Causes and countermeasures for low liquid production in low-permeability reservoirs in Shengli region

Majordiscoveries have been made in the tight sandstone and strongly-cemented carbonate reservoirs in the deep formations of the Shengli region in the recent years. However, provenreserves have failed to increasesince the productionratefor liquids is low in a singe well. Oil-bearing core samples were collected from the wells with low permeability and low productionrate, and were tested to find out the causes for that low liquid productionrate. The complicated lithologic characteristics of reservoirs, crude oil properties and technical supporting measures were correlated with liquid shortage. Some internal and external factors for low liquid productionrate were identified. Low flow amountsresultingfrom the tight rock structure, an unclear oil/water relationship resultingfrom rock heterogeneity, various sensitivityresultingfrom clay variety, discontinuous output of crude oil resulting from low oil saturation, and oil flow deviationresultingfrom heavy oil were regarded as the internal causes. Clay particles in pore throats during fracturing and deposits from the reaction between acid frac-fluid and the reservoir made permeability become worse, which were regarded as the external causes. For different problems, the improvement measures for some single well layerswere formulated and producedgood results.