Research On Underbalanced Drilling Technology Aiming For Drilling Rate-raising In Western Sichuan

The formation in western Sichuan basain characterize by tight lithology,poor drillability, abnormal formation pressure,coexistence of multi-pressure system, existence of numerous gas sand,complex relationship between gas and water. The complexity of geological features led to low drilling rate in the region,complex accidengts taking place frequently and long well construction cycle period, which limits the progress of exploration and development in the west of Sichuan. Liquid underbalanced drilling technology have obvious superiority in raising drilling rate, reducing complex situation underground, as a result, it was widely used and promoted in western Sichuan.Based on investigation of pertinent literature home and abroad about underbalanced drilling, combining with statistics of the complex situation appeared during the liquid underbalanced drilling construction in western Sichuan region, this paper summarized the contents of underbalanced drilling adaptability evaluation, coupled the related standard for underbalanced drilling and on-site experience, obstained the adaptability evaluation process of underbalanced drilling. And this paper analyzed the liquid underbalanced drilling technology adaptability to every single layer of every structure in western Sichuan area. Formation fluid seepage and wall rock temperature changing will produce induced stress, which would affect the state of stresses of wellbore and the evaluation of wellbore stability. With considering the influence of temperature and formation fluid seepage, this paper analyzed the stresses of wellbore under the underbalanced conditions, as a basis for establishing the design procedure of differential pressure for fluid underbalanced drilling targeting to raise the drilling rate. The paper gather real drilling data from scene, obstain drilling rate equation for liquid underbalanced drilling in western Sichuan and the law of single bit's drilling rate with variation of accumulated footage through regression, established a drilling parameters optimization model with comprehensive consideration of drilling costs and rate by introducing the drilling cost coefficient and drilling rate coefficient.Taking Xin22 well for example, paper discussed its adaptability analysis, differential pressure design and and drilling parameters optimization.The comparisons between results of theoretical analysis and calculation and actual construction conditions verify that the proposed theory and model is correct.It proved that the results of this thesis could certainly guid the design and construction of liquid underbalanced drilling and contribute to optimize and promote the underbalanced drilling technology targeting to raise the drilling rate in western Sichuan region.