变形三重介质三渗模型的压力动态分析

在应力敏感油藏的试井分析中,常岩石特性的假设对于确定传导率和储存系数可能引起较大的误差。研究了应力敏感地层中三孔三渗流动模型的压力响应,不仅考虑了储层的三孔三渗特征,而且考虑了井筒储集效应和应力敏感地层中介质的变形,引入了渗透率模数,建立了应力敏感地层三孔三渗流动的数学模型,渗透率依赖于孔隙压力变化的流动方程是强非线性的,因而采用数值方法求解数学模型,并探讨了变形参数和三重介质参数变化时压力的变化规律,给出了典型的压力曲线图板,这些结果可用于试井分析。     

变形介质双渗模型非线性流动模拟

在碳酸盐油藏和低渗油藏的渗流问题研究中,传统的研究方法都是假设地层渗透率是常数,然而对于地层渗透率是压力敏感的,这样的假设,对压力的变化将导致较大的误差。研究了应力敏感地层中双渗流动模型的压力不稳定响应,不仅考虑了储层的双渗特征,而且考虑了应力敏感地层中介质的变形,建立了应力敏感地层双孔隙度、双渗透率流动的数学模型,渗透率依赖于孔隙压力变化的流动方程是强非线性的,采用Douglas-Jones预估-校正法获得了圆井定产量生产和定压生产时无限大地层情况下的数值解,并探讨了变形参数和双重介质参数变化时压力变化规律,给出了典型压力曲线图版和应用实例。     

各向异性双重孔隙介质的应力与油水两相渗流耦合理论模型

针对天然裂缝性油藏的特性,建立了描述双重孔隙介质中油水两相流体流动特性的流固耦合理论模型。该模型不仅考虑了渗透率的各向异性,而且考虑了岩石固体骨架变形的各向异性。渗流方程是依据双重孔隙的概念建立起来的,而固体骨架变形控制方程则是根据Biot 的等温、线性孔隙弹性理论建立起来的。同时,给出了横向各向同性及结构各向异性、固体材料各向同性时的双重孔隙介质的应力与油水两相渗流耦合理论模型。对该模型进行了简化,并将其简化后模型与单相流的各项同性和各向异性双重孔隙介质流固耦合理论模型进行了比较。     

压裂措施单井渗流数学模型技术

压裂措施单井渗流数学模型技术主要是通过对低渗透地层的裂缝性特征进行简化后,建立一个以基质向裂缝内的径向流和裂缝向井简内的线性流的组合式变形介质低渗透油藏压裂井渗流数学模型,从而实现对油井产能进行逐渐优化式求解,并对油田的压裂增产增注措施的合理参数设计与实施提供科学的指导方法。     

低渗透油藏流入动态分析

随着石油资源的不断开发与利用,低渗透油田在我国油田开发中所占的比例越来越大。低渗透油气田将是我国石油工业增产的资源基础。在低渗透油藏的开发中,即使渗透率和孔隙度下降值不是很大,但由于原始渗透率和孔隙度很低,其相对变化幅度对油藏开发产生的影响仍然较大,所以需要考虑介质变形的影响。目前对于渗流机理较为复杂的低渗透油藏的研究主要集中在单一因素对试井解释模型的影响,也将影响到后续工作的开展。因此研究考虑启动压力梯度和介质变形影响的低渗透油藏试井解释模型能够更加科学地指导低渗透油藏试井应用,具有重要的理论价值和实用价值。     

基于相似结构的双孔油藏非线性渗流模型研究(英文)

根据油气藏的渗流机理,建立了考虑二次压力梯度项、有效井筒半径、井筒储集的变流率生产状态下的双孔油藏非线性渗流模型.利用Laplace变换和合理的近似处理,获得了无量纲地层压力和井底流压的Laplace空间解的相似结构(只与内边界条件有关)和相似核函数(相似核函数与渗流定解方程的基础解系及外边界条件有关,不同外边界条件对应于不同的相似核函数,且与内边界条件无关).此项研究揭示了双孔油藏中流体渗流的本质特征,为深入研究该类油藏的非线性渗流规律提供了又一个理论分析方法,也方便了相应的试井分析软件的快捷地编制,具有广泛的应用前景.     

中高渗油藏压裂渗流特征的数值模拟研究

为研究中高渗油藏分段压裂井开采机理和渗流规律,通过分段压裂物理模型的岩样筛选、模型制作和封装、模型抽真空及有效驱动的物理模拟评价等方法研究,进一步结合油藏压裂渗流规律。在相同驱替压差下,分段压裂井的压力梯度值要比普通井的压力梯度值高,且随着压裂裂缝半缝长的增加,压力梯度值也增加;当井段长度一定时,储层渗透率越低,分段压裂井的最佳分段数越多;当储层渗透率一定时,井段长度越长,压裂的最佳段数也越多。最佳裂缝半缝长反而呈现减小的趋势;对于油藏压裂井开采来说,对产量最为敏感的是压裂段数,其次是裂缝半缝长,而裂缝导流能力最为不敏感。     

