Simulation of stress fields and quantitative prediction of fractures distribution in upper Ordovician biological limestone formation within Hetianhe field, Tarim Basin, NW China

The carbonate is the main gas producing system in the Hetian River gas field of Tarim Basin, within which structural fractures serve as the main seepage channel and accumulation spaces. The development process of carbonate gas field in the Hetianhe area shows that the enrichment of gas is closely related to the development of fracture parameters. On the basis of core data and imaging logging data, the characteristics of tectonic fractures parameters were determined. Combining three dimensional finite element numerical simulation method, we simulated paleo tectonic stress field of two key fracture periods(late Hercynian and Himalayan period) and current stress field in Hetian river gas field. The fracture linear density and aperture formulas were established to calculate the distribution of tectonic fractures in different periods. Then the impacts of faulting and folding on the development of fractures could be analyzed. The simulation results showed that the value of maximum principal stress during the Late Hercynian period in the Hetianhe area is 300-320 MPa with a direction of NW-SE(310-130 degrees), and the direction of maximum principal stress is NE-SW(40-220 degrees), with a 500-520 MPa value. The folding play the primary role, and the faults paly the secondary control in the generation of fractures during the late Hercynian and Himalayan periods. The 3-D finite element geo-mechanical numerical modelling and fracture density, aperture calculation methods are not only for carbonate fractures in the Hetianhe area, but also for the development of other reservoir fractures.