Abstract:

Algal limestone reservoirs in Xiayoushashan Shangganchaigou Formations in Huatugou oilfield in western Qaidam basin mainly consist of algal laminated limestone,algal micrite,oosparite,sparry coquina,sparry algal lump limestone and terrigenous clastic micrite,of which the former two types of limestone have relatively good reservoir properties.The formation of algal limestone reservoirs has mainly been controlled by the stability of sedimentary environment,early eluviation and late cementation filling.Algal limestone reservoirs appear to have relatively high gamma ray value in well logs and strong reflectance signatures in seismic profiles.These characteristics can be used to determine lateral distribution of algal reservoirs.Formation testings in several wells have got oil/gas shows in algal limestone reservoirs,verifing that this type of reservoirs has good prospectiveness.

Key words: Huatugou oilfield, algal limestone, fresh water eluviation, secondary solution opening, lateral distribution