克拉2异常高压气田开采特征影响因素分析

异常高压气藏与常压气藏的开采特征明显不同 ,边底水侵入、储集层岩石膨胀以及束缚水膨胀均是重要影响因素。研究储集层膨胀驱动能量大小时 ,存在采用常岩石压缩系数还是变岩石压缩系数两种观点。克拉 2气田岩石覆压试验结果表明 ,本区岩石压缩系数在原始条件下要比压降后期高 5～ 10倍。显然 ,考虑储集层膨胀作用时 ,采用变岩石压缩系数更符合实际情况。应用AdelMElsharkawy提出的气藏物质平衡方程 ,将低估异常高压气藏边底水侵入、储集层膨胀以及孔隙束缚水膨胀等驱动力的作用。考虑各种影响因素改进了气藏物质平衡方程 ,使之能更准确地反映不同压力阶段各驱动机制所提供驱动能量的大小。研究表明 ,采用根据异常高压气藏开发初始阶段数据作出的压力与采出程度关系图进行预测 ,有可能过高估计气藏的地质储量和剩余可采储量。

计算凝析气顶油藏油气界面移动距离的新方法

凝析气顶油藏气顶油环协同开发须厘清油气界面的移动规律。假设凝析气顶油藏呈椭圆锥状,利用物质平衡原理,综合考虑气顶反凝析、水蒸气含量、岩石压缩性等因素的影响,推导出计算凝析气顶油藏油气界面移动距离的新方法。应用实例表明,当气顶出现反凝析后,油气界面的移动速度开始不断增大;当忽略反凝析、岩石压缩性或水蒸气含量时,油气界面纵向移动距离的计算值均偏小,且反凝析现象对油气界面纵向移动距离的影响最大,其次为岩石压缩性,水蒸气含量影响最小;新方法得到的油气界面纵向移动距离与压力梯度法的结果吻合较好。

双重介质页岩气藏水平井压力动态特征

研究页岩气水平井开发渗流规律。依据页岩气藏储层地质及开发特征,建立页岩气渗流模型,充分考虑页岩气在基质中的吸附-解吸、Knudsen扩散及渗流作用,采用表观渗透率函数、岩石压缩性吸附影响系数,对常规油气藏渗流方程进行修正,并考虑球型基质向裂缝不稳态扩散窜流,建立无穷大外边界双重介质页岩气藏水平井渗流模型,绘制页岩气藏水平井渗流压力曲线图版,分析储层、渗流及水平井等敏感参数对水平井压力变化特征影响。结果表明在页岩气藏渗流中后期阶段,表观渗透率函数、岩石压缩性吸附影响系数对水平井压力特征影响较大。扩散-渗流、吸附-解吸特征是准确描述页岩气渗流规律的重要因素。

Experimental study on energy storage and dissipation characteristics of granite under two-dimensional compression with constant confining pressure

To study the energy storage and dissipation characteristics of deep rock under two-dimensional compression with constant confining pressure,the single cyclic loading-unloading two-dimensional compression tests were performed on granite specimens with two height-to-width(H/W)ratios under five confining pressures.Three energy density parameters(input energy density,elastic energy density and dissipated energy density)in the axial and lateral directions of granite specimens under different confining pressures were calculated using the area integral method.The experimental results show that,for the specimens with a specific H/W ratio,these three energy density parameters in the axial and lateral directions increase nonlinearly with the confining pressure as quadratic polynomial functions.Under constant confining pressure compression,the linear energy storage law of granite specimens in the axial and lateral directions was founded.Using the linear energy storage law in different directions,the elastic energy density in various directions(axial elastic energy density,lateral elastic energy density and total elastic energy density)of granite under any specific confining pressures can be calculated.When the H/W ratio varies from 1:1 to 2:1,the lateral compression energy storage coefficient increases and the corresponding axial compression energy storage coefficient decreases,while the total compression energy storage coefficient is almost independent of the H/W ratio.

Failure mode and strength anisotropic characteristic of stratified rock mass under uniaxial compressive situation

A stratified rock mass model was founded by FLAC^3D. The failure mode and anisotropic characteristic of strength for stratified rock mass were analyzed. The analysis results show that the numerical simulation can visually reflect the failure modes of rock samples under different inclination angles β of structural plane. The stiffness of rock sample before peak strength changes in the compressive procedure. With the increase of β, the compressive strength σc of rock sample decreases firstly and then increases; when β is in the range of 20°-30° and 80°-90°, σc has the largest sensitivity to r; while β falls in the range of 30°-70°, σc varies little. When φj〈β〈90° （ φj is friction angle of structure plane）, the results obtained from numerical simulation and theoretical analysis are in almost the same values; while β〈 φj or β=90°, they are in great different values. The results obtained from theoretical analysis are obvious larger than those from numerical simulation; and the results from numerical simulation can reflect the difference of compressive strength of rock samples for the two situations of β≥φj and β=90°, which is in more accordance with the real situation.

Non-Darcy flow seepage characteristics of saturated broken rocks under compression with lateral constraint

Using an MTS816.03 test system and self-designed seepage apparatus, seepage tests of saturated broken rocks were conducted, and the influence of lithology, axial stress, grain size distribution and loading rate on seepage characteristics was analyzed. The results show that： （1） Under the same axial stress （12 MPa）, the permeability of different lithologic samples increases in the order： gangue 〈 mudstone 〈 sandstone 〈 limestone. The permeability of gangue is 3 magnitudes lower than that of limestone. The absolute value of the non-Darcy coefficient β increases in the order： limestone 〈 sandstone 〈 mudstone 〈 gangue. The non-Darcy coefficient β of limestone, which is positive, is 5 magnitudes lower than that of gangue. （2） With increasing axial stress, the permeability of saturated broken sandstone decreases, and the absolute value of the non-Darcy coefficient β increases. After the axial stress exceeds 12 MPa, the curves of permeability and non-Darcy coefficient β all tend to be stable. （3） With increasing Talbol power exponent, the permeability increases, and the absolute value of the non-Darcy coefficient β decreases. （4） With increasing loading, the permeability increases, and the absolute value of the non-Darcy coefficient β decreases. When the loading rate is 0.5 kN/s, the non-Darcy coefficient β is positive.

Numerical simulation of triaxial compression test for brittle rock sample using a modified constitutive law considering degradation and dilation behavior

The understanding of the rock deformation and failure process and the development of appropriate constitutive models are the basis for solving problems in rock engineering. In order to investigate progressive failure behavior in brittle rocks, a modified constitutive model was developed which follows the principles of the continuum damage mechanics method. It incorporates non-linear Hoek-Brown failure criterion, confining pressure-dependent strength degradation and volume dilation laws, and is able to represent the nonlinear degradation and dilation behaviors of brittle rocks in the post-failure region. A series of triaxial compression tests were carried out on Eibenstock(Germany) granite samples. Based on a lab data fitting procedure, a consistent parameter set for the modified constitutive model was deduced and implemented into the numerical code FLAC3 D. The good agreement between numerical and laboratory results indicates that the modified constitutive law is well suited to represent the nonlinear mechanical behavior of brittle rock especially in the post-failure region.