Interwell Connectivity and Characterization of Seepage Capacity for Tight Oil Wells in Ordos Basin

The tight oil reservoir (Ordos Basin, Yanchang Formation) is characterized by low porosity, ultra-low permeability, and strong heterogeneity, leading to low productivity and inefficient waterflooding due to complex interwell connectivity and variable seepage capacity. We studied three pilot well areas (Z211, Z230, Z288) at near-well, interwell, and injection-production unit scales. At the near-well scale, well tests from 21 wells were interpreted using a composite reservoir model with circular boundaries, variable wellbore storage, and constant skin. Results: Normal wells have inner-zone permeability 0.5–1 mD and outer-zone 0.1–1 mD; low-productivity wells have inner-zone 0.1–1 mD and outer-zone 0.1–0.5 mD. Outer-zone permeability is always lower, indicating that fracturing enhances inner-zone permeability, while poor outer-zone properties limit productivity. Low inner-zone permeability in low-productivity wells reflects both insufficient fracturing and poor rock quality. At the interwell scale, a self-tracer-based model quantified channeling paths. All three areas contain high-permeability channels. Average channel permeabilities: Z211 = 26.09 mD, Z230 = 34.60 mD, Z288 = 211.69 mD; permeability contrast increases in the same order, with Z288 being most heterogeneous. Channeling is the main geological cause of water-cut rise in inefficient wells. At the injection-production unit scale, virtual boundary and flowing-pressure vs. cumulative-liquid-production diagnostics evaluated 30 horizontal wells. Most wells show weak injection-production connectivity; fracturing scale is not the main control. Low-productivity wells suffer from continuous energy depletion, while low-productivity-and inefficient wells exhibit both depletion and local channeling. Cross-validation confirms: low productivity is controlled by poor reservoir properties and insufficient energy; inefficiency is dominated by high-permeability channels; their combination causes low-productivity and inefficient wells. This work provides a theoretical basis for diagnosing and treating such wells in tight oil fields.