The Standard Division of Tight Oil Reservoirs in Chang 6-8 Members of Changqing Oilfield based on CQ Index

The tight oil reservoirs in the Chang 6-8 Member of the Triassic Yanchang Formation in the Ordos Basin are characterized by low porosity, low permeability, low pressure and low production. In order to optimize the geological engineering sweet spots on the single-well section, a practical method for standard division of tight oil reservoirs has been proposed in accordance with the geological characteristics of Chang 6-8 tight oil reservoir. The first step involved calculating and extracting the minimum horizontal principal stress, fracture pressure, brittleness index, porosity, permeability and water saturation of reservoir etc. This allows them to establish the comprehensive evaluation index of the reservoir completion quality (CQ), and then, to classify the reservoirs “good, medium and bad” based on the relationship chart of CQ and single well productivity. And then to optimize the perforating and fracturing intervals in terms of the CQ value. Using this method, reservoir division was performed in Well L375 of the Changqing Longdong Area, and the comparison of division result and the oil test result showed that the perforating/fracturing interval optimized by the CQ index was completely consistent with the actual intervals of high, medium and low production-yields. Study results also indicated that this method could meet the requirements for optimizing the perforating/fracturing intervals of tight oil and and for identifying engineering geological sweet spots, and can be used for a classification standard for block reservoirs.