准噶尔盆地吉木萨尔凹陷陆相页岩油开发实践

新疆准噶尔盆地吉木萨尔凹陷二叠系芦草沟组陆相页岩油资源丰富,估算资源量超过15.8×108t。为实现页岩油有效开发,近年来通过对芦草沟组陆相页岩油地质特征、工程技术、生产特征及规律等详细分析,结合开发实践的总结,取得了以下成果及认识:①吉木萨尔凹陷芦草沟组页岩油是陆相咸化湖相细粒沉积的页岩,烃源岩品质优、厚度大,源储一体,页岩段原位聚集,"甜点"段邻源供烃为主、自生为辅的特征,是典型的陆相页岩油;②明确了页岩油体积压裂水平井裂缝控制区内游离孔隙度和游离油储量丰度是页岩油高产的基础;③随着埋深增大,水平两向应力差增大,压裂缝复杂性降低,是部分含油性好的"上甜点体"水平井低产的主要原因;④原油黏度是影响"下甜点体"水平井产量的关键因素;⑤优质"甜点"钻遇长度及压裂米加砂量是吉木萨尔页岩油水平井高产的工程关键因素;⑥页岩油压裂液与基质孔隙原油存在渗吸置换作用,压裂后适当焖井可以提高生产效果;⑦水力压裂缝长度有限,合理井距不应大于200m。通过持续研究和开发实践,页岩油开发取得了较好的效果,水平井单井最高年产突破1.3×10~4m^3,2019年已基本进入规模试验建产,为中国陆相页岩油的工业化开发积累了丰富的经验。

Development practice of continental shale oil in Jimsar sag in the Junggar Basin

The Permian Lucaogou Formation in the Jimsar sag,Junggar Basin,Xinjiang is rich in continental shale oil resources,with an estimated resource of more than 15.8×108t.In order to realize the effective development of shale oil,in recent years,based on the detailed analysis of geological characteristics,engineering technologies,production characteristics and laws of continental shale oil in the Lucaogou Formation,combined with the development practice,the following achievements and understandings have been obtained:①The source rocks of the Lucaogou shale oil in the Jimsar sag are fi ne-grained continental shale deposited in saline lakes,which are high quality source rocks with large thickness,and characterized by integrated sources and reservoirs.Oil accumulated in-situ in the shale intervals,and in the sweet spot intervals,hydrocarbons were mainly supplied from adjacent source rocks with self-generation as auxiliary.All these characteristics indicated a typical continental shale oil.②It is clear that the free porosity and free oil reserves abundance in the fracture controlling areas created by volume fracturing from horizontal wells are the basis of high production for shale oil.③With the increase of burial depth,the difference of horizontal stress between the two directions increases,and the complexity of hydraulic fractures decreases,which is the main reason for the low production of some horizontal wells with good oil-bearing property in the“upper sweet spot interval”.④The oil viscosity is the key control factor of the production from horizontal wells in the“lower sweet spot interval”.⑤The penetration length of high quality“sweet spot”and the proppant volume per meter during hydraulic fracturing are the key engineering factors for the high production from shale oil horizontal wells in the Jimsar sag.⑥Due to the imbibition and replacement between the fracturing fl uid and the shale oil in the matrix pores,the production can be improved by shutting in wells after fracturing for some time.⑦Due to the limitation of hydraulic fractures length,the appropriate well spacing should not be larger than 200m.Through continuous researches and development practice,shale oil development has obtained good results.The maximum annual production of single horizontal well has been more than 1.3×104m3.Since 2019,it has basically entered the stage of scale productivity construction test,which accumulated rich experiences for the industrial development of continental shale oil in China.