水力压裂增透技术在高瓦斯低渗透煤层中瓦斯抽采过程中起到了重要作用。针对控制孔孔隙水压力作用下压裂孔周围地应力场分布的研究还不充分，各影响因素综合作用下控制孔导控水力裂缝的扩展规律不清楚，无法为控制孔导控煤层水力裂缝扩展工艺设计提供技术支撑的问题，论文采用理论分析、数值模拟、物理模拟试验以及现场试验等多种方法相结合，开展控制孔导控煤层水力裂缝起裂及扩展规律研究，建立控制孔导控水力裂缝起裂及裂缝扩展的力学模型，揭示孔隙水压力作用下水力裂缝导控扩展机理。主要研究成果如下：

基于H.Kastner钻孔围岩起裂力学原理，分析控制孔孔隙水压力作用下压裂孔周围地应力场分布特征，建立控制孔导控水力裂缝起裂和裂缝扩展的力学模型，获得控制孔导控水力裂缝起裂及扩展规律，揭示孔隙水压力作用下水力裂缝导控扩展机理。研究发现：压裂钻孔的起裂压力与控制孔孔压呈负相关，与孔间距呈正相关，当控制孔注水压力越大，控制孔到压裂孔之间的距离越小时，水力裂缝起裂压力就越小；在控制孔孔隙水压力作用下，λ>1或λ<1时压裂钻孔的起裂角不受控制孔的影响；当λ>1时，裂缝起裂角为θ=0°或θ=180°，随着λ从1.1增加到1.3时，裂缝扩展时受到原始地应力的控制作用越强，裂缝在扩展过程中偏转越困难；当λ<1时，裂缝起裂角为θ=90°或θ=270°，随着λ从0.7增加到0.9时，裂缝扩展时受到原始地应力的控制作用越弱，裂缝在扩展过程中偏转越容易；当λ=1时，裂缝起裂角为θ=β+π，裂缝沿着两孔中心连线的方向扩展到控制孔所在位置附近；随着裂缝扩展过程中裂缝长度的增加，裂缝扩展时所需要的注水压力逐渐减小。

应用岩石渗流力学理论，基于控制孔孔隙水压力作用下压裂孔周围地应力场分布特征，建立控制孔导控水力裂缝扩展渗流-应力耦合模型，采用RFPA^2D-Flow软件对控制孔导控水力裂缝扩展规律进行了数值模拟研究，分析控制孔对水力裂缝定向扩展的导控作用，研究孔间距、控制孔孔压、控制孔位置和地应力等因素对水力裂缝起裂及扩展的影响，获得了控制孔各参数影响下水力裂缝扩展过程中裂缝转向规律。研究表明：控制孔导控压裂与常规压裂相比，压裂钻孔起裂所需的注水压力较小，在压裂孔和控制孔两孔中心连线周围产生最大拉应力，引导水力裂缝偏转；当控制孔距压裂孔之间的距离越小，控制孔注水压力越大时，裂缝的起裂压力越小，裂缝扩展方向的转向角越大，裂缝向控制孔方向扩展时的诱导作用效果越好。当最大主应力方向与两孔中心连线方向之间的夹角越小时，裂缝更容易偏转到控制孔附近，且最大主应力方向与两孔中心连线方向一致时，裂缝起裂压力最小，裂缝扩展最快；裂缝扩展方向的转向角随水压力的增大呈抛物线递增，在现场应用时要根据诱导方向需求合理的布置控制孔的参数。

通过自制水泥砂浆试块，组合水力压裂模拟实验室试验装置，开展控制孔导控压裂物理相似模拟试验，分析不同孔间距、控制孔孔压及控制孔所在位置对水力裂缝扩展形态的影响。研究发现：两孔间距越小，控制孔孔压越大，裂缝起裂时所需的注水压力越小，压裂完成所需用的时间越短，裂缝扩展时偏转角度越大，控制孔导向压裂裂缝定向扩展的诱导作用越明显；当两孔连线方向与最大水平主应力方向一致，裂缝起裂时所需的注水压力最小，压裂完成所需用的时间最短。

采用现场试验对控制孔导控压裂和常规压裂技术增透效果进行了对比分析。现场试验结果表明：控制孔导控压裂方法的定向增透效果要优于常规水力压裂方法；两孔间距越小，控制孔导控压裂方法增透效果越好。控制孔导控压裂相对于常规水力压裂方法和普通钻孔抽采方法，在平均瓦斯浓度上分别提高了1.64 倍和6.57倍；孔间距从6m增加到10m时，在平均瓦斯浓度上降低了1.24倍。在钻场抽采一个月后，采用控制孔导控压裂技术进行瓦斯抽采时，平均瓦斯浓度的衰减速度相对较慢，衰减了4个百分点，衰减率为8.8%；当孔间距从6m增加到10m时，控制孔导控压裂技术的平均瓦斯浓度的衰减增加了10个百分点，衰减率增加了22.3%。

