Abstract: Tarim Oilfield has done a lot of work to optimize the casing program of development well and appraisal well in block LN to achieve "fast, cost saving and efficient" drilling. Reduced number of casing strings result in long open hole section with cementing difficulties such as HTHP, large temperature difference and coexistence of multiple formation pressures, which in turn impose more rigorous requirements on the properties of cement slurry. Based on the difficulties encountered in the past in cementing long lowpressure open hole section in which mud losses are easy to occur, and the well cementing techniques commonly used in block LN, laboratory experiments were conducted to evaluate the adaptability of BX cement slurry to the practical situation in that area. It was found that BX cement slurry had high initial consistency, strong thixotropy and good anti-channeling capacity, and was thus compatible with the geologic nature of the block LN. The cement slurry, during WOC, was able to prevent mud losses from occurring. The cement slurry was designed to have two densities and two thickening times, effectively reducing the liquid head of cement slurry, and in turn reducing the risks of lost circulation during operation. With this technique, the job quality of well cementing has been improved and the needs for cementing long low-pressure open hole section have been satisfied.