Wettability of Tight and Shale Gas Reservoirs

  • Author / Creator
  • Abstract
    Abundant hydrocarbon resources in low-permeability formations are now accessible due to technological advances in multi-lateral horizontal drilling and multi-stage hydraulic fracturing operations. The recovery of hydrocarbons is enhanced by the creation of extensive fracture networks. Fluid invasion into the rock matrix has been identified as a possible mechanism that could enhance hydrocarbon recovery, however, low levels of fracturing fluid are recovered after fracturing operations. Therefore, studying the mechanism of spontaneous liquid imbibition into reservoir rocks is essential for understanding (1) rock wetting affinity, (2) enhanced hydrocarbon recovery, and (3) the fate of non-recoverable fracturing fluid.
    The primary aim of this study is to investigate the wettability characteristics of shales and tight rocks by conducting a series of comparative and systematic imbibition experiments. Using multiple samples, we study functional dependence on petrophysical properties, petrographic properties, rock fabric, depositional lamination, and gamma ray response. Moreover, we investigate the relationship between water loss and rocks’ petrophysical properties, and the correlation between water loss and soaking time (i.e., well shut-in time). Finally, we present a simple method for estimating the degree of water loss at the field level.
    The results of spontaneous imbibition experiments show that the imbibition rate of water is significantly more than that of oil for shale samples drilled from the Horn River (HR) Basin. This observation is in contrast to the measured contact angle. We also measured and compared spontaneous imbibition of oil and water into crushed packs of similar HR samples. Interestingly, in contrast to the intact samples, the crushed samples consistently imbibed more oil than water. Therefore, clay swelling, micro-fracture induction, depositional lamination and osmotic potential are collectively responsible for excess water uptake. In similar comparative imbibition experiments of several binary samples collected from cores drilled in the Montney (MT) tight gas play, samples did not show any visible physical alteration. Both the measured contact angle and imbibition data indicate that MT tight sandstone is strongly oil wet. The comparative study suggests that the connected pore network of HR samples is strongly hydrophilic due to the presence of clay minerals and precipitated salt crystals coating the rock grains, while the well-connected pore networks of the MT samples are dominantly hydrophobic and very likely to be coated with pyrobitumen.

  • Subjects / Keywords
  • Graduation date
    Fall 2014
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.