Hydraulic fracturing technology plays an important role in the process of gas extraction in high gas and low permeability coal seam. In view of the fact that the research on the distribution of in-situ stress field around the fracturing hole under the pore water pressure of the control hole is not sufficient, and the propagation law of the hydraulic fracture controlled by the control hole under the combined action of various influencing factors is not clear, it can not provide technical support for the design of the hydraulic fracture propagation process of the coal seam controlled by the control hole. In this paper, theoretical analysis, numerical simulation, physical simulation test and field test are combined to study the initiation and propagation law of hydraulic fractures in the coal seam controlled by the control hole, and the mechanical model of the initiation and propagation of hydraulic fractures controlled by the control hole is established to reveal the propagation mechanism of hydraulic fractures under the action of pore water pressure. The main research results are as follows:

Based on the mechanical principle of H.Kastner borehole surrounding rock crack initiation, the distribution characteristics of in-situ stress field around the fracturing hole under the pore water pressure of the control hole are analyzed, and the mechanical model of the crack initiation and crack propagation of the hydraulic fracture controlled by the control hole is established. The crack initiation and propagation law of the hydraulic fracture controlled by the control hole is obtained, and the mechanism of the hydraulic fracture propagation under the pore water pressure is revealed. It is found that the initiation pressure of the fracturing borehole is negatively correlated with the pore pressure of the control hole and positively correlated with the hole spacing. When the water injection pressure of the control hole is larger, the distance between the control hole and the fracturing hole is smaller, and the hydraulic fracture initiation fracturing is smaller. Under the control of pore water pressure, when λ>1 or λ<1, the crack initiation angle is θ=0° or θ=180°. With the increase of λ from 1.1 to 1.3, the crack propagation is controlled by the original in-situ stress. The stronger the control, the more difficult the crack deflection during the expansion process; when λ<1, the crack initiation angle is θ=90° or θ=270°. When λ increases from 0.7 to 0.9, the crack propagation is less controlled by the original ground stress, and the crack is more easily deflected during propagation. When λ=1, the crack initiation angle is θ=β+π, and the crack extends to the vicinity of the control hole along the direction of the connection between the two holes. With the increase of fracture length in the process of fracture propagation, the water injection pressure required for fracture propagation gradually decreases.

Based on the theory of rock seepage mechanics and the distribution characteristics of in-situ stress field around the fracturing hole under the pore water pressure of the control hole, the seepage-stress coupling model of the hydraulic fracture propagation controlled by the control hole is established. The RFPA^2D-Flow software is used to numerically simulate the propagation law of the hydraulic fracture controlled by the control hole, and the control effect of the control hole on the directional propagation of the hydraulic fracture is analyzed. The effects of hole spacing, control pore pressure, control hole position and in-situ stress on the initiation and propagation of hydraulic fractures are studied, and the fracture steering law during the propagation of hydraulic fractures under the influence of control hole parameters is obtained. The results show that compared with the control hole guided fracturing, the water injection pressure required for fracturing borehole initiation is reduced, and the maximum tensile stress is generated around the center line of the two holes of the fracturing hole and the control hole to guide the deflection of the hydraulic fracture. When the distance between the control hole and the fracturing hole is smaller, the water injection pressure of the control hole is larger, the crack initiation pressure is smaller, the steering angle of the crack propagation direction is larger, and the induction effect is better when the crack propagates to the control hole. When the angle between the direction of the maximum principal stress and the direction of the connection between the two holes is smaller, the crack is more likely to deflect to the vicinity of the control hole, and when the direction of the maximum principal stress is consistent with the direction of the connection between the two holes, the crack initiation pressure is the smallest and the crack propagation is the fastest. The turning angle of the crack propagation direction increases parabolically with the water pressure. In the field application, the parameters of the control hole should be reasonably arranged according to the demand of the induced direction.

Through the self-made cement mortar test block, combined with the hydraulic fracturing simulation laboratory test device, the physical similarity simulation test of the control hole guide control fracturing is carried out, and the influence of different hole spacing, control hole pore pressure and control hole location on the hydraulic fracture propagation morphology is analyzed. It is found that the smaller the distance between the two holes is, the larger the pore pressure of the control hole is, the smaller the water injection pressure required for the initiation of the fracture is, the shorter the time required for the completion of the fracturing is, the larger the deflection angle of the fracture propagation is, and the more obvious the induction effect of the directional propagation of the fracture guided by the control hole is. When the direction of the connection between the two holes is consistent with the direction of the maximum horizontal principal stress, the water injection pressure required for the initiation of the fracture is the smallest, and the time required for the completion of the fracturing is the shortest.

The field test is used to compare and analyze the anti-reflection effect of control hole guided fracturing and conventional fracturing technology. The field test results show that the directional anti-reflection effect of the control hole guided fracturing method is better than that of the conventional hydraulic fracturing method. The smaller the distance between the two holes, the better the anti-reflection effect of the control hole guided fracturing method. Compared with the conventional hydraulic fracturing method and the ordinary borehole drainage method, the average gas concentration of the control hole guided controlled fracturing is increased by 1.64 times and 6.57 times respectively. When the hole spacing increases from 6m to 10m, the average gas concentration is reduced by 1.24 times. After one month of extraction in the drilling field, when the gas extraction is carried out by using the control hole guide control fracturing technology, the attenuation rate of the average gas concentration is relatively slow, which is attenuated by 4 percentage points, and the attenuation rate is 8.8%. When the hole spacing increases from 6m to 10m, the attenuation of the average gas concentration of the control hole guided fracturing technology increases by 10 percentage points, and the attenuation rate increases by 22.3%.

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