Water Loss versus Soaking Time: Spontaneous Imbibition in Tight Rocks

Lan, Qing; Ghanbari, Ebrahim; Dehghanpour, Hassan; Hawkes, Robert

doi:10.2118/167713-ms

Cited by 44 publications

(31 citation statements)

References 24 publications

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“…Similar observations were also reported by other researchers (Zolfaghari et al, 2014;Ghanbari et al, 2014). Clay leaching is a possible reason for this phenomenon (Keller and Da-Costa, 1989).…”

Section: Spe-175925-mssupporting

confidence: 90%

Chemical Analysis of Flowback Water and Downhole Gas Shale Samples

Zolfaghari¹,

Tang²,

Holyk³

et al. 2015

SPE/CSUR Unconventional Resources Conference

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Recently, flowback chemical analysis has been considered as a complementary approach for evaluating fracturing operations and characterizing reservoir properties. Understanding the source of flowback salts and the mechanisms controlling the water chemistry is essential but also challenging due to the complexity of water-shale interactions. In this study, samples of flowback water and downhole shales are analyzed to investigate the mechanisms controlling the chemistry of flowback water.The water samples at different flowback times and the shale samples are collected from three wells completed in the Muskwa, Otter-Park, and Evie members of the Horn River Basin. The water samples consist of aqueous solution and precipitated salts. The water samples are digested in nitric acid to dissolve the precipitated salts, and are analyzed at both intact and acid-digested conditions using ICP-MS. The flowback salts are weighted and analyzed using XRD and SEM-EDXS. A sequential ion-extraction is performed on the shale samples; and the extracted ions are categorized into three tiers of loosely-, moderately-, and strongly-attached ions. Acid digestion is also performed on the shale samples to characterize their elemental composition.The concentration of monovalent cations in both intact and acid-digested samples is higher than that of divalent cations. Also, the concentration of all cations is higher in the acid-digested samples compared with that in the intact samples. Chemical analysis of the flowback water samples suggests that the majority of the ions in the early flowback water are loosely-attached monovalent ions. These ions can be originated from the mixing with in-situ formation brine, dissolution of soluble precipitated salts, or leaching of exchangeable cations from the clay minerals. Similarly, the role of relatively slow water-shale interactions (such as leaching of divalent exchangeable cations, e.g. Ca 2ϩ ) increases at the later flowback stages. XRD and SEM-EDXS analyzes of the flowback salts indicate that sodium chloride, potassium chloride, and calcium carbonate are the major salts. The sequential ion-extraction reveals that the majority of the monovalent cations are in the loosely-attached tier. However, majority of the divalent cations are moderately or strongly attached to the rock. The strongly-attached portion of the ions is determined by acid digestion of the rock sample at the final stage of sequential ion-extraction process. These stronglyattached ions cannot be easily released by hydraulic fracturing and therefore, has small effect on the flowback water chemistry. Flowback chemical analysis indicate that sodium is the major ion in the flowback water and its concentration is higher than the potassium concentration. While, according to the results of acid digestion of rocks, potassium is the major constituent of our shale samples and its concentration is about five times higher than the sodium concentration. Moreover, although barium is not a major constituent of our shale samples (ϳ0.05%), the concentratio...

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Section: Spe-175925-mssupporting

confidence: 90%

Chemical Analysis of Flowback Water and Downhole Gas Shale Samples

Zolfaghari¹,

Tang²,

Holyk³

et al. 2015

SPE/CSUR Unconventional Resources Conference

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“…In this section, the increase in pore pressure induced by gas entrapment and its impact on the microfracture generation are studied. To evaluate the conditions of entrapped gas to induce microfractures during the water leakoff into shale matrix, the criterion proposed by Ozkaya (1988) ( Lehner 1991;Lash and Engelder 2005) is used in this study. Aimed primarily at qualitative insight, the shale is idealized by assuming it to be an elastic and isotropic material, and therefore, this investigation is based on strongly idealizing model assumptions, and qualitative results reported in the following should therefore be viewed with some caution.…”

