Huge oil reserves are located in ultra-low permeability reservoirs in the Ordos basin in China. There are three key characteristics associated with these reservoirs: low reservoir quality (10 to 13% in porosity), low reservoir permeability (0.3 to 2.0 mD), and low reservoir pressures (pressure gradients of 0.0075 to 0.009 MPa/m). The Chang 6 formation in the Huaqing field is classified as ultra-low permeability reservoirs. Water injection to maintain reservoir pressure is important to develop the Chang 6 formation in horizontal wells. Fracturing design optimization is the key to improving well production and reservoir development effectiveness. Reservoir simulation studies were performed to determine optimal well pattern and well spacing. Fracture modeling studies were also conducted to determine the optimal number of fracture stages in each horizontal well and to optimize fracture design for each stage in order to take into consideration the relative location between each individual stage and nearby injection wells, with the objective of postponing water breakthrough and reducing water production. Completion, stimulation and cumulative production data from 24 horizontal wells were compiled and compared with 121 vertical wells under similar reservoir conditions. Oil production from horizontal wells was increased by four folds on average in comparison with vertical well completion.

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