【摘要】 水平井定面射孔是致密油气藏体积压裂的一种新型射孔技术,但以往的研究较少考虑射孔对近井区域裂缝起裂位置、破裂形态的调控作用,并将定面射孔的各孔道空间位置均简化为平面,忽略了定面射孔角度参数对水平井破裂压力与近井筒裂缝形态的影响。为了弥补上述不足,建立了流固耦合形式的近井筒破裂力学模型,采用基于连续损伤力学的裂缝单元表征射孔局部三维破裂位置、形态变化,开发了耦合模型有限元数值求解程序以研究裂缝起裂与扩展规律,并运用长庆油气田现场水平井射孔完井参数,定量分析了射孔转角、射角参数变化对初始破裂压力、起裂位置的影响,对比了水平井定面射孔、螺旋射孔近井筒破裂形态的差异。研究结果表明:①射孔可调控水平井破裂压力及初始破裂位置,随射孔转角、射角改变,孔道破裂压力变化显著,初始破裂会产生于射孔—井筒界面、孔道中部等不同位置,定面射孔器材应控制射孔射角介于15°～30°;②定面射孔通过改变孔道射流方向,增加了孔道间应力干扰,能够有效降低水平井破裂压力2.0～3.5 MPa;③定面射孔能够引导和调控近井筒裂缝走向,形成垂直于水平井筒的初始破裂面、避免螺旋射孔导致的近井筒裂缝扭曲,提高了水平井近井筒裂缝系统的完善程度。结论认为,所建立的近井筒破裂力学模型可以模拟水平井射孔—近井筒动态破裂过程,模型计算结果与现场测试数据具有较好的一致性。更多还原

【Abstract】 The in-plane perforation is a new type of well completion method for the stimulated reservoir volume(SRV) of tight oil and gas reservoirs. Previously, however, the regulatory effects of perforation on fracture initiation position and fracture geometry near the wellbore were less studied, the spatial position of each channel of in-plane perforation was simplified as a plane, and the effects of the angle parameters of in-plane perforation on the fracturing pressure of a horizontal well and the fracture geometry near the wellbore were neglected. In order to make up for these shortcomings, a near-wellbore fracture mechanics model in the form of hydro-mechanical coupling was established in this paper. Then, local 3 D fracture initiation position and geometric change of shots were characterized by using the fracture element based on continuous damage mechanics, and the finite-element numerical solving program of a coupling model was developed to investigate fracture initiation and propagation laws. Finally, the effects of perforation angle and departure angle on the initial fracturing pressure and fracture initiation position were analyzed quantitatively based on the actual perforation completion parameters of horizontal wells in the Changqing Oilfield. What’s more, the fracture geometry near the wellbore of horizontal wells with in-plane perforation was compared with that with helical perforation. And the following research results were obtained. First, the fracturing pressure and fracture initiation position of the horizontal wells with controllable perforation vary with perforation angle and departure angle. The fracturing pressure of channel varies greatly, and fracture initiation occurs at different positions, e.g. the perforation—wellbore interface and the middle part of the channel. The in-plane perforator shall control the departure angle in the range of 15°–30°. Second, by changing the jet direction of channels, in-plane perforation increases the stress interference between the channels, so as to reduce the fracturing pressure of horizontal wells by 2.0–3.5 MPa. Third, the in-plane perforation can guide and control the fracture strike near the wellbore,so as to produce the initial fracture plane perpendicular to the wellbore of horizontal wells and avoid the distortion of near-wellbore fractures caused by helical perforation. In this way, the completion degree of the fracture the system near the wellbore of a horizontal well is improved. In conclusion, the near-wellbore fracture mechanics model established in this paper can simulate the perforation and near-wellbore dynamic fracture process of a horizontal well, and its calculation results are better accordant with the field test data.更多还原