Abstract
Natural fractures play an important role in the seepage system of Paleogene sandstone reservoirs at Nanpu Sag. Characteristics and formation mechanisms of natural fractures and stress-sensitivity permeability are comprehensively investigated and their impact on water injection is discussed based on core and log data (FMI and diplog data) as well as stress-sensitivity permeability measurement. Results show that high-angle shear fractures, including NE-SW strike fractures and NW-SE strike fractures, are widely developed in the study area, which were primarily developed during the late Paleogene and late Neogene. The present maximum horizontal principal stress is orientated at N60°–80°E, approximately parallel to the NE-SW fractures, contributing greatly to the seepage system at the early oilfield development stage. Fractures in the study area can be divided into three phases and are characterized by obvious stress-sensitivity permeability, which is closely related to fracture aperture and throat size. Since the fracture occurrence enhances stress sensitivity of permeability, it is necessary to regulate well pattern based on dynamic behaviors of fractured reservoirs at different development stages.
Highlights
As oil and gas resource consumption continuously increases, identifying and producing reserves from wide-distributed low-permeability reservoirs has attracted increasing attention (Shanley and Cluff, 2015; Alhuraishawy et al, 2018; Qing et al, 2021)
In this paper, taking the Paleogene Shahejie low-permeability sandstone reservoir in Gaoshangpu Oilfield, Nanpu Sag, as an example, we investigate the genetic mechanisms and growth features of natural fractures, and discuss their stress sensitivity as well as their influence on water injection through integrating core data, log data, and a stress-sensitivity permeability experiment
This study focuses on the Paleogene sandstone reservoir at Gaoshangpu Oilfield
Summary
As oil and gas resource consumption continuously increases, identifying and producing reserves from wide-distributed low-permeability reservoirs has attracted increasing attention (Shanley and Cluff, 2015; Alhuraishawy et al, 2018; Qing et al, 2021). Fractures with porosity are commonly less than 0.5% and generally contribute little to the storage capacity of low-permeability reservoirs (Zeng et al, 2016; Lin et al, 2020; Liu et al, 2020). They can improve permeability significantly and bring strong heterogeneity Pressure drops can commonly induce stress sensitivity of fractures, sharply close fractures around wells, and significantly decrease permeability, exerting a negative impact on oil and gas development
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