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

2016 ◽  
Vol 19 (03) ◽  
pp. 511-519 ◽  
Author(s):  
Junjian Wang ◽  
Sheik S. Rahman
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Shale Gas ◽  
Mathematical Formulation ◽  
Fracture Propagation ◽  
Water Displacement ◽  
Gas Reservoir ◽  
Capillary Effects ◽  
Shale Gas Reservoir ◽  
Gas Entrapment

Summary 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.

Application of Heat Treatment to Prevent Fracturing Fluid-Induced Formation Damage and Enhance Matrix Permeability in Shale Gas Reservoirs

2021 ◽  
Author(s):  
Mingjun Chen ◽  
Peisong Li ◽  
Yili Kang ◽  
Xinping Gao ◽  
Dongsheng Yang ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Gas Transport ◽  
Formation Damage ◽  
Transport Capacity ◽  
Fracturing Fluid ◽  
Gas Reservoir ◽  
Shale Gas Reservoir ◽  
The Matrix

Abstract The low flowback efficiency of fracturing fluid would severely increase water saturation in a near-fracture formation and limit gas transport capacity in the matrix of a shale gas reservoir. Formation heat treatment (FHT) is a state-of-the-art technology to prevent water blocking induced by fracturing fluid retention and accelerate gas desorption and diffusion in the matrix. A comprehensive understanding of its formation damage removal mechanisms and determination of production improvement is conducive to enhancing shale gas recovery. In this research, the FHT simulation experiment was launched to investigate the effect of FHT on gas transport capacity, the multi-field coupling model was established to determine the effective depth of FHT, and the numerical simulation model of the shale reservoir was established to analyze the feasibility of FHT. Experimental results show that the shale permeability and porosity were rising overall during the FHT, the L-1 permeability increased by 30- 40 times, the L-2 permeability increased by more than 100 times. The Langmuir pressure increased by 1.68 times and the Langmuir volume decreased by 26%, which means the methane desorption efficiency increased. Results of the simulation demonstrate that the FHT process can practically improve the effect of hydraulic fracturing and significantly increase the well production capacity. The stimulation mechanisms of the FHT include thermal stress cracking, organic matter structure changing, and aqueous phase removal. Furthermore, the special characteristics of the supercritical water such as the strong oxidation, can not be ignored, due to the FHT can assist the retained hydraulic fracturing fluid to reach the critical temperature and pressure of water and transform to the supercritical state. The FHT can not only alleviate the formation damage induced by the fracturing fluid, but also make good use of the retained fracturing fluid to enhance the permeability of a shale gas reservoir, which is an innovative method to dramatically enhance gas transport capacity in shale matrix.

Research and Exploration of High Energy Gas Fracturing Stimulation Integrated Technology in Chinese Shale Gas Reservoir

2012 ◽  
Vol 524-527 ◽  
pp. 1532-1536 ◽  
Author(s):  
Jin Jun Wu ◽  
Li Cai Liu ◽  
Guo Hua Zhao ◽  
Xiao San Chu
Keyword(s):  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Design Method ◽  
High Energy ◽  
Field Application ◽  
Low Permeability ◽  
Gas Reservoir ◽  
Integrated Technology ◽  
Shale Gas Reservoir ◽  
Development Technology

The reserves of Chinese shale gas is very rich, but still haven’t ever formed a mature technology. According to Chinese shale gas reservoir characteristics, the development technology situation and the principle of high energy gas fracturing, the research and exploration of HEGF stimulation integrated technology which is suitable for the development of Chinese shale gas reservoir need to be carried out. Through a series of analysis and study, compositing high energy gas fracturing technology achievements, this paper discusses the research idea and feasibility of the integrated technology, formed by the liquid gunpowder fracturing technology, in-fracture deeply explosive fracturing technology in low permeability oil layers, composite perforating technology, the multi-pulse fracturing technology and the hydraulic fracturing, simultaneous fracturing ,which transforms shale gas reservoir and develops shale gas. Launching field application test is suggested, and studying the way to optimize the theory and design method of integrated technology, so as to promote the development of shale gas.

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