Investigation on the experimental determination of the apparent preconsolidation stress and effective-sealing condition
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ORIGINAL PAPER
Investigation on the experimental determination of the apparent preconsolidation stress and effective-sealing condition for clay cap rock Jun-xin Liu 1,2,3 & Feng Xiao 2 & Wei Liu 1 & Jian-jun Gan 4 & Liang Huo 3 & Hai-jun Mao 3 Received: 14 October 2017 / Accepted: 17 August 2018 / Published online: 30 August 2018 # Saudi Society for Geosciences 2018
Abstract Seal ability of clay cap rock is impacted by not only the current physical and mechanical characteristics but also the diagenetic experiences and stress state. Thereby, both the diagenetic actions and stress state when conversing from brittleness to ductility should be further investigated. Only by this way can the oil/gas generation and the transportation relationship be thoroughly revealed and then the seal ability of cap rocks be accurately evaluated. Aimed at the clay rocks subjected to different diagenetic states from E’xi-Yudong regions, a thick-wall steel sleeve was manufactured and utilized as the lateral restrictor to implement the uniaxial strain compression experiments. Based on the thick-wall cylinder theory, the procedure of calculating the apparent preconsolidation stress (APS) was established. To reveal the factors that influence the APS, the relationships between APS and uniaxial compression strength, ultrasonic velocity, and porosity as well as clay mineral content were investigated, respectively. The mechanisms of the lateral pressure coefficients’ variations were also discussed. The transition condition of Bbrittleness to ductility^ is preliminary discussed, so is the calculation method for the effective-sealing burial depth. This study could provide a significant indication of evaluating the seal ability of diagenetic clay cap rocks. Keywords Clay cap rock . Apparent preconsolidation stress . Brittleness to ductility . Critical burial depth . Sealing capacity
Introduction Seal ability is a decisive prerequisite for the abundance degree, reserves, and types of the oil/gas reservoirs (Fu et al. 2012; Liu et al. 2015). Thus, the study on the seal ability of cap rock of oil/gas reservoirs remains long term a hot topic in petroleum geology and related fields. In the recent years, along with the increasing requirement of energy, as well as the rapid exploitations of complex reservoirs and unconventional gas fields, surveys on the cap rock have become systematically and
significantly prosperous. Generally, cap rock of oil/gas reservoirs predominately consists of three different types of sedimentary rocks, among them argillaceous rock takes up approximately 70%, salt gypsum rock 20%, and other rocks 10%. Salt gypsum possesses almost the best effectiveness of seal ability due to its extremely low permeability, low porosity, and excellent plasticity (Yang and Aplin 2007; Zhang et al. 2014; Chen et al. 2013). Argillaceous rocks, which mainly refer to clay rock, are the largest distributed cap rocks. Nevertheless, they have large
* Wei Liu [email protected]
1
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chon
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