Key technologies for drilling and completion in sub-salt carbonate reservoir with high pressure and low permeability

The sub-salt carbonate reservoir in Kenhkiak,Kazakhstan is an oil pool with abnormal pressure,low permeability and complicated geological conditions.At the initial stage of development,problems encountered in drilling practice were the complex of casing program,thick salt dome difficult to drill and low production rate due to perforation completion.The drilling cost was about 10 million USD.Based on careful study about the geological features of the reservoir,pore pressure and drilling technical requirements,the casing program was simplified from 4-string design to 3-string design,anti-salt drilling fluid system like twitterion polymer system was screened out to use on field and open hole completion was tested.As a result,the drilling duration of vertical wells were reduced from initial over 500 days to 180 days or so.The daily production rate of a single well increased from the original 30 tons to over 200 tons in average.So far,many wells have been into production with initial daily output over 500 m3/d.The shortening of drilling duration and the increase of initial production rate of a single well can be attributed to many factors.However,the simplification of casing program,break-though of salt dome drilling and open completion are undoubtedly the key factors.