人工压裂形成多裂缝的可能性研究

人工裂缝形太对压裂效果至关重要，压裂设计中首先要考虑的就是裂缝裂态。随着固井质量提高和射孔深度加大，井周应力集中变得复杂，射孔壁的应力集中已不容忽视，每一个射孔都能成为一个独立的破裂源，射孔方位不同，应力集中也不同，这可能影响人工裂缝的形成与形态，并存在出现多条人工裂缝的可能性，分析套管射也壁的应力集中状态，讨论裂缝延伸的阻力和每一次射孔诱发人工裂缝的优先顺序，并讨论应力状态对裂缝形态的影响和初裂缝缝态与射孔方位的关系。依据大庆喇萨杏油田应力测试结果，分析深射孔条件下的人工裂缝裂，结论是：若射忆方位随机，800－1200m深度出现人工直立初裂缝或水平初裂缝的概率大体相同，所需破裂压力也相近，一次压裂可能出现多条裂缝；控制射孔方位可以控制人工初裂缝形态；由于该水平最小主主应力与垂向主应力相近，初裂缝可以保持原来的形态独立延伸。图3表2参5（刘建中摘）。

Possibility study on multi-fracture creation during artificial hydraulic fracturing

The shapes of hydraulic fracture are very crucial to the results of fracturing treatment, with the primary consideration of fracture shapes. Stress concentration around the wellbore becomes much complex when the quality of well cementing is improved and the well depth is increased, which makes the stress concentration around the perforated wellbore important enough to be noticed. Each perforation can become single fracturing source, and stress concentration difference from different perforation orientation will affect the process and shape of artificial fractures, and the possibility of multi-fracture also exists. In this paper, the stress concentration around the perforated casing is analyzed, and the resistance against fracture propagation and the priority of artificial fracturing during each perforation treatment are discussed. Meanwhile, the influence of stress states on fracture shape and the relationship between the initial fracture shape and perforation orientation is elaborated. Several conclusions are reached based on the testing results of underground stresses in Lasa oil field of Daqing, and the analysis of artificial fracture shape under the condition of deep perforation. If the perforation orientation is stochastic, the possibilities of vertical initial fracture and horizontal initial fracture from 800 to 1200 meters of depth are approximately the same, without obvious difference between both fracturing pressures, and multi-fracture may be created during one treatment. The artificial initial fracture shape can be controlled by proper perforation orientation. And the original shapes of initial fractures can be maintained during propagation for the minimum horizontal stress is about equal to the vertical principal stress.