Characteristics of shale gas reservoir in Jiyang depression and its significance in drilling and exploitation

Document Type: Original Article

Author

School of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China

Abstract

Physical and geochemical characteristics of shale play conclusive role in confirming operation measures during drilling and stimulation. These properties of shale samples from Jiyang depression were investigated through X-ray diffraction, scanning electron microscope, adsorption isothermal, high pressure mercury intrusion, methylene blue trihydrate, pressure pulse decay, tests of specific water wettability, shale stability index, etc. Correlations, geological and engineering significances of them were discussed. Results show that shale reservoir in Jiyang depression has exploitation value corroborated by better characteristic parameters: 2.86% TOC, 69.9% brittle mineral, 26.14% clay mineral, higher permeability of 0.011 × 10-3μm2, larger Langmuir volume (5.82 cm3/g) and Langmuir specific area (0.91 m2/g), effective porosity (3.77%) and thickness (130.66m). Langmuir specific area is key control on methane adsorption and storage verified by its moderate positive relativity with Langmuir volumes rather than TOC. Higher illite content (69.29%) may lead to instability of borehole and velocity sensitivity damage. Microfractures provide channels for filtration invading and loss of drilling fluid. Larger specific water wettability (4.36 × 10-7g/m2) and smaller shale stability index (19.99 mm) confirm that shale formation were unstable contacting with fresh water. Countermeasures must be adopted during drilling and fracturing to reduce reservoir damage and overcome difficulties.

Keywords