Analysis of key controlling factors for water injection deficiency in low-permeability oil reservoirs: A case study of Chang-8 reservoir in Ordos Basin

Low-permeability sandstone reservoirs in the Ordos Basin face significant challenges, such as severe water injection deficiencies and short effective durations of enhanced injection measures, leading to poor water flooding development performance. To improve the injection capacity of deficient wells, geological and injection water quality data from severely deficient areas in the western Ordos Basin were analyzed. The overall injection situation of these areas was examined, and the influence of geological factors and injection water quality on injection deficiencies was explored. Nine factors affecting water injection effectiveness were selected, divided into two major categories. Using the Spearman correlation analysis method, the correlation coefficients between injection deficiencies and these factors were calculated. Results indicated that the interaction between injection water quality and formations exhibited cumulative effects, leading to a gradual increase in injection pressure during prolonged water injection, ultimately reducing reservoir injection rates. Taking the Chang-8 reservoir re-injection area in the western Ordos Basin as an example, the correlation coefficients ranked as follows suspended solids content > oil content > median pore throat radius > variation coefficient > suspended particle size. Based on correlation analysis and field data, targeted recommendations for mitigating injection deficiencies were proposed to improve water injection performance.