Abstract
Due to the limited space of offshore platform, it is unable to implement large-scale multistage hydraulic fracturing for the horizontal well in Lufeng offshore oilfield. Thus, multistage hydraulic fracturing technology in directional well was researched essentially to solve this problem. Modeling of fracture propagation during multistage fracturing in the directional and horizontal wells in artificial cores was carried out based on a true triaxial hydraulic fracturing simulation experiment system. The effects of horizontal stress difference, stage spacing, perforation depth, and well deviation angle on multifracture propagation were investigated in detail. Through the comparative analysis of the characteristics of postfrac rock and pressure curves, the following conclusions were obtained: (1) multistage fracturing in horizontal wells is conducive to create multiple transverse fractures. Under relatively high horizontal stress difference coefficient (1.0) and small stage spacing conditions, fractures tend to deflect and merge due to the strong stress interference among multiple stages. As a consequence, the initiation pressure for the subsequent stages increases by more than 8%, whereas in large stage spacing conditions, the interference is relatively lower, resulting in the relatively straight fractures. (2) Deepening perforation holes can reduce the initiation pressure and reduce the stress interference among stages. (3) When the projection trace of directional wellbore on horizontal plane is consistent with the direction of the minimum horizontal principal stress, fractures intersecting the wellbore obliquely are easily formed by multistage fracturing. With the decrease of well deviation angle, the angle between fracture surface and wellbore axis decreases, which is not conducive to the uniform distribution of multiple fractures. (4) When there is a certain angle between the projection trace of directional wellbore on horizontal plane and the direction of minimum horizontal principal stress, the growth of multiple fractures is extremely ununiform and the fracture paths are obviously tortuous.
Highlights
With the development of unconventional oil and gas reservoirs and the advancement of technology, directional wells, horizontal wells, and multistage fracturing technology are combined to increase the drainage area of the reservoir, to improve oil recovery and economic benefits
(3) When the projection trace of directional wellbore on horizontal plane is consistent with the direction of the minimum horizontal principal stress, fractures intersecting the wellbore obliquely are formed by multistage fracturing
To shed a light on the problem mentioned above, this paper presents the physical simulation research of staged fracturing and multifracture propagation in horizontal and directional wells using the true triaxial hydraulic fracturing physical simulation experiment system
Summary
With the development of unconventional oil and gas reservoirs and the advancement of technology, directional wells, horizontal wells, and multistage fracturing technology are combined to increase the drainage area of the reservoir, to improve oil recovery and economic benefits. In addition to the theoretical model research, the physical simulation experiment is an important means to study fracture initiation and propagation. Physical hydraulic fracturing simulation experiments of directional wells conducted by domestic and foreign scholars showed [12,13,14,15,16,17] that the controlling factors of hydraulic fracture initiation in directional wells mainly include well deviation angle, borehole azimuth, horizontal stress difference, and perforation parameters, and the fracture propagation is easy to deflect to produce complex forms. The effects of horizontal stress difference, perforation depth, stage spacing, well deviation angle, and wellbore azimuth (the angle between projection of wellbore axis in the horizontal plane and the direction of maximum horizontal principal stress) on fracture propagation morphology and pressure curve characteristics of multistage fracturing were considered
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