高压含气致密砂岩气体钻井扩径机理研究

发布时间：2018-04-20 03:12

本文选题：气体钻井 + 致密砂岩　；参考：《西南石油大学》2015年硕士论文

【摘要】：气体钻井能够有效的减小储层损害并及时发现储层,近几年逐渐用于致密砂岩气的勘探开发。采用气体钻井打开高压致密砂岩储层过程,出现一些不同于常规气体钻井的井眼垮塌现象。实钻显示高压含气致密砂岩储层扩径严重,并多次诱发井下恶性垮塌埋钻事故,严重制约了致密砂岩气藏的勘探开发。本文结合气体钻井打开高压含气致密砂岩储层现场工况,通过室内岩石力学实验和应力敏感性实验,以渗流理论和弹塑性理论为基础,建立了气体钻井井周弹性应力分布模型和弹塑性应力分布模型,研究了致密砂岩储层井眼扩径机理和影响因素,为气体钻井安全打开高压含气致密砂岩储层提供理论基础。主要得到以下几个结论： (1)分析了气体钻井钻开致密砂岩储层的现场工况和地质特征,表明高压含气致密砂岩储层段气体钻井井眼扩径不同于常规气体钻井,在打开储层过程中,井周会形成剪切带和压实带,井周岩石处于复杂应力场中,从而导致致密砂岩储层容易发生失稳。 (2)通过致密砂岩力学实验研究了孔隙压力、围压和轴向压力对岩石力学参数的影响。致密砂岩孔隙含压时的三轴抗压强度大于不含压时的抗压强度,随着孔隙压力的增加,岩石抗压强度减小。随着有效围压的增加,岩石的弹性模量呈幂函数增长。轴向加载速率越大,岩石残余阶段应力下降速率越快,岩石越容易完全破碎。 (3)通过变围压和变孔隙压力两种不同的方法测试了致密砂岩的应力敏感性。采用常规变围压应力敏感性实验比变孔隙压力应力敏感性实验敏感,并且在常规变围压应力敏感性实验过程中发现,渗透率下降到一定程度后继续增加有效围压,致密砂岩渗透率基本没有变化。 (4)基于常规气体钻井井周弹性应力分布模型,综合考虑孔隙压力、弹性模量非线性和井眼形状,分析了气体钻井井周应力变化规律。当采用气体钻井的方式打开致密砂岩储层后由于孔隙压力的变化导致井眼周围岩石的应力场发生变化,井眼附近地层渗透率降低,形成一个压实带,阻止地层中气体向井眼中渗流。随着井眼垮塌,由于应力集中,井眼进一步向地层中发展,但是由于岩石残余强度的影响,井眼最终会稳定。 (5)利用气体钻井井周弹塑性应力分布模型研究了井眼垮塌后地层中稳定渗流和没有渗流情况下井周弹塑性区分布和影响因素。研究结果表明：当岩石内聚力和内摩擦角角减小时,井周塑性区域增加,井眼容易发生垮塌失稳；当气体渗流量增加时,井周塑性区域会增加。
[Abstract]:Gas drilling can effectively reduce reservoir damage and timely discovery of reservoir, in recent years gradually used in the exploration and development of tight sandstone gas. When gas drilling is used to open high pressure tight sandstone reservoir, there are some hole collapses which are different from conventional gas drilling. The actual drilling shows that the high pressure gas-bearing tight sandstone reservoir has serious dilatation and many times induces the downhole malignant collapse and burying drilling accident, which seriously restricts the exploration and development of the tight sandstone gas reservoir. In this paper, based on seepage theory and elastic-plastic theory, combined with gas drilling to open high pressure gas-bearing tight sandstone reservoir, through laboratory rock mechanics experiment and stress sensitivity experiment, The elastic stress distribution model and elastic-plastic stress distribution model around gas drilling wells are established. The hole expansion mechanism and influencing factors in tight sandstone reservoirs are studied, which provides a theoretical basis for the safe opening of high-pressure gas-bearing tight sandstone reservoirs in gas drilling. The main conclusions are as follows: 1) the field working conditions and geological characteristics of tight sandstone reservoir drilled by gas drilling are analyzed. The results show that the hole expansion of gas drilling in high pressure gas-bearing tight sandstone reservoir is different from that in conventional gas drilling, and in the process of opening the reservoir, The shear zone and compaction zone are formed around the well, and the rock around the well is in the complex stress field, which leads to the instability of tight sandstone reservoir. 2) the effects of pore pressure, confining pressure and axial pressure on the mechanical parameters of rock are studied by means of the mechanical experiments of tight sandstone. The triaxial compressive strength of tight sandstone with pore pressure is greater than that without pore pressure, and the compressive strength of rock decreases with the increase of pore pressure. With the increase of effective confining pressure, the elastic modulus of rock increases by power function. The higher the axial loading rate is, the faster the stress decreases in the residual stage of rock, and the easier the rock is completely broken. 3) stress sensitivity of tight sandstone was tested by two different methods: variable confining pressure and variable pore pressure. The conventional stress sensitivity test of varying confining pressure is more sensitive than that of the stress sensitivity experiment of varying pore pressure, and it is found that the permeability decreases to a certain extent and the effective confining pressure continues to increase. The permeability of tight sandstone is basically unchanged. 4) based on the elastic stress distribution model of conventional gas drilling wells, the variation of borehole stress in gas drilling is analyzed by considering the pore pressure, elastic modulus nonlinearity and borehole shape. When the tight sandstone reservoir is opened by gas drilling, the stress field of the rock around the borehole changes due to the change of pore pressure, and the formation permeability near the borehole decreases, forming a compaction zone. Prevent gas in the formation from percolating to the hole. As the borehole collapses, the borehole develops further into the formation due to stress concentration, but due to the influence of rock residual strength, the borehole will eventually be stable. (5) the elastic-plastic stress distribution model around the borehole in gas drilling is used to study the distribution of elastic-plastic zone and the influencing factors in the condition of stable percolation and no percolation in the formation after hole collapse. The results show that when the cohesive force and angle of friction decrease, the plastic region around the well increases and the hole collapses easily, and the plastic region increases when the gas flow rate increases.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE24

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