单井产量最大化的合理流压确定

流压是油井正常生产时的油层中部压力,是油藏供给压力在地层传导至井筒时的剩余压力,也是井筒中的流体流动的初始压力。流压同时也是渗流力学和工程流体力学的分水岭。因此在油井生产、方案设计和油藏管理时流压是一个非常重要的参数。不同类型的油藏,同一油藏的不同开发阶段对流压的界定也不同。针对目前油田高含水率,低流压,本文根据油气水三相流的渗流规律,结合地质资料利用IPR曲线对某采油井合理流压进行确定。     

考虑二次梯度项影响的双重介质流动分析

传统的试井模型与物质平衡方程都是不一致的。在非线性偏微分方程中根据弱可压缩液体的假设忽略了二次梯度项，对于混气石油和低渗透储层这种方法是有疑问的，我们已经知道在试井较长时间忽略二次梯度项将产生误差。本文对于双重介质流动系统建议了与物质平衡方程一致的方法，保留了非线性偏微分方程中所有项，建立了双重介质流动模型。采用Douglas-Jones预估-校正法获得了无限大地层定产量生产时和定压生产时双重介质模型的数值解，分别讨论了液体压缩系数和双重介质参数变化时压力变化规律，做出了典型压力曲线图版，这些结果可用于实际试井分析。     

大庆油田台肇地区低渗透储层裂缝及其开发对策研究

介绍了大庆油田外围典型的低渗透储层——台肇地区葡萄花油层中东西向、南北向、北西向和北东向4组高角度构造裂缝，其发育程度依次由强变弱。受现今地应力影响，近东西向裂缝连通性好，地下张开度和渗透率大，是该区主渗流方向；其次是北西向、北东向裂缝，近南北向裂缝渗透性较差，裂缝发育程度受岩性、层厚、断层、构造应力等因素影响。根据地质条件和油藏数值模拟，认为该区适应于用矩形井网和菱形井网开发，效果比反九点和五点井网好。低渗储层由于裂缝发育，降低了地层破裂压力，注入压力容易超过地层破裂压力，使注入水沿裂缝快速流动，引起水     

Modeling of multicomponent diffusions and natural convection in unfractured and fractured media by discontinuous Galerkin and mixed methods

Computation of the distribution of species in hydrocarbon reservoirs from diffusions (thermal, molecular, and pressure) and natural convection is an important step in reservoir initialization. Current methods, which are mainly based on the conventional finite‐difference approach, may not be numerically efficient in fractured and other media with complex heterogeneities. In this work, the discontinuous Galerkin (DG) method combined with the mixed finite element (MFE) method is used for the calculation of compositional variation in fractured hydrocarbon reservoirs. The use of unstructured gridding allows efficient computations for fractured media when the cross flow equilibrium concept is invoked. The DG method has less numerical dispersion than the upwind finite‐difference methods. The MFE method ensures continuity of fluxes at the interface of the grid elements. We also use the local DG (LDG) method instead of the MFE to calculate the diffusion fluxes. Results from several numerical examples are presented to demonstrate the efficiency, robustness, and accuracy of the model. Various features of convection and diffusion in homogeneous, layered, and fractured media are also discussed.     

A two‐scale approach for fluid flow in fractured porous media

A two‐scale numerical model is developed for fluid flow in fractured, deforming porous media. At the microscale the flow in the cavity of a fracture is modelled as a viscous fluid. From the micromechanics of the flow in the cavity, coupling equations are derived for the momentum and the mass couplings to the equations for a fluid‐saturated porous medium, which are assumed to hold on the macroscopic scale. The finite element equations are derived for this two‐scale approach and integrated over time. By exploiting the partition‐of‐unity property of the finite element shape functions, the position and direction of the fractures is independent from the underlying discretization. The resulting discrete equations are non‐linear due to the non‐linearity of the coupling terms. A consistent linearization is given for use within a Newton–Raphson iterative procedure. Finally, examples are given to show the versatility and the efficiency of the approach, and show that faults in a deforming porous medium can have a significant effect on the local as well as on the overall flow and deformation patterns. Copyright © 2006 John Wiley & Sons, Ltd.     

计算射孔井产率比的三维有限元新方法

为了更精确更全面地计算射孔井的产率比, 该文建立了一种射孔井的三维无量纲稳态渗流模型, 推导了模型的三维有限元求解方程, 采用高密度四面体网格并使用并行计算, 获得了模型的数值解. 与传统计算射孔井产率比方法的对比发现:Karakas方法的精度要明显高于Hagoort方法, 但Karakas方法在一些参数下存在一定误差且不能计算特定条件下的产率比;该文提供的有限元方法在相位角、污染区影响等方面更具普适性. 分析了射孔几何结构、井周污染区、射孔压实区和储层渗透率各向异性等因素对射孔井产率比的影响, 结果表明:增加射孔长度能不断地提高产能;射孔密度和相位角均存在一个最优值;射穿污染区是减小污染区影响产能的有效手段;射孔压实区和低垂向渗透率都会严重降低射孔井的产能. 该研究为射孔井的完井设计、产能预测提供理论指导.     

