Integrated controls of tectonics, diagenesis and sedimentation on sandstone densification in the Cretaceous paleo-uplift settings, north Tarim Basin

Abstract

The densification mechanism of the Lower Cretaceous sandstone in the western Tabei Uplift is still unclear, restricting successful petroleum exploration and development. Seismic interpretation, thin sections observation, Field emission scanning electron microscope (FE-SEM) and cathodoluminescence (CL), porosity and permeability measurements, mercury injection porosimetry (MIP) are compiled in this study, to investigate the paleo-uplift and facies co-evolution, tight reservoir characteristics, and densification mechanism of the Lower Cretaceous sandstones around the paleo-uplift. Results indicate the sedimentary facies around the Xinhe and the Sandaoqiao uplifts were controlled by the decreasing geomorphic slope and rising lake level, their evolution exhibited difference. The Xinhe area developed a fan delta with a reducing distribution in region, while the sandaoqiao area transitioned from fan delta to beach bar, eventually developing a braided river delta. Reservoir physical properties are primarily influenced by intense compaction, calcite and clay cementation and weak dissolution. Severe calcite cementation, compaction and weak dissolution predominantly influence the physical properties of the beach bar. Moderate compaction, weak cementation and moderate quartz and feldspar dissolution are the key factors impacting the physical properties of braided river delta. Additionally, reservoir quality varies with sedimentary facies where the sandstones of the braided-river delta have the best petrophysical properties and pore connectivity than those of the fan delta and beach bar. Tectonic movements around the uplift affected the distribution of various sedimentary facies, which later governed the diagenesis processes pathways. Collectively, this study can serve as a valuable reference for exploration and development of clastic reservoirs in the Tabei Uplift and analogous reservoirs with a paleo-uplift context.