictions of the model have a good agreement with experimental results. GRAPHICAL ABSTRACT

Experiment and Capillary Bundle Network Model of Micro Polymer Particles Propagation in Porous Media

In this paper, a microscopic visualization experiment is conducted to explore the heterogeneous flow pattern of micro polymer particles in micron pore. A capillary bundle network model for micro polymer particles in porous media is established. The migration and retention mechanism of polymer particles can be clearly observed in the experiment and simulated with this numerical model. The result demonstrates that the block of large particles is one of the main factors by which micro polymer particles increase the flow resistance. The simulation results are consistent with the experimental results.

Experimental research on remaining oil distribution and recovery performance after immiscible and miscible CO2-WAG injection by direct visualisation

More than half of oil remains in the reservoir pores after water flooding. A microscopic visualised physical model under high temperature and pressure was created to simulate a reservoir pore network. It is an efficient way to study the formation and distribution of microscopic remaining oil which can enhance oil recovery. Displacement mechanisms were researched for CO2/water alternative flooding (CO2-WAG). The remaining oil morphology and migration characteristics were directly observed and analysed. The distribution of the remaining oil of models in different flooding stages was quantitatively obtained by grey images processing technology. Comparing the distribution of different occurrences of microscopic remaining oil, the multiphase fluid transport characteristics in the experimental porous media is described. Experimental results show that the recovery efficiency under the CO2-oil miscible state can be enhanced 5.75% more than the immiscible state. There exist four types of remaining oil after CO2-WAG with different effects, namely: 1) clusters; 2) columnar; 3) membrane; 4) blind-end remaining oil. Miscible CO2-WAG could efficiently improve oil recovery of cluster, column, and membrane types of remaining oil. Immiscible CO2-WAG only caused an obvious recovery improvement for the cluster type of remaining oil. In order for CO2-WAG flooding to be used to improve oil recovery most efficiently, the occurrence state and distributions of remaining oil should first be considered. [Received: June 23, 2015; Accepted: March 1, 2016]