Development practice of continental shale oil in Jimsar Sag in the Junggar Basin
(2.PetroChina Xinjiang Oilfield Company)
【Abstract】The Permian Lucaogou Formation in the Jimsar Sag, Junggar Basin, Xinjiang is rich in continental shale oil resources, with an estimated resource more than 15.8 × 108 t. In order to realize the effective development of shale oil, based on the detailed analysis of geological characteristics, engineering technologies, production characteristics and laws of continental shale oil in the Lucaogou Formation, and combined with the development practice, we have obtained the following achievements and understandings in recent years: (1) The source rocks of the Lucaogou shale oil in the Jimsar Sag are from the continental shale of saline lacustrine fine-grained deposit, which are high-quality source rocks with large thickness and characterized by integrated sources and reservoirs. Oil is 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 the typical continental shale oil. (2) It is clear that the free porosity and free oil reserve abundance in the fracture-controlled areas created by volume fracturing from horizontal wells constitute the basis of high production for the shale oil. (3) With the increase in buried depth, the difference of horizontal two-direction stress increases, and the fracture complexity 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”. (4) The oil viscosity is the key control factor of the production from horizontal wells in the “lower sweet spot interval”. (5) The penetration length of high-quality “sweet spots” 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. (6) Due to the imbibition and replacement between the fracturing fluid and the shale oil in the matrix pores, the production can be improved by proper soaking after fracturing. (7) Due to the limitation of hydraulic fracture length, the appropriate well spacing should not be larger than 200 m. Through continuous research and development practice, shale oil development has obtained good results. The maximum annual production of a single horizontal well has been more than 1.3 × 104 m3. Since 2019, it has basically entered the stage of large-scale trial production, which accumulated rich experiences for the industrial development of continental shale oil in China.
【Keywords】 Jimsar Sag; shale oil; development practice; geological characteristics; well spacing;
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