地热对井系统裂隙岩体三维渗流传热耦合的等效模拟方法

研究地热对井系统中的裂隙岩体渗流传热问题对于开采深层地热能和发展可再生清洁能源利用技术具有重要价值。基于渗流传热耦合理论和离散裂隙网络模型,提出了裂隙岩体三维热流耦合的等效模拟方法:考虑由岩块基质及复杂离散裂隙网络组成的双重介质,采用无厚度单元模拟裂隙、线单元模拟对井,通过裂隙、对井和岩块三者之间的流量和热量交换实现渗流和传热过程耦合分析。通过与解析方法和精细模拟方法相比较,验证了等效模拟方法的有效性;并将其应用于含大规模裂隙岩体地热对井系统热采过程的数值模拟,获取了储层内温度场的分布规律,评价了裂隙开度对储层平均温度和整体开采率的影响。结果表明:该文方法能够对裂隙及井筒中的渗流传热行为进行细致模拟,在保证精度的前提下,可大幅减小计算量和计算时长;裂隙网络的非均匀及各向异性分布导致岩体温度场分布呈现高度不均匀性,反映了热流耦合的早期热突破和长尾效应等特点;裂隙内水的对流传热作用明显,冷锋面沿储层内的主要贯通裂隙网络移动,裂隙开度是影响岩体温度场分布的重要因素。     

低渗高粘稀油油藏蒸汽采油技术研究

为了探索高粘稀油油藏降低储层原油粘度、提高渗流能力、增加流度,进一步研究区块加密后提高采收率的新技术、新方法,2006—2008年开展了“蒸汽驱油现场先导试验”。针对油藏原油粘度高、渗透率低、粘土含量高、有效厚度小等特点,开展了室内物模实验,进行了蒸汽驱油可行性研究;应用数值模拟技术优选了注汽参数和驱替方式;开展了地层防膨预处理和井筒隔热技术研究。现场试验3个井组,累积增油1.81×104 t。通过试验研究,给出了低渗高粘稀油油藏适合蒸汽驱油技术的地质条件。     

Simulation of the transport and placement of multi-sized proppant in hydraulic fractures using a coupled CFD-DEM approach

The productivity of fractured wells is mainly governed by propped fractures, so it is of significant importance to find out where the injected proppants go during hydraulic fracturing treatments, as this is essential to scheduling proppant injection in fracturing design. Using a coupled CFD-DEM model, the transport and placement of multi-sized proppants in fractures in vertical and horizontal wells were systematically investigated, and the effects of having multi-sized particles relative to uniformly-sized ones on the proppant placement were quantitatively characterized. When a proppant-laden fluid is injected into a fracture in vertical wells, a small proppant bank quickly forms. The injected large and small proppant particles are almost uniformly mixed, with just a small-proppant region at the back side of the bank. In comparison in horizontal wells, a proppant dune first forms near the wellbore in a fracture, and the large proppant particles are more likely to accumulate near the wellbore while the small particles are transported deeper into the fracture. The main transport mechanisms of proppant particles are settlement and fluidization, which cause a three-layer flow pattern (stationary proppant bed, fluidization layer and clean fluid layer) to form. In addition, vortex is also an important proppant transport mechanism, especially in a fracture in horizontal wells, where the vortex drags the injected proppant particles to different locations causing a dual-dune profile. The effect of fracture tip screen-out on the proppant placement was investigated. Screen-out can significantly change the flow field in a fracture and this will subsequently affect final proppant placement. Ultimately, the process of graded proppant injection was realistically modeled, which shows small proppants to be transported deeper into the fracture, while large proppants accumulate near the wellbore.     

A numerical contact algorithm in saturated porous media with the extended finite element method

In this paper, a coupled hydro-mechanical formulation is developed for deformable porous media subjected to crack interfaces in the framework of extended finite element method. Governing equations of the porous medium consist of the momentum balance of the bulk together with the momentum balance and continuity equations of the fluid phase, known as formulation. The discontinuity in fractured porous medium is modeled for both opening and closing modes that results in the fluid flow within the fracture, and/or contact behavior at the crack edges. The fluid flow through the fracture is assumed to be viscous and is modeled by employing the Darcy law in which the permeability of fracture is obtained using the cubic law. The contact condition in fractured porous medium is handled by taking the advantage from two different algorithms of LATIN method and penalty algorithm. The effect of contact on fluid phase is employed by considering no leak-off from/into the porous medium. The nonlinearity of coupled equations produced due to opening and closing modes is carried out using an iterative algorithm in the Newton–Raphson procedure. Finally, several numerical examples are solved to illustrate the performance of proposed X-FEM method for hydro-mechanical behavior of fractured porous media with opening and closing modes.