A Systematic Approach to Fracturing Optimisation of Unconventional Resources

Abstract

Abstract Owing to the low productivity of single well, rapid productivity decline and low ultimate recovery of low-permeability reservoirs, multistage fracturing is usually employed for reservoir stimulation of horizontal wells, which helps to increase fracture conductivity and single well productivity by creating artificial fractures. It is very vital to accurately characterize and simulate 3D spatial distribution of fracture networks for hydraulic fracturing technology. Sufficient production data has proved that the hydraulic fracture geometry simulation integrating 1D geomechanics, without considering natural fractures, resulted in low accuracy of fracture modeling, which could not effectively support the deployment and implementation of oilfield development plan. Thus, artificial fracture networks simulation technology fully coupling 3D geomechanics with natural fracture model will be urgently required to guide oilfield development economically. The technical research process is divided into 4 steps. Step 1, set up 1D geo-mechanical modeling in single well using conventional and image logging data, formation integrity testing, drilling logs, as well as rock mechanical laboratory tests. Then, 3D static geomechanical modeling of the reservoir can be performed by incorporating seismic data and structural modeling. Step 2, identify natural fractures in single well based on image logging data and core data to create fracture intensity curve modeling. Establish 3D natural fracture model constrained by fracture sensitive seismic attributes analysis and 3D fracture intensity trend body. Step3, based on rock and fracture mechanics, simulate hydraulic fracture extension of stimulated well coupling 3D geo-mechanical model with 3D natural fracture model. Then, verify modeling accuracy through micro-seismic data. Step 4, compare and analyze differences in fracture geometry, proppant placement, and fracture conductivity between 3D coupled fracture modeling (3DCFM) and 3D uncoupled fracture modeling (3DUFM). After gridding 3DCFM and 3DUFM to geological modeling, predict production post fracturing using numerical simulation technology. Finally, crosscheck the accuracy of 3DCFM and 3DUFM with predicted and actual production data. By comparing and analyzing the fracture geometry and numerical simulation results of 3DCFM and 3DUFM, it was concluded that 3DUFM could not characterize natural fracture shielding effect and diversion during fracture extension due to 3D geo-mechanical spatial anisotropy. Thus, greater uncertainties of the fracture modeling occurred, resulting in low consistency between single well productivity prediction and numerical simulation. Compared with 3DUFM, the uncertainty of the fracture modeling geometry can be greatly reduced in 3DCFM verified by micro-seismic patterns, so the consistency between productivity prediction and numerical simulation will be significantly increased. Hydraulic fracture simulation technology fully-coupling geomechanics with natural fracture model was applied in the low permeability fractured reservoirs of the northwestern margin of Junggar Basin, China. The cross-over analysis among research results, the actual micro-seismic patterns and production data indicated that compared with 3DUFM, the uncertainty of 3DCFM reduced by 25.2%;, and the consistency of numerical simulation and productivity prediction increased by 18.5%. The research results would be a guideline on location optimization of horizontal wells, stimulation optimization of multistage fracturing and strategy optimization of oilfield development.