No abstract

Exploratory and developmental data show that connate water has a significant effect on the gas content of a shale. On the basis of its mobility in shales, connate water could be classified as free water and irreducible water, and the latter is generally dominant in highly mature or overmature shales. However, it is still not fully understood how the irreducible water is distributed in different nanopores of shales at the overmature stage. In this study, two groups of overmature Lower Paleozoic shale samples from southern China were selected for water adsorption experiments based on the ASTM standard (D1412-07, 2010), and the distribution of irreducible water in different nanopores was investigated. The results show that the equilibrium irreducible water contents for the two sample sets range from 5.4 mg/g rock to 15.58 mg/g rock. Although irreducible water is actually mainly stored in inorganic pores for the most of our shale samples, the equilibrium irreducible water contents of these shales are found to be positively correlated with TOC contents, indicating that irreducible water in shales could be hosted in organic pores as well as in inorganic pores. For a given irreducible water content, the percentages of nonmicropore surface area and pore volume occupied by irreducible water are larger than those of the microspore surface area and pore volume, implying that irreducible water is more easily stored in nonmicropores than in micropores for our overmature shale samples, and that the irreducible water may be mainly stored in an absorbed state in nonmicropores but in a condensed state in micropores. Furthermore, there is still approximately 50% of micropore volume or surface area available for gas adsorption even when the shale sample is equilibrated with absorbed water at a relative humidity of 96−97%. This study provides new data for understanding the distribution of irreducible water in the nanopores of highly mature or overmature shales and is helpful for accurately evaluating the shale gas content under geological conditions.

No abstract

The Lower Paleozoic shale in south China has a very high maturity and experienced strong tectonic deformation. This character is quite different from the North America shale and has inhibited the shale gas evaluation and exploration in this area. The present paper reports a comprehensive investigation of maturity, reservoir properties, fluid pressure, gas content, preservation conditions, and other relevant aspects of the Lower Paleozoic shale from the Sichuan Basin and its surrounding areas. It is found that within the main maturity range (2.5 % \ EqR o \ 3.5 %) of the shale, its porosity develops well, having a positive correlation with the TOC content, and its gas content is controlled mainly by the preservation conditions related to the tectonic deformation, but shale with a super high maturity (EqR o [ 3.5 %) is considered a high risk for shale gas exploration. Taking the southern area of the Sichuan Basin and the southeastern area of Chongqing as examples of uplifted/folded and faulted/folded areas, respectively, geological models of shale gas content and loss were proposed. For the uplifted/folded area with a simple tectonic deformation, the shale system (with a depth [ 2000 m) has largely retained overpressure during uplifting without a great loss of gas, and an industrial shale gas potential is generally possible. However, for the faulted/folded area with a strong tectonic deformation, the sealing condition of the shale system was usually destroyed to a certain degree with a great loss of free gas, which decreased the pressure coefficient and resulted in a low production capacity. It is predicted that the deeply buried shale ([3000 m) has a greater gas potential and will become the focus for further exploration and development in most of the south China region (outside the Sichuan Basin).

No abstract

No abstract

No abstract

No abstract