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Summary Proppant bed can play a critical role in enhancing oil and gas production in stimulated wells. In the last 2 decades, there have been consistent efforts to improve shape characteristics and mechanical strength properties to guarantee high permeability in the resultant propped fracture. However, engineering the surface properties of proppants, such as tuning their wettability, has not received considerable attention. Considering that water-wet proppants can not only limit production because of reduced hydrocarbon relative permeability but also facilitate fines migration through the proppant bed, a methodology is presented here to alter the wettability of proppants using graphite nanoplatelets (GNPs). The idea benefits from the intrinsic hydrophobicity of graphitic surfaces, their relatively low cost, and their planar geometry for coating proppants. Conductivity tests are conducted according to ISO 13503-5:2006 (2006) and API RP 19D (2008) to examine how the coating process changes the relative permeability to water and oil. According to the simulation results, the newly developed graphite-coated proppants speed up the water cleanup and increase long-term oil production in an oil-wetreservoir.

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Proppant bed plays a critical role in enhancing oil and gas production in stimulated wells. In the last two decades, there have been consistent efforts to improve shape characteristics and mechanical strength properties to guarantee high permeability in the resultant propped fracture. However tuning wettability of proppants have not yet engineered considerably maybe because natural sand has been a typical raw material for proppant manufacturing. However, water wet proppants may not only limit production due to reduced hydrocarbon relative permeability but also facilitate fine migration through the proppant bed. Fine migration and increasing water saturation may deteriorate oil production over time. Intrinsic hydrophobicity of graphitic surfaces and their two-dimensional geometries made them a promising candidate for coating proppant to alter its wettability. In this paper, we present a methodology for treating proppant surfaces with graphite nanoplatelets. Standard laboratory tests following modified API RP61 have conducted to show the effectiveness of the proposed methodology.

Methane leakage due to compromised wellbore cement integrity may result in operational complications and environmental contaminations in oil and gas wells. In this work, the problem of fluid-driven fracture propagation at the cement interfaces is revisited by a thorough and comprehensive consideration of the non-uniform cement bonding to the formation along the wellbore. While previous works were mainly focused on discharge without attention to mechanical failure or mechanical failure without ties to seepage rate, here we couple these two analyses to provide a practical aspect of this approach. As revealed by cement evaluation logs, the quality of the cement behind the casing varies and may include flaws in the form of channels or pockets of mud residuals. A novel methodology, initiated with laboratory-scale cement bonding properties using the push-out test, is introduced to estimate the cohesive properties of the cement interface, considering mud removal and mud residuals in the rock. Then the measured cohesive properties are applied to a field-scale numerical model with an embedded cohesive layer between cement and formation to evaluate the susceptibility of the wellbore to develop cement debonding. The excessive fluid pressure at the casing shoe is assumed to be the source for the fracture initiation. The proposed numerical model has been tested against actual SCP field tests for validation purposes. This model may estimate the geometry of leakage pathways and predict leakage flow rate within acceptable ranges. The effect of several key factors in the development of SCP due to the cement debonding is investigated. The results show that the early stage of SCP build up is controlled by the cohesive properties of the cement interfaces (i.e., cement properties), but the cohesive properties have minor effects on the stabilized pressure. The method proposed herein presents a method to evaluate the cement bond quantitatively to be further integrated in cement design.