Section: Resultsmentioning

confidence: 99%

“…where k ¼ S h =S v is the stress ratio, and the range of k is set from 0.79 to 1.0, on the basis of an analysis for Dunkirk Shale (Lash and Engelder 2005). The increase in average pore pressure with time for each component with different initial water saturation is listed in Fig.…”

Section: Resultsmentioning

confidence: 99%

Investigation of Water Leakoff Considering the Component Variation and Gas Entrapment in Shale During Hydraulic-Fracturing Stimulation

Wang

Rahman

2016

SPE Reservoir Evaluation &Amp; Engineering

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The water leakoff into the shale matrix during the hydraulic-fracture treatment has been a critical issue in determining fracture geometry. Furthermore, water leakoff also affects mechanical properties of the surrounding rock matrix which, in turn, affects fracture propagation. Conventional approaches for the prediction of leakoff were inadequate because several important phenomena are ignored. In this paper, several effects on water leakoff into shale matrix during shale-gas reservoir stimulation are considered. A simplified structure is used to depict the complex pore network in shale. Different interactive forces involved in water displacement considering the osmotic and capillary effects are taken into account in the mathematical formulation of the model. The proposed numerical model is used to study the water leakoff and the consequent pressure increase caused by gas entrapment. The potential influence of the increase in pore pressure on the generation of microfractures is also discussed.The simulation results show reasonable agreement with the previous studies, and indicate that the water leakoff greatly depends on composition and structure of shale matrix. Clay minerals, for example, are naturally prone to water invasion, and draw water faster than hydrophilic minerals and organic matter because of the osmotic effect. Furthermore, the invaded water significantly increases the pore pressure within the shale matrix because of gas entrapment, which leads to a strong nonlinear relationship between leakoff and the square root of time. An increase in pore pressure also results in a decrease in effective stress that leads to the generation of tension-induced microfractures in shale matrix.This study emphasizes the significance of osmotic and capillary effects as well as gas entrapment on hydraulic-fracturing treatment of shale-gas reservoirs. Moreover, the new leakoff model can be applied to assist the investigation of fracture-propagation behavior in a shale-gas reservoir.

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“…However, field data show that only a fraction of the large water volume used in hydraulic fracturing treatments is recovered during the flow-back operation. The spontaneous imbibition properties of tight sand and shale reservoirs have been investigated by many experts [9][10][11][12][13][14]. However, there is less research related to volcanic reservoirs.…”

Section: Introductionmentioning

confidence: 99%

Impact of Petrophysical Properties on Hydraulic Fracturing and Development in Tight Volcanic Gas Reservoirs

Shen¹,

Meng²,

Liu³

et al. 2017

Geofluids

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The volcanic reservoir is an important kind of unconventional reservoir. The aqueous phase trapping (APT) appears because of fracturing fluids filtration. However, APT can be autoremoved for some wells after certain shut-in time. But there is significant distinction for different reservoirs. Experiments were performed to study the petrophysical properties of a volcanic reservoir and the spontaneous imbibition is monitored by nuclear magnetic resonance (NMR) and pulse-decay permeability. Results showed that natural cracks appear in the samples as well as high irreducible water saturation. There is a quick decrease of rock permeability once the rock contacts water. The pores filled during spontaneous imbibition are mainly the nanopores from NMR spectra. Full understanding of the mineralogical effect and sample heterogeneity benefits the selection of segments to fracturing. The fast flowback scheme is applicable in this reservoir to minimize the damage. Because lots of water imbibed into the nanopores, the main flow channels become larger, which are beneficial to the permeability recovery after flow-back of hydraulic fracturing. This is helpful in understanding the APT autoremoval after certain shut-in time. Also, Keeping the appropriate production differential pressure is very important in achieving the long term efficient development of volcanic gas reservoirs.

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Water Loss versus Soaking Time: Spontaneous Imbibition in Tight Rocks

Cited by 44 publications

References 24 publications

Chemical Analysis of Flowback Water and Downhole Gas Shale Samples

Chemical Analysis of Flowback Water and Downhole Gas Shale Samples

Investigation of Water Leakoff Considering the Component Variation and Gas Entrapment in Shale During Hydraulic-Fracturing Stimulation

Impact of Petrophysical Properties on Hydraulic Fracturing and Development in Tight Volcanic Gas Reservoirs

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