钻井—压裂—生产全过程储层应力演化与加密井压裂优化

Reservoir stress evolution and fracture optimization of infill wells during the drilling-fracturing-production process

水平井水力压裂是致密油藏的有效开发模式,而新钻井则可以提高油藏的开采程度。钻井、压裂和生产过程均诱发储层应力发生变化,进而影响加密井的压裂设计。国内外尚未有相关研究使用同一种方法实现钻井—压裂—生产全过程储层应力演化模拟,从而指导加密井的压裂施工优化。采用基于有限元的非连续离散裂缝数值方法,在钻井和压裂过程中通过动态网格技术描述井筒和裂缝的延伸,非连续离散裂缝模型可采用常规有限元网格进行计算,可以与离散裂缝模型完美契合,从而实现钻井—压裂—生产一体化数值模拟。以致密油区块加密井施工为例,对加密井区域待施工井进行钻井—压裂—生产一体化模拟,并以井区开采经济最大化为导向,为加密井压裂优化提供指导方法。模拟结果显示:老井的长期生产过程使得加密井区域地层压力和地应力均减小,最大水平主应力方向发生偏转;考虑老井生产的影响,加密井钻进过程中的钻井液密度不能再使用原始地层压力剖面设计;在钻井液柱压力不大于现阶段最小水平主应力的情况下,井筒钻开后,加密井周围最大水平主应力方向进一步发生偏转,使得裂缝初始扩展方向沿井筒偏转;在加密井压裂前对老井进行注水增压可以改善加密井压裂效果。所建立的数值方法可以实现钻井—压裂—生产全过程储层应力演化模拟,以及压裂—生产一体化数值模拟,进而优化加密井压裂设计。

Hydraulic fracturing of horizontal wells is an effective development mode for tight reservoirs,where new wells are continuously drilled to enhance reservoir recovery.The drilling,fracturing and production processes all can cause changes in reservoir stresses,which in turn affect the fracture design of infill wells.At home and abroad,no research has been conducted to simulate the reservoir stress evolution during the whole process of drilling-fracturing-production using the same method,and there is a lack of guidance for improving fracturing construction in infill wells.Therefore,this paper proposes a discontinuous discrete fracture numerical method based on finite element to describe the wellbore and fracture extension by use of dynamic grid technology during drilling and fracturing;the discontinuous discrete fracture model can be calculated using conventional finite element grid,which fits perfectly with the discrete fracture model,thus realizing the integrated numerical simulation of drilling-fracturing-production process.Taking the construction of infill well in a tight oil block as an example,this paper performs the integrated simulation of drilling-fracturing-production process for the wells to be constructed in the infill well area,so as to provide a guiding method of fracturing optimization for the infill well under the guidance of maximizing the economic hydrocarbon recovery in the well area.The simulation results show that:the long-term production process of old well has reduced the formation pressure and ground stress in the infill well area,and the direction of the maximum horizontal principal stress is deflected;considering the influence of the old well production,the original formation pressure profile design is not applicable for the design of drilling fluid density during the drilling process of infill well;under the condition that the drilling fluid column pressure is not greater than the minimum horizontal principal stress at this stage,after the wellbore is drilled,the direction of the maximum horizontal principal stress around the infill well is further deflected,making the initial fracture extension direction deflected along the wellbore;water injection and pressurization of the old well before infill well fracturing can improve the fracturing effect.The established numerical method can realize the simulation of reservoir stress evolution during the whole process of drilling-fracturing-production and the integrated simulation of fracturing-production process,and then optimize the design of fracturing in infill wells.