CAJ | 학술논문

水力压裂起裂与扩展压力的确定是压裂设计最为重要的参数之一，与水平孔或垂直孔水力压裂相比，任意方向钻孔水力压裂的起裂与扩展更加复杂。根据最大拉应力准则，分析任意方向钻孔裂缝起裂压力及起裂方向，得出量纲一起裂压力(pb/σv)随钻孔方位角和钻孔倾斜角的变化规律；并以王台铺煤矿顶板岩层水力压裂为例，进行起裂压力与起裂位置计算，通过有限元计算分析扩展压力较大的原因。研究结果如下：(1)当水平主应力相等时，钻孔从垂直方向逐渐旋转至水平方向过程中，所需起裂压力不断减小，水平孔由σh方向逐渐旋转至σH方向过程中，裂缝起裂压力保持不变；(2)随着σH/σh或σH/σv的增大，裂缝起裂压力的变化规律与地应力场类型密切相关；(3)钻孔由垂直方向转向水平方向过程中，对于3种类型的应力场(正断层型、平滑断层型、逆断层型)，裂缝起裂压力有着各自独特的变化规律；(4)水平孔由σh方向逐渐旋转至σH方向过程中，对于不同类型的应力场，合理布置钻孔方向可使起裂压力最小；(5)当岩石抗拉强度与地应力大小相近时，增大抗拉强度使裂缝起裂所需的压力明显增大；(6)有限元计算结果表明，裂缝起裂后旋转扩展会导致较高的扩展压力；(7)在进行水力压裂作业时，地应力的大小、方向和类型是进行钻孔参数设计的基础。
수력압렬기렬여확전압력적학정시압렬설계최위중요적삼수지일，여수평공혹수직공수력압렬상비，임의방향찬공수력압렬적기렬여확전경가복잡。근거최대랍응력준칙，분석임의방향찬공렬봉기렬압력급기렬방향，득출량강일기렬압력(pb/σv)수찬공방위각화찬공경사각적변화규률；병이왕태포매광정판암층수력압렬위례，진행기렬압력여기렬위치계산，통과유한원계산분석확전압력교대적원인。연구결과여하：(1)당수평주응력상등시，찬공종수직방향축점선전지수평방향과정중，소수기렬압력불단감소，수평공유σh방향축점선전지σH방향과정중，렬봉기렬압력보지불변；(2)수착σH/σh혹σH/σv적증대，렬봉기렬압력적변화규률여지응력장류형밀절상관；(3)찬공유수직방향전향수평방향과정중，대우3충류형적응력장(정단층형、평활단층형、역단층형)，렬봉기렬압력유착각자독특적변화규률；(4)수평공유σh방향축점선전지σH방향과정중，대우불동류형적응력장，합리포치찬공방향가사기렬압력최소；(5)당암석항랍강도여지응력대소상근시，증대항랍강도사렬봉기렬소수적압력명현증대；(6)유한원계산결과표명，렬봉기렬후선전확전회도치교고적확전압력；(7)재진행수력압렬작업시，지응력적대소、방향화류형시진행찬공삼수설계적기출。
The initiation pressure and propagation pressure are essential to hydraulic fracturing operation. The initiation and propagation of an arbitrarily inclined borehole is considered more complicated compared with a horizontal or vertical borehole. By means of maximum tensile stress criterion,initiation pressure and orientation are analyzed and dimensionless initiation pressure(pb/σv) varying with borehole azimuth and inclination is obtained. With regard to hydraulic fracturing treatment carried out in the roof of Wangtaipu coal mine,initiation pressure and corresponding location are calculated. Finite element method is employed to explain the excessive propagation pressure during the fracturing process. The results are that:(1) When σh=σH , initiation pressure keeps ever-reduced as borehole rotates gradually from vertical direction to horizontal direction and maintains constant as borehole rotates fromσh direction toσH direction. (2) Change rule of initiation pressure is closely related to in-situ stress regime with increase ofσH/σh orσH/σv. (3) During the process of borehole rotating from vertical to horizon, initiation pressure performs uniquely subjected to normal faulting stress regime,striking slip faulting regime and reversing faulting stress regime,respectively. (4) The horizontal borehole direction requiring minimum initiation pressure exists for corresponding in-situ stress regime as it rotates fromσh direction toσH direction. (5) Initiation pressure increases dramatically with the growth of rock tensile strength as it is close to the magnitude of in-situ stress. (6) The fracture turning during propagation would generate high pressure. (7) The magnitude,direction and type of in-situ stress are the groundwork for borehole design of hydraulic fracturing operation.