Abstract
Compressive model experiments with laminated sand medium were conducted to simulate the compressional-strike fault pattern in the Oriente Foreland Basin to better understand structural controlling factors important in locating oil accumulations. Unilateral, horizontal compression models were followed by more complicated geometric alteration and deformation schemes using different boundary conditions and substrates. With this information, a better appreciation of controls on structural evolution of the basin can be predicted, helping in understanding future exploration areas.
Laminated sand model simulation experiments were carried out at the China University of Petroleum laboratory in 2013. During the compression simulation experiments, attention was given to simulate Oriente Basin characteristics including pressure and shear stress background, basement detachment layer, western steep fault boundary, tectonic deformation influence, parallel (2D) boundary conditions for the thrusted piedmont belt, planar and curved (3D) boundary conditions for the central rift reversed foredeep belt, and 3D boundary slope simulation accounting for strike slip configurations.
The Ecuadorian Oriente basin is a foreland basin with structures running in a roughly north-south trend. From west to east, structural trends are also separated into three belts: western thrusted piedmont belt, central rift reversed foredeep belt, and eastern conjugate strike-slip belt. For the depositional setting, it also can be divided into three sedimentary cycles, that is, the "basal bed" of Pre-Cretaceous, the Cretaceous "sedimentary cycle" and the "molasse formation" of Tertiary age. Compressional model experiments show many similarities to the structural framework of the Oriente Basin.
From the parallel boundary conditions (2D) zone compression simulation for the western piedmont thrust, the Oriente Basin basement should be developed as a set of plastic slip layers, which would correspond to the Pre-Cretaceous series under the unconformity.
From planar and curved boundary conditions (3D) compression simulation for the central fore deep tectionic reactivation zone, outcomes were surprising, because results were very comparable to the Oriente Basin relative configuration of the faulted structures of Lago Agrio, Libertador, Sacha, Shushufindi and Mariann Fields. The middle structural belt is mainly due to the eastern part of the basin upwarping, and the transfer and vertical uplift of asymmetric conjugated blocks formed by compressional stress.
For the 3D boundary slope simulation for the eastern structure belt, it was observed that torsional shear stress and conjugate strike-slip movement generate the oil bearing, faulted structures such as occur at Mariann and Eden/Yuturi areas.
Compressional stress simulations conducted in the laboratory clarify the tectonic genesis of the structural trends of the Oriente Basin and on the oil accumulation controls. Main oil fields correspond to transpressive structures developed along three NNE-SSW right-lateral convergent wrench-fault zones, which form the plays of the Oriente basin. In the central and western regions, compression causes the development of the large faulted anticlines with oil accumulations. In eastern regions, strike-slip stress creates high angle, faulted, anticlines.
