Assessment of causes of overpressure different from sub-compaction: Application in unconventional reservoir

Abstract

The necessity for hydrocarbon-producing countries to increase their reserves has led to companies exploring the deposits available in source rocks that might be over-pressured and thus, strict rules are required for their development. Overpressure, which may result in wellbore stability problems, could result from several causes such as mechanical effects, dynamic transfer, chemical stress, thermal stress, among others, in which undercompaction is frequently the main cause, generated when the sediment deposition velocity exceeds the fluid ejection rate.The expansion of fluids generated by thermal stresses and the reduction of porosity caused by chemical stresses may be among the other causes of overpressure in shales.
 The new methodology presented in this paper makes it possible to determine the pressure due to thermal stresses caused by the cracking of kerogen and oil in shales. In addition, petrophysical and geochemical models are considered in order to precisely ascertain the increase in pore pressure due to temperature andfluid expansion. An increase of 20% in pressure is seen when compared with undercompaction. As a result of this methodology, the mud window was optimized and the hydrocarbons, generated under subsurface the conditions (pressure, temperature) analyzed, were quantified.

Features of forecasting abnormally high reservoir pressures when drilling wells in areas of south-western Turkmenistan

“…Analyses of field deposits show that the relationship between anomalously high formation pressures and filtration-capacitance properties of rocks can be the cause of the formation of these pressures (2) . For example, low values of porosity and permeability of sandy silty rocks indicate the important role of fracture-pore reservoirs and secondary pore-type reservoirs in the formation of formation pressure anomalies (8) . Thus, the formation of anomalously high formation pressures can be associated with a variety of genetic features, including tectonic, hydrogeological and gravity factors, as well as features of fluid systems and rock properties.…”

Multiple drivers and controls of pockmark formation across the Canterbury Margin, New Zealand

“…Other processes associated with methane generation and flow (e.g. reservoir overcharging, buoyancy) (Hedberg, 1974; Law & Dickinson, 1985; Timko & Fertl, 1971; Vargas‐Silva et al, 2019; Zhao et al, 2018) as well as a reduction in hydrostatic pressure due to sea‐level lowering (Riboulot et al, 2014), could have played a role. We do not have enough information at the Canterbury Margin to numerically test these hypotheses.…”

Coupling relationship between reservoir densification and hydrocarbon emplacement in the Jurassic Badaowan Formation sandstone reservoirs of the southern Junggar Basin, China

“…In this context, overpressure plays an important role, and its genetic mechanism has been extensively investigated. In previous studies, overpressure is ascribed to several factors, including the source‐reservoir rock pressure difference induced by hydrocarbon generation, the faults with good sealing performance (Beaudoin, Lacombe, Bellahsen, Amrouch, & Daniel, 2014; Cai et al, 2019; Duan, Li, Luo, Chen, & Bao, 2018; Feng, Lei, Qu, & Huo, 2019; H. Liu et al, 2017; Lu et al, 2018; Y. Luo, Wang, Liu, Wang, & Zhao, 2020; Zhang et al, 2017), the tectonic compression (Beaudoin et al, 2014; X. Guo, Liu, Jia, Song, Zhao, & Lu, 2016), and the under‐compaction related to rapid basin subsidence (Fu et al, 2016; X. Guo, Liu, Jia, Song, Zhao, Zhuo, et al, 2016; Y. Liu et al, 2019; Vargas‐Silva, Gambús‐Ordaz, & Calderón‐Carrillo, 2019).…”

“…Luo, Wang, Liu, Wang, & Zhao, 2020;Zhang et al, 2017), the tectonic compression (Beaudoin et al, 2014;, and the under-compaction related to rapid basin subsidence (Fu et al, 2016;X. Guo, Liu, Jia, Song, Zhao, Zhuo, et al, 2016;Vargas-Silva, Gambús-Ordaz, & Calder on-Carrillo, 2019).…”