Abstract
In order to determine the effective stress factor of proppants during the multi-stage hydraulic fracturing operation in horizontal wells and select the appropriate proppant type, the analysis of the effective stress characteristics of proppants is carried out. This analysis considers the geomechanics and long-term production characteristics of multi-stage fractured horizontal wells in reservoirs like Xinjiang Mahu shale oil and Southwest China shale gas. The analysis of influencing factors is also carried out. The results show that, during the multi-stage hydraulic fracturing operation in horizontal wells, the stress on proppants is not only related to geological factors such as reservoir closure stress, but also closely related to total injection volume, cluster spacing, liquid type, injection displacement and post fracture management. First, increasing injection intensity, reducing fracture spacing, using low viscosity fracturing fluid, adopting high injection displacement and utilizing reasonable flowback system can effectively supplement reservoir energy, postpone the effective stress peak of proppants, and increase the effective conductivity of proppants. Second, the production performance analysis results of nearly 300 horizontal wells (from Xinjiang oil field, Erdos tight oil reservoir, Sichuan shale gas reservoir, etc.) shows that: the effective stress of proppants in horizontal wells is only 50–60% of that in vertical wells, which results in a different proppant selection criterion in the volume stimulation of horizontal wells and provides the geomechanics basis of replacing ceramsite proppant with quartz sand to reduce cost and increase efficiency. Based on the above conclusions, the field test of replacing ceramsite proppant with quartz sand was carried out. The proportion of quartz sand increased from less than 30% in 2014 to 69% in 2019. Without any impact on production, the annual investment cost was decreased by more than 1 billion yuan, which set a great example for the promoted low-cost development of unconventional oil and gas reservoirs under low oil price background.
Highlights
Common reservoir stimulation techniques include matrix acidizing, acid fracturing [1, 2] and hydraulic fracturing
New understandings of the effective stress acting on the proppant in multi-stage fracturing of horizontal wells were gained in this research, which can be guidance for the design optimization of horizontal well stimulation in shale gas and tight oil development. e volume injected during multistage fracturing of horizontal wells is at least 5 times more
Analysis of production performance of nearly 300 horizontal wells in the tight oil fields in Xinjiang and Ordos, and shale gas fields in Sichuan showed that the effective stress on proppants during and after multi-stage fracturing of horizontal wells is only 50–60% of that for the vertical wells. is finding changed the criterion for selecting proppant for the multi-stage fracturing and provided a theoretical basis for promoting the use of low-cost sand as proppant
Summary
Common reservoir stimulation techniques include matrix acidizing, acid fracturing [1, 2] and hydraulic fracturing. Due to the difference in low-cost operation approach in North America and the “Practice first, theory second” philosophy in unconventional resource development, there is less research on the theoretical basis of sand application In this context, some research work on this issue has been carried out domestically, and especially in the last five years, the research has been getting more and more in-depth. Under the influence of the persistent low oil price, the research and application of low-cost materials has become an important focus of the business For this reason, the characteristics and influential factors of the effective stress acting on the proppant during massive fracturing of horizontal wells in unconventional reservoirs were analyzed in this paper, in combination with the tracking of long-term production performance of horizontal wells in Xinjiang tight oil and Southwest shale gas fields. Indepth understanding of all the issues will have important guiding significance to selection of proppants and optimization of fracturing operations
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