Abstract
An integrated hydraulic fracturing followed by waterflooding was conducted in a heterogeneous sandstone formation in the Northern Shanxi Slop of Ordos Basin in Western China. Water breakthrough quickly occurred, and the underlying mechanism of water breakthrough has not been well understood. Such mechanism needs to be investigated comprehensively from the spatial connectivity of multilayer sand bodies and characterization of hydraulic-natural fracture networks. Here, an integrated approach is proposed to tap the remaining oil in the individual sand layer during the late-stage development of tight sandstone reservoirs. A case study is utilized to demonstrate the applicability of the integrated method. It is found that the six sand layers could be further divided within the target oil layers. These sand layers have a variety of physical and mechanical properties, leading to the asymmetric spatial distribution of hydraulic fractures after performing the integrated fracturing of whole oil layers. The spatial difference of sand bodies conforms to the features of the multiperiod superimposed channel in the sedimentary environment of fan delta front. The natural fractures were generated from the tectonic movement in the Mesozoic period with a dominant orientation of approximately NE 67°. The asymmetric hydraulic fractures propagated and connected with the preexisting natural fractures, forming the intricate natural-hydraulic fracture networks. The water breakthrough pattern in each sand layer is primarily ascribed to the spatial distribution of the hydraulic-natural fracture networks and sedimentary microfacies. The refracturing operations based on the remaining oil distribution in sand layers are proven to be effective in further developing the formation. The average oil production of related wells increased from 0.61 t/d to 2.18 t/d. This practical development strategy provides insights for further development of likewise heterogeneous tight sandstone reservoirs.
Highlights
In Western China, along with the long-term water injection development, the oil production within pay zones is uneven in the naturally fractured tight sandstone reservoirs and usually accompanied by the increasing water cut [1, 2]
The results suggested that if the interlayers developed in the pay zones, it was necessary to perform fracturing stimulation for each single oil layer, as the interlayers may function as the barriers to restrain the vertical propagation of hydraulic fractures
A case study is utilized to demonstrate the effective applicability of this integrated method
Summary
In Western China, along with the long-term water injection development, the oil production within pay zones is uneven in the naturally fractured tight sandstone reservoirs and usually accompanied by the increasing water cut [1, 2]. The fracture-induced water breakthrough is frequently observed shortly after the integrated fracturing operations targeting the whole oil layers ([3, 4]; Van et al, 2018). The trigger mechanisms of such fracture-induced water breakthrough have not been well investigated, especially in consideration with the spatial connectivity of multistage sand bodies and the intricate hydraulic-natural fracture networks after the integrated fracturing operations [1,2,3, 5]. It is necessary to conduct the comprehensive study to characterize the hydraulic-natural fracture networks based on the multistage sand layers subdivision in these reservoirs. The improve understanding of individual layer-based fracture network could help propose proper strategy to tap the remaining oil in the late stage development of tight sandstone reservoir. The hydraulic fracturing technology has been widely utilized in the development of the tight sandstone reservoirs.
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