Water Blocking Caused by Fracturing Fluid Leakage in Mixed-Wet Unconventional Tight Reservoirs

Kong, Bing; Chen, Shengnan

doi:10.2118/180475-ms

Cited by 5 publications

(1 citation statement)

References 17 publications

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“…Well shut-in for a specific time after hydraulic fracturing is the technical way to improve the efficiency of liquid utilization. Shut-in time after fracturing is an important factor influencing the utilization efficiency of fracturing fluid [34][35][36]. In this study, the dualmedium single-stage fracturing model was used to study the utilization law of fracturing fluid during shut-in after fracturing and the effect of shut-in time on the efficiency of fracturing fluid utilization.…”

Section: Well Shut-in Timementioning

confidence: 99%

Insight into the Methods for Improving the Utilization Efficiency of Fracturing Liquid in Unconventional Reservoirs

Xu¹,

Lei

Cheng-mei³

et al. 2021

Geofluids

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A large amount of fracturing fluid will be injected into the unconventional reservoirs during hydraulic fracturing. At present, the maximum amount of fracturing fluid injected into shale oil reaches 70000 m3 in Jimsar. The main function of fracturing fluid is to make fractures for traditional reconstruction of fracturing; for unconventional reservoirs, fracturing fluid is also used to increase formation energy by large-scale injection. It is of great significance to improve the utilization efficiency of large-scale hydraulic fracturing fluid for shale oil to increase production and recovery. In this study, the method of improving the utilization efficiency of the large-scale hydraulic fracturing fluids is explored by experiment, numerical simulation, and field test of Jimsar shale oil formation. This research shows that fracture complexity can effectively increase the contact area between the fracturing fluids and the formation. The water absorption rate of the fractured core is increased, which lays the foundation for improving the liquid utilization efficiency. Reasonably, well shutting before production ensures the pressure balance in the fractures, and the fluid pressure can be transmitted to the far end, which improves the fracture effectiveness, increases formation energy, and promotes imbibition and oil displacement. By using the additive of enhanced imbibition displacement, the displacement efficiency and the displacement amount of crude oil in the micro-nanopores can be greatly improved, and the utilization ratio of liquid can be further enhanced. The experiment adopted in the field proves that improving energy utilization efficiency has an important impact on production. This study has great guiding significance for the efficient development and practical production of unconventional reservoirs.

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Section: Well Shut-in Timementioning

confidence: 99%

Insight into the Methods for Improving the Utilization Efficiency of Fracturing Liquid in Unconventional Reservoirs

Xu¹,

Lei

Cheng-mei³

et al. 2021

Geofluids

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Why Re-Fracturing Works and Under What Conditions

Asala

Ahmadi

Taleghani

2016

Day 2 Tue, September 27, 2016

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Stimulated shale wells show sharp decline rates after several months of production imposing the need for rejuvenating production via re-fracturing or other methods. The sharp decline in production from shale gas/oil wells is attributed to full or partial closure and damage of the induced fracture network within the rock. The poor economic conditions stirred by low oil prices has persuaded operators to consider re-fracturing as an affordable option but the mechanisms behind this technique is not fully understood. In this paper, we utilize a fully coupled model to understand stress re-distribution and identify different modes of fracture closure during production from initial hydraulic fractures. Rock creep, proppant failure and differential fluid depletion are identified as primary causes of closure within shale fracture networks. We incorporate these phenomena into a poroelaso-plastic model that simulates fracture conductivity evolution during production, and re-fracturing treatments illustrated by re-fracture propagation, fracture coalesce or fracture extension along pre-existing fractures. This methodology provides a realistic initial condition to simulate varying re-fracture designs - different treatment schedules and fracturing fluids. The Influence of degradable mechanical and non-mechanical diverters is also incorporated in this model. Our results reveal major stress redistribution in the fracture network especially at the intersections due to depletion. The results show how fracture closure at the fracture intersections causes abrupt or time dependent shrinkage of the drainage area. Under certain conditions, re-fracturing may effectively open up these bottlenecks while in extreme situations, it creates new fractures which reorient obliquely. Results also reveal the role of in-situ stress anisotropy, magnitude of depletion and complexity of fracture networks in the successful re-fracturing of lower- clay content naturally fractured formations such as the Barnett shale. The results do not suggest strong dependency on stress anisotropy and natural fractures orientation in high clay content reservoir rocks like Haynesville or Marcellus. It shows the quantifiable effect of creep on closure rate and conductivity loss. Results show diverters have a profound effect on the expansion of the re-fracture network, although it hinders reactivation of some clogged fractures. Using adaptive cohesive elements provides the opportunity to model longitudinal, transverse or oblique re-fracture propagation. The Proposed model introduces a realistic fracture closure mechanism and stress re- distribution during drainage, prior to re-fracturing. This plays a vital role in explaining initial fracture extension, re-frac propagation, fracture coalesce, re-fracture re-orientation, and therefore the effectiveness of re-fracturing treatments. This model offers a practical tool for identifying potentially successful re-fracturing candidates.

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Performance Comparison of Novel Chemical Agents for Mitigating Water-Blocking Problem in Tight Gas Sands

Huang

Babadagli

Chen

et al. 2020

Day 1 Wed, February 19, 2020

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Water-blocking can be a serious problem, causing a low gas production rate after hydraulic fracturing; a result of the strong capillarity in the tight sandstone reservoir aggravating the spontaneous imbibition. Fortunately, chemicals added to the fracturing fluids can alter the surface properties and thus prevent or reduce the water-blocking issue. We designed a spontaneous imbibition experiment to explore the possibility of using novel chemicals to both mitigate the spontaneous imbibition of water into the tight gas cores and measure the surface tensions between the air and chemical solutions. A diverse group of chemical species has been experimentally examined in this study, including a cationic surfactant (C12TAB), two anionic surfactants (O242 and O342), an ionic liquid (BMMIM BF4), a high pH solution (NaBO2), two nanofluids (Al2O3 and SiO2), and a series of house-made deep eutectic solvents (DES3-7, 9, 11, and 14). Experimental results indicate that the anionic surfactants (O242 and O342) contribute to low surface tensions, but cannot ease the water-blocking issue due to yielding a more water-wet surface. The high pH solution (NaBO2), ionic liquid (BMMIM BF-4), and brine (NaCl) significantly decrease the volume of water imbibed to the tight sand core through wettability alteration, and the cationic surfactant (C12TAB) leads to both surface tension reduction and an oil-wet rock surface, helping to prevent water-blocking. The different types of DESs and nanofluids exhibit distinctly different effects on expelling gas from the tight sand cores through water imbibition. This preliminary research will be useful in both selecting and utilizing proper chemicals in fracturing fluids to mitigate water-blocking problems in tight gas sands.

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Water Blocking Caused by Fracturing Fluid Leakage in Mixed-Wet Unconventional Tight Reservoirs

Cited by 5 publications

References 17 publications

Insight into the Methods for Improving the Utilization Efficiency of Fracturing Liquid in Unconventional Reservoirs

Insight into the Methods for Improving the Utilization Efficiency of Fracturing Liquid in Unconventional Reservoirs

Why Re-Fracturing Works and Under What Conditions

Performance Comparison of Novel Chemical Agents for Mitigating Water-Blocking Problem in Tight Gas Sands

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