Geological characteristics and abnormal pore pressure prediction in shale oil formations of the Dongying depression, China

Abstract

Pore pressures in shale oil formations in the Dongying depression of the Bohai BayBasin are highly overpressured. Understanding overpressure principles not only can reveal the mechanism of shale oil generation to provide prospects for shale oil exploration and production, but also can reduce potential drilling risks and provide insights for sweet spot identification. Overpressure generation mechanisms are analyzed based on petrophysical data, core analysis, sedimentation rate, oil saturation, and smectite and illite data. We find that undercompaction, oil generation, and smectite and illite transformation are primary causes of overpressures. Undercompaction is the major cause of overpressures in the Es3 formations because of their rapid deposition rate of 300-700 m/m.y. For the overpressures primarily generated by undercompaction, sonic transit time can be used to predict shale pore pressure with correctly selected depth-dependent normal compaction trend. In the Es3 and Es4 formations, overpressure data are consistent with the increase of vitrinite reflectance and oil saturation, indicators of oil generation. Additionally, in shallow formations, starting at about 2000 m, the smectite to illite transformation occurs, which makes rock property changes with depth. A composite normal compaction trendline is proposed to account for the smectite to illite transformation. Using well log data, the shale oil formations can be identified and there are two shale oil formations in the studied area, and a shale oil geo-marker is found. At this geo-marker, the pore pressure gradient reaches the highest value. This high pore pressure behavior is beneficial for shale oil production because of a higher pore pressure corresponds to a higher production. K E Y W O R D Soil generation, petroleum geology, pore pressure prediction, shale oil, sonic transit time, undercompaction

Production Capacity Prediction Method of Shale Oil Based on Machine Learning Combination Model

“…In the evaluation process of shale oil production capacity, understanding the extent of influence and interrelationships among various factors is crucial [16]. However, within these factors, inevitable correlations or overlaps among certain parameters may affect the final evaluation outcomes.…”

Quantitative Characterization of Excess Pressure Gradient in the Upper Interval of Es4 Member of Dongying Depression and Its Indicative Significance for Oil Migration and Accumulation

“…Previous studies have suggested that the overpressure generated by different mechanisms should be predicted in different methods [24]. The overpressure in the Dongying Depression is mainly caused by oil generation from the source rocks [1,25], while compaction disequilibrium may have contributed to the overpressure in the north Steep Slope zone of the Dongying Depression [26,27]. Thus, the pore pressure can be calculated by the Eaton Formula [28,29]:…”

The impact of diagenesis on the reservoir quality of the early Cretaceous Lower Goru sandstones in the Lower Indus Basin, Pakistan

“…Reservoir characteristics of the sandstone such as geometry, mineralogical composition, pore characteristics, porosity, permeability, textural framework, and maturity are evaluated by depositional settings of the sandstones, whereas the diagenesis may affect the reservoir porosity by post-depositional processes (Bjørlykke 2014;Cantarero et al 2020;Mangi et al 2020). Reservoir quality is the main factor controlling the prospectivity during the exploration and production of hydrocarbon (Zhang et al 2020). Lower Goru sandstone reservoirs in the Lower Indus basin have been studied with the help of core cuttings of well KD-01 well from the sandstone intervals.…”