3D Geomechanical Modeling for Accurate In-Situ Stress Characterization of a Reservoir in Mahu Oilfield, China

ABSTRACT: Mahu oilfield in Junggar basin is rich in oil and gas resources, because the reservoir has the characteristics of low porosity and permeability, horizontal well and stimulated reservoir volume were applied here. The conventional 1D MEM (mechanical earth model) obtained from single well logging data can not reflect the changes of reservoir geomechanical parameters in long horizontal section, 3D geomechanical modeling is carried out to achieve the fine description of reservoir geomechanical characteristics. During the development of the 3D geomechanical model, a variety of field data and core experimental data were used to ensure its accuracy. The 3D structural model of the reservoir was interpreted from seismic data and a fine description of wave velocity distribution in the 3D model was obtained by a combined interpretation of the acoustic logging data and seismic data. Rock mechanical test data were used to calibrate the predicted geomechanical parameters in the model, ensuring its accuracy. Furthermore, the in-situ stresses determined from diagnostic fracture injection tests and 1D MEM were used to verify the stress calculation results of the 3D geomechanical model. The modeling results show that the direction of the maximum horizontal principal stress in the Mahu oilfield is east to west. The minimum and maximum horizontal principal stresses are in the regions of 42-55 MPa and 63-70 MPa, respectively. There are obvious stress differences between layers, in the range of 10-25 MPa. A comparison of the modeling results against the micro-seismic signals and instantaneous shut-in pressure data recorded during hydraulic fracturing operations further confirmed the reliability of the model. The 3D geomechanical model can provide important guidelines for new drilling and hydraulic fracturing designs in this oilfield. 1. INTRODUCTION Mahu Oilfield is a large conglomerate tight oil reservoir under development. It is difficult to apply conventional reservoir development methods because of the deep burial of the reservoir, the large natural in-situ stress difference, the low porosity and permeability, and the strong heterogeneity which is caused by the poor particle size sorting of the gravel in the rock mass. In order to realize the efficient development of the Baikouquan Formation conglomerate reservoir in Mahu Oilfield, Mahu Oilfield engineers applied horizontal wells and volumetric hydraulic fracturing based on the idea of multi-layer 3D development.