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Drilling and fracturing fluids can interact with reservoir rock and cause formation damage that impedes hydrocarbon production. Tight sandstone reservoir with well-developed natural fractures has a complex pore structure where pores and pore throats have a wide range of diameters; formation damage in such type of reservoir can be complicated and severe. Reservoir rock samples with a wide range of fracture widths are tested through a multistep coreflood platform, where formation damage caused by the drilling and/or fracturing fluid is quantitatively evaluated and systematically studied. To further mitigate this damage, an acidic treating fluid is screened and evaluated using the same coreflood platform. Experimental results indicate that the drilling fluid causes the major damage, and the chosen treating fluid can enhance rock permeability both effectively and efficiently at least at the room temperature with the overburden pressure.

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The hydraulic fracturing is a nonlinear, fluid-solid coupling and transient problem, in most cases it is always time-consuming to simulate this process numerically. In recent years, although many numerical methods were proposed to settle this problem, most of them still require a large amount of computer resources. Thus it is a high demand to develop more efficient numerical approaches to achieve the real-time monitoring of the fracture geometry during the hydraulic fracturing treatment. In this study, a reduced order modeling technique namely Proper Generalized Decomposition (PGD), is applied to accelerate the simulations of the transient, non-linear coupled system of hydraulic fracturing problem, to match this extremely tight response time constraint. The separability of the solution in space and time dimensions is studied for a simplified model problem. The solid and fluid equations are coupled explicitly by inverting the solid discrete problem, and a simple iterative procedure to handle the non-linear characteristic of the hydraulic fracturing problem is proposed in this work. Numeral validation illustrates that the results of PGD match well with these of standard finite element method in terms o f fracture opening and fluid pressure in the hydro-fracture. Moreover, after the off-line calculations, the numerical results can be obtained in real time.

Fiber-laden fluid systems have been successfully applied for reorientation fracturing in tight gas and shale gas reservoirs around the world. Although many successful cases have been reported in the literature, there is a lack of a deep understanding of the mechanical mechanism of fiber-assisted diverting fracturing. Hence, this paper presents a systematic study of the fracture diversion mechanisms of the fiber-diverting fracturing technique. A series of laboratory experiments is conducted with a real tri-axial stress simulation system. Degradable fibers are applied to large-size natural outcrop samples (300 mm × 300 mm × 300 mm) under true triaxial stress conditions. The dynamic filtration experiment to test the temporary plugging ability showed that the fractures were effectively plugged by fiber fluids. A variety of factors related to the fracture reorientation are tested and compared, including injection rate, fracture width and horizontal principal stress difference. The additional pressure drop caused by the fiber filtration cake is calculated and used to quantitatively analyze the effects on fracture reorientation. The net pressure increase is the driving force of the fracture diversion and formation of the fracture network. The conclusions were used to guide carbonate reservoir stimulations in the Tarim oil field, in northwest China. The phenomenon of fracture diversion was evident as the pumping pressure increased considerably after injecting the degradable fiber. The hydraulic fracturing treatment and production results showed substantial pressure responses and excellent hydrocarbon production.