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Performance Evaluation of Water Control with Nanoemulsion as Pre-Pad Fluid in Hydraulically Fracturing Tight Gas Formations Mingliang Luo, Xiaodong Si, Yu Zhang, Zhenhe Yuan, Daoyong Yang, and Jun Gong Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b03291 • Publication Date (Web): 23 Feb 2017 Downloaded from http://pubs.acs.org on March 5, 2017
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Performance Evaluation of Water Control with Nanoemulsion as Pre-Pad Fluid in Hydraulically Fracturing Tight Gas Formations Mingliang Luo*, †, ‡, Xiaodong Si†, Yu Zhang†, Zhenhe Yuan†, Daoyong Yang‡, and Jun Gong‡‡ †
College of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, People’s Republic of China
‡
Petroleum Systems Engineering, Faculty of Applied Science and Engineering, University of Regina, Regina, Saskatchewan, Canada S4S 0A2 ‡‡
Offshore Oil Production Plant, Sinopec Shengli Oilfield Branch, Dongying, 257237, People’s Republic of China
ABSTRACT: Experimental techniques have been developed to evaluate performance of nanoemulsions as pre-pad fluid for reducing water-cut in tight gas formations with multistage hydraulic fractures. More specifically, an amino-polysiloxane nanoemulsion was prepared and formulated in the laboratory for effective and efficient water control. The water-control mechanisms of nanoemulsions as pre-pad fluid in hydraulically fracturing were identified by performing the scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), spontaneous imbibition tests, and wettability measurements. The SEM and XPS tests confirm that certain changes occur in the element compositions and microstructure of the core surface before and after introducing the prepared nanoemulsions on the reservoir rock surface. Such changes irreversibly alter its wettability, indicating by the measured contact angle from 75° to 128°. During the displacement experiments, there exists a disproportionate permeability reduction on relative permeability of the gas-water systems. Gas relative permeability has
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only a small decline by less than 20% at different water saturations, while water relative permeability is reduced up to 60%. In addition, effective gas permeability for the core samples treated with nanoemulsions can be rapidly restored by the potential acid hydrolysis. This leads to not only creating new paths for gas flow in hydraulic fractures or invaded zones, but also reducing the inertial resistance of gas flow in porous media by nanoemulsion retention.
1. INTRODUCTION
Since new discoveries have been declining steadily over the last few decades, the rising energy demand has imposed increasingly interests in exploiting unconventional resources (such as tight oil/gas formations) and developing them to the maximum potential. Although volumes of the original-oil/gas-in-place are huge, the inherent low permeability makes it a challenging task for viable production from such formations.
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Recently, profitable gas
production from tight formations has been made possible after long horizontal wells are drilled and massively fractured. 2 Hydraulic fracturing technology, however, has seen its limitations in tight formations containing natural fractures where there exists a quick increase in water-cut and thus productivity decline, corrosion induction, and scale formation. 3, 4 Therefore, it is of fundamental and practical importance to develop reliable water control agents for efficient gas production. In the past few decades, cost-effective methods like polymer- or gel-treating fluids have been extensively applied to reduce the unwanted water production in conventional oil and gas formations. The polymer- or gel-based fluids became very popular due to their high success rates, 5-10 though they can only restrict water influx into wellbore to a certain degree for oil 2
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and water wells and lead indeed to a selective reduction of permeability, known as “disproportionate permeability reduction (DPR)”.
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The experimental results indicated that
water permeability is dramatically declined, though gas permeability is slightly affected due to polymer adsorption on pore surface.
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The traditional water shutoff agents including
inorganic substances, polymers, or crosslinking agent-polymers for oil wells are found to impose a great negative impact on gas wells, especially for tight gas formations.
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Subsequently, a modified polymer-crosslinking process was developed to not only induce gas channels within gel, but also re-establish gas permeability near the wellbore, selectively reducing water permeability. 17 Another sequential gel/gas slug injection process was also proposed to perform water control in gas wells only in medium or high permeable porous media, which can significantly reduce water-gas ratio. 18 Since tight gas formation usually possesses very low permeability (i.e.,
