缝洞型多孔介质中多相流的有限体积法数值模拟

本文研究的碳酸盐岩油藏储集体属于缝洞型多孔介质.这类缝洞型多孔介质由裂缝、溶蚀孔洞和低孔隙度低渗透率的基岩组成.裂缝是空隙流体流动的主要通道;溶蚀孔洞大小从几厘米到数米不等,渗透率和孔隙度都很高,是流体主要的储集空间.由于缝洞型多孔介质空隙空间的复杂性和强非均质性,数值计算中基本控制方程的空间离散应采用非结构化网格的计算模型.本文采用有限体积法模拟缝洞型多孔介质中多相流体的流动,并给出了相应的单元中心格式有限体积法的计算公式.裂缝介质和溶洞介质中单元间多相流体的流动考虑为高速非达西流,其质量通量采用Forchheimer定律计算.非线性方程的离散选取全隐式格式,并采用Newton-Raphson迭代进行求解.通过两个二维模型注水驱油的数值模拟,验证了本文方法的有效性.     

振动对充填裂隙渗透率影响的实验研究

为了研究振动和充填泥沙的共同作用对裂隙岩石渗透率的影响,通过对裂隙试件在充填和振动后条件下的渗流实验,得到了频率和振幅与充填裂隙岩石渗透率的关系曲线。结果表明,充填泥沙后的相对渗透率低于充填前,最小降幅为10.19%,最大降幅为59.74%。在相同的振幅下,试件的相对渗透率随频率的增加都基本呈下降趋势;振动后的渗透率低于振动前的渗透率;充填试件在较大频率振动下,渗透率减小的更为显著。在相同的频率下,充填试件振动后的渗透率基本上都减小了,最小降幅为8.90%,最大降幅为51.23%;而未充填试件振动后的渗透率与振幅存在一定关系;相对渗透率与振幅的变化之间存在拐点,相对渗透率并没有随着振幅的增加而一直减小。     

Determination of oil reservoir radiotracer (SCN) in a single step using a plastic scintillator extractive resin

The analysis of radiotracers is important in the study of oil reservoir dynamics. One of the most widely used radiotracer is S¹⁴CN⁻. Prior to activity measurements by Liquid Scintillation (LS), routine determinations require the pretreatment steps of purification and concentration of the samples using anion exchange columns. The final elution media produces samples with high salt concentration that may lead to problems with phase separation during the LS measurement. Plastic Scintillation (PS) is an alternative technique that provides a solid surface that can be used as a platform for the immobilisation of selective extractants to obtain a PS resin. The proposed procedure unifies chemical separation and sample measurement preparation in a single step, serving to reduce the number of reagents needed and manpower required for the analysis while also avoiding mixed waste production by LS.     

Diffusion Mass Transfer in Miscible Oil Recovery: Visual Experiments and Simulation

Co-and counter-current type transfers due to diffusion and -free- convection caused by the buoyant forces between fracture and matrix were studied experimentally using 2-D glass-bead models. Mineral oil and kerosene were used as the displaced phase. The model saturated with oil was exposed to solvent phase (pentane) under static conditions (no flow in fracture) to mimic matrix-fracture interaction during gas or liquid solvent injection in naturally fractured reservoirs. Displacement fronts and patterns were analyzed and quantified using fractal techniques to obtain correlations between the fractal properties and displacement type. Displacements resulted in a mixture of bulk diffusion and -free- convection mainly depending on the interaction type (co- or counter-current), oil type, and displacement direction (horizontal and vertical). Conditions yielding different types of displacement patterns were identified. Finally, a stochastic model that was inspired from invasion percolation and diffusion limited aggregation algorithms was developed for the horizontal displacement cases. The experimental observations were matched to the displacement patterns obtained through the stochastic modeling.     

Efficiency of diffusion controlled miscible displacement in fractured porous media

Experiments were performed to study the diffusion process between matrix and fracture while there is flow in fracture. 2-inch diameter and 6-inch length Berea sandstone and Indiana limestone samples were cut cylindrically. An artificial fracture spanning between injection and production ends was created and the sample was coated with heat-shrinkable teflon tube. A miscible solvent (heptane) was injected from one end of the core saturated with oil at a constant rate. The effects of (a) oil type (mineral oil and kerosene), (b) injection rates, (c) orientation of the core, (d) matrix wettability, (e) core type (a sandstone and a limestone), and (f) amount of water in matrix on the oil recovery performance were examined. The process efficiency in terms of the time required for the recovery as well as the amount of solvent injected was also investigated. It is expected that the experimental results will be useful in deriving the matrix–fracture transfer function by diffusion that is controlled by the flow rate, matrix and fluid properties.     

各向异性双重介质垂直裂缝井两相流体渗流

建立了各向异性双重介质中垂直裂缝井两相渗流数学模型,用有限差分法求得了其解,进行了算例分析。得到了含水饱和度沿径向、最大及最小渗透率方向的分布和水驱油前缘等饱和度面随时间的变化,分别讨论了各向异性、吸渗作用对这种介质中两相流体渗流的影响。结果表明：渗透率较在的方向,前缘推进速度较快,油井见水较早;吸渗使前缘推进速度减慢,使油井见水晚。注水开发这种油藏时,见水前注入率不能太大以充分发挥吸渗作用,存在最佳注入率。这对于水力压裂垂直裂缝井注水开发碳酸盐岩裂缝性油藏有指导意义。     

Solution of pressure diffusion in radially composite reservoirs

This paper presents a new general method for solving the pressure-diffusion equation in cylindrically radial composite reservoirs, where the rock and fluid properties may change radially as a function ofr. Composite systems, such as formations with wellbore filtrate invasion and reservoirs with peripheral water encroachment, can be encountered as a result of drilling, secondary oil recovery, and water influx.The new solution method utilizes the reflection and transmission concept of electromagnetics to solve fluid flow problems in three-dimensional cylindrically radial reservoirs, where heterogeneity is in only one direction. The Green's function for a point source in a three-dimensional radially composite system is developed by using the reflection and transmission method. The method as well as the point source solution are sufficiently general that they may be applied to similar fluid flow and well testing problems involving single-phase flow.     

Optimization of the production of hydroelectric power systems with a variable head

We present in this paper a new approach for optimization of the production of hydroelectric power systems with a variable head. The problem is formulated as a minimum norm problem.The method takes into account the water head variation. To avoid underestimation of production for rising water levels and overestimation for falling water level, an average head (of begin and end of time step) is used. The method also takes into account the stochasticity of the river flows. Numerical results for a real system in operation including up to six reservoirs are reported for different water conditions. The proposed method is computationally efficient compared to other approaches.This work was supported by the National Research Council of Canada, Grant No. A-4146. The authors would like to acknowledge the data obtained from British Columbia Hydro.     

The effect of plasma treatment on the mechanical behavior of UHMWPE fiber–reinforced thermoplastic HDPE composite

Ultra‐high‐molecular‐weight polyethylene (UHMWPE) fibers have been modified by plasma treatment to increase adhesion in high‐density polyethylene (HDPE) matrices. Results showed that surface roughness predominates for modified UHMWPE fibers, indicating that the plasma treatment favors the interaction with HDPE. Unmodified HDPE composite samples gave a lower interlaminar shear strength than did the samples that were incorporated with UHMWPE. The addition of unmodified UHMWPE fibers to the neat HDPE significantly increases interlaminar shear strengths of composites, up to 20 vol%. The oxygen concentration increased from 16.16 %to 21.99%, and the ratio of oxygen to carbon atoms increased significantly from 0.194 to 0.284 after oxygen plasma treatment for 5 minutes with a power of 300 W.