Study on the Estimate Method of Ultra Deep Fractured Low Porosity Sandstone Water-Influx Gas Reservoir Type and Proven Developed Reserves—The Kelasu Gas Filed of Tarim Basin

The Kelasu gas field, located in the Kelasu structural belt of the Tarim Basin, is a typical ultra-deep fracture low-pore sandstone gas reservoir. Its production and PD reserves account for more than 50%, directly affecting the operating efficiency of the oilfield. In recent years, due to the severe water situation in the gas reservoir, PD (confirmed developed) reserves have decreased significantly and oilfield consumption has risen sharply, posing a huge challenge to the operational efficiency of the oilfield. In order to assess PD reserves in water-exposed gas reservoirs in a reasonable and compliant manner, based on the study of the geological and dynamic characteristics of gas reservoirs of different water types, a classification evaluation standard and board of water-inundated channels were established, gas-water assessment units were reasonably divided, and differentiated PD reserve assessment strategies matched with the characteristics of different gas reservoirs were proposed to assess PD reserves in water-exposed gas reservoirs in a reasonable and compliant manner. The results show that gas reservoirs can be classified into three types: limited edge bottom water, strong edge water, strong bottom water, etc. ① Affected by reservoir physical properties, fractures, ground stress, water size, etc., in some gas reservoirs, after water exposure, the edge and bottom water forms non-uniform water intrusion channels along the high-angle fracture development zone or micro-fractures, dividing the entire gas reservoir into several different water and gas units such as the pure gas zone and the water-flooded zone, with the pure gas zone maintaining stable production. At this point, directly using the diminishing method for assessment would result in the loss of reserves in the pure gas area; ② In combination with the division of water and gas units, the assessment units were optimized. The PD reserves were split into two assessment units, namely the flooded area and the pure gas area, and differentiated assessment methods were proposed for different types of water-exposed gas reservoirs. The reserve assessment results reflect the current production status of the gas reservoirs. The conclusion suggests that differentiated assessment strategies should be adopted for different types of water-exposed gas reservoirs. The PD reserves of the gas reservoirs and the reserst-production ratio can better reflect the production status of the gas reservoirs, and the oilfield consumption has decreased significantly, providing some reference for the reasonable and compliant assessment of reserves of the same type of water-exposed gas reservoirs.