Abstract
Multilayered tight sandstone gas reservoirs with low porosity and low permeability are usually developed by two kinds of hydraulic fracturing techniques, including general fracturing (simultaneously fracturing multiple target zones) and separate layer fracturing (sequentially fracturing the target zones from the bottom-up). However, fractures from different target zones are likely to communicate in the fracturing process which detrimentally causes the waste of fracturing fluid and proppants and finally affects the efficiency of fracturing treatment. Therefore, investigation related to hydraulic fracture configurations under different fracturing stimulation treatments is necessary with the objective of optimizing the fracturing design and predicting the production rate. In this paper, a 3D finite element model is established to simulate the propagation of multiple hydraulic fractures in the vertical well, and fracture configurations under different fracturing techniques and formation properties are analyzed and compared. The results indicate that, in vertical wells, stress interference between the fracture tips will accelerate the communication of adjacent vertical fractures along the height direction. And separate layer fracturing is preferable for stimulating multilayered tight sandstone gas reservoirs. Also, adjacent pay zones and barriers with high in situ stress contrast, high tensile strength contrast and low elastic modulus contrast are able to effectively prevent the communication of fractures along the height direction and lead to the increase of fracture length and width, and so does the barriers with large thickness.
Highlights
Multilayered tight sandstone gas reservoirs are gradually playing a more and more significant role in the oil and gas exploration and development from northeast China
General fracturing and separate layer fracturing techniques are the prevalent methods for developing multilayered tight sandstone gas reservoirs; investigation of the fracture configurations under these treatments should be carried out for increasing the success rate during operation
Even though there are a number of field fracturing treatments for multilayered tight sandstone gas reservoirs, the fundamental mechanism for fracture propagation is still not completely understood
Summary
Multilayered tight sandstone gas reservoirs are gradually playing a more and more significant role in the oil and gas exploration and development from northeast China. Wang et al (2012) used a more sophisticated model involving six layers to research the fracture geometry under different formation properties. A 3D fluid–solid-damage coupling model using finite element method is built to investigate the problem and fracture configurations under different fracturing techniques and formation properties are analyzed. Hydraulic fracture propagation is such a complex physical phenomenon which involves dynamic coupling between fluid flow and rock deformation, and the theory of poroelasticity introduced by Biot (1962) can be adopted to describe the fluid and solid mechanical interaction process. The continuity of reservoir fluid is governed by the equation below in which the increase rate of fluid volume stored at a point equals the rate of volume of fluid flowing into the point within the time increment (Wang 2015; ABAQUS 2014; Feng et al 2016, 2017):
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