Advances in Understanding Liquid Flow in Gas Shales

Abstract

Understanding water uptake of gas shales is critical for designing fracturing and treatment fluids. Previous imbibition experiments on unconfined gas shales have led to several key observations. The water uptake of dry shales is higher than their oil uptake. Furthermore, water imbibition results in sample expansion and microfracture induction. This study provides additional experimental data to understand the effects of rock fabric, complex pore network, and clay swelling on imbibition behavior.We systematically measure the imbibition rates of fresh water, brine and oil into the confined and unconfined rock samples and crushed packs from different shale members of the Horn River Basin. We also measure the ion diffusion rate from shale into water during imbibition experiments. The results show that confining the shale samples decreases the water imbibition rate of samples tested parallel to the bedding. However, it has a negligible effect on water uptake of samples tested perpendicular to the bedding and on ion diffusion rates. The comparative study suggests that, for both confined and unconfined samples, water uptake is higher than oil uptake. The liquid imbibition and ion diffusion rates along the bedding are higher than those against the bedding. Surprisingly, the crushed samples show a completely different behavior. The oil uptake of crushed packs is higher than their water uptake. The data suggest that the connected pore network of the intact samples is water wet while the majority of rock including poorly connected pores is oil wet. This argument is backed by complete spreading of oil on fresh break surfaces of the rock.

Acid Treatment as a Way to Reduce Shale Rock Mechanical Strength and to Create a Material Prone to the Formation of Permanent Well Barrier

“…Mass transport inside sedimentary rock matrices has been shown to be highly dependent on the direction in respect to rock bedding plane [29][30][31][32]. Typically, the diffusion rates in the direction perpendicular to the bedding plane are shown to be lower than that parallel to the bedding plane [30][31][32]. The anisotropy of the permeability and diffusivity are due to the anisotropy of pore structure of the bedding.…”

“…Our observations in contrast to literature findings suggest that the etching reaction of carbonates with acid proceeds faster in A significantly higher etching rate was observed for the sample exposed in the parallel configuration, i.e., when the sample surface parallel to bedding was exposed to acid. Mass transport inside sedimentary rock matrices has been shown to be highly dependent on the direction in respect to rock bedding plane [29][30][31][32]. Typically, the diffusion rates in the direction perpendicular to the bedding plane are shown to be lower than that parallel to the bedding plane [30][31][32].…”

A Critical Review of Osmosis-Associated Imbibition in Unconventional Formations

“…The common perception is that water imbibition could cause water blockage and clay swelling, which decrease the permeability of the formation. There were many experiments and studies to indicate the decrease due to water blockage [108,[120][121][122][123] and clay swelling [124,125]. There was also an argument about whether the decrease is temporary or permanent.…”

Complexities Driving Wettability Evaluation of Shales toward Unconventional Approaches: A Comprehensive Review

“…The measured wettability of a rock by various available methods should be comparable and conclusive. However, the literature shows many inconsistencies between the two most commonly applied methods of characterizing shale rock wettability: the “contact angle” and the “spontaneous imbibition”. ,,− On the other hand, in some of the other published studies, the contact angle and spontaneous imbibition techniques provided consistent results. − …”

“…If the studied shale core samples are not confined, microfractures could be induced during imbibition experiments, especially if clay-rich and naturally laminated. ,,, Consequently, the porosity and permeability of samples are enhanced, and in turn, a higher water imbibition rate is observed, which affects the reliability of the results. The above judgments have been concluded from experimental studies with no confining stress.…”