M6 is an SW bearing faulted anticline which is divided into 8 small blocks by the fault .The depth of the reservoir varies from 1,345m to 1,565m. Oil bearing section is from 30 to 225m. It has good physical property and it is a massive extra-ultra heavy oil reservoir with bottom water. The block was exploited by cyclic steam stimulation with well spacing 100m since 1997. Up to December 2007, the block has 124 producing wells and oil recovery of OOIP is 16.7%, which is coming to end of CSS. During the development, six difficulties took on：